Net metering allows residential and commercial customers who generate their own electricity from solar power to feed electricity they do not use back into the grid. Many states have passed net metering laws. In other states, utilities may offer net metering programs voluntarily or as a result of regulatory decisions. Differences between states' legislation and implementation mean that the benefits of net metering can vary widely for solar customers in different areas of the country.
Read More: http://www.seia.org/policy/distributed-solar/net-metering