Converting Reservoirs and Hydro Power Plants to Renewable Energy’s Spare Power

If we move to an energy system based on renewable sources, how do we ensure a sufficient power supply even when the wind is not blowing and the sun doesn’t shine?

The question of back-up power has rightly been seen as the most important remaining obstacle on the way of an energy system based on renewable energy, only.

At the moment the cheapest way to store extra wind and solar power is pumped-storage hydropower. In practice it means pumping water upstream when there is extra power and opening the gates and letting the same water run through hydro turbines, whenever there is need for extra power-producing capacity.

The method has some very clear benefits. The most important is that typically 15 and sometimes only 5 per cent of the power is lost in the process. 85 or even 95 per cent of the electricity that was used in pumping the water upstream can be “taken back” when the same water is run downstream, through the hydro turbines. When more power is needed, the power-producing capacity of a hydro power plant can be raised from zero to 1,000 megawatts in 12 seconds.

At the moment we only have 127 gigawatts or 127,000 megawatts of pumped-store hydro power, globally. However, we have a huge amount of conventional hydroelectricity: dams, hydro turbines and reservoirs behind the dams. The maximum power-producing capacity of the world’s currently existing hydro power plants is 1,100 gigawatts. Their average power production, however, is only 400 gigawatts. Most hydro power plants run on less than full capacity for most of the year, because the flow of the rivers fluctuates a lot. In the rainy season there is more water in the rivers than during the dry season.

Many, if not most, of the world’s major hydro power plants and reservoirs form long series or rows of reservoirs. The reservoirs behind the world’s already existing large dams higher than one hundred meters have a combined storage capacity of 6,000 cubic kilometers of water. Could we transform this already existing hydro power and reservoir potential, or a major part of it, also to pumped storage hydro power?

If we would use the extra power to pump water upstream, whenever our wind turbines and solar power plants produce more than we need, the world’s already existing reservoir and hydro power potential could theoretically give us 700 gigawatts of new back-up power. If we need more, would it be possible to equip the existing hydropower plants with larger turbines, during the next major overhaul of the dam? Or could we install a larger number of parallel turbines on each hydro power plant?

Theoretically, it should be possible to provide thousands of gigawatts of back-up power, this way, with only marginal additional costs. Is this the way to solve the problems related to storing the extra solar and wind power, and the problems related to securing sufficient back-up power for our energy system? But to make this a reality, we need feasibility studies and other research. Feasibility studies related to the possibilities, potential and problems of the approach, concerning small, middle-sized and large dams and reservoirs. Feasibility studies concerning the possibilities of the approach in the national level, in different countries with different situations.

Is it technically possible to equip the existing dams with larger hydro turbines, or with a larger number of parallel turbines? How could this be done? What would it require? How much does it cost? Would the pumping of huge amounts of water back and forth, over and over again, aerate and oxygenize the deep water at the bottom of reservoirs, in a way that would reduce the methane emissions from them?

We welcome all the interested experts of related subjects to participate in a dialogue and exchange of ideas about this crucially important possibility!