Juan Gabriel Rueda-Bayona
email: ruedabayona@gmail.com

Andres Guzmán
email: faguzman@uninorte.edu.co

Juan José

Cabello Eras
email: jcabello2@cuc.edu.co

Rodolfo Silva-Casarín

Emilio Bastidas-Arteaga

José Horrillo-Caraballo
email: j.m.horrillo-caraballo@swansea.ac.uk

Renewables energies in Colombia and the opportunity for the offshore wind technology

Keywords: wind energy, offshore, renewable energy, Colombia, wind turbines

Global offshore wind technology shows increasing progress evidenced in the recent reports of wind power capacity, expectations of market expansion and international research projects. Colombia is privileged with several types of natural resources (e.g. wind, sun, water) but there is not a clear legal context to regulate sustainable and safe exploitation of the offshore wind energy considered nonconventional. The development of offshore wind technology in Colombia could attend the energy demand when the hydroelectric system presents low electricity generation during dry hydrological conditions and El Niño -South Oscillations events. This paper analyses international actions that have motivated different countries to establish strategies to reduce CO2, and their advances and challenges in implementing offshore wind technology. The review of the administrative framework of renewable energy in Colombia proved the lack of information for implementing offshore wind

Introduction

Nowadays, climate change is one of the major environmental problems which most of it has been generated by anthropogenic greenhouse gas (GHG) emissions. According to [START_REF] Mem ; Meyer | Moroccan project of wind energy 2.000 MW[END_REF], electricity, heat production, agriculture, industry, and transport account together for over 80 % of the GHG. The Paris agreement (United Nations Climate Change, 2017) to limit GHG was adopted by 169 out of 197 countries (the United States withdrew from it). Several countries recognised their responsibility for the GHG. Therefore, they emitted and set its compromises to limit it [START_REF] Burch | In pursuit of resilient, low carbon communities: An examination of barriers to action in three Canadian cities[END_REF]. The massive implementation of Renewable Energy Sources (RES) to electricity generation is one of the main strategies to do it, and the European Union have a target of 45 % electricity from RES in 2030 [START_REF] Resch | RES targets for Europe -a brief pre-assessment of feasibility and impacts[END_REF], while the United States forecasts 10 % to 27 %. [START_REF] Ahuja | Sustainable energy for developing countries[END_REF] suggested in their study that developing countries have the challenge to supply electricity access for millions of people while moving its energy paradigms towards clean, low-carbon energy systems implementing RES.

Latin America and the Caribbean have a large extension and variety of renewables energies [START_REF] Hoogwijk | Global potential of renewable energy sources: a literature assessment[END_REF]. Excluding hydroelectric energy, the other energy sources have not achieved an important extraction development. The potential in the region is higher than 78 000 TW.h [START_REF] Flavin | Study on the Development of the Renewable Energy Market in Latin America and the Caribbean[END_REF]. The study presented by the Colombian Mining Energy Planning Department (UPME, Unidad de Planeación Minero Energética) reported the countries with the most representative wind energy capacities installed by 2014 in Latin America: Peru (148 MW), Panama (220 MW), Chile (836 MW), Mexico (2.3 GW), and Brazil (5.9 GW). Colombia produces 19.5 MW, an amount that compared with the listed nations is not competitive. Since 2003, the capacity in Colombia has not increased (UPME, 2015a).

The onshore wind energy potential in Colombia has been studied throughout the country [START_REF] Ideam | Pan-Arab Renewable Energy Strategy 2030, Roadmap of Actions for Implementation[END_REF] and there are in specialized literature several researches at the local level [START_REF] Álvarez Castañeda | Aplicación de la ecuación de Weibull para determinar potencial eólico en Tunja-Colombia, in: XX Simposio Peruano de energía solar -XXSPES. Presented at the XX Simposio Peruano de energía solar[END_REF][START_REF] Ordóñez | Wind and Solar Energy Potential Assessment for Development of Renewables Energies Applications in Bucaramanga, Colombia[END_REF][START_REF] Delgado | La energía eólica como energía alternativa para el futuro de Colombia[END_REF][START_REF] Jimenez | Electricity generation and wind potential assessment in regions of Colombia[END_REF]. Specifically to Caribbean region, Pabón [START_REF] Hernández | Geospatial assessment of the wind energy for an onshore project in the Caribbean region of Colombia[END_REF] assessed wind potential applying georeferential technology, and [START_REF] Mejía | Simulation of wind energy output at Guajira, Colombia[END_REF] evaluated wind potential in La Guajira, the most promising locality. However, the offshore wind potential has been less researched, only averaged wind speed [START_REF] Ideam | Pan-Arab Renewable Energy Strategy 2030, Roadmap of Actions for Implementation[END_REF] and offshore extreme wind speed [START_REF] Devis-Morales | Assessment of extreme wind and waves in the Colombian Caribbean Sea for offshore applications[END_REF]. Offshore wind energy shows several advantages respect to the onshore wind energy [START_REF] Breton | Status, plans and technologies for offshore wind turbines in Europe and North America[END_REF][START_REF] Perveen | Off-shore wind farm development: Present status and challenges[END_REF]. One of the main advantages is that in the ocean, the wind speed is higher and less unstable due to the roughness of the sea surface, which is smaller than land (continental) surfaces. The main disadvantages of offshore wind energy are the construction and maintenance costs wherein these offshore turbines require an efficient structural design [START_REF] Cheng | A reliability based design methodology for extreme responses of offshore wind turbines[END_REF]. [START_REF] Weaver | Financial appraisal of operational offshore wind energy projects[END_REF] analysed the commercial appeal of the wind energy market and pointed considerations about financial values of the life cycle of a wind farm. The research concluded that CAPital EXpenditures (CapEx) could be an objective tool to reduce the cost of energy.

The offshore wind projects generate economic benefits but present risks associated with the industry. [START_REF] Gatzert | Risks and risk management of renewable energy projects: The case of onshore and offshore wind parks[END_REF] reviewed the risks and solutions of renewable energy projects. They discussed the risks of onshore and offshore projects from the investor perspective and the solutions for risk handling of the European energy market. They concluded that constructive risks would be reduced with technological development. In addition, to ensure sustainable development of renewable energy market, it is necessary to guarantee the stability of policies and regulations. The improvement of the international cooperation, for instance, the World Bank, offers guarantees of partial risks in some risk policies.

This research shows the possible scenarios of renewable energies that Colombia could face according to the World Energy Council approach, and the highlights of the recent energy trilemma index results. Additionally, the research presents different experiences and projects about offshore wind energy and estimations of wind power density in four offshore locations in Colombia. Section 1 presents the motivation of several countries to reduce carbon emissions and the general advantages of offshore wind technology. Section 2, devoted to the methodology, shows the literature review approach and the database and equations used for the wind speed and wind power energy analysis. Section 3 shows the approach of the World Energy Council to diversify the energy matrix through the cogeneration among renewable and non-renewable energies. In Section 4 of this study, the official organisations and the administrative framework of the renewable energies in Colombia are presented. The Renewable Energy policy framework and the guidelines and methodologies for the associated activities to produce Non-conventional sources of renewable energy in Colombia are depicted in Section 5. Section 6 shows the offshore wind energy potential in Colombia for the locations with the highest wind speeds and presents a preliminary suggestion of types of offshore wind turbines to be used. Section 7 presents several studies that show the potential of marine renewable energies in Colombia and Section 8 shows the needs and challenges that Colombia has to overcome for taking advantage of the potential of renewable energies. Finally, Section 9 denotes the limitations of the study and future research directions associated with the offshore wind energy technology.

The research significance of this paper relies on the updated quantitative characterisation of the offshore wind potential in Colombia, evidencing the feasibility to implement the OWE technology due to the identified wind power densities and the positive wind-speed trends. Also, the literature review allowed recognising the limitations and future developments that Colombia must face, considering the past, present and futures international and national events.

Methodology

This study was performed using online scientific databases such as Science Direct, Research Gate and official databases of the Colombia government: Ministry of Mines and Energy, Planning Unit Energy Mining, Superintendence of Public Utilities, Superintendence of Industry and Trade, Institute of Planning and Promotion of Energy Solutions for non-interconnected zones, Ministry of Environment and Sustainable Development, and Institute of Hydrology, Meteorology and Environmental Studies (IDEAM). In addition, we examined online books and proceedings related to the renewables energies in Colombia and overseas through the Google search engine.

The keywords considered for the literature search (English and Spanish) were the following: offshore wind energy, renewable energy, marine energy, Colombia, Colombian Caribbean, energy policy framework, energy regulations and energy progress. The Science direct database showed 1987 articles related to offshore wind energy, 188 394 for renewable energy, 189 674 for marine energy, Colombia, 8631 for Colombian Caribbean, 114 921 for energy policy framework, 448 732 for energy regulations, and 642 491 for energy progress. Due to the massive number of results, this study only selected papers related to the main experiences and the progress of the energy industry of several locations in Europe, China, United States, Latin America, Middle East, and Asia.

Moreover, this research used the Reanalysis database of NARR project (NOAA, 2016) to estimate the wind power density for 4 locations along the Colombian Caribbean coast: Cartagena (10.511342° N, 75.531002° W), Barranquilla (11.101637° N, 74.767269° W), Santa Marta (11.264067° N, 74.223011° W) and La Guajira (12.446068° N, 71.720533° W). The data has been collected from the 1 st of January 1979 up to the present with a spatial resolution of 0.3 degrees (approximately 32 km), every three hours of time interval. Previous research has shown that the quality of the Reanalysis data allowed to analyse the wind speed information for the study areas properly [START_REF] Rueda-Bayona | Identificación de patrones de variabilidad climática a partir de análisis de componentes principales, Fourier y clúster kmedias[END_REF]. Fig. 1 shows an example of the extraction of wind speed (m/s) from Reanalysis database. To estimate the wind power density (W/m 2 ), this research applied the same equation (1) used by IDEAM (2018):

3 1 2 P V A (1)
Where:

P = power density (W/m 2 )
= air density (kg/m 3 )

A = area (m 2 )
We generated the density data using the ideal gas law equation (2) [START_REF] White | Wind in power 2017, Annual combined onshore and offshore wind energy statistics[END_REF]:

atm P R T (2)
Where:

atm P = atmospheric pressure (N/m 2 ). R = ideal gas constant (286.8 Nm /kg K) T = air temperature (K).
This research utilised the air pressure and temperature Reanalysis data of 10 m, 110.8 m, and 323.2 m, to calculate the air density (2) at those levels, required by the wind power density equation (1).

