Tesla recently announced that its Gigafactory, which will produce electric car batteries, will be located near Reno Nevada. More interesting to me, being an engineer and renewable energy advocate, is Tesla’s commitment to renewable energy. In his press conference, Elon Musk stated that the factory will produce all of its own energy using a combination of solar, wind, and geothermal. That’s a tall order, so let’s look at the numbers to see how feasible that is.
The factory is expected to be 10 million square feet (about 929,000 square meters), sitting on nearly a thousand acres of land. Tesla’s drawings show the plant covered in solar panels with a field of wind turbines in the distance. Musk said that the factory would be aligned with true north so equipment could be located with GPS and so the solar panels would be aligned with true south for maximum production. Although the picture shows panels on the roof, there’s a lot of land available for a ground mounted array and/or more turbines.
Image: Tesla Motors
Navigant Research estimates that a battery factory of that size would consume up to 100 megawatts (peak). For a worst-case analysis I’ll assume it runs at peak constantly. The factory would consume 2400 MWh per day. For comparison, that’s the equivalent electricity consumption of about 80,000 homes.
Reno gets an average of five peak sun hours per day. Assuming PV panels with 20% efficiency on a fixed (non-tracking) mount, the rooftop array should generate about one kWh per square meter per day. You can’t cover the entire roof with panels, so using a roof area of around 850,000 square meters, that gives us 850 MWh of solar energy production each day.
Reno’s average wind speed is not particularly friendly toward wind energy production. At 150 meters high, the average wind speed is only about 7 m/s. A 3 MW utility-scale turbine would generate 900 kW at that wind speed. I counted about 85 turbines in the picture, so that would give roughly 1836 MWh of wind energy per day.
Reno is no stranger to geothermal energy - it has several plants in operation already. The newest has a 20 MW capacity. Let’s say Tesla goes small and builds one with only half of that capacity. That 10 MW plant would produce 240 MWh of daily geothermal electricity.
I started doing some back-of-the-envelope calculations (literally), but it became too unwieldy and I wanted to run some what-if scenarios, so I created a spreadsheet. Here it is, with the totals:
If you want to run your own numbers, here are the formulas I used:
The numbers don’t lie. The site could realistically produce more than 2900 MWh of renewable electricity each day ... 20% more than it needs. These are conservative estimates on production and worst-case estimates on consumption, and it’s clear that there’s enough renewable energy to run the plant with some to spare.
All of the calculations are for energy, not power. In other words, you might produce 2400 MWh per day, but that doesn’t mean you’ll always have 100 MW available at any given instant. Sometimes you’ll generate more, other times less. Obviously there will be no solar production at night and less wind production on calm days. To be fully off-grid, Tesla will need some form of storage. As I surmised in a previous article, Tesla is probably shooting for more than the EV market; it seems logical for them to be looking into grid-level storage as well. What better way to showcase that than to include Li-ion batteries for on-site storage?
But that’s a lot of batteries, the plant isn’t built yet, and the factory needs to produce enough batteries in time for Tesla’s planned rollout of their newest car. My guess is that they won’t be off-grid for a while. Instead, they’ll be grid-tied and take advantage of net-metering, with storage as a future possibility. Either way, the Gigafactory will be a net-zero energy facility that should offer plenty of lessons on energy-efficient building construction and management.
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