Climate-anxious Liberal: “Whew, finally solar installations at scale are helping to turn the tide on fossil fuel generated electricity! Put it everywhere! Life’s a trade-off!”
Food-security-anxious Liberal: “Horrors! The solar farms are stealing all the agricultural land, we’ll starve!”
Tree-hugging Liberal: “The solar armies will spare no forests in their quest to dominate the surface of the planet!”
Landscape enthusiast Liberal: “Ughh, I’m getting a headache just thinking about the future endless monotony of photovoltaics dominating my cherished views!”
Can these over-wrought liberals find solace and mutual understanding on the subject of deploying renewable energy infrastructure? Unsurprisingly, we recommend they start by looking at some numbers.
In a recent column we mentioned that, of the 10 acres of forest per person in Maine, if one acre were replaced with solar panels that would more than compensate for the average carbon footprint. Here we want to get a little more quantitative with that concept: How much land would be required if we were to get most of our energy from renewables?
All renewable energy sources require substantial land area. As usual, the question is “How much?” To figure this out is straightforward in concept. You need to know (a) how much energy a given area of land can produce, and (b) how much total energy is needed. Divide (b) by (a) and voila!
To know how much energy is available over a given area of land, we use a quantity of “power per unit of area.” This is a measure of the “intensity,” or how quickly energy flows onto some fixed unit of area. We measure this in units of watts per square meter (W/m2). We’ll use the kilowatt-hour (kWh) as our energy unit. As an example, the sun’s peak intensity on the earth’s surface is about 1000 W/m2.
Different renewables have different intensities. Solar is currently the highest. Here in Maine it is possible to have an average of about 22 W/m2, while in Phoenix AZ you can get around 33 W/m2. The average for the U.S. is around 26 W/m2. (This average accounts for day/night, seasons, weather, and efficiency)
Wind energy depends very strongly on location—they are practically useless where windspeeds are low or unsteady. In appropriate locations, with the turbines spaced so that they don’t interfere with each other, they typically produce around 5 W/m2. (Of course, the land in between the turbines is still useful for tree growth or farming.)
Hydropower is dependent on area as well. There is the area that is flooded when a dam is built, but in terms of total energy potential it depends on the amount of rain that falls on a given area (say a watershed) and the vertical drop of the water as it passes through hydroelectric turbines. By this measure the intensity of hydropower is quite low, ranging from 0.02 W/m2 to 0.25 W/m2. Of course virtually all of this land and water area is used in other ways as well.
So then how much is needed to power the country? That number is well established and is very close to 30 trillion kWh per year. That is hard to picture, so, on a “per capita” basis it comes out to an average of about 10,000 W per person. (That’s total power for everything we do, not just electricity. It includes transportation, manufacturing, heating, commercial use, etc.)
Producing that much power from solar alone would require about 400 square meters per person. That is approximately one tenth of an acre per person. In Maine it would be about 0.11 acres. In terms of total area it would be about 150,000 acres or about 0.7% (7 tenths of a percent) of the land area of the state.
To produce it all from wind would require about 4 times as much area, so around 3% of the land area. To produce it from biomass with an intensity of around 0.1 W/m2 would take more area than the entire state!
In Maine, there are about 1.3 million acres of farmland in use today. That means that the total area required for enough solar to completely power the state is equal to 12% of the current total farmland. So while it makes sense not to put solar farms on our best farmland, there is no danger that we will be replacing all of our farmland with solar projects. It’s also unlikely that all of our energy would come from PVs anytime soon, making the total required considerably less.
The question of which to choose is made complicated by the fact that wind and solar are intermittent while hydro is very controllable. In the end, it is clear that most of our renewables will come from wind and solar as the intensity of hydro is too low. Because of this intermittency we need a way to store the energy and ways to control when it is used. Large-scale batteries and hydro will serve as storage devices to smooth out the fluctuations in the wind and solar, and a smart grid will help control peak usage.
Please keep in mind that these are “ballpark figures.” This simplified picture is intended to give the scale of the problem we are trying to solve.
United Liberals: “OHHHH, now we get it! If we all just spend a little more time considering the NUMBERS, maybe we will get through this energy transition without ulcers! What are the chances…”
Paul Stancioff, PhD., is a professor of Physics at the University of Maine Farmington who studies energy economics on the side. He can be reached at pauls@maine.edu. Cynthia Stancioff is a former English major who enjoys re-writing things. Previous columns can be found at https://paulandcynthiaenergymatters.blogspot.com/.