• Adam H. Cooke

Solar on Rooftops could match Annual U.S. Electricity Generation I

Researchers performed a global assessment on rooftop solar PV power potential using high resolution imagery, big data and machine learning.

According to research on global solar potential, the United States has enough rooftop space to install solar power equal to its current national generation levels. Researchers from the University of Cork in Ireland used big data, machine-learning, and geospatial analytics to arrive at their conclusions, which were published by Nature Communications.

The report identified 77,000 square miles of rooftop space worldwide as usable PV surface area. (For context, Florida's 65,000 square mile area is approximately 65,000). If this area is completely covered with conventional photovoltaics, it could produce 27 petawatt-hours or 27 million GWh.

This amount of potential energy will exceed the 2018 global electricity consumption. In 2018, 6 petawatt-hours of electricity were consumed by households alone. Globally, there have been 23 PWh. estimates.

Further, the report stated that the United States' rooftops could produce 4.2 PWh annually. This would be equivalent to the nation's current energy output of approximately 4 PWh.

According to the Energy Information Administration (EIA), approximately 60% of U.S. electricity generation in 2020 was generated from fossil fuels and 20% from nuclear and renewable energy sources. EIA estimates that 42 billion kWh of electricity was also produced by the United States from small-scale, distributed solar. This is about 1% of total generation. The 2.2% of total generated electricity that year was from large-scale solar.

Nature Communications' paper stated that there are mitigation factors to this potential PV outlook. These include constraints around transmission and storage requirements due to intermittent solar energy generation cycles.

One of the many methods that were used to create the report was a bottom-up geospatial assessment.

The high potential of rooftop solar could be good news for American ratepayers as it may bring some savings back into their pockets. Local Solar for All recently estimated that $109 billion could be saved annually in utility bills if rooftop solar was scaled up 2 to 4 times faster than an all-utility-scale deployment scenario.

This report can be used as a powerful talisman for people who are concerned about energy spread, or the development land for energy generation. Clemson University's study found that the United States would need approximately 500,000 square miles to develop new energy sources by 2040. This is more than Texas. Rooftops can be used to save land that is otherwise valuable.

James Glynn (senior researcher at Columbia University) said, "The open data generated by this research helps quantify, locate, and prioritize investment in zero carbon electricity systems."

The Nature Communications paper also examined the potential costs of rooftop solar around the world. It was discovered that prices vary depending on where you live. China ($68) was the lowest and India ($66) the highest, while the U.K. ($251 and the U.S. ($238) had the highest.