Californians installed nearly as much rooftop solar in 2013 as they did over the last 30 years.

The state topped 1,000 megawatts of solar energy in early 2013, making headlines all over the country. But, at the close of the year, the California Public Utilities Commission reported 1,917 megawatts of rooftop solar – nearly twice what it had at the start and without all the utilities reporting on their new rooftop solar capacity.

That’s some explosive growth. It means home and business owners installed almost twice as much rooftop solar in 2013 as they did in 2012 and doubled the rooftop solar capacity it took them 30 years to establish.

That robust solar industry growth isn’t just happening in California.

Nationally, there’s a new rooftop solar installation going up every four minutes, according to a recent article in National Geographic. Rooftop solar photovoltaic installations were up 35 percent year-over-year in the third quarter of 2013 and it was the first year in 15 that the U.S. installed more solar than Germany, known internationally for its strong solar industry.

With growth like that, there’s no wonder utilities in half a dozen states have launched campaigns against net metering – the practice of utilities buying the excess power their solar customers generate, usually at the retail electric rate.

While solar currently accounts for less than 1 percent of electricity generation in the country and in most utilities’ regions, fast-paced industry growth like this could quickly turn the tables.

That’s exactly what centralized utility trade group, Edison Electric Institute, warned its members of in 2012 when it wrote that distributed rooftop solar was a “significant threat” to the centralized utility business model. Utilities heard that warning and have been fighting back against net metering around the country, arguing that solar customers aren’t carrying their weight when it comes to paying for grid maintenance and improvement.

While utilities argue that solar customers are shifting grid costs to their neighbors, the solar industry counters that utilities realize more benefits than they pay for through distributed generation because utility customers are producing their own power during peak demand periods and it doesn’t have to be transmitted far if it’s transmitted at all.

Fights over net metering erupted in Louisiana, Idaho, California, Arizona and Colorado in 2013. The solar industry declared the $5 fee for solar customers approved in Arizona a victory because utility Arizona Public Service was asking to tack $50 to $100 onto solar customers’ monthly bills.

The fight is just getting started in Colorado, where the Public Utilities Commission will beginning hearing argument Feb. 3 from the state’s largest utility, Xcel, to cut net metering credits from 10.5 cents per kilowatt hour to 4.6 cents.

Utilities and solar advocates nationally will be watching the Colorado debate closely.