Energy Return on Energy Invested (ERoEI) is a useful concept if interpreted correctly!

An Essay by S. Tom Bond, Retired Chemistry Professor and Resident Farmer, Lewis County

There are two very important unfamiliar quantities connected with depletion of resources: “energy return on energy invested” and “net energy”.

In simple mathematical form one measures or calculates the amount of output energy of a process, then adds all the input energies and divides output energy by input energy, deriving a ratio. The larger this ratio is, the better the process. If it falls below 1:1, the process takes more input energy than it produces and reduces the energy available. Thus 1:1 is an upper limit on viable input energy. In fact, the useful limit is not a fixed number, but a limit. In practice a useful minimum ERoEI is reached long before 1:1.

To get ERoEI, one must consider all the energy used to produce the energy required for a particular purpose. This is not a trivial exercise. It is full of pitfalls, from setting improper boundaries to the problem to carful attempts to mislead the reader. It is not the purpose of this article to calculate EROEI’s but to help the reader appreciate the difficulty of such calculations, and why such a variety of values appears in the literature.

Let’s consider two cases. First, the energy for fracking gas to make electrical energy used in the home and elsewhere. The energy to find the gas, the surveys, including the energy used by support personnel, their transportation and food, the energy to make the equipment and use it and to get the data into usable form, including the office staff and publication. Next the drilling and fracking, personnel, all the equipment, transportation of fluids and dispose some of it, to process liquids co-produced, (their value must be considered a plus), enrgy for manufacture of chemicals used, steel, including miles of pipe, and the energy to run all that.

Then all the energy to make the pipe to transport the gas to market, to compress it, the energy to support many kinds of workers involved. The energy to store it for later use, and energy to get it to the electrical generating plant. A lot of gas is lost along the way, including the compressors , ect,. so enough must be produced to cover that loss along the way.

Then there is the energy used to run the plant to generate the electricity. Some 60% or more is lost if the gas is used to heat water which turns a turbine. In a “combined cycle” generating plant the gas is used to fire a turbine and the waste heat from the turbine heats water the theoretical loss is as little as 40%, but I read in practice it is nearer to 50%. Then there is the transmission to the customer.

The energy going into the copper and aluminum power lines must be counted. Both are rare elements requiring a lot of energy. When I took my first college chemistry course there was section in the book explaining how they obtained copper from less than 1% ore, 60 years ago. Aluminum must be made by electrolysis at high temperature, in nations where electricity is cheap, from bauxite ore that usually has to be transported to the refining plant. These are hugely expensive in terms of energy. Also, steel towers for the high tension lines and specially grown and treated wooden poles add to the energy costs. Then it can be used in homes, public places and factories.

Compare this with photovoltaic solar. It costs a lot of energy to produce the special glass used in solar panels. Rare elements frequently are called for, and these are expensive to find, mine and manufacture. The panels are expensive, but can be shipped like any other merchandise. They can be placed by local people with little more than usual electrical training. If energy is to be stored for night or cloudy days, some battery must be provided.

A present, this is the weak link, but Tesla is building a “gigafactory” in Nevada, $5 billion dollars worth, to build lithium ion batteries to power its electrical automobiles. It is expected these can be used to store electrical energy from photovoltaic, too. Last week’s Science, journal of the American Association for the Advancement of Science, one of the two most prestigious places for scientists to publish, had a cover article on a lithium-air battery development which overcomes all disadvantages of previous lithium-air batteries. It appears to set the way for 10 times more dense electrical storage. Again, rare elements mined far away are needed.

Wire for conducting the electrical current is minimal if no supply from a remote source is required, as in home and small business installation. How do you think ERoEI compares between these? A caveat applies here. Home and small business photovoltaic must be higher ERoEI than for a city, because there is only one or two stories involved and land is cheap. For cities, remote land must be involved if many stories are involved, and sunlight is a premium. Some can go on roofs, but you cannot block the canyons between buildings, because they are needed for light and air. This, along with conductors for the current, decreases EROEI.

Caution to the reader, you will see all kinds of figures given for each kind of energy production. One to beware of for solar energy, is that people who want to find an unfavorable value for it will want to count the energy input from the sun as a part of energy invested. No, no, no! Energy from the sun is not depleted; it is there day after day, year after year. It doesn’t take away from the future supply from the sun. It is true that energy conversion is in the range of 15 to 20%, but sunlight is not an economic input. It is free.

One to beware of with gas stops the analysis with the energy content of the gas itself, say at the wellhead, i.e. energy content of the gas over energy to get gas out of the ground. Not enough! What you really want is to compare electrical power to the customer when comparing gas production with other processes. You must go all the way to the final consumer. Boundaries of the analysis must be correctly chosen!

Net energy is the difference between the total energy put into a process and the energy recovered from the process, a subtractive operation, rather than a division. It determines how much energy is available for society to use. Generally speaking, a society needs a certain amount of energy to function at the current level. If the ERoEI is high, it is relatively easy to meet the societies’ needs. The lower the ERoEI, the less energy there is to meet needs other than getting more energy.

Unfortunately, it is possible to make money on such schemes with low ERoEI and that will be covered in the next article which is on “rate of return”.