Ruzizi IV Hydropower Project
Murchison Falls, Uganda (Source: stock)

Energy storage will be a key component in accelerating global efforts to meet the ambitious climate mitigation and sustainable development goals set under the Paris Agreement. Does energy storage in the form of pumped hydropower storage (PHS) have the potential to achieve this goal?

This article first appeared in ESI Africa Issue 2-2020.
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Whilst a number of energy storage technologies are being developed to manage electricity grids, most technologies only fulfil short-term cycles (daily or shorter). PHS systems are currently the most mature and widespread method for large-scale electricity storage. Given the current costs reduction in other technologies offering daily energy storage (particularly batteries), PHS is anticipated to gain importance as a seasonal energy and water storage alternative.

Seasonal pumped hydropower storage

A team of researchers is exploring the concept of seasonal pumped hydropower storage (SPHS) plants. SPHS plants have lower land requirements than conventional hydropower dams, for a comparable energy and water storage potential, because the off-river reservoir design permits higher hydraulic head variations.

SPHS can also be attractive to deal with the load problems emerging from electricity consumption and supply seasonal variations and increasing use of intermittent sources of generation. The storage of water can also help to overcome water shortage problems. Because storage is also not near the main river, possible negative impacts of hydropower can be better managed.

The research team reference a recent study that investigates the global potential for PHS and assumes the construction of two reservoirs in a closed loop for daily and weekly operation. They found a global potential of 23 × 106GWh in more than 600,000 plants, but the project sizes appear to be impractical for seasonal storage or water storage and do not include detailed cost analysis or water availability. Other studies have been developed to find the potential for PHS projects in Europe and Iran; however, these are regional models and they do not include costs.

The research paper reviews the global landscape alongside rivers for attractive sites to build artificial reservoirs for water and energy storage purposes with SPHS plants. The research team evaluates all land grid points for project suitability at a ~450 m resolution, using a detailed siting assessment methodology for developing and costing SPHS projects with topography, river network, and hydrological data. Their estimates show that the global technical and economic potential for water and energy storage with SPHS is vast but with an unequal spatial distribution across the world.

Considering all the energy storage projects with the cascade, the total storage capacity is equivalent to 17,325TWh, or ~79% of the world electricity consumption in 2017. While the team considered a maximum of one SPHS per 1-degree grid square (100 × 100 km), in some locations a series of SPHS plants in cascade could further increase the energy storage potential.

Global potential of SPHS

The SPHS world potential model identified more than 5.1 million potential projects, all of which have a fixed generation/pumping capacity of 1GW. SPHS plants built adjacent to main rivers can provide water management and energy storage services while avoiding the large land footprint associated with conventional hydropower dams.

The estimated potential is restricted to mountainous regions with reasonable water availability and high hydraulic heads supporting cost-efficient SPHS system design. Significant potential exists in the lower part of the Himalayas, Andes, Alps, Rocky Mountains, Northern part of the Middle East, Ethiopian Highlands, Brazilian Highlands, Central America, East Asia,
Papua New Guinea, the Sayan, Yablonoi and Stanovoy mountain ranges in Russia, with energy storage costs with cascade varying from 1.8 to $50MWh.

The needs for energy and water storage with SPHS plants should be complementary. This is because during the dry season there will be low volumes of water available to be used for energy storage. This complementarity is usually the case in high latitude countries, where during the summer river flow is higher due to ice melting and energy demand is lower compared to the winter.

In conclusion

Given that this is the first global assessment for SPHS, the model was developed with the intent of focusing on its technical potential. Other restrictions that impact socio-economic feasibility, such as population, land use, biodiversity, transmission, etc. are not included in this work with the intent of presenting the existing potential and not its viability.

With the needs for reducing CO2 emissions to mitigate the impacts of climate change, SPHS provides short-term and long-term energy storage services allowing the development of 100% renewable energy grids. SPHS also increases water security in regions with unsuitable topography for conventional dams, high evaporation, and sedimentation rates. It is, thus, a prominent alternative for sustainable development on a worldwide scale. ESI

References
Hunt, J.D., Byers, E., Wada, Y. et al. Global resource potential of seasonal
pumped hydropower storage for energy and water storage
. Creative Commons 11, 947 (2020).

International Hydropower Association: The world’s water battery: Pumped
hydropower storage and the clean energy transition