We seem to feature new ideas for methods of generating power every week on EcoGeek. Varieties of methods for harnessing energy from wind, waves, and the sun are being investigated and developed by scientists and inventors all over the globe. But many of these power sources are intermittent, compared to the steady output that is available from combustion of (most often) non-renewable fossil fuels.
One of the regular complaints from opponents of wind or solar power is that it is sporadic or unreliable. "The sun doesn't shine at night;" "The wind doesn't always blow when you need it;" and other complaints are leveled against renewable power systems. That doesn't mean they aren't useful, though. Instead, the grid needs to be better equipped to store that power when it is generated and then draw from it again when demand rises. It's part of the 21st century grid our power system will need.
Ars Technica has a story on power storage that is well worth reading. It looks at some of the theoretical options for power storage, as well as current technologies that are already in use.
Hydroelectric storage is one of the most common methods for storing energy, and has been around for nearly a century. Water can be pumped uphill when surplus power is available, and then allowed to flow back through generating turbines when demand for electricity rises.
From the article:
[I]t's no surprise that grid-level storage actually dates back to 1929 in the US, when the first pumped-water plant opened. These facilities combine a standard hydroelectric facility with a pump that runs when electric supply exceeds demand. The excess power pumps water uphill into a reservoir, where it can be harnessed when power supplies drop. All told, pumped hydro now has the capacity to supply about three percent of a typical day on the US grid. So, grid-level storage isn't a possibility; it's a reality.
One such facility in Ludington, Michigan on the shore of Lake Michigan has the capacity to generate up to 1,872 megawatts of electricity.
Battery storage systems are another option. Batteries intended for grid storage are different from more familiar battery types such as lithium-ion or lead-acid. Large scale systems using technologies such as flow batteries or sodium sulfur batteries may find a growing place in grid energy storage solutions. Already, in Japan, a wind farm has been equipped with 34 megawatts of sodium sulfur battery storage capacity to store wind power generated at night for use during the day, and, in Minnesota, Xcel Energy is testing a similar system with about 1/10th the capacity. A lot of these batteries are ill-suited for small scale, portable applications (where lithium ion systems are the batteries of choice), but are well suited for large scale, fixed location installations. And grid-tied storage is just that kind of industrial scale application. While not every location has the water resources to be able to do pumped storage, large chemical battery systems offer very high energy storage density and can be installed almost anywhere.
For locations without the water resources or elevation changes necessary for water storage, compressed air energy storage is another possibility. Abandoned mines can be used as pressure vessels into which air is compressed when surplus power is available, and then that pressure is used to generate electricity when demand for power rises.
Flywheel systems are also receiving some attention. Flywheels are wheels which spin at high speeds; when energy from an outside source is applied to a flywheel, it is stored as rotational energy. Flywheels are currently used to provide backup power in certain scenarios, but because they can store intermittent power, they lend themselves to renewable power storage as well.
All of these technologies should find their way into greater use as part of the updating and modernization of the current grid infrastructure. As more renewable sources are added to generating capacity, it only makes sense to have the ability to effectively use that energy. And even the most benighted renewable energy deniers must admit that having capacity in the grid for dealing with peak demands is a benefit to the electrical infrastructure.
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