Previously, on ObscureBlog:

Ethanol sucks.  To be more specific, let's explore the effectiveness of ethanol as a renewable resource. 

Fundamentally, all energy, except for nuclear energy, comes from the sun (the great nuclear reactor in the sky).  Fossil fuels are a means of extracting solar energy that fell on the earth millions of years ago.  However, this solar energy reserve is running out.  We need to come up with ways of converting the solar energy that is falling onto the earth today into energy we can use without waiting the millions of years it takes for the generation of oil, coal, and natural gas beneath the earth.  Here are some numbers to start:

The intensity of solar radiation is 1 kW/m^2.  That means, if you had a 100% efficient solar converter, for every square meter of land it covered, you would get one kilowatt of power.   If that sunlight was collected for an hour, you would have one kilowatt-hour of energy.  Power is a measure of rate - how fast you've gone - and energy is a measure of quantity - how far you've gone.  With me so far?

However! This solar radiation is on a surface perpendicular to the sun.  If you have your collector on a flat surface at all times, you must correct for the incoming angle of the radiation.  This is why you are cold in the winter, when the sun angle is low, and warm in the summer, when the sun angle is high.  Science!

In addition to the effect of the angle of the incoming solar rays (called the "cosine effect"), you must also consider the length of each day and the typical amount of cloud cover in the area where your collector is located.  Fortunately, there is a government agency whose job it is to determine these things for us - the National Renewable Energy Laboratory.  Your tax dollars at work.

So, we can get all the information we need to calculate how much solar energy falls on the corn.  Now we need to know some things about corn.  Specifically:

When is it planted, and how long does it take to grow?
It depends on the area.  We are going to use Iowa as our test region, so we will say planting day is roughly on April 1st.  The time it takes to grow depends on the variety.  We will use 80 days as an estimate.

How much land is required to get us a single bushel?
In 2007, Iowa farmers harvested 2.5 billion bushels on 13.9 million acres, for a land-usage average of 180 bushels per acre.  Doing some math gets us to 1 bushel per 22.5 square meters.

How much ethanol do we get from a single bushel?
2.7 gallons per bushel, per the Department of Agriculture.
 
How much energy is in that amount of ethanol?
76,000 BTU per gallon, or roughly 60 kWh per bushel.



Let me pause here to make an observation.  Many people reading this by now will be completely confused; if they aren't confused yet, they will be by the end.  That is because energy is complicated unnecessarily.  Let's take a quick look at some of the power and energy units we encounter in our daily lives.

* Kilowatt hours (kWh) - this is how you are charged for electricity energy on your utility bill
* Therms - this is how you are charged for natural gas energy on your utility bill
* British Thermal Units (BTUs) - commonly used as a power rating for air conditioners
* Gallons of gasoline - energy you put into your car
* Barrels of oil - energy put into gasoline to put into your car
* Joules - standard metric unit for energy
* Erg - energy unit commonly found in crossword puzzles
* Horsepower - a unit of power used to rate car engines
* Calorie - energy unit used in food

If you want to be an educated consumer of energy, you should know what these (and other) units mean, and how they compare... I smell another Word Problem. Anyway, moving on.

We will use Des Moines, Iowa as our example location, since we used to only hear about ethanol subsidies at the beginning of each election cycle for the Iowa caucuses.  According to data from the Renewable Resource Data Center (a part of NREL), Des Moines, Iowa, typically sees 257.5 kWh per square meter for the 80-day period that starts on April 1st. 

All the hard work is done, so let's see what we get:

1 bushel requires 22.5 square meters.  If each square meter receives 257.5 kWh worth of solar energy, 1 bushel receives 5800 kWh.  From each bushel that is converted into ethanol, we get 60 kWh worth of energy.  This is a conversion efficiency of just over 1%. For comparison's sake, the worst solar panels - you know, the ones you refuse to put on your house because they are ugly - get 10%.  Corn is 10 times worse at converting sunlight into energy as the worst photovoltaics.