As the penetration of solar PV increases in the system, flexibility and storage become crucial to further renewable energy deployment. As of 2018, the largest form of grid energy storage in Africa has dammed hydroelectricity, with both conventional hydroelectric generation (272,078 MW) as well as pumped storage (3,196 MW).
Pumped water systems have high dispatch ability, meaning they can come on-line very quickly, typically within 15 seconds, which makes these systems very efficient at soaking up variability in electrical demand from consumers. On a slightly larger time scale, excess energy from renewable sources can be stored and therefore increase kinetic water volume which can be released later. Hydroelectric dams with large reservoirs can also be operated to provide peak generation at times of peak demand.
Water is stored in the reservoir during periods of low demand and released through the plant when the demand is higher. The net effect is the same as pumped storage, but without the pumping loss. Depending on the reservoir capacity the plant can provide daily, weekly, or seasonal load. Thermal energy storage is achieved with widely differing technologies. Even though it might be less efficient for storage of excess energy from PV directly, it is worth mentioning as it already appears to be economical and it contributes to the system balance. Indeed, heat-storing infrastructure can decouple heat and power production and help to meet peak demands.
Heat storage in tanks and rock caverns or in hot rocks, concrete or pebbles is being investigated in combination with wind energy in Germany. Molten salt can be employed as a thermal energy storage method to retain thermal energy. This technology has been chosen for the phases I and III of the Noor project in Morocco to store the solar energy from the CSP installation up to respectively 3 and 8 hours. As the costs and the performance of batteries are improving rapidly, these could grow significantly in the coming years. The question is whether the falling costs will be sufficient to create new economic opportunities in Africa. The competitively of batteries is directly related to their cost. However, the business case for delivering ancillary services such as frequency response or capacity reserve depends on the price network operators. In the end consumers, are willing to pay for grid stability and power reliability. Power supply in many African countries is expensive and often not reliable. Storage will be crucial to accelerate renewable energy deployment, both in mini-grids and in the transmission and distribution grids. Batteries will play a pivot role in mini-grids and has the potential to increase energy access and living standards in remote areas.
However, the African transmission and distribution grids face other challenges to improve grid management. Indeed, as the basic structure of the electric power grid has remained unchanged for more than a hundred years, existing power generation infrastructure is outdated and not able to keep pace with the growing power demand.
To integrate more renewables and to unlock the potential of batteries to support the grid, smart grids must be implemented. Thanks to digitalization, distributed communication and computing technology, smart grid enable active participation by consumers and optimizes asset utilization and efficiency.
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