We can’t shake the conviction that using actual quantitative analysis – the numbersS – in making energy decisions would help the world along on the road toward making sense.

Take for instance nearly everything that’s said about energy policy in opinion pieces in the media. It’s no place for opinion, this energy transition stuff.  The stakes are high, the impacts of policy are vast, the costs can be enormous, the benefits can be transformative.  Let’s do it right:  At least let’s make every attempt to base our opinions on quantitative analysis, not “intuition,” hearsay, and “common sense.”

One tool that we’ve found instructive in analyzing the impacts of renewable alternatives to fossil fuels is an examination of the land area required for a net yield of energy from a given fuel.  Fossil fuels take up little surface area – they are underground, and moreover incomparably concentrated.

Renewables all come from the surface of the planet. There is a finite amount of surface on the Earth, of course, and our task is to figure out how to get all the energy we need using that surface.

One spectacular example of a renewable energy policy NOT based on an analysis of net-energy-yield-per-acre is the U.S. ethanol subsidy program.

Today in the US around 90 million acres of land are used to grow corn for all purposes. About 45% of the grain from those acres goes into producing ethanol. So a little less than half our corn production goes toward producing around 17 billion gallons of ethanol per year.  Is this a lot? Well let’s do some calculations.  First, the area used for this is almost twice the area of the state of Maine!

How much energy do we get from these 17 billion gallons of ethanol?  Let’s put the numbers in terms of how much energy you get per acre: about 450 gallons of ethanol per acre per year.  Sounds like a lot. However, energy is required to make the ethanol. These energy inputs include things such as fertilizer, running farm equipment, transportation and, mostly, processing the grain into ethanol.

Currently this energy comes mostly from fossil fuels. While the estimates range quite a bit, according to most sources this amounts to almost as much energy as the ethanol contains. Some sources even say that there is no net energy from ethanol–that it takes as much energy to make a gallon of ethanol as it produces.

Being a little more generous, we could use an average result of 1.4 units to 1, meaning  that 1 unit of input energy produces 1.4 units of output energy. So to produce 450 gallons of ethanol it takes the equivalent of 320 gallons of ethanol. This leaves a net energy of 130 gallons per acre per year.

If that acre were covered in photovoltaics here in Maine it would produce about 950,000 kWh of electrical energy per year.  So how do we compare those 130 gallons of ethanol with 950,000 kWh?  The pure energy content of 130 gallons of ethanol is equivalent to 2900 kWh. Dividing 950,000 by 2900 we get 328.  So the acre of PVs produces more than 300 times as much energy as the corn ethanol.

Another way to look at it is to compare how many miles the ethanol could move a car compared to the PVs.  A car that gets 30 mpg on gasoline would get around 20 mpg on ethanol because of its lower energy content. So 130 gallons would move that car around 2600 miles. 950,000 kWh would be enough energy to move a Chevrolet “Bolt” between 2 and 3 million miles. So the PVs can move the car around 1000 times farther.

(You’re perhaps wondering why, if photovoltaics are only 300 times more productive of energy than ethanol, PVs move the car 1000 times farther. The answer is the electric motor is 3 to 4 times more efficient than the internal combustion engine.)

Incidentally, even if it took no extra energy to make the ethanol and you netted the full 450 gallons per acre, the PV electric car would still go 300 times farther than the ethanol powered car. The main reason for that is that PVs are much more efficient than photosynthesis (which made the corn) at converting solar energy into usable energy.

Remarkable fact: If an area of land currently used for ethanol production were instead covered with PVs it would produce more energy than the entire usage of the US.  This includes all forms of energy usage: transportation, electrical, industrial, commercial, residential and anything else.

Of course, it wouldn’t be feasible to literally substitute PVs for all current ethanol corn farms. They would necessarily be spread out all around the country, with concentrations in the sunnier southwest regions, and would include wind energy.  (The corn acreage could go back to food production!) But we hope you find the concept encouraging and worth toying with in our efforts to design rational energy policy for the future.

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 [email protected]  Cynthia Stancioff is an amateur naturalist who likes to write. Previous columns can be found at https://paulandcynthiaenergymatters.blogspot.com/

Comments are not available on this story.