Despite advances in renewable energy technologies, one of the largest hurdles in their widespread adoption has been their intermittent reliability. Energy is only useful if it is available as the grid demands it, which is why concerns about carbon emissions are overridden in favor of the more dependable oil, coal and gas for baseload power.
In order for renewable sources such as wind and solar power to provide a constant source of electricity day or night, excess energy must be generated and stored whenever the sunshine or wind is plentiful. This can be done several ways. Large solar thermal arrays like the Andasol power plant in Andalusia, Spain use tanks of molten salt to store solar heat energy that allow the plant to continue to produce power when the sun is not shining. In 2011, another Spanish solar power plant, Torresol, became the first of its kind to produce uninterrupted power for a full twenty-four hours, relying on molten salt storage to provide the heat energy needed to power turbines after the sun went down.
Pumped-hydro storage is another potential technology that has been used for over a century to store energy from conventional fossil and nuclear fuel sources. As wind and energy become more prevalent, hydro storage is a way to make sure none of the energy generated goes to waste. Hydro-storage allows for electricity generation much like a hydroelectric dam does, except that hydro-storage plants are able to use electricity generated in off peak hours to pump water uphill back into the reservoir it came from. Storing energy this way is advantageous to power plants because pumping the water uses electricity that would otherwise be wasted in the grid at times when demand is low. There are pumped hydro storage plants found worldwide, with the United States, China and Japan home to the largest hydro storage power stations.
Batteries also play a critical role in storing the energy made by renewable sources. For homes or businesses that generate renewable energy on-site, a battery pack can provide energy even when renewable sources are intermittent or provide additional energy during peak times to help owners avoid high energy rates. The problem with many batteries, however, is that conventional solid electrode batteries—the kind you find in everything from cars to cell phones—are not very cost-effective at storing large amounts of electrical energy.
Looking forward, advancements in flow batteries by researchers at Harvard could soon change the battery used to store renewable-generated electricity. Flow batteries use liquid chemicals to store energy that can be kept separate from the components that convert the chemicals to electricity. This allows flow batteries to be scaled to match energy demands. Current flow batteries on the market use expensive chemicals and rare metals for energy conversion and storage, which curtails their use. The work done at Harvard demonstrates that the use of quinones—a molecule found in plants—can be an effective source of electrolytes in a flow battery that can be produced cheaply. Their durability is still being tested.
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