Each year, Larry Sherwood of the Interstate Renewable Energy Council (IREC) releases an annual report summarizing recent trends in the U.S. solar energy market. And guess what? (Get excited…)

His latest report, U.S. Solar Market Trends 2010, was released just a couple of days ago.

In it, you’ll read about the phenomenal growth witnessed by the solar industry in 2010. Main highlights include:

• The capacity of photovoltaic (PV) installations completed in 2010 doubled compared to the similar figure in 2009.
• Much of this gain was due to growth in utility-scale solar PV projects, the capacity of which doubled in 2010, nationwide. But there was strong growth as well in residential and non-residential solar installation, where capacity increased by 60 percent.
• New Jersey, Arizona, Colorado, Massachusetts, Pennsylvania, New Mexico, Pennsylvania and Texas all saw a doubling of solar growth; California, the biggest market of all, saw its share of new solar capacity slide to 28 percent from 49 percent in 2009.

But what really caught my eye was this:

Clearly, the average size of residential solar PV systems in the U.S. is increasing. We’ve known this for a while, but for some reason this chart jumped out at me. Several years ago, when we started GetSolar, we would tell homeowners that the average system size was between 3 and 5 kilowatts (kW). In 2010, the average was approaching to six.

As the cost of solar panels has come down in the past 18 months or so, homeowners are opting for larger systems. A rough rule of thumb: the bigger the system, the smaller the monthly electricity bill.

If you’re curious, you can get an idea how much would a 6-kW solar array save you by tinkering around with our solar cost calculator.

Photo (above) of a residential photovoltaic installation in Plymouth, Wisconsin via IREC.