Private solar installations are really taking off nationwide. In just two years, (about the same length of time it takes to get a pair of 250 MW solar power plants approved in California, for example), homeowners and businesses have added that much power to the Californian grid, just from individual rooftops throughout the state.

By July last year, 50,000 installations were supplying the California grid with 500 MW of solar power; the equivalent of two average sized solar power plants now under review in the state.

Nearly all solar installations are now grid -connected in California, by contrast with the first wave of solar power in the 70’s when a battery was needed to supply power at night, and early adopters had to be careful not to exceed their power, turning off dishwashers on cloudy days.

Now however, nearly all solar is grid-connected, meaning that the power generated is stored in a giant battery: the grid. Output is measured as it enters the grid, by the utility, which gives a credit for the electricity generated.

Solar installers are able to size each system so that it generates the same kwh a month as the homeowner or business uses in total (including both nights and days), with the result that the credits on the utility bill will zero out the debits from night time use. Because of the grid acting as a cheap or free battery, whereas in 1999 average installed systems were 2.5 KW and included an expensive battery, now the average system for homeowners is 4.8 KW and is grid-connected.

The growth in solar power has been fast among homeowners, and even faster among commercial building owners. The faster adoption of commercial solar is due to the lower prices for larger scale installs (over 500 KW cost 17% less per watt than the under 10 KW systems typically installed on homes) and the wider availability of Power Purchase agreements, which are usually only available to businesses. Commercial installations grew from 19% in 2005 to 46% of all installations in 2008.

As the percentage of non-utility solar being added to the grid increases, some states, like California, are looking at raising the state imposed limit. Californian non-utility solar is now close to the current 2.5% of the state’s electricity coming from rooftops.

The Solar Alliance has sponsored a bill to allow up to 10% of the state’s electricity  to be generated by private homeowners and businesses. Other states, like North Carolina, are proposing no cap at all.

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