The World Energy Council approach

The World Energy Council proposed three possible scenarios for the energy market for the year 2050: Modern Jazz, Unfinished Symphony and Hard Rock (World Energy Council, 2016). Modern Jazz is a focused approach to achieve individual access and accessibility to energy through economic development. This approach considers creating new market mechanisms, generate technology innovation and open access to energy for everyone. The Unfinished Symphony is a government-led policy to achieve sustainability through coordinated practices and international policies. The approach mentioned above is characterised by strong policies, long-term planning, and concerted climate action. The Hard Rock approach is considered as a fragmented approach motivated by the desire for energy security in a world with low global cooperation. Therefore, their policies or strategies have a local perspective.

Considering the three scenarios of renewable energies in the world ( [START_REF] Vargas | Perspectiva mundial de las energías renovables[END_REF] According to the Intergovernmental Panel on Climate Change (IPCC), from the year 2030 is expected that annual emission of carbon decreases to avoid the 2ºC of global temperature increment. Then, the three approaches consider decreasing the CO 2 emissions from 31 GTon to 13 GTon through the Unfinished Symphony, from 36 GTon to 23 GTon through Modern Jazz and from 37 GTon to 34 GTon through Hard Rock [START_REF] Vargas | Perspectiva mundial de las energías renovables[END_REF].

The three approaches applied to the Latin America and the Caribbean showed that the wind energy is the greatest contributor to the renewable electricity generation. In 2014, the wind energy generated 19 TW.h with 1.47 % of participation in the energy market, the solar energy produced 1 TW.h with 0.08 % of participation, geothermal produced 4 TW.h with 0.31 % of the contribution, and others technologies generated 1 TW.h with 0.08 % of participation. The Unfinished Symphony approach is identified as the most effective strategy compared to the other approaches, which would produce 191 TW.h in 2030, being the 11.00 % of participation in the energy market [START_REF] Vargas | Perspectiva mundial de las energías renovables[END_REF].

The world energy council published in 2016 a list of the top 10 countries in the energy trilemma index (environmental sustainability, energy equity, and energy security) (World Energy Council, 2016). The report mentioned that Denmark, Switzerland, and Sweden top the index where Denmark stands out due to the efforts in energy security. Luxembourg was not in the top 10 but showed progress in energy equity (affordable and accessible), and the Philippines is leading the environmental sustainability dimension of the trilemma. Uruguay has the highest rank in Latin America, Israel in the Middle East, Mauritius in Sub-Saharan Africa and New Zealand kept in the top 10 considered as a regional leader.

The top three countries in the environmental sustainability dimension of the trilemma were Philippines, Iceland, and Colombia. Although these three countries have high geothermal or hydropower capacities, they have an important challenge to diversify their energy systems. In addition, they must strengthen the institutional framework that motivates the creation and implementation of policies through research (World Energy Council, 2016).

Progress and challenges in the offshore wind industry

Due to the high offshore wind energy potential for exploitation, several countries in Europe performed technical and economic consultancies for setting the extraction and distribution feasibility of this renewable energy in their States (Rodrigues et al., 2015). According to the review of the situation and projection of the offshore wind energy in Europe carried out by the same author, the installed yearly capacity grew 36.1 % from the construction in 2011 of the first offshore wind project. By 2015, the installed capacity was 7748 MW and 3198 MW of construction capacity.

The European Wind Energy Association informed in 2015 that 3230 turbines had been installed in Europe, distributed in 84 offshore wind farms. It was reported a generation of 11 027 MW of total capacity, an average water-depth installation of 27.2 m and a mean average distance to the coastline of 43.3 km [START_REF] Ho | The European offshore wind industry -key trends and statistics 2015[END_REF].

According to Rodrigues et al. (2015), is expected that, shortly, Germany and UK remain as the leaders of the offshore wind industry in the world. Germany in 2015 reported a 10.5 GW installed capacity and UK from 2008 begun its offshore development program to increase the total capacity to 28.9 GW.

UK is considered as a world leader in the offshore wind energy extraction. [START_REF] Kota | Offshore wind energy: A comparative analysis of UK, USA and India[END_REF] compared the installed capacity and potential of the offshore wind industry, and their conclusions mentioned that the UK to 2016 had more than twice the installed capacity of any country in the world.

Ireland in 2002 through a consultancy study established the costs and benefits that could generate the offshore wind energy (OWE). The study evidenced the political barriers and financial restraints in that year. Ireland wanted to reduce the annual emission of 2400 Ton of CO 2 and the import of fossil fuel up to 100 000 euros implementing OWE technology. The consultancy report recommended a demonstrative or pilot program, which would improve the confidence of investors, financial creditors, and technology developers [START_REF] Sei | Cost Benefit Analysis of Government support options for offshore wind energy[END_REF].

The Netherlands in 1972 suffered the first oil crisis, what motivated this country to diversify its technologies and industries of energy extraction. [START_REF] Verhees | The role of policy in shielding, nurturing and enabling offshore wind in The Netherlands (1973-2013)[END_REF] presented details about the actions taken by the Netherlands in 1986 to expand the energy industry. The research pointed several events related to the initiative of the country to promote the OWE. As a result, the Netherlands achieved through an energy company to build the first offshore wind farm in the North Sea, with an installed capacity of 100 MW. The report presented by the Netherlands Enterprise Agency in 2015 showed that the Netherlands has an installed capacity for OWE of 1000 MW, and is working to increment the capacity to 4000 MW for the 2023 (Netherlands Enterprise Agency, 2015).

In 2012, it was estimated an installed capacity of 4 GW of OWE in the marine zones in the north of Europe and was planned to increment the installed capacity to 40 GW in 2020 and 150 GW in 2030. The projections of installed capacity of tides and waves energy by 2020 are 2 GW, what shows the priority of OWE regarding others marine renewable energies (VLIZ, 2015).

The European Union between 2012 and 2016 carried out the MERMAID project, which tried to develop the next generation of multipurpose offshore platforms for marine energy extraction and mariculture. The project was integrated by 11 universities, 8 research centres, 5 large companies and 4 small and medium-sized enterprises (SMEs). Several projects had relation to MERMAID and were the followings: SI OCEAN, MARINET, SOWFIA, TROPOS, H2OCEAN, DEMOWFLOAT, MARINA platform, HiPRWind Project, UPWIND Project, PolyWEC project, ORECCA, SAFEWIND, 7MW-WEC-BY-11, NORSEWIND, PROTEST, RELIAWIND, TOPFARM, WAVEPORT, SEANERGY 2020 (VLIZ, 2015).

In Spain, there are not energy policies that guarantee a stable regulation frame that protects the interests of the investors, leading to a low motivation to develop the OWE technology. Contrary, the syndicate of renewable energies in France try to generate 15 GW for 2030 through offshore wind turbines [START_REF] Colmenar-Santos | Offshore wind energy: A review of the current status, challenges and future development in Spain[END_REF].

The French Government committed to Europe to generate 6000 MW of OWE by 2020. In 2013, France produced 3000 MW of OWE, but according to the inspection of the established projection in 2013, the expectation will not be achieved in 2020. As a result, France decided to extend the accomplishment of the objective to 2030, to increase the OWE production to 15 000 MW and to create 30 000 new job positions (Syndicat des énergies renouvables, 2013).

Turkey shows an annual increase of 8 % of energy demand. Therefore, this country had to import the 72 % of its energy. While the energy potential was 48 000 MW, the installed capacity for exploitation to 2014 was 2959 MW [START_REF] Kaplan | Overview of wind energy in the world and assessment of current wind energy policies in Turkey[END_REF]. It has been identified that the complexity and slowness of government administrative processes have limited the development of OWE technology in Turkey. However, the Turkish Wind Energy Association (TWEA) commits to producing 20 GW by 2023 through the improvement of the national energy network (GWEC, 2016).

The US Department of Energy reported that in 2030 the country would attend the 20 % of the domestic demand, through the development of the installed capacity of the wind energy industry. The wind energy potential that will attend the future demand is 251 GW, which 54 GW will come from offshore wind farms in shallow waters (U.S. Department of Energy, 2008).

The fast growth of China has increased the domestic energy demand. Thus, the Chinese government has to face the pressure of the economic development and the environmental deterioration due to the fossil fuel utilisation (D. Zhang et al., 2017). D. Zhang et al. (2017) presented the development status of renewable energies to 2017 in China and made a preliminary prediction of the renewable energies in the next decades. The researchers concluded that the only way to manage the problem of economic growth and high dependence of oil-gas energy would depend on the government initiatives to encourage the construction of hydroelectric and wind farms in the short-term. Despite the high wind energy potential and the social acceptance in some regions of China [START_REF] Yuan | Social acceptance of wind power : a case study of Shandong Province[END_REF], the Chinese government recommends in the long-term to promote the solar, biomass and geothermic energy (D. Zhang et al., 2017); the marine energies were not considered in the short or mid-term due to the technology for exploitation requires more development.

Due to the coastal wind farms are more energy efficient, China plans to shift the energy extraction from inland to offshore. Therefore, the country must promote a moderated long-term growth of the offshore wind power (J. Zhang et al., 2017).

In the southwest coast of Younggwang region, South Korea plans to install the first offshore wind farm by 2019. The project is located 15 km from the coast, and there were measured winds between 6.9-7.5 m/s and an average water depth of 20 m. The project is supported by public and private resources, with 92.7 billion dollars (USD) available to generate 2500 MW of energy [START_REF] Lee | Assessment of offshore wind energy at Younggwang in Korea[END_REF]. [START_REF] Nesamalar | The drive of renewable energy in Tamilnadu: Status, barriers and future prospect[END_REF] analysed the status, barriers, and potential of renewable energies in the Tamilnadu state (India), and showed that the state planned to generate 10.65 GW of renewable energy by 2023, which 127 428 MW are associated to OWE (WISE, 2012).

Morocco is considered as one of the pioneer countries in the exploitation of renewable energy in the Arab nations. Morocco plans to install 42 % of the national capacity for renewable energy extraction by 2020 and a 52 % by 2030 (IRENA, 2014). The program was widely supported because the country imports 96 % of the energy, and it is estimated that by 2030 the domestic energy demand will triple [START_REF] Mem ; Meyer | Moroccan project of wind energy 2.000 MW[END_REF]NRF, 2012).

