But these projects could also potentially uproot imperiled Joshua trees and cactus, kill or displace threatened desert tortoises, block wildlife migratory paths and harm local communities. This puts conservationists and policymakers in the difficult position of having to choose between saving the desert — or the planet. 

There are other ways, however, and other locations for solar panels, from residential rooftops to farm fields fallowed by drought. France, for instance, recently required large parking lots to be covered by solar canopies that shade cars and provide up to 11 gigawatts of new generating capacity, equivalent to about 10 times the three proposed projects in Arizona. 

This inspired us to ask: How much power could be generated by slapping solar panels not only over the West’s vast parking lots, but also on its 21,000 big-box store rooftops? We did the math, and this is what we found out.  

 

1,155 megawatts
Estimated generating capacity if solar panels covered all 370 miles of the Los Angeles Aqueduct, as LA officials propose.

37,500 gigawatt-hours per year
Energy output of solar canopies if all of Phoenix, Arizona’s 12.2 million parking spots were covered. 

139
Number of desert tortoises relocated to make way for the Yellow Pine Solar Project in southern Nevada in 2021. Within a few weeks, 30 of them were killed, possibly by badgers.

4,200 (215,000 acres)
Grazing leases bought and retired in the Mojave Desert in California by Avantus this year to protect wildlife habitat and Joshua trees. The Onyx Conservation Project is a partnership with federal and state land management agencies to “offset” the impacts of the company’s developments elsewhere in the region.

1.3 million
Estimated number of Joshua trees destroyed by the 2020 Dome Fire, thought to be exacerbated by climate change, in the Mojave National Preserve in California. 

Note: We worked from two figures that were calculated by Greta Bolinger and Mark Bolinger in “Land Requirements for Utility-Scale PV: An Empirical Update on Power and Energy Density,” published in the IEEE Journal of Photovoltaics in March 2022:

Power density: .35 megawatts per acre for utility-scale, fixed-tilt photovoltaics. Most residential solar systems are about 400 watts, or .0004 megawatts. 

Energy density: 447 megawatt-hours per year per acre for utility-scale fixed-tilt photovoltaics. An average American household uses about 10 megawatt-hours of electricity annually. 

We used Environment America’s figures and Google Earth’s measurements to determine that an average big-box store has 3.25 acres of rooftop. We used American Planning Association calculations to estimate that one acre contains about 145 parking spaces. 

Additional sources: BLM, EIA, Basin & Range Watch, UC Davis, Berkeley Lab, Avantus, Primergy, American Planning Association, USGS, Environment America, Google Earth.