Glück Auf is loosely translated as "good luck to us all".

Sunday, August 12, 2012

Thermoelectric Power Generation

It's been terribly hot in Texas these last few weeks, so I haven't been willing to work in the Airstream. So, I've been doing some research and fiddling with various power generation techniques. As I mentioned in a previous post, thermoelectric generators (TEG) seem like a very efficient way to produce a great deal of electricity from heat. However, the more I researched the use of TEG to charge batteries, the more I became discouraged about the price and complexity of thermoelectric power generation.

The manufacturer of the F2F200 TEG claims it can generate over 200 watts if the heat source is over 270° C and the cooling water flow is 1500cm3/minute at 30° C. Those are some pretty impressive specifications, but I'm having trouble imagining a practical design that could safely deliver that much heat to the TEG to maximize the power output.

The retail price for this unit is $1,919.99 and if I was to invest that kind of money I would need to be pretty sure that I can push the temperatures to the optimal 270° C. If I was to attempt to generate power with this type of TEG, I would probably build some sort of parabolic solar collector that could be easily deployed with the TEG whenever I setup camp.

Due to the extreme temperature and pressure required by this TEG, I would want to keep it far enough away from my Airstream to minimize the risk of injury in case of a leak or break in the pipes. I would also want to include some sort of a pressure release valve that would automatically safely bleed the pressure out of the system automatically and by a safety valve that can be activated from a safe distance.

I've found at least one copper pipe manufacturer (Mexflow) that discuss "maximum working pressures at temperature up to 650° C". I've also read some discussions about "brazed joints" that can withstand very high temperatures because the alloys used melt above 600°C. Unfortunately all of the brazing alloys I've found seem to recommend a maximum working temperature of about 200° C. So I might have to exceed the safety recommendations to achieve the temperature of the TEG.

I ran these ideas by some of my family who are engineers and my cousin pointed out that if the fluid is not taking the heat away from the solar collection point excessive heat can occur and would probably quickly destroy several of the components. So he suggested that I would need something that could handle the heat as a buffer.

When I started researching heat buffers, I stumbled across discussions about using 1000-2000 ton water tanks with layered heat chambers for this exact application. Now I am beginning to think that it would be difficult for a TEG to compete with PV solar at twice the cost and at least four times the complexity. I still really like the idea of using a TEG for generating electricity because I could use the TEG with a wood fired stove to generate electricity at night and then use a solar collector during the day.

As I was researching, I found a similar device called a thermoelectric (peltier) cooler (TEC). The TEC modules are mostly used in portable coolers and refrigerators and they are much cheaper then the TEG modules that are designed for power generation. The TEC modules also seem to have a much lower heat requirement for generating electricity. So, I started to wonder if a large quantity of the TEC modules could possibly be used at about 100° C instead of trying to deliver 270° C to these very expensive TEG modules.

A nice fellow named Jack posted some very detailed videos about his power generation experiment with TEC modules. Below is the last of the videos which shows the end result of his project.

I actually ordered about twenty thermoelectric cooling modules that are very similar to the ones Jack used in his experiment. I ordered the TEC modules in the hopes that I can cool and heat my Airstream and maybe even build a custom refrigerator with them. I was planning to try to generate some power with the TECs, but it seems that these modules just don't produce nearly enough energy to justify the cost of a large-scale implementation. From what I can tell, these TEC modules are designed to use minimal power for heating and cooling. So I guess I would not be using the TEC modules for the purpose they were intended and it would take a large temperature difference to create a relatively small amount of power.

So, I don't think I will attempting thermoelectric power generation until I find a more practical and cost effective TEG module.

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