Currently, sodium sulfur batteries operate at very high temperatures - above 300 degrees C (572 degrees F), and the components in them are corrosive. This isn't the sort of thing that you would want in your home, and, for efficiency, they work best at a much larger size; they aren't really at a home-scale size. On the other hand, there are some advantages to sodium sulfur batteries. They use very common and inexpensive materials, which makes them attractive. And the high energy density means that a small battery is all that is needed for a large amount of energy storage.
The Ceramatec battery separates the sulfur and sodium from each other with a thin ceramic membrane which allows electricity to be stored while operating at a much lower temperature. Ceramatec envisions a refrigerator-sized unit that would remain below 98 degrees C (208 degrees F), the melting point of sodium. Keeping the sodium solid makes for a much safer battery. The battery could store 20 kWh worth of energy, either from local, sustainable sources such as wind or solar, or from off-peak recharging from the grid, much like a plug-in hybrid car recharges when the grid demand is low.
One of the biggest obstacles for implementing home-based power generation has been the lack of storage options. Grid tied net-metering options are available in many states, but not in all. And net-metering is, in many cases, not an especially attractive option when the homeowner's overproduction of electricity simply becomes the utility's windfall. And off-the-grid homes don't have this option available at all; some kind of storage is necessary. Conventional lead-acid type batteries need frequent, regular maintenance to be kept in proper condition. They also should be kept in special enclosures with ventilation to allow hydrogen gas (which can escape from the batteries in their normal course of operation) to escape and prevent an explosion hazard. Lead acid batteries are also only good for a limited number of cycles before they need to be replaced.
Ceramatec says its new generation of battery would deliver a continuous flow of 5 kilowatts of electricity over four hours, with 3,650 daily discharge/recharge cycles over 10 years. With the batteries expected to sell in the neighborhood of $2,000, that translates to less than 3 cents per kilowatt hour over the battery's life. Conventional power from the grid typically costs in the neighborhood of 8 cents per kilowatt hour.This technology is of potential interest to everyone, not just to homeowners with their own power generation systems. Many parts of the country offer off-peak rates for electricity that are lower than daytime costs. This is because demand is lower during evening and overnight hours. Along with overnight recharge of plug-in hybrid automobiles, houses with their own battery storage could store electricity overnight for use the following day. This would provide cheaper electricity for the homeowner, while also reducing the daytime demand on the grid. This, in turn, would be a more efficient use of existing grid infrastructure, and could help reduce demand for new generating plants.
This kind of distributed storage of electricity will also potentially make it much easier to incorporate sustainably-based generation into the grid. Methods to tell home storage units when to recharge could readily be based on existing utility systems that can turn off power for air conditioning during peak demand periods. This way, intermittent sources and local sources can more easily be incorporated into the grid, and a locally produced electricity (along with increased efficiency from reduced transmission losses) can only be helped by this technology taking off.