Storing energy in ponds is nothing new, but renewable energy sources demand more regulating power.

Wind power and other renewable energy sources will replace current European coal-fired plants. The new energy sources may be green, but they also contribute to a more volatile energy production. Wind and solar power are not as easy to regulate as coal and nuclear power plants. This means that effective regulation systems are becoming increasingly important.

As demand for electricity does not correlate with production – people want their lamps lit even when there is no wind or when it is cloudy – producing an energy surplus is the name of the game when the conditions are good. This excess must then be stored and used when production possibilities are diminished.

Pump power is part of the solution

Pump power is a technique used to store energy, where the energy surplus is used to pump water from a low-lying reservoir to one at a higher altitude. This excess energy is thus converted into potential energy. When production cannot keep up with demand, when the wind dies down for example, the water can be directed to turbines that generate power in a classic hydroelectric setup.

In addition to regulating production from renewable energy sources, pump power allows nuclear power plants to continue producing electricity at their most efficient level.

Vattenfall’s German pump power plants

Many companies operate pump power plants. Vattenfall has, eight in Germany, all of which are controlled centrally by a plant in Goldisthal.

The upper dam in Goldisthal has a circumference of about three and a half kilometers, and holds twelve million cubic meters of water. That’s enough to produce electricity at maximum capacity for eight hours. The water flows from the upper to the lower pond through two tubes that are 800 meters long and has a vertical drop of 302 meters, passing through turbines that can generate 1,060 megawatts (MW).

In total, the eight sites that are controlled by Goldisthal generate 2810 MW, with an efficiency of up to 80 percent. The high efficiency combined with the fact that the operating mode of the turbines can be changed between 100 and 200 times a day allows the plants to store energy in the most efficient way.

The world’s largest pumped storage power plant is in Virginia, USA. The Bath Country Pumped Storage Station has a capacity of over 3000 MW. The soil and rock mass that was moved to build the plant would create a mountain over 300 meters high. And the concrete that was used could make a 320 kilometer-long highway. The height difference between the two large dams is 385 meters, and the water can flow at a rate of 852 cubic meters per second. This allows the water level in the upper pond to vary by as much as 32 meters.

Future developments

There are proposals to build pump power facilities completely run on renewable energy. In this way, the plant generates the energy needed to pump the water between the dams. Such plants therefore run totally on renewable energy stocks.

There are other proposals to for example generate electricity with ocean tides by allowing water to flow into a pond when it is high tide, and out at low tide thereby generating electricity.

Is there a future for energy-guzzling plants?

Despite continuous technological development, a pump power plant is a net consumer of energy. Because of friction and energy losses more energy is used to pump the water uphill than can be extracted when discharged down through the turbines. In an environment where energy efficiency is the height of fashion, it may seem odd that the interest in pumping power remains high.

Pump power’s advantage however, is that it represents a much needed, balancing complement to the volatile renewable energy production that is steadily increasing. The need for regulating power will continue to increase at the same rate as the renewable energy sources are being rolled out. Therefore, the interest in the easy-regulated pump power system will continue to increase.

The article was published in January 2012