In 2013, Azerbaijan established the goal in the short-term to produce 2500 MW where 800 MW were associated with wind energy [START_REF] Vidadili | Transition to renewable energy and sustainable energy development in Azerbaijan[END_REF]. As a result, in 2010 were installed the first two offshore wind turbines by the Caspian Technology Company (CTC) in the waters of the Caspian Sea. The project reported a 1.7 MW of installed capacity and avoided the utilisation of 2.5 mln m 3 of natural-gas [START_REF] Baker | Azerbaijan Alternative Energy Sector Analysis and Roadmap[END_REF].

Mexico has an onshore installed capacity that extracts 2621 MW of wind energy. By 2024 expects to attend the 35 % of the domestic demand, 40 % by 2035, and 50 % by 2050 through the renewable energies (solar, wind, biomass, geothermic, hydroelectric) [START_REF] Pérez-Denicia | Renewable energy sources for electricity generation in Mexico: A review[END_REF].

Brazil has an offshore wind energy potential of 1.3 TW in marine areas with water-depth of 50 m. The offshore wind energy availability in Brazil is complementary to the availability of hydropower accounting for 61.2 % of the national generation capacity (GWEC, 2016). Also, nowadays Brazil has the challenge to reduce the costs of development of his offshore wind industry [START_REF] Green | The economics of offshore wind[END_REF].

Considering the experiences of every country mentioned above is remarkable the development of OWE in Europe. The latest reports of installed offshore wind power capacity (MW) showed that the United Kingdom led worldwide, followed by Germany and China (Statista, 2018;Wind Europe, 2018). Examples of the increasing interest to develop OWE is evidenced in the increment of 10 % of global offshore capacity in 2017 [START_REF] Richard | Offshore capacity grows by 10% in H1 2017[END_REF], the start in 2019 of the offshore wind research centre funded by United Kingdom and China (Richard, 2018), and the expectation of expansion of global OWE market up to USD $60 billion by 2024 [START_REF] Froese | Offshore wind market expected to exceed $60 billion by 2024[END_REF].

Colombia is lagging in the development of wind energy onshore compared to other Latin American countries. According to the wind projects in progress, non-notable increases are foreseen in the coming year, so it is understandable a latency on OWE technologies arrival. While other Latin American countries such as Brazil and Mexico have a significant wind installed generation capacity, and the USA, China and European countries are investing in the OWE technology, there is no plan to develop the OWE technology in Colombia (UPME, 2015b). Hence, we should give special attention to prior experiences of developed and developing international OWE projects to reduce this development gap.

The Renewable Energy policy framework in Colombia

In Colombia, six entities regulate, control and incentivize the energy market. MINMINAS (Ministerio de Minas y Energía) manages the mineral and energy resources and guarantees the execution of energy projects to attend the energy demand [START_REF] Minminas | Misión y visión-Ministerio de Minas y Energía[END_REF]. The Colombian Commission for the Regulation of Energy and Gas (CREG) regulates and promotes a sustained development of the provision of public utilities for electric energy, gas fuel and public liquid fuel services (CREG, 2018a). The UPME is a special administrative unit of the national order with technical nature, attached to MINMINAS, which plans and supports the formulation of public policy and coordinates information with sector agents and stakeholders [START_REF] Upme | Plan indicativo de expansión de cobertura de energía eléctrica, PIEC 2016-2020[END_REF]. The Superintendence of Public Utilities monitor, watches and controls the entities and utility companies, including the energy sector (Superservicios, 2018). The Superintendence of Industry and Trade protects the rights of the consumers, and the free and healthy competition (Superintendencia de Industria y Comercio, 2018). The Institute of Planning and Promotion of Energy Solutions for non-interconnected zones (IPSE, Instituto de Planificación y Promoción de Soluciones Energéticas para las Zonas No Interconectadas), is an office ruled by MINMINAS. Its mission consists to improving the living conditions of communities, through the identification, development, promotion and operation of projects to bring energy to the localities that do not receive energy or where the service is limited (IPSE, 2018). These six institutions attend the energy demand and manage the energy market through their specific functions.

The CREG has created and integrated several guidelines to regulate the Non-conventional renewable energy sources, NCES (FNCER, Fuentes No Convencionales de Energía Renovable en Colombia) as seen in Table 2. Climático), planned the strategies to achieve the agreement of Paris [START_REF] Murillo | La paz está en nuestra naturaleza, in: 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética[END_REF].

The authorisation of projects to generate energy from Non-Conventional Energy Sources (NCES) is given by two entities of MADS in Colombia: The National Agency of Environmental Licenses (ANLA, Autoridad Nacional de Licencias Ambientales) and the Regional Environmental Corporation (CAR, Corporación Autónoma Regional). The ANLA controls the exploration and generation projects of NCES with an installed capacity equal or higher than 100 MW. The CAR controls projects with an installed capacity equal or higher than 10 MW and less than 100 MW [START_REF] Murillo | La paz está en nuestra naturaleza, in: 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética[END_REF].

Colombia established the action plan 2010-2015 of the Rational and Efficient Use of Energy and Non-Conventional Sources (PROURE, Programa de Uso Racional y Eficiente de Energía y Fuentes No Convencionales), to consolidate the culture of sustainable management of natural resources along the energetic chain (Prias Caicedo, 2010b). The plan pretended to generate economic, technical and regulatory conditions to encourage the energy market in Colombia and strengthen the national institutions and private organisations to develop subprograms and execute renewable energy projects.

After the UPME presented the "Expansion Generation Plan 2015-2029", to guarantee the energy reliability, which pretends to install the new hydroelectric capacity and the growth projection of minor plants, integrating conventional technologies such as the thermic and hydroelectric plants with non-conventional renewable energies (wind, geothermic, biomass and solar). The plan tries to motivate the generation of 1.2 GW from wind energy in La Guajira region. Additionally, the plan analysed the distribution of new 3.12 GW of wind energy in La Guajira region through integrating new technologies (UPME, 2016a).

Since the enactment of Law 697 of 2001 the use of renewable energy sources in Colombia have gained legislative status; the development programs to encourage and promote companies that import or produce parts or equipment that use the renewable energies was established as a duty of the National Government. The Ministry of Energy and Mines plans guidelines for policies, strategies, and instruments for the promotion of non-conventional sources of energy (Senado de la República de Colombia, 2001). After 17 years, the impact of the Law 697 has been limited, due to that Colombia barely reached the 2 % of the installed capacity and the 1.2 % of electricity generation of nonconventional renewable energy by 2017.

The establishment of a policy that would allow the design of guidelines to implementing nonconventional renewable energy projects, with attractive incentives for the Colombian companies included in the national energy market became a reality until 2014. Accordingly, the Law 1715 was promulgated to "promote the development and use of non-conventional sources of energy, mainly those of a renewable nature, in the national energy system, through its integration into the electricity market, its participation in non-interconnected areas and other energy uses" (Senado de la República de Colombia, 2014). This legislation incorporates into the environmental policies, the criteria of NCES, and the mechanism of generation and efficient management of the energy for its development in Colombia. Additionally, the law establishes the environmental parameters for the development of projects, and support to the MADS to regulate the CO 2 emissions.

The Law 1715 was a milestone for the development of the renewable non-conventional energy sources projects. The proposed incentives in that law are: a) annual reduction of income in projects to promote research, development and investment in the field of the production and use of energy from NCES, as well as the efficient management of energy, b) exclusion of the Value Added Tax (VAT) to encourage the use of energy from NCES, c) exemption from payment of Tariff Rights for new investments in new NCES projects and d) accelerated depreciation of assets for the generation activity from non-conventional energy sources [START_REF] Gaona | Rural microgrids and its potential application in Colombia[END_REF]. The foreseeable impact of these incentives has been assessed by Castillo-Ramírez et al. ( 2017) as a very positive. However, [START_REF] Olaya | How capacity mechanisms drive technology choice in power generation: The case of Colombia[END_REF] pointed out that some incentives that have been successful in other countries have been ignored. Up to 2017, 221 NCES application projects have been certified, with an estimated generation capacity of 1240.88 MW, which are in different stages of execution [START_REF] Valencia | Hoja de ruta para la incorporación de energías renovables en Colombia, in: 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética. Presented at the 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética[END_REF].

Although Law 1715 is an important step forward in the development of the application of the nonconventional energy sources in Colombia and its insertion in the Interconnected National System, Pereira Blanco (2015) considered a limited scope in the Law 1715 because only promotes activities to the application of the no conventional energy sources in Colombia. Also, [START_REF] Olaya | How capacity mechanisms drive technology choice in power generation: The case of Colombia[END_REF], mentioned that the law does not indicate mechanisms for implementing the NCES projects.

Since 2006 it has been pointed out the deficiencies in the regulation and the lack of adequate tariffs [START_REF] Ruiz | Renewable energy sources in the Colombian energy policy, analysis and perspectives[END_REF], a situation that still is maintained [START_REF] Edsand | Identifying barriers to wind energy diffusion in Colombia: A function analysis of the technological innovation system and the wider context[END_REF][START_REF] Román | Analysis of the main drivers of CO2 emissions changes in Colombia (1990-2012) and its political implications[END_REF]. There is uncertainty regarding the implementation of non-conventional renewable sources because the lack of regulations for the rate of adoption, prices, and problems of security of supply in the Colombian energy market [START_REF] Jimenez | Diffusion of renewable energy technologies: The need for policy in Colombia[END_REF]. The lack of a methodology and rules to calculate the contribution of wind and other energy sources limited the estimation of reliability payments in energy auctions [START_REF] Botero | Evaluation of methodologies for remunerating wind power's reliability in Colombia[END_REF]. [START_REF] Olaya | How capacity mechanisms drive technology choice in power generation: The case of Colombia[END_REF] has also criticised that Law 1715 leaves unresolved structural problems of the electricity market that lead non-conventional renewable energy sources to compete under disadvantageous conditions against conventional energy sources.

Although there is a national indicative plan (UPME, 2016b), which establishes the actions and sectorial measures for the fulfilment of the goals in the energy sector by 2022, in the case of the nonconventional renewable sources, there are no mandatory compliance targets established. Then, Roman et al. ( 2018) strongly recommend following the example of countries such as Chile, Mexico and Argentina that have established by law the goal of 10 % of electricity generation from nonconventional energy sources. The UPME (2015c) showed that the use of the non-conventional energy sources in Colombia is in a primary state. Also, the technical developments, capacity and experience have not been achieved, what may delay the implementation of Law 1715.

