Approximately one year ago, I decided to start adding small-scale solar generation (mostly rooftop solar generation) estimates to the electricity generation data the US Energy Information Administration provides (see our exclusive “US Electricity Generation Reports” for previous reports on that matter), and to also start adding estimates to small-scale solar capacity additions to data gathered by the Federal Energy Regulatory Commission (see our “US Electricity Capacity Reports“).
I simply wanted the data and couldn’t find it anywhere else on a monthly basis (only in annual reports). However, I was also not shy to shame the EIA and FERC for not providing small-scale solar data (or at least estimates) in their generation and capacity reports, and in press releases or other materials referencing those reports as if they were comprehensive assessments of the US energy landscape.
Well, it looks like I no longer need to make the estimates for the generation reports. Potentially stimulated by CleanTechnica to add this to its monthly reports, the EIA reported this week that, “With the release of today’s Electric Power Monthly (EPM), the U.S. Energy Information Administration (EIA) begins regular reporting of monthly estimates of small-scale distributed solar photovoltaic (PV) electricity generation and capacity by state and sector. Until now, EIA had provided monthly state-level data only for utility-scale generation sources, including solar, but only annual national-level generation and capacity estimates for small-scale solar PV.”
Congrats and thanks to the EIA for stepping up to the plate.
But while we’re on the subject… I should note that the EIA’s estimates have been considerably lower than mine in 2015. Here are comparisons (in GWh):
- [September 2015] EIA = 1137, CleanTechnica = 1429
- [May 2015] EIA = 1202, CleanTechnica = 1623
- [April 2015] EIA = 1094, CleanTechnica = 1536
- [December 2014] EIA = 651, CleanTechnica = 685
Why the differences in 2015? Well, we’d have to get a bit more detailed than I can right now to answer that question, but I can share some information on how my estimates were done and some information on how the EIA estimates were done.
My estimates were, in the end, based on the assumption that small-scale solar generation = 70% of utility-scale solar generation in the US. This assumption was based on last year’s capacity totals and generation totals as well as capacity forecasts from SEIA/GTM Research regarding 2015, a rooftop solar DC to AC capacity conversion of 0.8570186875 (obtained from GTM Research), and a utility-scale solar DC to AC capacity conversion of 0.6490250696 (obtained from GTM Research).
The EIA uses a very sophisticated and very different system for estimating small-scale solar, so I’m happy it has taken on this task. Here’s more from an article the EIA wrote on its blog about the new system:
EIA uses its surveys of electric utilities to collect information on the number of customers with distributed PV systems and the aggregate capacity of those systems. Because electric utilities do not necessarily know how much electricity is generated by rooftop PV on their distribution systems, generation from these systems must be estimated. To make comprehensive estimates of monthly generation for all small-scale solar PV at the state level, EIA developed methods that use the data it collects from electric utilities and third-party owners (TPOs) in conjunction with other information. TPOs are energy service providers that own rooftop PV systems located on customer premises and provide electricity directly to ultimate customers.
The National Renewable Energy Laboratory’s System Advisor Model and PVWatts tools were used to develop estimates of generation for a number of weather locations around the United States and provided effective insolation data—essentially, how much solar energy reaches the PV systems—on a monthly basis. Data from the California Solar Initiative on commonly used tilt angles and orientations for PV systems were used as inputs to be representative of tilt angles and orientations in other states. Data reported to EIA on utility service territories and capacity were used to estimate monthly state generation. EIA’s generation estimates were then compared with reported TPO data.
It’s unclear from this if there are batches of the small-scale solar market that are being left out of the estimates, but exploring that matter could be a story for another day.
With all of that news out of the way, here’s how things shook out in September 2015 (remember, it takes the EIA a couple of months to get electricity generation numbers together):
Clearly, the overall story isn’t going to change much at this point whether we use the EIA’s estimates or our own estimates, but adding in estimates for small-scale solar does boost solar to 1% of US electricity generation, up from 0.7% in 2014 (January through September). As the solar market grows (which it is definitely doing), having an estimate for rooftop solar will become more and more important — and hopefully a relatively accurate one.
Altogether, renewables accounted for 11.4% of electricity in September and 13.2% for the year through September, slightly down from 13.3% for the same period in 2014. Why the drop? Solar electricity generation is up significantly, and wind generation is up as well — however, hydroelectric generation is down by about the same amount, while nuclear and natural gas generation increased by a large amount.
US electricity generation infrastructure is so vast that it will take quite a long time to transition from fossil fuels and nuclear power to renewables. New capacity is heavily on the renewables side, but there are hundreds of coal, natural gas, and nuclear power plants already installed across the country. They won’t all be retired in one night, one month, one year, or even one decade. But let’s hope we get serious about transitioning in time to keep the planet livable for humans… as well as countless other species.
While you can’t force anyone to retire a coal power plant, many of you can do your part by putting solar power on your roof.
Top image via Shutterstock
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