Thermoelectric Generators to supplement wintertime solar.

Since the topic of solar shortfalls in winter seasons comes up often, these devices are on the top of my experimentation list. For many seeking extra power and heating with a wood heater, these devices can fill the gap of low sun or no sun part of the year.

I first read about TEG technology in Home Power Magazine around 2002. The article said that these were in use extensively in Scandinavia, where sunny days are scant during part of the year.

Does anyone currently use one of these or a similar device?

http://www.devilwatt.com/products

100w output 24/7 in the sun- scarce heating season!

We have a small demonstrator that uses candles to power a light that is 20x brighter than the light output of the candle that powers it. There are quite a few camp and villiage type cooking pans and fuel stoves that have this technology and have been around for several years.

https://www.tellurex.com/shop/  (company makes cooling modules also and designed the coleman cooler/warmer devices that are around.)

http://www.tegpro.com/thermoelectric-generator-products

https://www.bioliteenergy.com/products/basecamp

One gentleman on here uses them.  A byproduct is that you generate hot water.  Here's a post by Byron Gagne on his greenhouse that is heated by the water from a TEG.  The TEG part of the discussion is near the bottom of the page.

I'm interested in them but I don't know if I could get enough juice from them to power my house.  But I'm all ears...

The efficiency of TEGs is between 5-8% (according to Wikipedia). To me this means a TEG should really only be used to harvest waste heat. You're better off capturing the heat from your fire in thermal mass than converting it to electricity.

My opinion is that solar PV and battery storage is so affordable now (and getting cheaper every day) that I won't bother with TEGs for anything other than just playing around. Assuming you already have a solar array, it makes even less sense to diversify into completely new tech. Just get a bigger solar array or think of ways to reduce your electricity demand in the winter.

EDIT: Having thought about this some more, I'd like to recognize that I have no idea where in the world you live and you know better than I do about your solar potential. If you live in the Arctic Circle then yep, get a TEG

Matt Coston wrote:The efficiency of TEGs is between 5-8% (according to Wikipedia). To me this means a TEG should really only be used to harvest waste heat. You're better off capturing the heat from your fire in thermal mass than converting)

EDIT: Having thought about this some more, I'd like to recognize that I have no idea where in the world you live and you know better than I do about your solar potential. If you live in the Arctic Circle then yep, get a TEG

Some areas, like mine at Michigan, experience 5-12 days of drab to dead overcast with spotty sun for a couple hours over those days, or say, 6 days of low to no charging followed by a sunny day or day and a half and then 4 or 5 more drab days!
This will likely happen a few times per winter especially november, december and part of january... lake effect clouds and on occasion during other months, april and march. Its not Seattle... but it is michigan

You can only design and afford so much. Our array will still output 5% to 10% of its name plate for a couple hours on many poor days, many days it will not even fire up the charger and much more than many days the array will produce much more than can be used and stored.
There is also a limit to how much power will insert into a common (lead) battery in a short time and a charging current limit to observe.
Some controllers will sync operation and some people have experience with logic and basic automation, which is a way to utilize a drastic oversized array without diversion and diversion may still be used.
Aside from conservation and elimination or defection of loads, the solutions involve extra cost or cost and complexity.

One set of things i remind myself of, is that the people i install for generally have much larger budgets and requirements than myself. When talking about what can be done, many people have budgets or requirements much lower than mine. And, there as many different system requirements as there are sites and users.

The efficiency of a TEG may not be paramount at all, where reliable operation is a prime requirement. Power availability at all, is sometimes perfect justification.
Most of these are used to drive a woodfired boiler fluid circulator when the fire is lit for heat with production to spare for lights, elegant regardless of efficiency percentage, it is waste heat or incidental to operation and offers minute loss of thermal characteristic of most heater or boiler arrangements. The areas where these are common have weeks of low light more than we do at Michigan and are proven effective.

Burning wood just for the 50-400 watts at 8 percent efficiency, that would not generally be good use of biomass!

What about gas generators, they get like 16-18% efficiency from a fuel that is energy intensive to produce, much less distribute, purchase and make use of in expensive machines.

My personal concept is to have no specialized fuels and no engine driven generators, while producing energy onsite. TEG systems are a viable option with a low parts count, some have no moving parts and operate silently.

I am looking at this as an alternative to generators in cases like mine, where we heat with wood during the cloudy season anyhow and battery sizing and array constraints make us look to other sources. Our woodstove is basically lit in october and burns until early may, it is our boiler for domestic hot water and has a circ pump that runs, from october to early may, which is also the season that our lighting requirement almost doubles... and there is no dependable weekly charging without conservation at times.

Frank, another advantage to the TEG is that the cooling water is heated and then can be used for heating distant rooms or a hot water tank.  Maybe that would be another selling point for you...

Frank, Mike: It sounds like we're all in agreement that TEGs are best reserved for waste-heat harvesting.

