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Energy Returned on Energy Invested, EROEI.

Balance

People sometimes refer to this as the energy balance. When we say we balance an equation or balance the books or balance just about anything we often think of a scale like that I posted here. However, often what we are really really interested in is “tipping the scales” in our favor.
That is exactly what I am going to talk about in this post.  We want more energy to be produced out of an energy project than we put into it.

Tonight on my facebook page the conversation came up about solar cells and it they produce more energy (and reduce CO2) than is required to make them.  I normally avoid the CO2 argument but the article I will reference later discusses it so I am running head on to it.  To me the CO2 jury is still out, I have heard scientists on both sides discuss it persuasively and effectively.  However, most of the argument is dictated by politics and I want to avoid that like the plague.  The energy part is something I can follow and can add something to.

The EROEI is simply: The amount of energy produced by something divided by he energy required to produce it.   A number greater than one means you get more out than you put in.   The bigger the ratio the better.   But that is when simplicity ends.  How far back do you go at calculating the energy inputs?  Do you include going back to the mine to produce the metal to produce the machinery used to produce the device?  Also once the device has lost its ability to produce energy do you include the energy required to recycle the material?  Something that sounds simple all of a sudden becomes very complex.   Something that sounds very “green” may not be green at all.

I have been told, meaning that I have never really looked it up and followed all the assumptions, that it requires more energy to use an old fashioned razor than it does to use an electric razor.  The reason:  The hot water used with the old fashioned razor takes more energy than the electric used by the electric razor.   Not intuitive is it?

I have looked in detail at some of the other “energy solutions”.  Ethanol from corn is one that to me makes no sense to me considering all the inputs going into it.  However, you can find scholarly papers out there that say the opposite.  Again it may be politics and as always look at the sponsors for the paper and most importantly, look at what was chosen for the numbers going into both the energy in and energy out parts of the equation.  (A google search for “ethanol energy balance” will provide you with much reading material. — Good luck on the sorting.)

Back to the solar cells and energy balance.  As I stated earlier the higher the number the better.  If you are looking into solar it is much cheaper to build and more cost effective to look at thermal projects with solar.  The technology is cheap and easy to understand.  Anyone who has ever went swimming and then while still wearing the swimsuit set on a black vinyl car seat of a car that had been closed and in the sun knows a thing or two about solar thermal heat production.

Most of the time when people think of solar the picture of solar photovoltaic cells come to mind. The energy balance of these may not be in your favor at all.  This is especially the case if you include the costs of energy storage.   While looking during the discussion I found the following article on the net.  I think it is worth a read.   Please note that it discusses assumptions made in in a previous article as well as it may not include everything such as the storage batteries.  The ugly side of solar energy.

Gary

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The picture of the scales is licensed under the Creative Commons Attribution-ShareAlike 3.0 License.  The original author and his work can be found here.

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