As a good estimate, it will take about 130,000 acres of solar cells to deliver the power of a typical nuclear facility, 26 TWhr/year. Since Donald Trump has proposed covering his wall with Mexico with solar cells, I came to wonder how much power these cells would produce, and how much this wall might cost. Here goes.
Lets assume that Trump’s building a double wall on a strip of land one chain (66 feet) wide, with a 2 lane road between. Many US roads are designed in chain widths, and a typical, 2 lane road is 1/2 chain wide, 33 feet, including its shoulders. I imagine that each wall is slanted 50° as is typical with solar cells, and that each is 15 to 18 feet high for a good mix of power and security. Since there are 10 square chains to an acre, and 80 chains to a mile we find that it would take 16,250 miles of this to produce 26 TWhr/year. The proposed wall is only about 1/10 this long, 1,600 miles or so, so the output will be only about 1/10 as much, 2.6 TWhr/year, or 600 MW per average daylight hour. That’s not insignificant power — similar to a good-size coal plant. If we aim for an attractive wall, we might come to use Elon Musk’s silica-coated solar cells. These cost $5/Watt or $3 Billion total. Other cells are cheaper, but don’t look as nice or seem as durable. Obama’s, Ivanpah solar farm, a project with durability problems, covers half this area, is rated at 370 MW, and cost $2.2 Billion. It’s thus rated to produce slightly over half the power of the wall, at a somewhat higher price, $5.95/Watt.
It’s possible that the space devoted to the wall will be wider than 66 feet, or that the length will be less than 1600 miles, or that we will use different cells that cost more or less, but the above provides a good estimate of design, price, and electric output. I see nothing here to object to, politically or scientifically. And, if we sell Mexico the electricity at 11¢/kWhr, we’ll be repaid $286 M/year, and after 12 years or so, Republicans will be able to say that Mexico paid for the wall. And the wall is likely to look better than the Ivanpah site, or a 20-year-old wind farm.
As a few more design thoughts, I imagine an 8 foot, chain-link fence on the Mexican side of the wall, and imagine that many of the lower solar shingles will be replaced by glass so drivers will be able to see the scenery. I’ve posited that secure borders make a country. Without them, you’re a tribal hoard. I’ve also argued that there is a pollution advantage to controlling imports, and an economic advantage as well, at least for some. For comparison, recent measurement of the Great Wall of China shows it to be 13,170 miles long, 8 times the length of Trump’s wall with China.
Dr. Robert E. Buxbaum, June 14, 2017.