Offshore wind energy potential in Colombia

The World Bank in 2010 pointed out that the dynamics of the wind energy availability in Colombia is complementary to the hydroelectrical energy regime. It means that during dry seasons, Colombia presents maximum wind speeds. According to the report, wind speed reaches 9 m/s [32 km/h] at the height of 50 m [START_REF] Dudhia | PSU/NCAR Mesoscale Modeling System Tutorial Class Notes and User's Guide: MM5 Modeling System Version 3[END_REF], generating possibilities to wind energy exploitation (ESMAP, 2010). Colombia has a wind potential of 18 GW just in La Guajira onshore areas, with the capacity to attend twice the domestic energy demand (Pérez [START_REF] Bedoya | Energía, pobreza y deterioro ecológico en Colombia: introducción a las energías alternativas[END_REF]. The annual mean wind speed map at surface level in Colombia was recently updated, where it is possible to identify velocities about 15 m/s close in the coastal and offshore areas of the Caribbean region (Fig. 2) (IDEAM, 2018). The IDEAM (2018) also published the study of annual wind energy power density in Colombia at 80 m of elevation, and reported values about 1728 W/m 2 in Barranquilla and Santa Marta and La Guajira region (Fig. 1), and 1000 W/m 2 to 1331 W/m 2 for Cartagena. For the calculation of the wind energy power density the study extrapolated to 80 m of elevation the wind speed from 10 m using the logarithmic wind profile equation, the air pressure and temperature using the equations of [START_REF] Dudhia | PSU/NCAR Mesoscale Modeling System Tutorial Class Notes and User's Guide: MM5 Modeling System Version 3[END_REF]. As a result, the assumptions stated by IDEAM in its research could have overestimated the wind power density in the study areas.

In order to verify the offshore wind energy potential of Colombia in the locations with the highest records of wind speed (Fig. 2), this research used the reanalysis database (NOAA, 2016) and extracted the wind, air temperature and air pressure data of 10 m, 110.8 m (1000 hPa) and 323.2 m (975 hPa) levels from 1979 to 2015 years.

The monthly variation of wind speed (m/s) in the study areas (Fig. 3) evidenced that the wind speed increase with an annual increment of 0.043 m/s for Barranquilla, 0.037 m/s for La Guajira, 0.036 m/s for Santa Marta, and 0.013 m/s for Cartagena. The wind rose of the study areas (Fig. 4) showed predominant winds from northeast in Barranquilla, Cartagena and Santa Marta cities, and winds from east in La Guajira location. The mean annual wind speed of 7 m/s in the study areas and the maximum wind speeds of 11.5 m/s in Barranquilla and Santa Marta (Fig. 5), showed a wind power class 7 according to the Wind Energy Resource Atlas [START_REF] Elliott | Wind Energy Resource Assessment of the Caribbean and Central America[END_REF]. The projects for commercial wind power extraction become feasible about wind power class 4.

In addition, considering the classification of wind power of the International Electrotechnical Commission (British Standard, 2006), it is possible to state that Barranquilla and Santa Marta are classified I (High wind) from December to April. Also, the annual mean wind speeds of Barranquilla (7.2 m/s), Santa Marta (7.3 m/s) and La Guajira (7.0 m/s) locations and their trend of increment evidenced in Fig. 3 allow a classification of III (Low wind), which suggest a high feasibility to develop wind energy projects.

A wind class III requires installing turbines with extra-large rotor (100 m to 150 m of diameter) to capture as much energy as possible. Furthemore, turbines of class III rarely needs wind monitoring because the expected wind loads will not affect the structural stability. Wind class II are the most commons turbines designed for sites with annual mean velocities up to 8.5 m/s, and wind class I are designed to work with velocities above 8.5 m/s. The class I turbines are the smallest type, heavierduty in design, with short blades to reduce the effect of wind loads over the structure (Renewables First, 2018).

The monthly mean of wind power density at 10 m of elevation (Fig. 6) evidenced that La Guajira showed values close to 200 W/m 2 during the year, except from September to November when the ITCZ is located over the study area. Santa Marta has the highest wind power density at 10 m, evidenced in the period from December to April with 658 W/m 2 in February. La Guajira, regarding the monthly mean of wind power density at 110.8 m of elevation (Fig. 7), increased the power density up to 482 W/m 2 . It is the location with the highest power density values of the study areas. Interestingly, Barranquilla reported the highest monthly mean of wind power density at 323.2 m of elevation (Fig. 8) with 857 W/m 2 in February. La Guajira area showed values over the 200 W/m 2 during the year except for the period from September to November, where wind speed decrease due to the effect of ITCZ mentioned above. Considering the wind speed and the wind power density of the four study areas, is possible to state that Barranquilla, Santa Marta and La Guajira have potential to implementing offshore wind farms. For La Guajira, is feasible to generate energy with offshore wind turbines class I, II or III with hub heights at 30 m, 50 m 100 or 300 m over the mean sea water level (MSWL); the lower is the power density, the higher should be the rotor diameter. Barranquilla has the highest power density at 323.2 m (Fig. 8), which could be utilised through wind turbines class I with 300 m of height and rotor diameter less than 100 m.

The wind speed at 10 m (Fig. 5) showed that Barranquilla, Santa Marta and La Guajira locations are feasible to implementing offshore wind turbines class III, which can generate energy with rotor diameter about 100 m and hub heights over the 70 m. Actually, the GE Renewable Energy company develops the project Haliade-X 12 MW, with a hub height of 260 m and 220 m of rotor diameter becomes the tallest offshore wind turbine class I in the world (GE Renewable Energy, 2018).

The offshore wind farms in the study areas could provide the maximum amount of energy to the Colombian energy system, from December to April and from June to August, mainly when hydroelectric plants are in low production. During the period of September to November when the wind speed is low, the increment of rainfalls due to the positioning of the ITCZ over Colombia contributes to increase the capacity of energy generation of the hydroelectric plants. This complementary generation system will reduce the risk of energy availability in Colombia, and could open opportunities to export energy to the Latin American and the Caribbean regions.

Marine renewable energies in Colombia

The marine renewable energy potential for Colombia (waves, tides, currents, winds and thermohaline gradients) had been studied thoroughly in the last decade. In this sense, the potential of marine waters in Colombia to generate energy through OTEC (Ocean Thermal Energy Conversion) was presented in 2014. The research concluded that the San Andrés Island is ideal to implementing the OTEC technology [START_REF] Devis-Morales | Ocean thermal energy resources in Colombia[END_REF].

Ortega-Arango (2010) reported the possible technologies for wave energy extraction; the study area was the Isla Fuerte Island in the Colombian Caribbean. The research recommended the Sea based Wave Energy Converter, because it works in very shallow waters, the simplicity of its components and the energy generation mechanisms. The results of the research were not conclusive for the energy extraction, due to the lack of technical information of the energy converter and the scarce wave in situ data, limited to establish recommendations for feasibility projects in the study area.

Alvarez-Silva and [START_REF] Alvarez-Silva | Salinity gradient energy potential in Colombia considering site specific constraints[END_REF] showed that in Colombia the energy potential of the saline gradient in the Magdalena River mouth is 15 157 MW and 187 MW for the León River in the Urabá Gulf, concluding that both study areas are ideal for energy extraction.

Realpe-Jiménez et al. ( 2012) evaluated the wind energy potential in the Colombian islands. Through numerical modelling, they estimated that the most wind energy potential was in the Island of San Andrés (North West of Colombia, near Nicaragua), with 5106 MWh/year at 70 m of height.

A research was carried out in 2016 to estimate wave energy potential in several places in Colombia [START_REF] Osorio | Assessment of the marine power potential in Colombia[END_REF]. The researchers calculated the energy potential of currents, waves, tides and thermohaline gradients. The study mentioned that there are different points or distributed zones in Colombia according to the energy source. For the Caribbean coast, they identified five points for energy saline gradient extraction and one point for wave energy; in the San Andrés Island, they report one point for temperature gradient. In the Pacific coast, they recommend three points for wave energy and three points for tide energy.

The study mentioned above has shown relevant information about marine renewable energy in Colombia, mainly currents, waves, tides and thermohaline gradients. This study recommended improving the knowledge about the availability and quality of the mentioned renewable sources and the technical and economic availability for exploitation. However, there are no public evidence about detailed offshore wind energy information for specific places, or technical, or financial feasibility studies for installation, extraction, and operation of offshore wind farms in Colombia.

Needs, challenges, and opportunities for Colombia

The high availability of hydric resources allows Colombia to have an electric system highly reliable and competitive. According to the World Energy Council (2014), the Colombian electric system is vulnerable to climatic phenomena that can decrease water availability. The El Niño -South Oscillation (ENSO) phenomenon has generated droughts during the periods 1991-1992, 2002-2003 and recently during 2015-2016. The report published by IDEAM mentioned that the most intense period led to Colombia to an energy saving regime, to avoid an imminent electrical rationing. Low water levels of dams during El Niño (2015-2016), the limited gas offer, and the high oil prices put at risk the Colombian electric system in 2016 [START_REF] Dinero | El fenómeno de El Niño revive la posibilidad de un apagón en Colombia[END_REF] The transition of Colombia to renewable energies has begun, and it is evidenced in recent decisions taken by the public and private sectors (CREG, 2018b). [START_REF] Contreras | Incentives for wind power investment in Colombia[END_REF] developed a proposal to improve the policies of the renewable energy management, through mechanisms of articulation, distribution, and financing of private sectors with public participation. They consider that private sector must facilitate resources for the execution of the project, and the public sector must acquire the responsibility of regulating and distributing the energy service.

As stated by [START_REF] Botero | Evaluation of methodologies for remunerating wind power's reliability in Colombia[END_REF] and [START_REF] Vergara | Wind Energy in Colombia: A Framework for Market Entry[END_REF], some incentive mechanisms are needed to increase wind power implementation; tax exemptions is one way but not the most efficient. In this regard, the reform proposed by Contreras and Rodriguez (2016) considers incentives that generate interest to develop renewable energy projects. The main recommendations given in the reform are:

Definition of the distributed generation as part of the power supply chain. Definition of the mechanisms to incentive renewable energy uses according to the characteristics of the country where potential menaces to wind energy project can be mitigated.

Franco [START_REF] Franco-Cardona | The energy trilemma in the policy design of the electricity market[END_REF] presented the energetic trilemma to develop the energy market, which guarantees the environment protection, the energy supply, and the economic sustainability. They pointed out that to study the economic effect generated by implementing non-conventional renewable energies, it is necessary to analyse the effect of the cost reduction in the energy rates through subventions. Additionally, they concluded that different policies in Colombia could be implemented for reducing the Carbon emissions, motivate the renewable energy industry, and guarantee the energy supply keeping the balance between offer and demand.

