This background paper is an overview of offshore renewable energy sources across coastal Africa, including a review of six technology types: wave power, tidal stream power, ocean current power, ocean thermal energy conversion (OTEC), offshore wind power, and marine floating solar power (FPV). It was commissioned by the African Natural Resources Centre (ANRC) of the African Development Bank as part of a series of studies to support the African strategy for the development of the ‘blue economy’. REGlobal presents an extract from this report

How can the ocean contribute renewable energy to the African ‘Blue Economy’, bringing opportunities to millions of Africans and reducing or replacing carbon emissions, and which strategic actions can help it reach this potential?

The power quality of offshore renewables is relatively high, being more predictable and less variable than many other renewables. The results indicate that coastal Africa, according to available data, has high technical potential for all offshore renewables, apart from tidal stream power.

In the near future, the outlook for utilizing offshore renewables is most promising for African small island states, where land is scarce and imported fuels are expensive. Here, fossil fuel power generation may be partly substituted by offshore renewables. Offshore wind power, OTEC, marine FPV, and wave power offer opportunities at different islands across Africa. At this moment, only offshore wind power is technically mature. Among small island states, Cabo Verde has the best wind resources. Marine FPV is currently being deployed in the Seychelles. The OTEC technology is not yet commercially viable but may eventually prove feasible due to its high capacity and the fact it produces freshwater as a highly attractive byproduct. On the basis of site screenings and an in-depth feasibility study on Mauritius, several African small island states have potential.

Continental Africa has plenty of offshore renewable energy sources but also an abundance of land-based renewable energy, which is more feasible to extract today. Nevertheless, countries with existing offshore industry such as oil and gas drilling may possess, or can develop, a strong offshore capacity that will enable them to use offshore renewables at scale – starting with offshore wind power.

In the longer term, several offshore renewables may become important contributors to the overall energy mix of African power pools, as well as producers for small grids at remote locations.

Eastern Africa has high and diverse potential for offshore renewables, including offshore wind power, wave power, OTEC, marine FPV, and ocean current power. The Indian Ocean island states have excellent conditions for renewable offshore technologies and the long coast of Somalia also holds great energy opportunities for the future.

Southern Africa is surrounded by energetic seas with high potential for offshore wind and wave power, and possibly even ocean current power. Mozambique seems to have conditions for all studied energy kinds, with certain potential for OTEC and wave power. Namibia and Angola have good opportunities too.

Countries of Central Africa have more limited potential for offshore renewables but some of the studied technologies can be used successfully for harvesting freshwater energy resources on rivers and lakes which could be an interesting opportunity to investigate.

Western Africa has good conditions for both offshore wind and wave power. Far offshore, at the continental shelf, conditions are prime for floating OTEC, although this potential may be more relevant for future production of energy carriers than for grid connection because of the distances to shore.

Surrounded by the enclosed Mediterranean and Red Sea, Northern Africa has limited potential for wave and tidal power. Strong winds however create potential for offshore wind power both along the Atlantic, Mediterranean, and Red Sea coasts.

The development of offshore capacity holds the key to offshore renewables. The sea is a challenging environment for any moored equipment and most of the technologies analyzed are still at pre-commercial stage. But the resources are there, ready to become part of a prospering ‘Blue Economy’ when circumstances are right. Since the African continent is blessed with renewable energy of many sorts, the suitability of offshore technologies will always be a compromise determined by the local availability of land-based, less challenging, alternatives.

Resource abundance and technical potential

Wave power potential: The instantaneous wave power resource of African waters has previously been estimated to be 324 GW or 422 GW. The World Energy Council recently estimated Africa’s theoretical potential for wave energy to reach a total of 3,500 TWh per year. The highest resource density is found at subtropical latitudes in the south and north-west. Equatorial Africa and the sheltered Red Sea and Mediterranean have relatively low wave energy densities.

