The phrase â€śutility-scale solarâ€ť is heard so frequently in discussions about renewable energy that it comes as a bit of a shock when one realizes that there is no commonly accepted definition as to what size constitutes â€śutility-scale.â€ť
If you donâ€™t believe it, a quick Google search reveals a staggeringly wide range of definitions, from greater than 25 kilowatts to greater than 50 megawatts, a difference of several orders of magnitude.
If itâ€™s difficult to agree on the size of a utility-scale solar facility, perhaps itâ€™s easier to agree on the shape. A utility-scale solar facility is one which generates solar power and feeds it into the grid, supplying a utility with energy. Virtually every utility-scale solar facility has a power purchase Agreement (PPA) with a utility, guaranteeing a market for its energy for a fixed term of time. (For more, check out the GTM articleÂ â€śAnatomy of a Utility-Scale PPA.â€ť)
Highland 1 and 2, in close proximity near Twentynine Palms, Calif. (image via SolarWorld)
That is where the similarities between facilities end. There was a time when the dominant paradigm in America was to build solar facilities on previously unused desert lands. While this is still occurring, more and more facilities are being built on abandoned agricultural lands, likeÂ in the solar boom town of Gila Bend, Arizona. A few years ago, one might have said that they tend to be sited in remote locations, but thatâ€™s also no longer true. Recurrent Energyâ€™s innovativeÂ Sunset Reservoir projectÂ in San Francisco is a 5-megawatt solar facility built on top of an enclosed reservoir in the heart of one of Americaâ€™s biggest cities.
Which brings us to the issue of size. When utility-scale solar burst onto the scene in the middle part of the last decade, people would have scoffed at the idea of a 5-megawatt project like Recurrentâ€™s qualifying as â€śutility-scale.â€ť
Many definitions put forth at that time, such as the definitive piece of academic research into the late 2000s solar boom in California, the University of Michiganâ€™sÂ Renewable Energy in the California Desert report, used 50 megawatts as a threshold for utility-scale. That number is largely based on the rush of applications at that time to develop truly huge facilities, like the famous (can we begin calling it infamous yet?) 377-megawattÂ Ivanpah SEGSÂ near the California/Nevada border. Given the tremendous permitting difficulties experienced by facilities like Ivanpah, someÂ pundits have foretoldÂ the coming end of utility-scale solar at such sizes.
More recent definitions are of a much more modest size. The Solar Energy Industries Association, the leading trade group for solar developers,Â defines utility-scale solarÂ [PDF] as greater than 1 megawatt. Project developerÂ Borrego SolarÂ agrees, while developer SunPower sellsÂ solar modules at a minimum sizeÂ of 1.5 megawatts.
Not everyone goes so low: in aÂ recent reportÂ [PDF], the National Renewable Energy Laboratory rather arbitrarily chose a 5-megawatt threshold; while the booster-ish websiteWiki-SolarÂ chose a 10-megawatt threshold.
So weâ€™ve determined that different entities claim different minimum size thresholds for utility-scale solar projects. But perhaps itâ€™s equally instructive to attempt to define what a utility-scale project is not.
Any solar project needs to sell its power to remain afloat. And, as noted, a utility-scale project, by definition, has a PPA. The only other way to sell solar power to a utility is throughnet metering, where generated power is used on-site (typically from the rooftop of a house or business), and excess power is fed into the grid, purchased by the utility from the producer on a per-kilowatt-hour basis. Net metering is enacted by state legislation, and each state has its own regulations as to the maximum size of a solar facility that is eligible for net metering. This may be our most promising avenue of inquiry yet, because any facility that is over the maximum size for net metering must have a PPA.