The reduction of hydroelectric energy during El Niño (2015-2016) and the elevated costs of oil fuel in that period [START_REF] Dinero | El fenómeno de El Niño revive la posibilidad de un apagón en Colombia[END_REF] motivated to increment and diversify the domestic energy offer. The recent decisions taken by the Colombian government evidence the interest to incentive the renewable energy exploitation.

Castro Ferreira (2017) showed that the guarantee of an efficient and sufficient electricity offer requires a reliable infrastructure, and the expansion of NCES. Then, to enhance the offer are necessary administrative mechanisms through contracts as "Take or Pay," "Energy Purchase Agreements (EPAs), "Pay the generated" and "Green Bonus." [START_REF] Zuluaga | Incentives for renewable energy in reformed Latin-American electricity markets: the Colombian case[END_REF] analysed simulations of the Colombian market and concluded that direct subsidies have a major effect on the renewable energy technology diffusion than initiatives such as fiscal policies (tax exemptions). [START_REF] Ortiz | Las energías renovables en la matriz energética de Colombia, in: 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética. Presented at the 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética[END_REF] specified that the development of NCES requires the retribution of self-generation surpluses, the improvement of information about NCES potential and availability, the definition of additional mechanisms to diversify the electric matrix, the adjustments of market mechanisms (bilateral contracts, reliability charge, auctions), and a normative for the exploitation of geothermal resources. Additionally, some challenges to overcome were identified for the NCES development: integration of climate change policy to the energy policy, coordination of licensing processes for generation and transmission, intermittency of NCES, and development of projects to expand the NCES.

The association of Renewables Energies (Ser Colombia, Asociación de energías renovables Colombia) sent several communications to the MADS and ANLA, about the environmental licensing requirements for NCES and Thermal (Fossil fuel) in Colombia. The communications pointed out that requirements for NCES could be reduced or modified due to the low environmental and social impact compared to thermal plants. Ávila (2017) [START_REF] Valencia | Hoja de ruta para la incorporación de energías renovables en Colombia, in: 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética. Presented at the 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética[END_REF].

The possible events of the distribution of generated additional capacity and associated cost reported by [START_REF] Valencia | Hoja de ruta para la incorporación de energías renovables en Colombia, in: 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética. Presented at the 1er encuentro internacional de energías renovables, viabilizando la diversificación de la matriz energética[END_REF], evidenced that condition 3 showed the lowest investment costs from all the scenarios (Table 3). The condition 2 suggests more additional expansion for wind energy and no additional expansion of coal, and condition 3 suggests more additional expansion for solar and geothermal energy and zero additional expansion for coal. The OWE technology is still not considered as an interesting alternative for the NCES projects. This technology requires a continuous research to reduce the associated costs and requires a specific research to evaluate the OWE potential to increment the domestic offer in Colombia. Accordingly, it is necessary a specialised personnel (interdisciplinary professionals and technicians) that support the research and development of the OWE industry.

Despite the authors has developed three studies carried out in Colombia related to the design of offshore wind turbines [START_REF] Rueda Bayona | Caracterización hidromecánica de plataformas marinas en aguas intermedias sometidas a cargas de oleaje y corriente mediante modelación numérica[END_REF], 2017;[START_REF] Rueda-Bayona | Alternative method to determine extreme hydrodynamic forces with data limitations for offshore engineering[END_REF] there are limitations to wind energy diffusion as referred by [START_REF] Edsand | Identifying barriers to wind energy diffusion in Colombia: A function analysis of the technological innovation system and the wider context[END_REF]. Even though there are advances in the offshore engineering, it is necessary that the Colombian government promotes and strengths the academic, research and development programs that lead to specialised personnel training, and through them, the country can take decisions that support the execution of offshore energy projects.

Limitations of the study and future research directions

Colombia has a tremendous opportunity to increase all the legal context and public policies to motivate investments related to non-conventional sources of renewable energies (NCES). Since the main source for power comes from water resources, Colombia is one country considered as privileged regarding this resource. There is not enough interest to develop opportunities and technologies. This lack of interest is represented in limited data to evaluate the oceanographic and maritime climate conditions for research and the design of offshore wind farms. It is expected that this study and further ones increase the interest in this area and encourage the private sector to explore alternative and renewable sources of energy for non-connected areas (i.e. rural regions) or as an alternative for dry seasons.

To advance into the offshore wind exploitation in Colombia, it is required a more detailed study to identify the best locations to install wind farms according to the energy potential. Hence, it is essential to evaluate the feasibility to install the appropriated technology according to the topography and soil mechanics of the seabed, the building materials performance and the identification of the social and environmental potential impacts that could be generated, through quantitative methods such as Life Cycle Assessment (LCA).

There is an upcoming initiative led by the Nueva Granada Military University (www.umng.edu.co) starting at 2019 focussed in pre-design the first offshore wind turbine in Colombia through the research project INV-ING-2985. The Project will analyse the hydromechanics, structural dynamics, fatigue, materials, foundations and the environmental and economic considerations considering the United Nations Sustainable Development Goals.

Conclusions

The transition to renewable energies requires a series of actions and events that guarantee its sustainability. The Colombian government must keep developing public policies that motivate the exploitation of marine renewable energies. Likewise, Colombia must increase the knowledge of the availability of renewable sources and the technical and economic feasibility of marine renewable projects. Additionally, Colombia needs to identify the potential effects due to the non-transition to clean energies and the costs of implementing offshore renewable technologies.

The onshore wind energy at present is dominated by Europe, where the land availability is scarce, and some communities do not accept the installation of these structures easily. As a result, the wind energy sector is increasing the number of offshore wind projects, not only by land restrictions but also because the offshore wind energy is abundant and a good quality source.

The knowledge of the availability of offshore renewable energies requires enhancing the acquisition of primary data through in situ techniques, and the improvement of policies to access to national databases. The measurement of currents, waves, winds, temperature, and salinity in the ocean require higher temporal and spatial resolutions.

The technical and economic feasibility of offshore energy projects need specialised personnel, then, Colombia must define an integrated industry-academia policy. Colombia can consider the experiences of Europe about the strategies of private sector investments for the execution of offshore wind energy projects. Colombia can establish tax incentives and financial alternatives to the development and innovation of companies that will allow the implementation of OWE pilot projects with the support of universities and research centres. The results of pilot projects will define the mechanisms to implementing the design, production, installation, generation, maintenance and dismantling processes and methodologies.

The Colombian government needs to improve the communication with different actors of society (communities, fishing industry, environmentalist), and economic sectors associated with tourism, mariculture, energy, naval, port, and security. A permanent and transparent communication between the State and the society will guarantee the execution of OWE projects and the sustainable production and distribution in the territory.

The estimates of offshore wind energy in the Colombian Caribbean region made by the IDEAM are over-calculated to a level over 1700 W/m 2 (IDEAM, 2018). Although using data from satellite measurements more accurate and improved modelling techniques, our results are much lower. We found that three of the regions studied, La Guajira (482 W/m 2 , at 110.8 m), Barranquilla (857 W/m 2 , at 323.2 m) and Santa Marta (658 W/m 2 at 10 m) have relevant energy potential. These results are at the same level as the bests onshore locations inside La Guajira peninsula but without a barrier of the rejecting of the indigenous people which have severely delayed the wind energy development (UPME, 2015a). Also, the high performance of winds in the studied areas during the dry season (energy density over 300 W/m 2 from December to April), in coincidence with the low electricity generation from hydroelectric facilities, evidence a complementarity that could reduce the gas-based power generation, which is increasingly needed due to the El Niño -South Oscillations events.

Although further more in-depth studies are required to identify the areas where it is feasible to place offshore wind farms, the energy potential obtained in this work makes possible to predict that the potential offshore generation capacity can exceed the identified 20 GW onshore. These findings could contribute to the path of Colombia for a completely clean and renewable electric matrix in the not too distant future reach.

Considering the latest reports of wind energy international markets and expectations, the recent investments to increase the OWE research, and the calculation of local OWE potential, now it is the opportunity for Colombia to be a relevant energy exporter and leader in OWE technology. This opportunity will help to reduce the carbon emissions and will increment job opportunities in the energy market and the associated economic sectors.

Figure captions

Fig. 1. Extraction of wind speed (m/s) from Reanalysis database for the study areas. The magenta polygon highlights the extracted pixel data that covers a specific study area (e.g. Cartagena city); the white line indicates the coastline.

Table captions

Table 1. Growth of the renewable energies in the World considering the three approaches.

Table 2. Guidelines and methodologies for the associated activities to produce Non-conventional sources of renewable energy in Colombia.

Table 3. Present and future scenarios according to conditions base installed capacity (MW) and additional expansion (MW).

Highlights.

Advances and challenges of the offshore wind energy around the world.

Legal and administrative framework of the renewable energy of Colombia.

Wind speed trends and power density results justify offshore wind energy research.

El Niño (2015Niño ( -2016) ) put at risk to the Colombian electric system.

Fig. 1 .

 1 Fig. 1. Extraction of wind speed (m/s) from Reanalysis database for the study areas. The magenta polygon highlights the extracted pixel data that covers a specific study area (e.g. Cartagena city); the white line shows the coastline.

Fig. 2 .

 2 Fig. 2. Distribution of annual mean wind speed (m/s) in Colombia. Black dots represent the climate stations used for the analysis, and contour colours are blended data with WRF modelled results (www.wrf-model.org). Modified from: IDEAM (2018).

Fig. 3 .Fig. 4 .

 34 Fig. 3. Monthly variation of wind speed (m/s) in the study areas from January 1979 to June 2015: a) Barranquilla, b) Santa Marta, c) La Guajira and d) Cartagena. The red line represents the linear trend.

Fig. 5 .

 5 Fig. 5. Monthly mean of wind speed at 10 m in the study areas (derived from 1979 to 2015).

Fig. 6 .

 6 Fig. 6. Monthly mean of wind power density at 10 m of elevation in the study areas (derived from 1979 to 2015).

Fig. 7 .

 7 Fig. 7. Monthly mean of wind power density at 110.8 m of elevation in the study areas (derived from 1979 to 2015).

Fig. 8 .

 8 Fig. 8. Monthly mean of wind power density at 323.2 m of elevation in the study areas (derived from 1979 to 2015).

Fig. 9 .

