Ceramatec Inc,. a Salt Lake City UT technology company has developed a battery attached to a disk that can store at least 20 kilowatt hours of solar energy. Home solar energy users are the ideal market for this new technology but non-solar homes would be able to use these batteries as well during off-peak hours.
The average American home uses approximately 25 kilowatts of energy per day so this battery-disk would save up to almost a days energy for later use. It's currently in development with an target of 2011 for testing how the market will react to these battery-disks. The current projected cost of one disk is approximately $2000.
Read more about the battery-disks at Popular Mechanics.