Fairly et al. recently classified wave power resources on a global scale, based on detailed wave and climate characteristics. South Africa was classified as having ‘high-energy coastlines influenced by long period swell and storm conditions’. Atlantic countries from Morocco to Liberia along with the Comoros, Madagascar and Southern parts of Mozambique were classified as having ‘moderate-energy coastlines primarily influenced by long distance swell.’ Equatorial West Africa and Central Africa were classified as having ‘moderate energy with influence of local storms’.

The most powerful wave climate is found in South Africa, Namibia, Mauritius, and Madagascar. Other locations with high potential for wave power (above 15 kW/m) are found in Cabo Verde, Morocco, Mozambique, Somalia, and Senegal. Many of the tropical countries have calmer but still good wave power conditions (≥8 kW/m). With the right type of WEC that targets a lower energy density, these milder wave climates might become of particular interest because of the lower stress on equipment.

Tidal power potential: Because of the strong dependence on site conditions, there are no reliable estimates of global or African theoretical potential for tidal stream power. Given that Africa does not possess globally remarkable tides, the tidal power potential is likely to be insignificant at most locations. Some scattered hotspots nevertheless exist in eastern and western Africa where the semidiurnal tidal amplitude is higher than elsewhere.

Water speeds corresponding to moderate technical potential are found at specific locations in Kenya, Tanzania, Mozambique, Guinea, Guinea-Bissau, and Morocco. Even at sites with sufficient tidal streams the extractable resource may be limited by coastal morphology and bottom structure. Also, it is typically assumed that only 10% of the available energy can be extracted to minimize environmental impact. Furthermore, the technical conversion efficiency delimits the available resource since all kinetic energy cannot be converted to electricity.

Importantly, the current speed at any location varies between maximum speed and zero several times per day because of the semidiurnal tidal cycle. This means that tidal power output from a single location varies and is often zero, which has implications for tidal stream contributions to small grids or off-grid applications. Still, some loads such as battery charging, and desalination can be suitable even where power output is variable.

Ocean current power potential: The fastest and most consistent nearshore water speeds are found in Somalia, at southern (Kismayo to Mogadishu) and northern (Puntland) locations, and in south-eastern South Africa. These areas seem to have a high technical potential for ocean current power. The Somali-Agulhas system may also provide a moderate technical potential in Kenya, Tanzania, northern Madagascar, northern Mozambique. Elsewhere, sufficient conditions may also be found suitable in Guinea-Bissau, and possibly in Guinea, and in Morocco by the Strait of Gibraltar.

Despite the promising conditions in eastern and southern Africa, the technical constraints of ocean current power are still substantial. Technologies for harvesting this resource are still in an early development stage and it is difficult to assess their technical potentials even at large orders of magnitude. Most sites with strong currents are also in deep water. The powerkite device, which can harness relatively slow currents, is moored to the sea bottom and may not be deployed of the continental slope. The combination of strong flows and relatively shallow depth will define the potential for ocean current power. On the other hand, long stretches of strong currents in combination with a homogeneous bottom slope seem available in Somalia. Site-specific studies could reveal the opportunities more accurately.

OTEC potential: Based on the heat gradient between the surface and deep water, the potential for floating OTEC is high along the African west coast from Guinea to Gabon. For instance, Adesanya et al. recently performed an economic analysis of the OTEC potential in Nigeria, finding that conditions are suitable for viable development of floating 100 MW OTEC plant which would return investment costs within 15 years. However, in this part of Africa, only Equatorial Guinea, San Tomé and Principe have access to the heat gradient resource from land, enabling land based OTEC.

In eastern Africa, temperature gradients are not as large, but some nearshore locations have steady differences of at least 22o C, which suggests good OTEC potential. Therefore, Comoros, Seychelles, and Mozambique have indications of high technical potential for land based OTEC. Several countries have more moderate potential, either because of lower heat gradient or based on the distance to land. The OTEC potential in this region has previously been reviewed by Hammar et al.

While coarse data indicate that Mauritius has only a moderate heat gradient but a remarkable proximity to land, a specific study on OTEC in south-western Mauritius deems conditions to be very suitable. According to Singh Doorga, a land-based 95 MW OTEC would return investment costs by a factor of four at this location.

