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Author Topic: Idea number 22,3467 , TEG's again !  (Read 1314 times)
waterworks
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« on: January 03, 2019, 01:55:39 PM »

I live on a boat with a wood burning stove for heating, I'm thinking of a square steel chimney clad in TEG units to generate from the waste heat , the chimney is today ( at 4 deg C outside ) with a low fire just ticking over, 40 deg at the base, and tapering to 20 deg 300 mm up the height, this would be space for 56 standard ebay 40 mm TEG units.

The estimates of what actual usable power ( say a 5 v USB charging port ) this would produce are far beyond my maths abilities, but here are the specs

Size: 40mm x 40mm x 3.4mm

20 Degree Temperature Difference: Open-circuit Voltage

0.97V,Generated Current: 225MA

40 Degree Temperature Difference: Open Circuit Voltage 1.8V,

Generated Current: 368MA

A basic calculation of the total ah looks like it would generate enough to make it a worthwhile project but I haven't figured in the voltages, or how to control the voltage output.

I know I should probably get out more. 





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azps
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« Reply #1 on: January 03, 2019, 02:45:49 PM »

Here's my quick and easy flow-chart for deciding whether a TEG is worth it:

Is it going into space?

Yes  -> a TEG may be worth it.

No -> a TEG is almost certainly not worth it.

HTH.
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gravyminer
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« Reply #2 on: January 03, 2019, 08:43:42 PM »

On a more basic note and its been discussed here a fair bit, its helpful to keep the flue pipe warm enough so that any unburnt tar will vent rather than condense and clog up the flue pipe, potentially causing a chimney fire.

I no longer leave my little woodburner shut down on tickover overnight. I burn it pretty hard to get heat into the walls etc and allow the fire to burn out around bed time.  Flue pipe runs clean.
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gravyminer
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« Reply #3 on: January 03, 2019, 08:49:44 PM »

I live on a boat with a wood burning stove for heating, I'm thinking of a square steel chimney clad in TEG units to generate from the waste heat , the chimney is today ( at 4 deg C outside ) with a low fire just ticking over, 40 deg at the base, and tapering to 20 deg 300 mm up the height, this would be space for 56 standard ebay 40 mm TEG units.

The estimates of what actual usable power ( say a 5 v USB charging port ) this would produce are far beyond my maths abilities, but here are the specs

Size: 40mm x 40mm x 3.4mm

20 Degree Temperature Difference: Open-circuit Voltage

0.97V,Generated Current: 225MA

40 Degree Temperature Difference: Open Circuit Voltage 1.8V,

Generated Current: 368MA

A basic calculation of the total ah looks like it would generate enough to make it a worthwhile project but I haven't figured in the voltages, or how to control the voltage output.

I know I should probably get out more. 

Don't forget that you would most likely have to place fans on the cold side of the TEGs to keep them cold. The result is likely to be that you use more electricity running the fans than you generate.
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Why bother? - well, there is no planet B
Countrypaul
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« Reply #4 on: January 03, 2019, 10:53:33 PM »

At 90p a TEG it is worth getting half a dozen or so just to try some experiments and post the results on here. Getting a bigger temperature difference like 100C+ would make a huge difference to the output so burning the stove hard might be beneficial in that respect to - but only if you can use the heat.  A large heat sink on the cold side might help especialy if you can cool it easily (with very little power use such as cold water form the river?) You might surprise us all.
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daveluck_uk
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« Reply #5 on: January 03, 2019, 11:28:45 PM »



A basic calculation of the total ah looks like it would generate enough to make it a worthwhile project but I haven't figured in the voltages, or how to control the voltage output.

I know I should probably get out more.  








Connect them to something like this?

https://www.ebay.co.uk/itm/DC-4-5-40V-To-5V-2A-USB-Charger-DC-DC-Step-down-Buck-Converter-Voltmeter-UK-FAST/401264810148?hash=item5d6d3f18a4:g:f9MAAOSwmYtbO43h&redirect=mobile

I've used these for a couple of projects. Normally wired up to a small PV panel. They don't seem too fussed by voltage fluctuations but they are a bit fragile.

You could wire up the regs in series and parrall, stick them on to an ali sheet for easy mounting and either buy or knock up your own heat sink.


Google throws up plenty of technical and not so technical articles. All seems possible.
« Last Edit: January 03, 2019, 11:52:24 PM by daveluck_uk » Logged
waterworks
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« Reply #6 on: January 04, 2019, 12:05:40 AM »

I was hoping the outside air temp in the winter would provide the temp difference without any heat sinks or fans.



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daveluck_uk
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« Reply #7 on: January 04, 2019, 09:38:48 AM »

I was hoping the outside air temp in the winter would provide the temp difference without any heat sinks or fans.





Give it a go and see!
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RIT
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« Reply #8 on: January 04, 2019, 04:51:48 PM »

I was hoping the outside air temp in the winter would provide the temp difference without any heat sinks or fans.

One of the issues with TEGs is that their internal resistances rise with temperature, which in turn increase the amount of electricity that the TEG is producing being turn directly into heat.

So good cooling is required to generate the temperature difference needed for a TEG to operate and to stop the direct heating effect. Basic air convection is a poor heat transfer agent unless it is working across a large surface area (big heat sink) and or forced air flow is used (fan).

As Countrypaul has already commented using water may be a better option. It will improve the temperature differential and be more efficient at heat transfer. The problem is that TEG water blocks are costly.
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2.4kW PV system, output can be seen at  - https://pvoutput.org/list.jsp?userid=49083

Why bother? - well, there is no planet B
waterworks
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« Reply #9 on: January 05, 2019, 01:37:11 PM »

If I have to pump water vertically 1.5 m up to the chimney its going to use all the power the thing produces . Plus canal water is full of weed and sediment and clogs pumps and filters in no time.

40 x 40 mm Aluminium heatsinks are 1 each off eBay,  this would double the cost but might be the best option.

My original heat readings were burning coal, I've discovered that burning wood doubles the chimney temperature as the gasses continue to burn higher up  in the flue .

I won't have time to start building it this winter, as I'm too busy, and it will only work in the winter, which is when the solar panels are dormant and I'm burning wood 24/7 in the stove. I burn free pallet wood mostly so there is no fuel cost involved in this TEG idea.



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Countrypaul
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« Reply #10 on: January 05, 2019, 06:05:10 PM »

If you use a loop of pipe then you don't have to overcome 1.5m height of water you only need to overcome the difference between warm water and coldwater in the pipework - much lower power requirement. If you could manage to keep a resovoir of water above the position of the TEGS, then you would need no pumping as the heating of the water by the TEGS could be used to circulate the water - afterall that is how gravity fed hot water systems work!  The resovoir would not need to be that big and the pipework could go via the canal to ensure that the water was cool enough even if you only have a small resovoir.
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