 9 Fig. 9. Distribution of annual mean wind speed (m/s) in Colombia. Black dots represent the climate stations used for the analysis, and contour colours are blended data with WRF modelled results (www.wrf-model.org). Modified from: IDEAM (2018).

Fig. 10 .

 10 Fig. 10. Monthly variation of wind speed (m/s) in the study areas from January 1979 to June 2015: a) Barranquilla, b) Santa Marta, c) La Guajira and d) Cartagena. The red line represents the linear trend.

Fig. 11 .

 11 Fig. 11. Wind rose (m/s) of the study areas from January 1979 to June 2015.

Fig. 12 .

 12 Fig. 12. Monthly mean of wind speed at 10 m in the study areas (derived from 1979 to 2015).

Fig. 13 .

 13 Fig. 13. Monthly mean of wind power density at 10 m of elevation in the study areas (derived from 1979 to 2015).

Fig. 14 .

 14 Fig. 14. Monthly mean of wind power density at 110.8 m of elevation in the study areas (derived from 1979 to 2015).

Fig. 15 .

 15 Fig. 15. Monthly mean of wind power density at 323.2 m of elevation in the study areas (derived from 1979 to 2015).

Table 1 )

 1 , the Unfinished Symphony scenario allows the highest development of renewable energy (RE) production to 2030, being the wind energy the most developed in the four scenarios.

Table 1 .

 1 Growth of the renewable energies in the World considering the three approaches.

		2013		2030		2030		2030
	Electricity generation			Modern Jazz		Unfinished		Hard Rock
	(TW.h)					Symphony
		TW.h	%	TW.h	%	TW.h	%	TW.h	%
	Coal	9595 41.17	8960 27.85	7741 25.09	9684 31.64
	Coal (with CCS)	0	0.00	20 0.06	95 0.31	0 0.00
	Oil	1048	4.50	560 1.74	381 1.23	733 2.40
	Gas	5081 21.80	9292 28.88	7014 22.73	7740 25.29
	Gas (with CCS)	0	0.00	0 0.00	82 0.27	0 0.00
	Nuclear	2478 10.63	3327 10.34	4367 14.15	3864 12.62
	Hydro	3790 16.26	4816 14.97	5109 16.56	4825 15.76
	Biomass	461	1.98	1069 3.32	1187 3.85	844 2.76
	Biomass (with CCS)	0	0.00	0 0.00	0 0.00	0 0.00
	Wind	635	2.72	2540 7.90	2918 9.46	1983 6.48
	Solar	145	0.62	1369 4.26	1694 5.49	793 2.59
	Geothermal	72	0.31	210 0.65	262 0.85	133 0.43
	Other	3	0.01	8 0.03	5 0.01	8 0.03
	Total Renewables	851	4.00	4120 13.00	4874 16.00	2908 10.00
	Total	23 307	100	32 171 100	30 854 100	30 605 100
	Adapted from

Table 2 .

 2 Guidelines and methodologies for the associated activities to produce Non-conventional sources of renewable energy in Colombia.To reduce the CO 2 emissions, Colombia improved the national economic development avoiding the increment of the GHG emissions(Prias Caicedo, 2010a). Then, between 2013 and 2015 the Ministry of Environment and Sustainable Development (MADS, Ministerio de Ambiente y Desarrollo Sostenible), created the Sectorial Action Plans (PAS, Planes de Acción Sectorial de Mitigación para el Cambio Climático), to integrate the other Ministries into the guidelines of MADS. In 2015, the PAS were approved through the law 1753 of 2015 for the period 2014-2018 (Senado de la República de Colombia, 2015); the Green Growth chapter gives the authorisation to the other Ministries to generate the implementation plan of PAS and the sectorial adaptation plans. In the COP21 held in Paris, Colombia was committed to reducing 20 % of GHG emissions (67 million Ton of CO 2 ) by 2030. Later, in February 2016, the National System of Climate Change (SISCLIMA, Sistema Nacional de Cambio Climático) was created, to manage the climate change in Colombia. As a result, SISCLIMA through the Intersectoral Commission on Climate Change (CICC, Comisión Intersectorial de Cambio

	Guideline/Methodology	Description
	Resolution CREG 85 (CREG, 1996),	About surplus sales of co-generation.
	and 005 (CREG, 2010)
	Resolution CREG 153 (CREG, 2013) About fuel supply contracts of agricultural origin
		for the reliability charge.
	Resolution CREG 132 (CREG, 2014a) Methodology to estimate the maximum
		electricity that can produce a generation plant
		permanently during low hydrologic conditions in
		one year (ENFICC, Energía Firme para el Cargo
		por Confiabilidad) for geothermal plants.
	Decree 2469 (CREG, 2014b)	Self-generation for big scale.
	Resolution CREG 024 (CREG, 2015a) Self-generation for big scale.
	Resolution CREG 061 (CREG, 2015b) Methodology ENFICC for wind plants.
	Resolution UPME 0281 (UPME,	Power limit for self-generation in small scale
	2015c)
	Resolution CREG 243 (CREG, 2016a) Methodology ENFICC for solar plants.
	Resolution CREG 026 (CREG, 2016b) Transient dispositions to adapt the entrance of
		new generation plants to the system.

Table 3 .

 3 Present and future scenarios according to conditions base installed capacity (MW) and additional expansion (MW).

	Condition 0	Condition 1	Condition 2	Condition 3	Condition 4

Acknowledgments

Authors thank Universidad del Norte for the financial support through UNINORTE doctoral Fellowship (2013-2017) [grant number UN-OJ-2013-22058].


Dr Valérie Malan
email: valerie.malan@nck.aphp.fr

Suzanne Chevallier

Gwendoline Soler

Christine Coubes

Didier Lacombe

Laurent Pasquier

Jean Soulier

Nicole Morichon-Delvallez

Catherine Turleau

Arnold Munnich

Vale ´rie Malan

Serge Romana

Michel Vekemans

Vale ´rie Cormier-Daire

Laurence Colleaux

Array-based comparative genomic

Keywords: array-CGH, overgrowth disorders, oncogenes, chromosome imbalance, tumor-suppressor genes

teaching and research institutions in France or abroad, or from public or private research centers.

INTRODUCTION

Overgrowth syndromes are a heterogeneous group of conditions characterized by either localized or generalized excessive growth for age and sex. Most overgrowth syndromes are associated with various anomalies, including an increased risk for neoplasia and/or cognitive impairment. The clinical importance of overgrowth syndromes was documented in the nineteenth century and conditions such as the Beckwith-Wiedemann syndrome (OMIM 130650), the Sotos syndrome (OMIM 117550), the Simpson-Golabi-Behmel syndrome (OMIM 312870) or the Bannayan-Riley-Ruvalcaba syndrome (OMIM 153480) were delineated by the 1960s. In contrast, the molecular cause of a handful of overgrowth syndromes has been elucidated only recently. Despite these recent advances, the diseasecausing mechanism remains unknown in 20-40% of patients, underlining the genetic heterogeneity of these disorders. Moreover, a large number of patients with overgrowth syndromes do not belong to any recognizable condition and remain unexplained.

Interestingly, several chromosomal duplications and deletions have been characterized in patients with overgrowth, suggesting that some still unclassified overgrowth syndromes may be caused by subtle genomic imbalanced rearrangements. Tall stature is observed in patients with dup(4)(p16.3) likely because of the dosage effect of the fibroblast growth factor receptor gene 3. [START_REF] Partington | Translocations involving 4p16.3 in three families: deletion causing the Pitt-Rogers-Danks syndrome and duplication resulting in a new overgrowth syndrome[END_REF] Trisomy of 15q26qter is frequently associated with tall stature and mental retardation caused by duplication of the insulin-like growth factor 1 receptor gene. [START_REF] Faivre | Overgrowth and trisomy 15q26.1-qter including the IGF1 receptor gene: report of two families and review of the literature[END_REF][START_REF] Tatton-Brown | 15q overgrowth syndrome: a newly recognized phenotype associated with overgrowth, learning difficulties, characteristic facial appearance, renal anomalies and increased dosage of distal chromosome 15q[END_REF] Various types of NSD1 aberrations have been identified in patients with Sotos syndrome, including 5q35 microdeletion. [START_REF] Kurotaki | Haploinsufficiency of NSD1 causes Sotos syndrome[END_REF] Interstitial deletions at 9q22.32q22.33 have been detected in two patients with macrocephaly, overgrowth and trigonocephaly. [START_REF] Redon | Interstitial 9q22.3 microdeletion: clinical and molecular characterisation of a newly recognised overgrowth syndrome[END_REF] Finally, del (22)(q13) has also been associated with overgrowth and macrocephaly. [START_REF] Phelan | 22q13 deletion syndrome[END_REF] These data strongly support the hypothesis that studying chromosomal aberrations in relation to overgrowth using sensitive tools may lead to the identification of a significant number of cryptic chromosomal anomalies.

In this study, we report the application of genome-wide array-based comparative genomic hybridization (CGH) at a 1-Mb resolution to the study of 93 patients with syndromic overgrowth. In addition to their clinical relevance, our results emphasize the importance of a chromosomal imbalance in the etiology of these conditions and may help to identify novel genes involved in growth anomalies.