Offshore wind power potential: The gross offshore wind energy resource in African waters has been estimated to be 27 TW, based on installed capacity of 3 MW turbines per km2. In brief, sufficient wind speed conditions occur in north Africa, east Africa and southern Africa and near surface wind conditions across the coast of Africa have been scrutinized by Olaofe, who concludes that southern Africa has excellent conditions for offshore wind power which has been strengthened by recent global climatological changes, with local drifts and particular along Africa’s south east coast.

Country-specific reports of technical potential for offshore wind power are available for selected countries. Their summary report states that sub- Saharan Africa has a strong potential for offshore wind (2.3 TW) while northern Africa has a moderate wind resource. In both cases however, most of the resource is in deep water that would require floating foundations. Based on wind speed data from these reports and the Global Wind Atlas, the technical potential for offshore wind power is high (≥ 10 m/s wind speed average at 100 m altitude) in Madagascar, South Africa, Namibia, Eritrea, Somalia, Mauritania, Cabo Verde, Morocco, and Egypt. Moderate potential (based on wind speed averages from 8 m/s) is found in Mozambique, Djibouti, Sudan, Kenya, Mauritius, Angola, Senegal, Algeria, Tunisia, and Libya. The scientific literature contains few country-specific studies but the existing analyses point at suitable conditions for offshore wind power in Benin and in Egypt.

Floating solar power potential: The insolation on African coastal and offshore waters provides an enormous theoretical potential for floating solar power. In theory, the resource is sufficient to power all coastal states with FPV. To fully cover the sea with solar panels would however neither be possible, legal, or desirable.

Energy policy recommendations

For offshore renewables to be of strategic value they must be competitive and complementary to land based renewables. Energy extraction from the sea will usually be more expensive, complicated, and risky compared to any comparable land based alternative. For instance, if winds are equally strong over land it will be more viable to build onshore wind farms instead of going offshore. Yet, energy abundance and power quality may lead offshore renewables to become viable and even advantageous in some parts of the continent. According to findings from this background paper the natural resources are in place for several types of offshore renewables. The development of offshore capacity might be the key to eventually utilizing their potential in the coming years.

Strategic preparedness may include:

1. Build domestic and regional offshore capacity – not limited to offshore renewables – and invest in enabling environments for Blue Economy business and industry. This approach would enhance African competence and readiness to “leap-frog” more fossil-fuel dependent nations and build a new momentum of inclusive economic growth based on harnessing ocean resources.

2. Address offshore renewables not in isolation but in relation to complementary energy alternatives and relevant energy mixtures: from local off-grid systems to regional power pools.

3. Development at scale is necessary for a viable industry. Strategic support for offshore renewables should target comprehensive investment programs at scale rather than single ventures. Such a focus must however not hamper parallel bottom-up driven initiatives. Following the Africa ‘Blue Economy’ Strategy, create a conductive regulatory environment to support offshore renewable industries in a sustainable way, and consider the development of integrated master plans.

4. Strategic support to offshore renewables should be linked to the wider offshore industry complex. This may go hand in hand with the Africa Blue Economy Strategy objective of modernizing ports and maritime infrastructure. It must also be recognized that African countries have many academics with practical expertise in the various research fields of offshore renewables.

5. It might be valuable to narrow the scope of offshore renewable energy in the African Blue Economy Agenda. Technologies suitable for the African geography and socio-economic context should be in focus. This background paper may serve as a step towards identifying initial target areas.

6. Strategic environmental assessments including socio-economic feasibility studies must be launched at an early stage of planning and investment. Some technologies may have detrimental impact on coastal ecosystem services at specific locations which should be carefully considered and avoided or mitigated. The Africa Blue Economy Strategy calls for the development of environmental impact assessment guidelines.

7. Support to offshore renewables should set conditions for African ownership and deep-rooted involvement of domestic industry and local workforce, thereby assuring project longevity, capacity building, local added value and the nurturing of domestic intellectual property.

8. Strategic planning of offshore renewables should be incorporated with Marine Spatial Planning (MSP), to utilize synergies and avoid future conflicts with competing interests and environment.

The complete paper can be accessed here