The percentage of renewable energy production is rapidly increasing globally. Costa Rica’s electricity has run entirely on renewables for 300 days in 2017.
As renewable energy systems grow to provide nearly 100% of energy production, issues related to the intermittent nature of wind and solar power generation, and fluctuating power demands, become increasingly important. The use of water reservoirs to store energy are called Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), or short-term off-river pumped-hydro energy storage (STORES).
As the proportion of wind and solar photovoltaics (PV) in an electrical grid extends into the 50-100% range a combination of additional long-distance high voltage transmission, demand management and local storage is required for stability [1, 2]. Pumped Hydro Energy Storage (PHES) constitutes 97% of electricity storage worldwide because of its low cost.Global pumped hydro atlas
We found about 530,000 potentially feasible PHES sites with storage potential of about 22 million Gigawatt-hours (GWh) by using geographic information system (GIS) analysis. This is about one hundred times greater than required to support a 100% global renewable electricity system. Brownfield sites (existing reservoirs, old mining sites) will be included in a future analysis.
Huge Global Study Just Smashed One of The Last Major Arguments Against Renewables, Science Alert, by DAVID NIELD, 31 MAR 2019
Pumped-hydro is one of the best technologies we have for storing intermittent renewable energy, such as solar power, which means these sites could act as giant batteries, helping to support cheap, fully renewable power grids.
ANU (Australian National University) is leading a study to map potential short-term off-river pumped hydro energy storage (STORES) sites that could support a much greater share of renewable energy in the grid.Hydro storage can secure 100 percent renewable electricity
STORES sites are pairs of reservoirs, typically 10 hectares each, which are separated by an altitude difference of between 300 and 900 metres, in hilly terrain, and joined by a pipe with a pump and turbine. Water is circulated between the upper and lower reservoirs in a closed loop to store and generate power.
Dr Matthew Stocks from the ANU Research School of Engineering said STORES needed much less water than power generated by fossil fuels and had minimal impact on the environment because water was recycled between the small reservoirs.
“This hydro power doesn’t need a river and can go from zero to full power in minutes, providing an effective method to stabilise the grid,” he said.
“The water is pumped up from the low reservoir to the high reservoir when the sun shines and wind blows and electricity is abundant, and then the water can run down through the turbine at night and when electricity is expensive.”
by Australian National University, Phys.org, February 27, 2017
The green areas in the figure below are times when electrical demand is low and some of the renewable energy generated is used to pump water to the elevated water reservoir. The areas in red are times when energy demand exceeds the power being supplied by the renewable sources. In that case, the water from the elevated water reservoir flows down, spinning turbines which generate electricity.
Pumped storage is the largest-capacity form of grid energy storage available, and, as of 2017, the United States Department of Energy Global Energy Storage Database reports that PSH accounts for over 95% of all active tracked storage installations worldwide, with a total installed nameplate capacity of over 184 GW, of which about 25 GW are in the United States. The round-trip energy efficiency of PSH varies between 70%–80%, with some sources claiming up to 87%. The main disadvantage of PSH is the specialist nature of the site required, needing both geographical height and water availability. Suitable sites are therefore likely to be in hilly or mountainous regions, and potentially in areas of outstanding natural beauty, and therefore there are also social and ecological issues to overcome. Many recently proposed projects, at least in the U.S., avoid highly sensitive or scenic areas, and some propose to take advantage of “brownfield” locations such as disused mines.Pumped storage hydroelectricity, Wikipedia