# Stirling Engines as form of Energy Storage



## The Paw (May 19, 2006)

In earlier threads, critics/skeptics of renewables always (correctly) point out the relative unreliability of renewable sources, which inevitably leads to the issue of energy storage. 

I came across this video which describes the Stirling engine, which is a zero carbon mechanism that drives off a temperature differential between a heat source and a heat sink. It goes on to highlight some current R&D work that uses Thermal Energy Storage in conjunction with Stirling engines to store and then use energy later. 

It is worth viewing the whole video, but the shorthand version is that you can use solar or wind energy to heat something like salt solution or molten aluminum which will hold the heat for weeks or even months. The heat can then be coupled with a Stirling engine to generate electricity on demand, at times when wind and solar aren't at peak. Efficiency rates of 30% are achieved, which is better than internal combustion. 

this seems quite promising, and pretty fascinating, so I thought I would share.


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## GunMonkeyIntl (May 13, 2013)

Thanks for sharing that.

That seems like it could be a very homesteadery solution to off-grid electricity. Solar and wind is big, and has a short life cycle. This seems like it could produce some usable power from something about the size of a small car. A parabolic mirror to heat a tank of water, a Stirling, and a gen-set.

Sufficiently insulated, with maybe a cap over the focal point of the mirror, to close up the insulation at night, and you’d have at least a little power at night. On cloudy days, you could pipe stove heat to the water or whatever your heated medium was.

Either way, a heat-differential engine connected to a gen-set seems like it could be endlessly useful to rural folks.


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## The Paw (May 19, 2006)

Regarding parabolic mirrors, I was reading an article on a steel manufacturing firm in Colorado that is tied to a Russian oligarch, and in passing they noted that the plant is manufacturing steel for railway rails using almost exclusively solar power via parabolics. I had no idea that they were already in production. 

But if you liked that other video, the same guy has a good video on developments in wind energy. It doesn't address the storage problem, but it reviews a bunch of alternatives to the massive 3-blade monster windmills. They include solid state wind generation, a vortex-based thing that looks and acts like an eight foot vibrator and a number of smaller scale turbines. All of these alternatives feature fewer moving parts, less maintenance and smaller footprint. Many of them are also scaleable to a homestead or urban single-family application.


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## doc- (Jun 26, 2015)

The Stirling Engine is basically a steam engine using something other than water to produce a heated gas....They exaggerate the efficiency (which is better than common gasoine ICEs but comparable to Diesels) by ignoring the energy cost of the production of the energy required to produce the driving heat.

All technologies have their risks (costs) vs benefits. Parabolic mirror set-ups are hard on the environment. They fry birds and insects and take up a lot of habitat, along with other drawbacks.

Research into Stirling Engines for cars was extensive-- final verdict-- continued R&D costs made in non-competitive. Stirling Engine - an overview | ScienceDirect Topics

There ain't no free lunches.


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## The Paw (May 19, 2006)

doc- said:


> The Stirling Engine is basically a steam engine using something other than water to produce a heated gas....They exaggerate the efficiency (which is better than common gasoine ICEs but comparable to Diesels) by ignoring the energy cost of the production of the energy required to produce the driving heat.
> 
> All technologies have their risks (costs) vs benefits. Parabolic mirror set-ups are hard on the environment. They fry birds and insects and take up a lot of habitat, along with other drawbacks.
> 
> ...


All due respect, but I disagree. I think you have missed the point.

1. the efficiency of the Stirling is not "exaggerated", the original source of energy is not part of the calculation of the conversion of potential energy to realized energy. By your logic, we would have to say that the efficiency of fossil fuels would have to take into account the kinetic energy of millions of years of pressure, using the earth's mantle to convert carbon from plant form to hydrocarbons. But the efficiency isn't even the main point, its just a relative benchmark for comparison.

2. the main point is that the Stirling (in conjunction with the Thermal Energy Solution) provides a way to convert solar and wind into storable energy and release it on demand. All without carbon emissions. You are right that there is no free lunch, but we can achieve a carbon-free lunch, so to speak. 

3. I can well believe that the Stirling engine would not be "competitive" for an automobile application. But (a) that's not the application we are talking about, and (b) if one accepts climate change as an existential threat, it seems clear we need to recalibrate the economics of competitiveness. 

4. I haven't read anything on the environmental impacts of parabolics, but will concede that there is going to be some negative impact. (as a side note, windmills are often critiqued for their impact on birdlife, but there are many more birds killed by housecats each year, and there are more than twice as many birds who die flying into windows than running into windmills) I think it is highly unlikely that those impacts are more negative than fossil fuels, and moreover, parabolics are only one energy option for supplying the Stirling set up. Wind and solar are viable options. 

I am not arguing that a transition to a carbon-neutral economy will be made without significant adjustment, some inconvenience, and some new limitations on how we do do things. But it's not impossible, its simply about embracing the challenge.


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## MichaelK! (Oct 22, 2010)

Can't find the link right now, but there was another story on Permies that outlined the frauduent scams that supposed sterling engine mavens had created. They threw together a prototype that proved to be completely non-functional, but through a combination of fake "likes" and fake testimonials, they created a crowd-funding scheme to milk cash out of the unsuspecting crowd-funders.

This was illuminated by a mechanical engineer with real working experience with sterling engines, and understands their true capabilities and limitations.

So, whenever I hear "sterling engine" get mentioned my first thought is "scam alert". So, please show some healthy skepticism here.


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## markt1 (Dec 15, 2013)

The power output of commercially available stirling engines is either a few watts at most, or scarce very expensive ones in the low kilowatt range. The big value to stirlings is that thay can run entirely from heat without using the dangerous pressures and risks of the steam engine. I would see an affordable stirling engine outputting a few hundred watts (to charge a battery bank) as something quite a few survivalist types would buy. Some designs have only a single moving part. Such as:





__





dedisoft






dedisoft.yolasite.com


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## CC Pereira (9 mo ago)

doc- said:


> The Stirling Engine is basically a steam engine using something other than water to produce a heated gas....They exaggerate the efficiency (which is better than common gasoine ICEs but comparable to Diesels) by ignoring the energy cost of the production of the energy required to produce the driving heat.
> 
> All technologies have their risks (costs) vs benefits. Parabolic mirror set-ups are hard on the environment. They fry birds and insects and take up a lot of habitat, along with other drawbacks.
> 
> ...


Parabolic mirrors (parabolic dishes or troughs) that are used for solar heat collection do not harm the environment or birds. They reflect and focus sunlight onto a small area such as a pipe, which is not far away enough from the reflector for birds to fly through. What can fry birds are the flat mirror solar collectors that surround, collect, reflect, and focus sunlight, from the ground, to a large tower above the solar collectors -- which is not likely to be done by homesteaders anyway, because it is so large scale it would be major overkill. Wind mills can also kill birds. Parabolic dishes or troughs really don't need much space or resources either.


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## CC Pereira (9 mo ago)

Solar evacuated tube hot water heating systems, and some solar collectors (such as parabolic dishes, parabolic troughs, and solar air heaters) are the bomb!

As for energy storage ... I am very interested in using a pumped hydroelectric system for that ... whereby renewable energy sources (such as solar, wind, or hydroelectric energy) are used for generating electricity when renewable energy is available, and for pumping water from a lower position to a higher position, and the water is allowed to fall from the higher position to the lower position, when ready to use the energy as electricity. This is already being done large scale, and has been for some time now, but I would really like to try something like this for small scale (1-1000 watts, that can be scaled up or down and customized) homesteader use.


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