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Efficiency and Effectiveness and Solar Energy.

Tonight’s post was intended to kick-off a discussion about solar energy, but as I was formulating how I was going to present it I kept running into a word … efficiency.  I know the thermodynamic use of the term very well, but we often throw the word around to mean lots of other things.   That seems to be a big problem with language, we often know what we mean, but  what we think we are saying may not mean the same as what someone else thinks it means.

In the case of solar energy, I might say that method A is not as efficient as method B.  I may be incorrect when talking about the energy produced, but I may be very correct when talking about the energy produced per dollar spent. So to be perfectly clear, I will define the terms and will try to be consistent in using them.  (“To be perfect clear”  should probably scare you… I have heard politicians use that term!)

When I use efficiency I will use it to describe useful output energy divided by energy input.  As normal, we will probably have very few places where we know actual values of either the input or the output, but we can say method A is more efficient than method B and give reasons for saying so.

When I use the term effectiveness it is as I defined it in the picture:  The most gain for the least amount of pain.   Usually the pain will be pain in the wallet and we will be talking about the most effective use for our money.  It could be effective use of space or of time.  Effective will almost always be a comparison of several choices.

As we talk about solar energy, mostly I am just going to be talking about principles and the pros and cons of various things. The thermistor circuit we have been designing is to allow us to take some thermal data as we experiment.  If you have a pocket full of money and are ready to “pull the trigger” and spend it right now on a system, this probably will be a waste of time.

Solar Energy Concepts

A generic diagram of solar energy is shown in the picture to the right. Slight modifications to this and the diagram would apply to any energy system.  All of the red arrow represent the losses in the system.  These are the things we want to minimize.  As we deal with effectiveness of our use of money, the only thing free in the whole system is the sun.  Everything else in the system will cost something.

The final use of the energy is probably the same uses we are using today.  The most effective use of our money may be (and probably is) to minimize the losses here.   For the most part we will have little control over the path of the sun to our collector.  (We can have some control… for a price.)  Since the sun in intermittent and at best we will have an average of 12 hours of light in a 24 hour day, we will need some way of storing the energy we collect  (It is actually much less than 12 hours, but we will get into that later.)  Storage will be our biggest challenge both with efficiency and cost effectiveness.

Since we are basically starting another project, the first step is always to work toward what are the goals of that project.   That will be the part I called “Final Uses” and that will be where we start.

I will leave tonight’s post with a simple example about effectiveness.   Probably the most cost effective solar energy project you can install is a clothes line.  It may not be the most effective use of your time.  Convenience is another item that has to be thought about as we consider the effective use of our time.  That decision will be up to you and/or your spouse.


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