By Thomas J Taylor, PhD, GAF.
It has been said that all of the US could be powered by a solar array covering 100 x 100 square miles in the desert, linked to storage batteries covering 1 x 1 square mile. A similar claim is that covering 0.6% of the nation’s land with solar panels could power the entire country. That is equal to 11,200,000 acres or 17,500 square miles, more than the 10,000 square miles of the first estimate. Obviously, these panels would need to be placed somewhere in the south west, where solar irradiance levels are high and land may be more available:
The blue square represents the size of one such proposed “solar farm,” located in a region of high solar irradiance. At first glance, this might represent a doable project; however, it may require a level of national dedication akin to the efforts to put a man on the moon.
This article will examine some of the assumptions behind these estimates and examine what would happen if similar logic was applied, not to an extremely large ground based solar farm, but to solar installations on commercial buildings. A single large solar farm would require:
The following picture of a solar farm in the Atacama Desert, Chile, gives an idea of the apparent simplicity of the idea:
The concept seems straight forward, but such a farm needs resources and a work force that might not be readily available on such a grand scale. Alternatively, solar arrays on roofs would represent a distribution of power generation to those locations that actually use it. Also, from a regulatory perspective, solar arrays on rooftops could be simpler and more easily connected to the existing electricity grid. Below is a picture of a large array on the Atlantic City Convention :
To examine the feasibility of supplying all or even a substantial amount of the US electricity demand from solar power, the size of that demand must be known. The first step would be to examine how much power a solar array actually produces versus the currently available energy supply and demand within the US.
It is beyond the scope of this article to fully analyze how power is generated in the US. However, the following facts are useful for purposes of this article:
Coal fired and nuclear generators are generally considered as base load plants, running at or close to capacity on a 24/7 basis.
It’s worth noting that renewable sources account for approximately 17% of electricity production in the US, and solar accounts for a little over 1%.
Solar Farm in the Desert – It is difficult to estimate the amount of power produced by a solar array, because much depends on the location and associate solar irradiation, whether the panels are fixed or track the sun, and other factors. Using data from a wide array of existing solar farms in the US, NREL has estimated that 1,000 megawatt hours of electricity requires on average, 2.8 acres of land installed with panels. This means that a single farm capable of producing all the nation’s electricity would occupy 11,241,451 acres or 17,564.8 square miles. To go back to the beginning of this article, this would be a square 132.5 x 132.5 miles, in line with other estimates.
A solar farm, located in the south west, sized between 100 x 100 and 132.5 x 132.5 square miles could supply all of the US electricity demand.
Commercial Roofing Solar Arrays – Since this analysis is forward looking, this article will use today’s commercial solar panels for the calculations.
Examining these numbers to calculate how much power can be obtained from commercial roofs shows that:
One possible option in this examination of the potential impact of solar arrays on commercial roofs is to evaluate how much roofing is installed every year. In general, solar arrays work best on large footprint buildings, such as big box stores. This building type commonly uses single-ply membranes, and therefore, are ideal platforms for solar array installations. Also, single ply membranes represent over 60% of the commercial roofing market and are therefore the basis for this first option.
If solar panels were installed on all new single ply roofing each year, it would be the equivalent of building two of the largest conventional generating plants each year.
An alternative option would be to look at the total existing low slope commercial roof area in the US. Few estimates exist, but an NREL study published in 2016 suggested the following:
Taken together, this suggests that, excluding small buildings, the total low slope roof area in the US is 34,552 million square feet or 1,239.38 sq.miles. This includes all membrane types.
How much power could be produced if all of those roofs were equipped with solar arrays? Using the same assumptions as before, and based on today’s solar panels:
Roof-based solar power can produce power close to actual demand. As shown above, requiring solar panels on all new single-ply roofing, or better yet, on all existing medium and large sized commercial roofs, would go a long way towards satisfying US electricity demand. Installing solar panels on all new single ply roofing would be equivalent to adding two large conventional power plants each year. Solar power generated from panels installed on all medium and large low slope roofs, would satisfy 58% of the US commercial demand. Granted, it might take a couple of decades to install rooftop solar as we are reroofing our buildings, but the opportunity for long-term renewable energy sources is right above our heads.
Finally, solar power produced on rooftops can be an important part of improving a building’s resilience. When coupled with electric storage, it could be used to power critical parts of a building’s infrastructure for significant periods of time during a storm-caused grid outage.
Learn more about GAF here.
Source: GAF.
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