Actually, California Got 7.4 Percent of Its Electricity from Solar in 2014

 

Federal energy number-crunchers reported on Tuesday that in 2014, California became the first state to generate 5 percent of its electricity from utility-scale solar power. A decade ago, in 2005, solar’s contribution in California was just 0.26 percent of generation, so ramping up to 5 percent is a remarkable achievement, especially in an era in which electricity demand is largely flat.

But that 5 percent figure actually shortchanges California’s solar progress.

That’s because the total revealed by the U.S. Energy Information Administration doesn’t take into account the electricity that flows from tens of thousands of small solar power systems on homes and businesses throughout the Golden State. The EIA doesn’t report this data, and as far as I’ve been able to determine, neither does anyone else.

But I think I’ve come up with a pretty good estimate.

By my calculation, alongside the EIA’s reported 9,981 gigawatt-hours of utility-scale solar generation in California in 2014, small solar power systems in the state generated another 5,024 gigawatt-hours.

That means California actually got around 7.4 percent of its electricity from solar last year.

That also means solar wasn’t fourth in renewable energy production in California, behind conventional hydro, wind and geothermal; it was second, trailing only the big dams.

 

Now, to be sure, this is just an estimate from a reporter – and a non-science major, at that. How good an estimate is it? You be the judge. Here’s how I came up with it:

Start with the fact that the EIA tallied up generation only from systems with capacities of 1 megawatt or larger, as the agency duly noted in its Today in Energy item. The EIA said such systems totaled 5,400 MW of solar capacity in California as of the end of 2014.

So that’s what goes into their 5 percent figure. What doesn’t go into it?

The EIA made reference to “rooftop and other small-scale solar capacity … whose generation is not included,” and put the total there at “more than 2,300 MW,” linking to info from the California Public Utilities Commission.

But according to Cory Honeyman at GTM Research, that still misses out on a lot of California solar, solar that was installed outside the state’s various incentive programs. Such systems make up a big portion of California’s recent installations.

According to GTM Research, California actually had 3,348 MW of non-utility solar as of the end of 2014. But since we’re aiming to calculate generation for all of 2014, instead of using the end-of-year capacity figure we’ll take into account where the state was at the beginning of the year and use an average, 2,887 MW.

Furthermore, GTM expresses solar capacities in direct current, while the EIA/California data uses alternating current. Honeyman recommended “derating” the GTM figure by a 0.87 multiple to convert it from DC to AC, which gets us to an average of 2,512 MWac of non-utility solar capacity in California for 2014.

That’s our capacity figure – but we’re after generation.

The best information I could find on generation levels for non-utility solar in California came in a report prepared for the California Public Utilities Commission in late 2013 by the firm Energy and Environmental Economics (E3). That report [PDF] stated that as of the end of 2011, California had “approximately 1,110 MW of installed generation” enrolled in its net metering program, generating “about 2,200 GWh of electricity.”

That translates to just shy of 2 gigawatt-hours per megawatt of installed capacity.

Most likely, that figure has improved in recent years, as solar has become more efficient. Still, we’ll be conservative and stick with 2 GWh per megawatt of installed capacity. Thus: 2,512 x 2 = 5,024 GWh, my estimate for small-scale solar’s heretofore overlooked contribution to California’s electricity generation.

A final thought: As you’ve no doubt gathered, solar data always comes with caveats. Over email and in conversation with GTM’s Honeyman, I came to realize there are myriad ways to express and calculate solar capacities and to categorize types of solar power generation, and that various methodologies make for a very confusing realm. I’ve tried to navigate my way through it to arrive at a meaningful if imprecise number. If you’ve got a critique, share it in the comments!