Re: If the whole USA was covered in solar panels....

Hi, Tim!

Let's try for a "ballpark" answer. We'll just use one significant digit, so we'll call the total US land area 1 x 10⁷ (10 million) sq. km. A square kilometer contains 1 x 10⁶ (one million) square meters, and bright sunlight's intensity is about 1 kilowatt per square meter. Let's use a figure of 20% efficiency for the solar cells. Multiply it all out and you get 2 x 10¹² kilowatts, or 2,000,000,000,000 (two trillion) kilowatts. Let's say we have 5 hours of bright sunlight on average available per day, and that makes ten trillion (1 x 10¹³) kilowatt-hours (kWh) per day.

According to the US government, we use about 3.4 trillion kWh of electricity per year. That's about 10 billion (1 x 10¹⁰) kWh per day.

Dividing our current needs by the potential supply of electricity from solar cells, we get: 

1 x 10¹⁰  kWh/day 
--------------------   =   1 x 10^-3
1 x 10¹³  kWh/day 

Multiply that by the total US land area and we get 1 x 10⁴ sq. km.  Arizona's land area is about 3 x 10⁵ sq. km, so a hunk of southwestern desert about 3% of the size of that state should suffice nicely.  Expressed more intuitively, we're talking about a square of desert only about 100 km (60 miles) on a side.

Regards,

Aaron