There are thousands of extremely good hydroelectric storage sites around the world with extremely low capital costs. When combined with batteries, the resulting hybrid system has large energy storage, low costs for both energy and power, and fast response. Storage is a problem solved.
By 2023, there would be twice as much solar generation capacity installed as all other generation technologies combined. The future of energy generation is solar photovoltaics, with the support of wind energy, and energy storage to balance the variability of wind and solar energy.
At least nighttime energy storage is required. Currently, pumped hydro energy storage (PHES) supplies more than 90% of the global total to the electricity industry. Batteries are becoming increasingly important. Demand management is an important development – for example, electric vehicles, hot water tanks and thermal storage in factories can be charged when demand is low and supply is high. Electric vehicles also offer ‘batteries on wheels’ with vehicle to grid (V2G).
Thermal power plants (coal and gas) can follow the load and operate in the same way as storage. For example, in Australia’s National Electricity Market, coal-fired power stations typically reduce daytime production to half that of evening peak production. Some even switch off completely for a few hours in the middle of the day. The motivation is to avoid negative prices on sunny and windy days.
For example, the figure shows power production from midnight to midnight during 4e October 2024 in Australia’s national electricity market (serving 20 million people), including coal (brown and black), gas (orange), hydro (blue), wind (green) and solar (yellow). Power demand peaked at 27 GW around noon. The area below the red line represents PHES charging and battery storage. From 7 a.m. to 4 p.m., prices were negative. Coal power varied from 7 GW in the middle of the day to 15 GW during the evening peak.
Image: ISES
Energy storage
As fossil fuel power plants close due to age and competition from cheap solar and wind energy, the gap must be filled by large-scale storage. When the amount of solar and wind energy is less than about 50%, batteries with a storage capacity of several hours are preferred. Ultimately, large energy storage is needed to cope with overnight and several days of cloudy weather. This is the role of PHES.
Hybrid storage systems that combine batteries and PHES are superior to either technology alone. Batteries are relatively cheap for storage power ($/GW), but expensive for energy storage ($/GWh). PHES is more expensive than batteries for storage power ($/GW), but much cheaper for energy storage ($/GWh). A hybrid system has both cheap energy (GWh) and cheap electricity (GW).
In a hybrid system, storage can charge storage. A large PHES reservoir can trickle charge batteries 24/7 for a week during a calm and cloudy period. For example, a PHES system with 350 GWh of energy storage and 2 GW of generation capacity can trickle charge twelve 4-hour batteries (48 GWh) every day for a week. Such a hybrid system effectively has an energy storage of 370 GWh and a storage capacity of 12 GW. A battery-only system would run out of energy after the first day, while a PHES-only system would run out of power.
An additional advantage is that the 12 GW batteries can harvest a negative price for four hours around noon, and for the next twenty hours trickle charge a large but energy-efficient PHES system – every day for a week before the afternoon. PHES system is full. In other words, the hybrid system harvests peak power prices of 12 GW and charges at negative prices.
The Global atlas for pumped hydropower storage lists 820,000 locations with a combined energy storage of 86 million GWh. This equates to the effective storage in approximately 2 trillion electric vehicles, which is far more storage than the world will ever need. That’s why only the very best sites are needed. The main cost parameters are a large hydraulic head (height difference between the upper and lower reservoirs, preferably 600-1600 m), a large water-rock ratio (a large volume of water is collected by a relatively small rock wall, preferably 15-50 m) and short pressure tunnels (several km).
Exceptional PHES locations have exceptionally low capital costs. Cost estimates applicable to regular hydropower projects do not apply to premium locations. There is a factor of 10 difference in the capital costs of the best and the least good locations in the Atlas. Because there is a large surplus of locations in most regions, only the very best locations need to be developed. Importantly, PHES are capital-intensive investments, but have a much longer expected lifespan than batteries.
Exceptionally good PHES locations can be found in most parts of the world, with extremely low capital costs. For example the Snow 2.0 The PHES system under construction in Australia is expected to have a capital cost of $8 billion for 350 GWh of storage, which equates to $23 per kWh ($8 billion/350 GWh). This is approximately 10 times lower than the capital cost of an equivalent battery. Australia has dozens of potential locations with similar costs.
Many regions have better PHES potential than Australia, including thousands of locations with indicative capital costs of $10-15/kWh. Large sizes on the order of 50 to 5000 GWh are preferred, which is enough storage for 1 million and 100 million affluent and fully electrified people respectively. The figure shows the location of 500 GWh sites around the world. One region with a notable lack of good locations is Northern Europe. Fortunately, the Balkans have excellent PHES potential, much more than enough to provide the European Union with all the storage capacity it needs.
The Atlas
Within the Atlas, the best sites are marked with stars (cost class AAA), triangles (class AA) or dark red dots (class A). Greenfield means 2 new reservoirs; Bluefield uses an existing reservoir; Brownfield uses a defunct mine; and Turkeynest means flat land. Users can pan, zoom, rotate and tilt. When you click on a reservoir or a tunnel route, various information pop-ups will appear containing 26 items with detailed information. Different sizes can be selected in the left panel, ranging from 2 to 5000 GWh. Select Map Settings/3D Terrain for a 3D view. Aqueducts or low-pressure tunnels in flat land often allow shorter pressure tunnels. The costs of new transmission can usually be shared with new solar and wind farms. Most Atlas sites are off-river and do not require new dams on rivers. A indicative cost model is included.
Authors: Prof. Ricardo Rüther (UFSC), Prof. Andrew Blakers/ANU
Andrew.blakers@anu.edu.au
rruther@gmail.com
ISESthe International Solar Energy Association is a UN accredited member NGO founded in 1954 working towards a world with 100% renewable energy for all, used efficiently and wisely.
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