By John Mott-Smith

Cross posted from the Davis Enterprise, 2-19-2015

Rooftop solar photovoltaic systems sprouted up on an increasing number of homes throughout Yolo County in 2014. Of course, many, many systems were installed prior to 2004, and it would be interesting to go backwards in time and count how many since 2000, or even earlier, but to my knowledge there is no database where that information is easily accessible.

However, it was relatively straightforward for each of the building departments in the county to get that information for 2014 and the “total” is impressive.

I put “total” in quotes because the data from each city, as well as the county, were not complete in all cases. The departments could tell me the number of systems installed on residential properties, but not always commercial installations or how much electricity each of these systems is capable of producing.

So, knowing there is a little bit of “apples and oranges” in looking at the data from the various building departments and, if anything, the true totals are greater than what I’m reporting here, there appears to be a more or less spontaneous rush by Yolo County homeowners, and some businesses, to install solar PV.

Starting with Davis, the city indicates that 251 permits were “issued” in 2014 with a combined capacity of just over 1.2 megawatts (MW) for an average system size of just about 4.9 kWh. “Issued” is in quotes because the city was not sure if all of these permits resulted in an installation, and the data from some of the other cities made a distinction in this regard if the permit had been withdrawn, if it was still in review, if it had been reviewed but not yet issued, it had expired. or if the system would be installed in 2015 and the permit not finalized until that time.

For example, according to the data from the city of West Sacramento, only 68 percent of applications for permits actually made it all the way through the process and were made final after the post-installation inspection. Still, even applying the 68 percent number to the Davis data leaves an impressive 171 systems and an estimated total of about 836 kWh, or 0.836 MW.

West Sacramento indicates that 244 permits were applied for, but only 165 were finalized in 2014. These systems averaged 5.23 kWh and together totaled 862 kWh (0.8 MW).

The city of Winters was able to identify the number of permits issued but did not have any records of how much electricity each system is capable of producing. Its building official estimated an average system size of 7 kWh for a total for 2014 of 357 kWh (0.357 MW). That’s not at all bad for a city with fewer than 2,000 homes.

The city of Woodland has instituted a system to track PV installations as one metric to evaluate the city’s progress toward achieving the greenhouse gas reduction targets in its Climate Action Plan so their data was readily obtainable. It indicates that in 2014 there were 309 permits finalized for PV systems with a capacity to produce 1,817 kWh (1.8 MW) for an average system size of 5.88 kWh. Woodland officials indicate that the pace of solar PV installations is increasing month to month and year to year.

Yolo County issued only 107 permits, but, like Winters, there are fewer households and businesses in the unincorporated areas than there are in the cities. However, these 107 installations accounted for nearly 3 MW (2,899 kWh) of capacity due to a couple of very large commercial installations out in the countryside.

Compare these numbers to information in the Yolo County Climate Action Plan that as of 2010 there was a total of only 194 PV installations in the unincorporated part of the county with just over 2MW of capacity.

These large-scale installations dot the landscape in Yolo County, some in the cities and some out in the country, and in a future column I will try to get a handle on these for a total installed capacity number. But for now, looking just at 2014, adding up the data from the cities and the county, there were 883 permits for solar PV with an installed capacity of 7,164 kWh (7.1 MW).

I’m very happy to report that 4.05 kWh of that total was installed on our roof in East Davis. Now, as I look around, I see so many rooftops with great solar access and wonder what holds people back from putting PV on their roofs.

I can’t really say what the trigger was for us, what made the time right, or why we had not done it before. In part it was because we had/have tree/shade issues, and there are other concerns as well. But given the 30 percent federal tax credit, the various new financing mechanisms, and the ability to purchase or lease, I can see why so many people are taking the plunge.

Our longer-term goal is to have solar on the roof, batteries in the garage, and an electric vehicle in the driveway.

— John Mott-Smith is a resident of Davis; his column is published on the first and third Thursdays of each month. Send comments to