MATERIALS AND METHODS Subjects

We recruited 93 patients born to unrelated parents who presented with unexplained syndromic overgrowth. All of them presented with (1) height 495th percentile and/or (2) occipito-fronto circumference 495th percentile and (3) developmental delay, and at least two minor features among the following: (a) bone age 490th percentile, (b) dysmorphic craniofacial features and (c) congenital anomalies or malformations. These patients were classified in two groups:

Group I (48 cases) included patients with a recognizable overgrowth condition. Among this group, 31 were classified as patients with Sotos syndrome because they fulfilled the diagnostic criteria defined by Cole and Hughes. [START_REF] Cole | Sotos syndrome: a study of the diagnostic criteria and natural history[END_REF] Five were considered as patients with Sotos-like syndrome because they presented with the specific facial gestalt and macrocephaly, but lacked one major criterion, namely, advanced bone age and/or overgrowth. Five presented the suggestive facial gestalt, overgrowth, macrocephaly, camptodactyly and accelerated skeletal maturation characteristic of Weaver syndrome. [START_REF] Rio | Spectrum of NSD1 mutations in Sotos and Weaver syndromes[END_REF][START_REF] Baujat | Clinical and molecular overlap in overgrowth syndromes[END_REF] Two patients with macrosomia, macroglossia, midline abdominal wall defects and neonatal hypoglycemia were diagnosed as having the Beckwith-Wiedemann syndrome. [START_REF] Weksberg | Beckwith-Wiedemann syndrome demonstrates a role for epigenetic control of normal development[END_REF][START_REF] Baujat | Paradoxical NSD1 mutations in Beckwith-Wiedemann syndrome and 11p15 anomalies in Sotos syndrome[END_REF] The diagnosis of macrocephaly-cutis marmorata telangiectatica congenita syndrome was established in three patients with skin abnormalities. [START_REF] Lapunzina | Macrocephaly-cutis marmorata telangiectatica congenita: report of six new patients and a review[END_REF] One patient presented with suggestive facial gestalt (shallow orbits), accelerated growth and skeletal maturation, overgrowth and broad middle phalanges characteristic of the Marshall-Smith syndrome. [START_REF] Williams | Marshall-Smith syndrome: the expanding phenotype[END_REF] One patient was considered as having the Simpson-Golabi-Behmel syndrome, because he presented with macrocephaly, the characteristic facial dysmorphism (large protruding jaw, broad nasal bridge), supernumerary nipples, rib abnormalities, hepatosplenomegaly and cardiac abnormalities. [START_REF] Neri | Clinical and molecular aspects of the Simpson-Golabi-Behmel syndrome[END_REF] Group II (45 cases) included patients with unclassified overgrowth syndromes.

All patients had a normal high-resolution karyotype with no evidence of unbalanced rearrangement. In both groups, a mutation within the NSD1 and GPC3 genes was excluded by direct DNA sequencing, as well as 11p15 region anomalies. Finally, fluorescence in situ hybridization (FISH) analysis was performed to exclude a deletion involving the 5q35 (NSD1 gene), 9q22 and 22q13.3 regions and a duplication of the 15q26.3 and 4p16.3 regions.

Blood samples were obtained from the probands and their parents after informed consent. Genomic DNA was isolated from blood leukocytes using a Nucleon kit (GE Healthcare, Amersham Biosciences, Piscataway, NJ, USA) according to the manufacturer's instructions.

Array-CGH

The microarray used in this study is the CytoChips microarray (BlueGnome Ltd, Cambridge, UK). These arrays are spotted with 4400 clones spread over the entire genome with a mean resolution of one clone per megabase. Subtelomeric regions and most of the characterized microdeletion syndromes are included in these clones. All clones are set in duplicate. Array hybridization was undertaken according to the manufacturer's recommendations. After hybridization, slides were scanned on a GenePix 4000B scanner (Molecular Devices, Sunnyvale, CA, USA). Fluorescent intensities were extracted and analyzed using BlueFuse software (BlueGnome, Cambridge, UK). Data were normalized by dividing the mean ratio of each clone duplicate by the median ratio of all autosomal clones. Clones were excluded in cases in which duplicate values differed from each other by more than 10%. A clone was considered to be positive for duplication or deletion if the log2 fluorescence intensities ratio exceeded a value of the mean plus or minus four times the standard deviations (SDs) beyond the mean ratio. Agilent 244K oligonucleotide microarrays (Agilent Technologies, Santa Clara, CA, USA) were used according to the manufacturer's recommendations and provide a mean resolution of 20 kb.

Fluorescence in situ hybridization

BACs were selected from several databases (University of California, Santa Cruz http://genome.ucsc.edu/ and National Center for Biotechnology Information http://www.ncbi.nlm.nih.gov/). FISH studies were performed using standard protocols. [START_REF] Romana | In situ hybridization to interphase nuclei in acute leukemia[END_REF]

RESULTS

Molecular karyotyping and FISH analyses

A total of 93 patients, 68 males and 25 females, who presented with syndromic overgrowth were studied using array-CGH on a BAC/PAC microarray at a mean 1-Mb resolution. To identify potentially clinically relevant anomalies from benign chromosomal variants, we first took advantage of the Database of Genomic Variants (http:// projects.tcag.ca/variation/) to exclude copy number variations (CNVs) previously observed in control individuals. Ten chromosome gains or losses detected in nine patients were thereby considered as being possibly pathogenic and were investigated further. Among these, four are deletions and six are duplications. All imbalances mapped to distinct nonoverlapping regions.

All potentially pathogenic imbalances were confirmed by FISH analysis. Patient 4 was found to carry an amplification of the 18q21.3 region. FISH studies performed on nuclei revealed -four to five hybridization signals. Retrospectively, the deletion of case 5 was visible on a high-resolution karyotype.

To further show the clinical relevance of these chromosomal aberrations, we tested clinically normal parents by FISH analysis to discriminate between de novo or inherited anomalies. Three CNVs were inherited from a phenotypically normal parent and were interpreted as likely benign variants with no clinical significance. One patient carries an 8q23.3 duplication inherited from a healthy father. Another case carries two chromosomal abnormalities (a 2q22.1 deletion and a 10p13 duplication) both inherited from his healthy father. Five rearrangements (patients 3-7) occurred de novo and are likely pathogenic. The two remaining imbalances are X-linked CNVs (an Xq28 duplication (case 1) and an Xp22.31 deletion (case 2)) inherited from a healthy mother. The mother of patient 1 showed a completely skewed X-inactivation pattern, supporting the potential pathogenicity of this CNV. Unfortunately, the DNA sample from the mother of patient 2 was not available to study the X-chromosome-inactivation pattern. The array-CGH profiles of these cases are shown in Figure 1.

Finally, high-resolution microarray analysis was performed to precisely define the size of the rearrangements. The size of the aneusomic segment varied from 0.32 to 18.2 Mb (0.32-3.74 Mb for duplications and 1.58-18.2 Mb for deletions).

These seven cases are summarized in Table 1 and have been submitted to the DECIPHER database (http://www.sanger.ac.uk/ PostGenomics/decipher/). This provides access to detailed phenotype information and allows to view the genomic imbalances within the context of the genome browser, Ensembl (http://www.ensembl. org/index.html).

Clinical data

The clinical features of patients with clinically relevant chromosomal abnormalities are described below.

Patient 1. Patient 1 was ascertained at 7 years of age because of developmental delay and dysmorphism. His birth weight was 2840 g (50-10th centile), length was 50 cm (50th centile) and head circumference was 35 cm (50th centile). He began to sit at 2 years and walk at 5 years. At 7 years, speech is absent, in contrast to his ability to understand. Some stereotypies were also noted. There was no history of feeding problems or infectious diseases. His physical examination showed macrocephaly 4+4SD (58.5 cm) with height 125 cm (+1SD) and weight 26.6 kg (+1SD). His mother and father were 150 and 168 cm in height, respectively. Severe hypotonia was noted.

Dysmorphic features include microstomia and large ears. He displayed livedo and contractures of several joints such as of the knees and elbows. This patient carries a 320-kb-long Xq28 duplication inherited from his healthy mother. Patient 2. The propositus was born at 38 weeks of gestation after an uneventful pregnancy with birth parameters above the mean (weight 3900 g (50-90th centile), height 55 cm (495th centile) and head circumference 41.5 cm (495th centile)). In early infancy, he showed developmental delay. He began to walk at 22 months and he had a speech delay. At 6 years of age, he had a height of 120 cm (+1.2SD), a weight of 29 kg (+3SD) and a head circumference of 57 cm (4+4SD). His mother and father were 168 and 183 cm in height, respectively. Clinical examination revealed skin abnormalities suggesting ichthyosis. The diagnosis of ichthyosis has also been proposed in the mother and grandfather. Cerebral resonance magnetic imaging showed mild ventricular asymmetry. This patient carries a 1.58-Mblong Xp22.31 deletion inherited from his healthy mother.

Patient 3. Patient 3 is an 11-year-old girl born at term with a weight of 3510 g (50-90th centile), a height of 49 cm (50th centile) and a head circumference of 37 cm (42SD). In the neonatal period, she had poor sucking and abnormal movements requiring medicine (Depakine). In early infancy, severe developmental delay was noted. She was able to hold her head at 9 months and began to walk at 5 years. She said only a few words at the age of 9 years and 6 months. Some stereotypies were also noted. On examination at 11 years of age, growth parameters were weight 33 kg (M), length 153 cm (+2SD) and head circumference 55.5 cm (+2SD). Her mother and father were 163 and 172 cm in height, respectively. She had dysmorphic facial features including a high forehead, a thin and long face, a narrow mandible, a short philtrum and prominent upper incisors. Deformity (genu valgum) in the lower limbs was observed. This patient carries a 3.19-Mb-long 16p12.3p13.1 de novo duplication.

Patient 4. Patient 4 was born at term with birth parameters in the normal range (weight 3180 g (50th centile), height 49.5 cm (50th centile) and head circumference 36.5 cm (50-90th centile)). Hypotonia and psychomotor development delay were noted. He held his head at 4 months, sat at 15 months and walked without help at 22 months. He had a speech delay. In the first years of life, he presented with feeding problems. He underwent surgery because of phimosis. On physical examination at the age of 3 years and 6 months, his length was 100 cm (+1SD), height was 17.5 kg (+3SD) and head circumference was 54 cm (42SD). His mother and father were 160 and 179 cm in height, respectively. Dysmorphic facial features included upslanting palpebral fissures, a small nose and a carp-shaped mouth. Ophthalmologic examination revealed strabismus. Triceps spasticity was noted. This patient carries a 1.42-Mb-long 18q21.33 de novo amplification.

Patient 5. Patient 5 was born prematurely at 33 weeks of gestation with a birth weight of 1940 g (50th centile), length of 45 cm (50th centile) and head circumference of 32 cm (50th centile). At the age of 3 years, he could walk without help and spoke a few words. On examination, his height was 119 cm (42SD), his weight was 19 kg (42SD) and his head circumference was 53 cm (+2SD). His mother and father were 170 and 187 cm in height, respectively. He displayed facial dysmorphism with epicanthus, a prominent nasal bridge, bulbous nasal tip and everted lips. In addition, the patient presented a double hair whorl and a shawl scrotum. This patient carries an 18.2-Mb-long 3q13.11q13.33 de novo deletion.

