A couple of weeks ago I posted about an article in the New York Times that described a new initiative to build solar farms on unused farmland. At the end of the article were some interesting statistics that begged for a follow-up:
Daniel Kim and Bob Dowds, the principals of Westside Holdings, the firm that has proposed the Westlands Solar Park, said the first phase of the project would consist of 9,000 acres leased from farmers. When covered in solar panels, that acreage would generate 600 to 1,000 megawatts of electricity. One megawatt is enough to power a Wal-Mart Supercenter.
Several readers did the math themselves in the comments of that post so I wanted to make good on my own promise to participate in some figuring as well - specifically, if 9000 acres of solar farm produces 600-1000 MW of power, and a Walmart Supercenter uses 1MW, could a Walmart Supercenter conceivably power itself from its own grounds?To give this a fighting chance of working, I'm picking a Walmart in a nice sunny place. Google gave me this Walmart Supercenter in Los Lunas, New Mexico.Using this AMAZING tool shared by commenter unfMeghan, I generally traced its area, actually rounding down a bit because I'm not sure how the rights work with the other stores in the complex.The tool tells me the parking lot and roof cover 16.231 acres. Commenter dogsix said the average is 16 acres. I have no idea how he/she knows that, but I feel comfortable that the store I've selected is probably average in size.Going back to the article's statistics, 9,000 acres produces 600 to 1000 megawatts. Even though the store I found is in New Mexico where it's probably sunny enough that I should claim the full 1000 megawatts of productivity, I'll say 800 megawatts just to give some compromise to reality.After the jump, the verdict!
According to my math then, a solar farm of moderate productivity the size of the area of this Supercenter, 16.231 acres, can produce 1.442 megawatts of energy, well above the required 1 megawatt specified in the article to power a Walmart Supercenter.Some folks did the math using only the roof area, but in fact, elevated solar arrays over parking lots exist in real life and apparently work really well so I've included the parking lot area in my assessment. I only know about solar parking lots incidentally from headlines I see coming out of New Jersey. Either solar parking lots are soon to be common or New Jersey has a lead on a new, good idea. Not only do you get the energy but your car doesn't cook and I understand the parking lot itself requires less maintenance as a result.This article on a new solar parking lot in New Jersey actually has better math than the numbers we're working with:
"The 1 MW array consists of more than 5,000 photovoltaic panels, and has a total area of 104,000 square feet."
104,000 square feet = 2.38751148 acres = 1MW. The math I did above requires 11.25 acres to produce 1 MW (using the 800MW compromise). That's a suspiciously large gap but doesn't change the answer to the Walmart question. And while one of the greatest obstacles to solar and wind power is getting that energy to the grid, it's hard to imagine how a Walmart Supercenter isn't already well positioned to access the grid.What's missing now is the cost difference between buying that energy through the grid and building a 16 acre solar farm over a shopping center. I'm not sure the data on that is as easy to find and break down. My guess is that the solar farm is still cost prohibitive, even with tax breaks and other incentives. If we can find enough info for a reasonable answer I'll post another update.