Solar thermal to power stirling engine

[thegreenman]

Do anyone know of any research or practical systems for converting the heat produce from solar thermal panels into electricity via a Stirling engine?

I am sure someone must have thought of this before, have tried searching the forums but couldn't find anything relevant.

My other thought was to do with combining grey water recycling with using it as a heat store for use with heat pumps.

A large water mass would hold quite a bit of energy which could be extracted with a heat pump. Any thoughts.

[clockmanFR]

Grey water storage. We have 200,000 litres pond, yes the water is stable, but the water coming from the underground spring is consistant temp wise. In the deepest winter at -23c where the spring water enters, it never freezers over and yet the boy's are skating on the ice on the rest of the pond.

One thing about a vast amount of deep water is stability. Over my spring outlet i have a wooden building with my 50v dc 600amp batteries and inverter so all stay nice and cosy.

I thought about a ground/water heat pump, but for me its the circulation energy required that is the stumbling block, for my needs a 3kw electric motor would need to be on nearly full time, and that defeats the purpose. 

[EccentricAnomaly]

My other thought was to do with combining grey water recycling with using it as a heat store for use with heat pumps.

Not sure what you have in mind exactly but storing grey water at elevated temperatures sounds rather toxic.

A large water mass would hold quite a bit of energy which could be extracted with a heat pump. Any thoughts.

Yes, that's what I have in mind: a large heat store (maybe about 10 tonnes) inside the thermal envelope of the house and segregated into multiple tanks at varying temperatures (mostly warm, maybe some pretty chilly). Use of a heat pump as the first dump load for PV and wind to pump from the cooler tanks to the warmer tanks. The cooler tanks would then be warmed up again using solar thermal when the sun shines not brightly enough to directly heat fully hot water.

[TimSmall]

Do anyone know of any research or practical systems for converting the heat produce from solar thermal panels into electricity via a Stirling engine?

Did you try google?  Most use parabolics tho', best are about 30% efficient...

http://colli239.fts.educ.msu.edu/1994/06/09/dish-1994/

http://www.stirlingenergy.com/maricopasolar

One domestic scale project using evacuated tubes that I've seen too.  15% efficient.

Tim.

[renewablejohn]

You can use thermal solar panels to heat thermal oil and then by using a thermal oil steam evaporator produce conventional steam upto 25 bar pressure for use in conventional steam engines and turbines.

[stuartiannaylor]

http://www.coolenergyinc.com/

There approach is quite interesting as they are oversizing thermal collector arrays which extends the useful collection period. The excess (excessive) heat is harvested via a Stirling.

Standard direct flow (not the heat pipe ones) evacuated tubes can reach much higher temps if sunlight is concentrated. Parabolic mirrors in a 3:1 ratio of the collector dia can easily get up to 250C and above.

http://www.cyclonepower.com/whe.html have a low pressure steam turbine and there is a lot of work in the arena or ORC (organic rankine cycles)

Higher heats do have some advantages as they allow more compact storage based on the ratio of temperature difference. Moving to a mineral oil heat exchange liquid negates all the nasty problems of high pressure steam.

All energy transfers have losses and it always makes me wonder that one of our primary energy requirements is heat, so why try and change it to electricity.
I do like the coolenergy idea though where they make use of the excess.

  

[cj]

The Cool Energy link looks interesting.

It says inexpensive, but I don't see a cost Hmmnnnn?

Despite saying COOL energy, it also has " * Solar Thermal Collectors must achieve a minimum stagnation temperature of 250°C (475°F) for optimal engine performance."

Now if they were in Alaska rather than Colarado, they might be on a winner, but I doubt the UK climate would be ideal? As there is so little recent info, does that suggest the cost per watt is not too good, and has not caught on big time?

What about the generation element of an Ecofan? http://www.woodburningstoveslimited.com/index.php?action=cms.details&itemid=272

Has this potential - 'scuse the pun?

I rather like the idea of a Rocket Stove CHP

http://www.squidoo.com/rocketstoves#module11997087

or making a simple one:-
http://video.google.com/videoplay?docid=797446823830833401

[stuartiannaylor]

If you have a look at these as they are one of the few designs that use CPC mirrors in conjunction with collectors http://www.rittersolar.de/english/index_e.htm.
They have stagnation temps of 270C but increasing the CPC mirror / collector dia ratio will increase this. The ritter models are about 2:1.

I did have a PDF and have been searching for it again from a student doing an MA/BA in thermal energy collection. I have a terrible habit of pruning my computer of dross and finding I require items after discarding so I will try and find it again. Due to the combination of CPC (Compound Parabolic Concentrator) the overall increases in direct and importantly diffuse light are linear to the ratio of the CPC / tube dia. The thesis was constructed in Germany and the design is very much aimed at northern europe and dear old blighty would very much be able to utilise such a system.

The mirrors lose about 5% to 20% of reflected energy due to choice of material. I remember some special stuff by 3M "Radiant Mirror Film" but the thesis went along the lines that polished aluminum did the job much more economically. You have to be really careful about the collector materials and insulation. Many use a polyester foam and this must be rockwool or other hi temp tolerant insulation or you hit probs.

Its not rocket science as many an evil child has burnt something with a magnifying glass. The ratio between Compound Parabolic Concentrator and collector dia sets how much surface area you collect from and conversely how much energy you will receive.     

[Ivan]

TimSmall - Do you have a link for the domestic evacuated tube CHP system - would be very interesting.

Coolenergyinc looks great, but their website, like most american better mousetraps is busy looking for investors rather than selling systems - which is always a fairly good indicator of the reality of their 'product', unfortunately.

cj - I didn't see any rocket stove CHP in that link - was it wishful thinking?

[stuartiannaylor]

Ivan your right as I did get intouch with them and got a very similar sales pitch.

I think they have a great product but they have one weal point in using standard evacuated collectors aimed at water glycol loops.
If they made a collector with a larger concentrator 3:1 or greater and moved to a thermal oil loop the system would work a treat.

I just see collecting heat and using it as heat is way more efficient and trying to convert always to grid connected electric systems somehow misses the point.
Even if its a hot water boiler or solar oven store that generates electricity with excess makes much more sense to my poor addled mind.

Do you have any input to this with your vast experince and evil genius

[TimSmall]

TimSmall - Do you have a link for the domestic evacuated tube CHP system - would be very interesting.

Hmm, I think it was the cool energy one which I'd seen too....

http://www.coolenergyinc.com/01182011News.html

They say "residential and small commercial" - but by the look of their testrig, I'd guess it'd be more large residential!  Maybe very large with UK insolation...

Tim.

[stuartiannaylor]

I dunno, there always seems to be an obsession to turn energy into electricity. Guess its all about infrastructure and its easier to convert and plugin to what we have.
I quite like the idea of a high-temp thermal boiler which is just a big highly insulated thermal store. This would be an excellent way to store energy as the technology and cost are simpler and smaller.
Current systems are specified at stagnation times of summer as the excess is waste.
Using the excess of summer to provide energy allows a more balanced winter system where some results can be expected.

I do like the coolenergy idea I just think they need to start producing collectors with higher concentration factors. They recomend Rittersolar CPC direct flow collectors which have a very small CPC:tube ratio.
Also Stirlings also do seem to require a higher temperature difference than ORCs and the ORCs are starting to get smaller.
If someone can get a chilling effect as a byproduct out of the conversion process they would be onto a winner.