Patient 6. The propositus was born at 38 weeks of gestation through spontaneous vaginal delivery. At birth, weight was 4030 g (495th centile), length was 55 cm (495th centile) and head circumference was 35 cm (50-90th centile). In early childhood, developmental delay was noted. At physical examination at the age of 12 years, his length was 173.5 cm (+3SD), weight was 63 kg (+4SD) and head circumference was 58 cm (+3/4SD). His mother and father were 173 cm and 183 cm in height, respectively. He presented with speech delay. He had dysmorphic features including dolichocephaly, upslanting palpebral fissures, hypertelorism and retrognathia. A single flexion crease of the hands and a lumbar hyperlordosis were noted. This patient carries a 7.29 Mb-long 10q23.1q23.2 de novo deletion.

Patient 7. This patient was referred to a medical center because of overgrowth and thumb abnormalities. He was born at 38 weeks of gestation after an uneventful pregnancy with a weight of 4270 g (90th centile), a height of 52 cm (90th centile) and a head circumference of 37.5 cm (495th centile). Triphalangy of the thumbs with clinodactyly was noticed. In early childhood, he presented with a mild developmental delay. He started walking at 18 months and had some language difficulties. At the age of 6 years and 6 months, he attended a regular elementary school with speech therapy once a week. On examination, he had a weight of 35 kg (43SD), a height of 133.5 cm (43SD) and a head circumference of 61 cm (43SD). His mother and father were 172 and 180 cm in height, respectively. He had a facial dysmorphism reminiscent of Weaver syndrome. A lumbar cutaneous angioma and cafe-au-lait spots were noted. He also displayed a moderate pectus excavatum. This patient carries a 3.74-Mb-long 2p24.3 de novo duplication.

DISCUSSION

Although some patients with syndromic overgrowth might have been subjected to array-CGH testing in the course of the systematic study of mentally retarded cases, we present in this study the first analysis using whole-genome array-CGH focused on such patients. A total of 93 patients were investigated and 7 potentially pathogenic chromosome imbalances were identified, providing a diagnosis yield of 7.5%. No recurrent abnormality was identified in this cohort and all but one aneusomic fragment have a size smaller than 5 Mb. Our results provide further demonstration for the extreme genetic heterogeneity of these conditions. They also suggest that array-CGH should be considered as an essential aspect of the genetic analysis of patients with localized or generalized syndromic overgrowth.

In two cases, however, the clinical relevance of the chromosomal anomaly remains uncertain. This is the case for patient 3 in whom a 16p13.11 duplication was observed. Recently, Hannes et al [START_REF] Hannes | Recurrent reciprocal deletions and duplications of 16p13.11: the deletion is a risk factor for MR/MCA while the duplication may be a rare benign variant[END_REF] described reciprocal 1.7 Mb deletions and duplications of this region resulting from nonallelic homologous recombination (NAHR) between distinct LCR16 subunits. Although deletion is a risk factor for MR/MCA, the duplication may be a rare benign variant. The duplication observed in patient 3 occurred de novo but is identical to those reported by Hannes et al, [START_REF] Hannes | Recurrent reciprocal deletions and duplications of 16p13.11: the deletion is a risk factor for MR/MCA while the duplication may be a rare benign variant[END_REF] making its clinical interpretation difficult.

Similarly, the clinical relevance of the Xp22.31 microdeletion detected in patient 2 remains questionable. This 1.5-Mb interstitial deletion encompasses the STS (steroid sulfatase) gene and was inherited from a mother with normal intelligence. STS deletion is known to be associated with X-linked ichthyosis (XLI), a feature observed in our patient. By contrast, overgrowth has not been described in males with XLI. High-resolution array-CGH showed that patient 2 carried the recurrent 1.5-Mb deletion, because of NAHR between duplicons, and is observed in 90% of XLI patients. [START_REF] Van Esch | Deletion of VCX-A due to NAHR plays a major role in the occurrence of mental retardation in patients with X-linked ichthyosis[END_REF] Presumably, this anomaly may account for the mental handicap and ichthyosis observed in patient 2; however, whether macrocephaly is linked to this deletion remains unanswered.

Five chromosomal abnormalities identified are clearly pathogenic and allow to draw some interesting conclusions. First, although chromosomal deletions are usually associated with growth retardation, three out of five patients have a duplication. Statistical analyses cannot be performed on such a small series; however, our results might therefore suggest that increased gene dosage could be responsible for a significant number of overgrowth cases.

Second, the identification of a 0.32-Mb Xq28 duplication including the MeCP2 (methyl-CpG-binding protein 2) and L1CAM genes in patient 1 provides further evidence of the phenotypic variability of MeCP2 duplications. Males with an MeCP2 duplication manifest infantile hypotonia, severe mental retardation, absence of speech, neurological problems (progressive spasticity and seizures) and recurrent respiratory infections, [START_REF] Van Esch | Duplication of the MECP2 region is a frequent cause of severe mental retardation and progressive neurological symptoms in males[END_REF] whereas growth parameters, including head circumference, are usually within the normal range. Our patient does not appear to fulfill this common phenotype associated with Xq28 duplication. Interestingly, two recent reports describe the association of MeCP2 duplication with macrocephaly. [START_REF] Del Gaudio | Increased MECP2 gene copy number as the result of genomic duplication in neurodevelopmentally delayed males[END_REF][START_REF] Lugtenberg | Structural variation in Xq28: MECP2 duplications in 1% of patients with unexplained XLMR and in 2% of male patients with severe encephalopathy[END_REF] We therefore suggest that severe psychomotor delay, absence of speech and macrocephaly in males may point to the screening for MeCP2 duplication, even in the absence of recurrent respiratory infections.

Finally, three aneusomic segments identified in this study involved oncogenes or tumor-suppressor genes. The MYCN gene maps within the 2p24.3 duplicated segment observed in patient 7. Overexpression of dMyc, the drosophila Myc ortholog, promotes cell growth and induces apoptosis in adjacent cells expressing lower dMyc, and larger wings are observed on ubiquitous overexpression of dMyc during wing development. [START_REF] De La Cova | Drosophila myc regulates organ size by inducing cell competition[END_REF][START_REF] Moreno | dMyc transforms cells into super-competitors[END_REF] Moreover, in humans, haploinsufficiency of the MYCN gene is responsible for Feingold syndrome. This disorder is characterized by intestinal atresias, digital anomalies, facial dysmorphism and learning disability. Microcephaly is one of the most common features present in about 90% of patients with Feingold syndrome. [START_REF] Marcelis | Genotype-phenotype correlations in MYCNrelated Feingold syndrome[END_REF] Altogether, these data are consistent with a function of MYCN overexpression in the etiology of the overgrowth observed in patient 7. Similarly, we observed a 4-5 times amplification of the genomic segment encompassing the BCL2 gene in patient 4. The translocation between chromosomes 14 and 18 (ie, t(14;18)(q32.3;q21)) is the hallmark of follicular B lymphomas. This chromosomal rearrangement leads to a fusion between an IgH enhancer and BCL2, resulting in the overexpression of the antiapoptotic BCL2 protein leading to uncontrolled cell proliferation. Noticeably, transgenic mice overexpressing human BCL2 protein in neurons underwent nervous system hypertrophy and reduced neuronal loss during naturally occurring cell death. [START_REF] Martinou | Viral proteins E1B19K and p35 protect sympathetic neurons from cell death induced by NGF deprivation[END_REF] Finally, patient 6 carries a 10q23.1q23.2 deletion, the distal break point of the rearrangement of which lies close to the PTEN gene (0.68 Mb). Deletions and mutations of PTEN have been encountered in various hamartoma-overgrowth syndromes, collectively designated as 'PTEN hamartoma tumor syndromes' . [START_REF] Eng | PTEN: one gene, many syndromes[END_REF][START_REF] Blumenthal | PTEN hamartoma tumor syndromes[END_REF] Recently, it has been shown that germ-line mutations of PTEN can also determine syndromes characterized by autism associated with macrocephaly. [START_REF] Butler | Subset of individuals with autism spectrum disorders and extreme macrocephaly associated with germline PTEN tumour suppressor gene mutations[END_REF][START_REF] Orrico | Novel PTEN mutations in neurodevelopmental disorders and macrocephaly[END_REF] Presumably, the haploinsufficiency of genes contained within the 10q23.1q23.2 deletion is responsible for some of the features observed in patient 6, such as lumbar hyperlordosis or facial dysmorphy. The deletion may also exert a position effect on PTEN gene expression resulting in overgrowth.

Altogether, these data provide further evidence that constitutional oncogene duplications or tumor-suppressor gene deletions are involved in the pathogenesis of overgrowth conditions. In addition, it suggests that an increased susceptibility to neoplasia may be suspected in these patients.

In conclusion, our results emphasize the benefits of whole-genome array-CGH for the diagnosis of overgrowth syndromes. Careful clinical examination of patients may allow the delineation of novel clinically recognizable overgrowth conditions. A detailed molecular analysis of the rearranged regions may pave the way for the identification of genes involved in growth regulation. More importantly, these data underscore the crucial need for a specific tumor surveillance program in patients with overgrowth syndromes.

Figure 1

 1 Figure 1 Array-based comparative genomic hybridization ratio profiles showing chromosomal imbalances. For each graph, the y axis marks the distance from the telomere of the short arm (Mb) and the x axis marks the hybridization ratio represented on log2. Vertical lines indicate the threshold for clone deletion or duplication (mean (4SD)). Aberrant clones are surrounded.

Table 1

 1 Patients with possibly pathogenic chromosomal anomalies

	Patient	Sex	Anomaly	De novo/inherited	Proximal and distal breakpoints (bp)	Size (Mb)	Candidate genes
	1	Male	dup Xq28	inherited (mother)	152 736 441-153 057 430	0.32	MeCP2
	2	Male	del Xp22.31	inherited (mother)	6 505 818-8 093 448	1.58	STS
	3	Female	dup 16p12.3p13.1	de novo	15399 818-18 599 558	3.19
	4	Male	amp 18q21.33	de novo	57 885 252-59 307 801	1.42	BCL2
	5	Male	del 3q13.11q13.33	de novo	104 531 502-122 804 242	18.2
	6	Male	del 10q23.1q23.2	de novo	81 638 258-88 931 854	7.29	Position effect PTEN
	7	Male	dup 2p24.3	de novo	15 056 071-18 805 733	3.74	MYCN
	Abbreviations: Del, deletion; dup, duplication.
	Data obtained from micro-array Agilent 244K.

European Journal of Human Genetics

ACKNOWLEDGEMENTS

We express our gratitude to the patients and their families. This study was supported by the Centre National de la Recherche Scientifique, the GIS-Maladies Rares and the Agence de Biome ´decine.

CONFLICT OF INTEREST

The authors declare no conflict of interest.