The buzzword in the solar industry these days is “storage.” Because solar only produces power when the sun is shining, technologies need to be developed to store solar energy so that it can be used when the sun is not shining in order for it to become a significant part of the U.S. energy supply. The same is true for wind.
In talking about storage, the renewable energy industry usually thinks batteries, with few being aware of a much more powerful source of storage that can be integrated with intermittent sources of power like sun and wind – pumped storage hydroelectricity. In fact, pumped storage hydroelectricity facilities have been called the world’s biggest batteries. For this reason, the United States is committing millions in technical and financial assistance to pumped storage projects to help meet peak electricity demand.
What’s pumped storage? The easiest way to explain it is to describe a pumped storage facility. I recently had the occasion to visit the Yards Creek Pumped Storage Electric Generating Station in Blairstown, N.J., in western New Jersey near the Delaware Water Gap. The 400-megawatt facility, which was built in 1965, provides power during the hours of peak electricity demand.
Here’s how it works: two lakes were created by the local utilities – one at the top of a mountain and one at the bottom. The lakes are connected by an enormous exposed steel pipe called a “penstock.” At nearly 20 feet wide and 1,800 feet long, the penstock is so big that it is visible from more than 40 miles away. And at the foot of the penstock is a powerhouse that houses three giant combination pumps/turbines. At night, when electricity rates are cheap, the water from the lower reservoir is pumped 700 feet uphill to the upper reservoir. During the day, when electricity demand is at its highest — and rates are also at their highest — the water from the upper reservoir is released into the lower reservoir. The water flows through the turbines, which harvest the hydroelectric energy, thus allowing fossil and nuclear generating plants to remain more fully loaded. The next day, the same water is reused to repeat the process.
The Yards Creek facility uses more energy than it produces: it takes 3 kilowatt-hours of electricity to pump the water uphill for every 2 kilowatt-hours of electricity that is produced — in other words, a loss of one kilowatt-hour of electricity. But the operation is still cost effective, due to the cost differential between off-peak and peak electricity rates.
Pumped storage hydroelectricity is considered one of the only economical forms of large-scale energy storage, accounting for more than 99 percent of bulk storage capacity worldwide. This means that pumped storage definitely has a role to play in balancing the large-scale generation of electricity from renewable sources. Since intermittent sources of energy do not yet make up a significant part of the U.S. energy supply, this role is still largely theoretical here. But Germany, which has a much higher rate of solar penetration, is already using pumped storage in conjunction with solar. Because of the abundance of afternoon solar power in Germany, utilities there are using low-cost solar power produced during off-peak afternoon hours to pump the water uphill, thus allowing pumped storage facilities to recharge during the daytime as well as at night.
Pumped storage can also be used with wind. The low-cost power produced by wind turbines, which is generated primarily at night, can be used to recharge reservoirs during the evening hours. Another possibility is to use solar power or wind turbines to drive the water pumps directly – in effect creating a renewable-powered hydroelectric storage facility. Finally, pumped storage can also be used to balance sudden changes in demand. Unlike coal-fired or nuclear plants, which are limited in their ability to respond quickly, pumped storage plants can respond to demand spikes with a flick of a switch, allowing utilities to quickly switch to pumped storage in the event — for example — that passing clouds cut solar power output at a period of peak demand.
In summary, while the storage conversation for solar and wind is focused on batteries, it’s well worth paying more attention to a form of storage that has already stood the test of time – it’s been around for more than a hundred years – and offers far greater storage capacity. One day it may be possible to use energy generated from intermittent sources to charge large-scale battery storage systems, but right now the cheapest, most practical storage solution is to harvest the hydroelectric energy from a pumped storage facility.
Though pumped storage is capital intensive and hard to site, the basic concept is simple – it’s also environmentally sound. The Yards Creek plant, which is owned by PSE&G and FirstEnergy Corp., makes no noise and creates no greenhouse gas emissions, air pollution or radioactive waste; it also preserves the area from development – an important consideration in New Jersey, which is the nation’s most heavily developed state.
Like many pumped storage facilities, the Yards Creek facility also doubles as a nature preserve for hiking, picnicking, hunting and birdwatching. If you’re interested in pumped storage, I highly recommend an excursion to a facility in your area.
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