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A number that comes up frequently is the “what is the percentage of US land needed to make all our electricity with PV?”

The answer is about 0.7%: approximately a square 160 miles on a side (or 25,700 square miles); or 260 km on a side (66,800 km2).

The assumptions needed to calculate this are:

1. The efficiency of the PV system (because that defines the area needed)
2. The fraction of land the modules cover within the deployed system (packing factor)
3. The output in kWh per installed W, which depends on the sunlight, tracking or not, and other losses within the system.

These numbers can vary quite a bit. For example, system efficiencies are between 5% and perhaps 15% at this time, and as they evolve, will almost certainly rise. Traditionally one is safe to choose 10% as the system efficiency, knowing full well it is likely to be better. (more…)