# Renewable Energy Concept - Stirling Engine Composting

• Waggles
In summary, an expert summarizer has read and understood the content of the conversation. They imagine a closed composting heap that can reach temperatures of up to 160 degrees without killing the microorganisms required to produce methane. They suggest using the heat from the composting to power a Stirling Engine, which is an efficient way to produce power. The expert also suggests using the methane produced by the composting to power devices like heaters or an alternator.
Waggles
So I've got this crazy idea. To put it simply, to use the heat from anaerobic composting to power hot-air engine, specifically a Stirling Engine.

Based solely on my own reading, the center of a closed composting heap can reach anywhere from 120-160 degrees without killing the microorganisms required to produce methane. By water cooling the cold side of an engine, a temperature differential of >100F.

I imagine a gamma configuration with opposed/linear cylinders: hot cylinder down, cold cylinder up out of the heap. Compressed helium as the working gas will increase efficiency. And a properly built Stirling Engine requires a regenerator to further increase efficiency.

I'm the guy with the ideas, but I don't know how to do the complex gas equations, cylinder computations, electrical computations and etc. required to calculate the dimensions. As well as the necessary torque to run, say, an alternator.

Any help would be much appreciated!

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Try working out how much power you can extract from a compost heap first. The simplest way would be to push some copper pipe through it and run some water through. You would need to know the flow rate and the temperature of the water going in and out. Leave it going for a few days to check you are measuring the long term rate.

Power = SHC * flow rate * (Tout - Tin)
where SHC is the specific heat capacity of water.

It might be better to use the hot water directly to heat your house/shower. Perhaps see..
https://www.hindawi.com/journals/ijce/2010/627930/

According to Google, compost generates heat at about 275 watts per cubic meter.

The other thing it generates is methane, which is already done on an industrial scale in landfills and sewage treatment plants. Usually, they just use the reactor heat to keep the waste warm for the microbes to do their jobs. If you cool it, you will at least need to insulate it to keep it warm.

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Thanks for the replies, y'all. I'll extrapolate and ask a few more things when I can. Thanks again.

## 1. What is a Stirling engine and how does it work?

A Stirling engine is a type of heat engine that operates on the principle of cyclic compression and expansion of air or other gas at different temperatures. It works by using a heat source to heat and expand gas in a confined space, pushing a piston to do mechanical work.

## 2. How does a Stirling engine composting system use renewable energy?

A Stirling engine composting system uses renewable energy by utilizing the heat generated from the composting process to power the Stirling engine. This eliminates the need for fossil fuels and reduces the carbon footprint of the composting process.

## 3. What are the benefits of using a Stirling engine composting system?

There are several benefits to using a Stirling engine composting system. Firstly, it reduces the amount of waste sent to landfills, which helps to reduce greenhouse gas emissions. Secondly, it produces high-quality compost that can be used as a natural fertilizer. Lastly, it harnesses renewable energy and reduces the reliance on fossil fuels.

## 4. How efficient is a Stirling engine composting system?

Stirling engine composting systems have a high efficiency rate, typically ranging from 30% to 40%. This is because they can operate at lower temperatures and do not require constant maintenance like other types of engines. Additionally, the heat generated from the composting process can also be used for other purposes, increasing the overall efficiency of the system.

## 5. Can a Stirling engine composting system be used on a large scale?

Yes, Stirling engine composting systems can be used on a large scale. In fact, they are already being used in some commercial composting facilities. They have the potential to significantly reduce the amount of waste sent to landfills and produce high-quality compost on a large scale, making them a sustainable solution for waste management.

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