Net metering is a service to an electric consumer under which electric energy generated by that electric consumer from an eligible on-site generating facility and delivered to the local distribution facilities may be used to offset electric energy provided by the electric utility to the electric consumer during the applicable billing period.

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Note added at 8 mins (2014-01-04 14:50:45 GMT)
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Net Metering in Maryland Can Reduce Your Electric Bill

It’s every homeowner’s dream: the numbers on your power meter flying backwards instead of continuing their ever-forward march. Your monthly bill dropping to a fraction of its original amount, all with the same level of comfort in your home and no inconvenience to you. It may seem too good to be true, but for homes with net metering, this dream is a reality.

What Is Net Metering?

On a normal home, energy flows only one way: It comes from the power plant, through the grid, and into the home. On a home with solar panels or another type of alternative power, though, the energy can flow both ways. When the home uses more energy than it produces, it draws from the power company’s grid just as a normal home does, and the homeowner pays the power company for however many kilowatt hours they use.

However, when the home’s solar panel or other system produces more power than the home needs, that excess energy flows in the opposite direction: Out of the house and into the company’s power grid, literally turning the home’s meter backwards. The homeowner’s net consumption from the power company is reduced, and therefore the monthly bill is lowered.
http://renewableenergysolar.net/net-metering/

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Note added at 12 mins (2014-01-04 14:54:37 GMT)
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Net Metering allows FPL customers to earn a payback from connecting approved renewable generation systems - such as solar panels - to the electric grid.
http://www.fpl.com/residential/savings/net_metering/index.sh...