Published on July 27th, 2019 | by Michael Barnard
July 27th, 2019 by Michael Barnard
What if we wanted to generate all the primary energy that the US uses for everything with wind generation? That’s all the energy the US uses for everything: industry, heating, cooling, shipping, Instagram, and driving to work? How many wind turbines would that take? How much of the US would be covered in big white pinwheels?
Obviously wind energy wouldn’t be the only form of primary energy in the US. Solar, hydro, geothermal, and biofuels will also play roles, with solar being at least equal to wind generation. But like the patch of sand in the Sahara covered in solar panels, it’s interesting and informative. No one is suggesting using wind or solar alone to generate all of the United States’ energy needs unless they are constructing a useful thought experiment such as this one or erecting a straw man to fire at with flamethrowers that tend to blow up in their hands.
What is primary energy? Well, the electricity coming out of our wall sockets is a mix of primary and secondary energy. The electricity that’s generated with renewables is primary energy. The electricity that’s generated from fossil fuels is secondary energy. Natural gas that we burn for heat or cooking is a primary energy source because we don’t do much to it except pump it and grade it. The gasoline and diesel that drives our cars and trucks is a secondary energy source, because it’s transformed extensively from the primary petroleum energy source. In general, it’s easy to say that the closer to primary energy we get, the more efficient energy use is because every step along the way has inefficiencies.
Let’s make some basic assumptions:
- We are going to replace all primary energy sources in the US.
- We are going to do it only with wind energy.
- We are only going to talk about the land that’s actually consumed by a wind farm, which is to say mostly the bases of the wind turbines. We can do lots of productive stuff with land right up to the base of the turbine, so it’s mostly irrelevant that they are spread out.
- We aren’t going to worry about grid balancing, as that’s going to be done in reality mostly by all the other forms of generation, continent scale HVDC and a bit of storage. What if, remember?
How much primary energy does the US use annually?
This energy flow chart from the Lawrence Livermore National Laboratory is crucial to understanding this. A lot of people have a very mistaken idea of how much energy we have to replace, the 101.2 quads at the top. They do the equivalent of counting up all the boxes on the left side of this diagram and come up with a huge number. But the actual number is closer to the small box on the right. The large grey box above that is rejected energy, mostly in the form of waste heat from burning fossil fuels.
Actually useful energy is “only” 32.7 quads. A quad is to 1.055 × 10^18 joules or 1.055 exajoules. For context, a quad is equivalent to about 172 million barrels of oil. That’s what we really have to actually replace, about 35 exajoules.
Electricity generation from wind energy is vastly more efficient at being generated and at being used than fossil fuels. There are a lot fewer steps between generation and use, and moving it around is a lot more efficient. That’s a big part of the reason the future for all energy is electricity. Of course, electricity isn’t 100% efficient either. We take some losses for transmission, battery storage losses for EVs, waste heat from LEDs (much less than incandescents and fluorescents, but still) and the like. When it’s used as heat, it turns into heat very efficiently, so that’s a wash.
Let’s call it a 20% increase required to cover efficiency losses. That gets us to about 41.4 exajoules.
Of course, we don’t measure electrical generation in exajoules, but in terawatt-hours (TWh). There are about 278 TWh in an exajoule. That means we need to generate about 11,500 TWh from wind farms in a year.
Yeah, that’s a lot. New wind farms average about 40% capacity factors, meaning the ratio between the actually generated electricity in a year vs the amount they could make if they generated at full nameplate capacity every hour of the year. For comparison, the US coal fleet is running around 54%, nuclear is running around 90% and solar is running around 20% these days. Nothing generates its hypothetical maximum year over year.
So we need enough wind generation capacity, running at a 40% capacity factor to generate 11,500 TWh over the course of a year. To get that, we need 3.3 terawatts (TW) of wind generation capacity.
The average wind turbine installed in the US in 2018 was 2.6 megawatts (MW) in capacity. Using this average size as our baseline, we would need about 1.26 million of them.
That’s a lot, of course. The US consumes a great deal of energy every year.
But each wind turbine only takes up about a quarter acre of land at the base, so that’s only about 470 square miles of land that would actually have a wind turbine on it. The US is about 3.8 million square miles, so that’s only about 0.01% of the land mass. I think the US could afford that much. After all, it’s only a little bigger than Delaware.
This is all hypothetical, of course. No grid can work on a single form of generation. We need a mix of generation sources and a bunch of ancillary services.
The US will end up with a continent-scale grid with lots of high voltage DC, a bunch of excess wind and solar because they are so cheap to build, a lot of hydro backfilling energy around the country and then a bunch of gap fillers such as geothermal, biofuels and tidal. Mark Z. Jacobson and his team at Stanford have the numbers for each state in the US (and 139 countries globally) in their 100% renewables by 2050 material.
But make no mistake about it. All primary energy will be supplied by renewable sources in a few decades. Petroleum, coal, and natural gas won’t be used as primary energy sources except in rare and tiny cases. The Age of Fossil Fuels is coming to an end, and there will still lots of fossil fuels left when it does.