I live in the UK where we have a feed-in tariff (excess power from your solar array gets pumped into the grid and offsets your consumption at other times). I have no idea if that exists where you live. So I guess what I'm saying is that there are areas of the world where it's almost impossible to have a solar array that's too big.

Here's a good video about what can be done with solar in the UK right now (using USA technology):

Matt Coston wrote:Frank, Mike:

Here's a good video about what can be done with solar in the UK right now (using USA technology):

Fun stuff. Here is Jack Rickard on tesla car battery packs from salvage (plenty) with a Missouri twist on teslas power wall...off the shelf and ready to buy!

85kwh storage!
http://evtv.me/2017/09/canticle-of-the-sun/

https://youtu.be/vkNLhutwz6E

Mike Jay wrote:Frank, another advantage to the TEG is that the cooling water is heated and then can be used for heating distant rooms or a hot water tank.  Maybe that would be another selling point for you...

Thanks, i wont sell them per say... i do like a wide toolbox though for solving problems and kicking combustion engines off of peoples property though! I eliminate them and the noise pollution and costs associated, where possible...

Thanks for the links, Frank. Very cool.

My only criticism of projects like that is the amount of expertise it takes to do it - it will never leave the domain of passionate/genius DIYers, so they'll never have any real impact.

You could also criticise Tesla for being "business as usual", but mass-produced products like the Powerwall are changing the way the general public feels about renewable power. That has real impact.

I'm sort of in the middle ground. I like the idea of DIY, but I also accept that 7 billion people can't all be DIYers.

How about wood prolysis -> destillation (getting the tar out) -> fuel cell.

That should be a lot more efficient.. I am missing a proper lab to build it.. (nor can I weld.)

With all of the rocket mass heater stuffs going on, has anyone tried adding these to the back side of a rocket mass heater with an aircrete backing? Seems like these would work better when making power isn't exactly your chief goal.

Considering how expensive TEG is and how cheap solar panels are, I'd just buy more solar panels.

Granted the output from solar panels is reduced when it's overcast, but they still produce some power.  I've had my solar array for 7 years now and on it's worst day it still produced ~10% of it's rated output.  You could use all the surplus power when the sun is out to heat up some thermal mass (perhaps a 500 gallon insulated water tank?) and then use that to provide heat/hot water as you coast through the days of low solar output.

How expensive is a TEG? Looks like 99¢ per 1.5" square.

How long does a TEG last? Do peltier devices have a known half life? I think they are magic.

Solar panels have a 30 year life. If I am remembering correctly the last spec I read boasted a linear decline of 3% per year in optimal conditions. I couldn't find optimal conditions but I'm pretty sure that includes a water cooled backside.

Joe Wamsley wrote:How expensive is a TEG? Looks like 99¢ per 1.5" square.

How long does a TEG last? Do peltier devices have a known half life? I think they are magic.

Solar panels have a 30 year life. If I am remembering correctly the last spec I read boasted a linear decline of 3% per year in optimal conditions. I couldn't find optimal conditions but I'm pretty sure that includes a water cooled backside.

Good solar panels decline less than 1% per year.  Most panels these days have a warranty to produce at least 80% of rated output at 25 years.  My experience with 30-40 year old panels indicate they will likely produce more than 80%.  I have some 30 year old panels that still produce over 85% of rated power.

Solar panels typically last a LOT longer than 30 years.  There are people still running panels that were installed 40-50 years ago, with no indication that they will stop working anytime soon.

TEG currently runs about $2-$2.50 a watt, solar panels are down to about $0.60 a watt, or less if you buy in bulk.  

Really!? These companies must be writing really safe specs. Which panels are you using? Do you have any long term data?

Yes well, no company wants to have to replace anything under warranty, so they typically write the warranty to end before they expect the product to wear out.

When I built my workshop I made it off-grid with 3 Solec SQ-80 panels that I bought used.  This was almost 10 years ago.  The panels had been from a commercial solar farm.  They were being replaced because they had reached the end of their original warranty.  There were at least 15-20 years old at the time.  At the time I bought them I tested them and they were still producing approx 90% of their rated power.

I installed a 3.4 kw grid tied array for my house back in 2010.  I'm using micro-inverters that are limited to 190 watts so I originally spec'ed it out for 215W panels. However, this was just before the solar panel prices started to take a nose-dive, by the time I was ready to start installing the price had dropped enough that shop I was buying them from just gave me a 'free' upgrade to 230 watt panels.
Anyway, even though the panels are rated at 3450 watts (15x230W) the inverters are only rated at 2850 watts, although on cold, sunny days the sometimes produce more than that (max I've seen is just under 3,000 watts)
The panels are  Canadian Solar CS6P-230P

I do collect data on the performance of my main array, however there are so many factors that effect performance that it's difficult to deter how much they have declined.  I don't clean the panels except when I notice a large splat of bird poop on them, plus the micro-inverters are often the limiting factor during the winter.

Best I can determine, over 7 years the output has dropped 2-3%, the largest drop hapend during the first year (which is typical).