Time is the enemy of most renewable energy systems. Winds can be stronger at night in California and Texas than in the day. Unfortunately, most regional customers are asleep, so utilities and power providers often have to dump the power generated by wind turbines during the small hours. When utilities dump power, not only do they lose a sale, they lose the attendant tax credits. Finding ways to store this ‘lost’ energy is one of the key advances that has to be made in order to transition smoothly to a renewable energy economy.
Recent announcements by utility giant American Electric Power (AEP), based in Columbus, OH, suggest that grid storage technologies are finally ready for commercial deployment in the United States. In September, AEP ordered three multi-megawatt battery systems and set goals of having 25 megawatts of storage in place by 2010, and 40 times that by 2020.
The AEP system uses a sodium-sulfur battery about the size of a double-decker bus (see above), plus power electronics to manage the flow of AC power in and out of the DC battery. Though new to the United States, the system has been used at the megawatt scale in Japan since the early 1990s; the battery was produced by NGK Insulators of Nagoya, Japan.
Geobattery is a company hoping to offer turnkey storage solutions to wind farms, solar farms and energy utilities, will try to solve this problem with sodium sulfur batteries, said CEO Dan Vogler. Sodium batteries are one of the best vehicles on the market for storing electrons. “They have the lowest cost and highest charge density of any battery,” he said.
Sodium batteries, however, are also extremely heavy. Worse, they only work at high temperatures of 285 Celsius and higher. Below that level, the batteries go into a dormant state. That makes them a tough choice for a notebook or an electric scooter.
However weight, temperature and extra real estate aren’t problems for wind farms. Geobattery’s plan is to build datacenter-like rooms of these batteries next to renewable energy facilities. A single 6U-tall sodium battery can hold a kilowatt hour worth of power. (A U is 1.75 inches tall. It comes from the computer industry and is not some ancient Celtic term.). A 25,000 square foot facility could hold enough batteries to store 10 megawatt hours worth of power.
Once in place, these sodium storage facilities could be used in a variety of ways. They could capture and store energy generated at night. Some wind farms could also try to work the system to sell their power at peak times, thereby increasing profits or reducing the time to break-even. Conceivably, these systems could also be used to store waste heat in factories.
Power storage is often called the Google opportunity in greentech. The various ideas for storing power include large-format fuel cells, vanadium flow batteries, molten sodium flywheels, compressed air and water columns. Most of these ideas are only moving out of the experimental stage now.