Harnessing Solar Power for a Sustainable Farm

[FarmerFred]

I am working on a solar trough power plant to power my farm and greenhouses.

 

[FarmerFred]

I am looking for a inexpensive heat tranfer liquid to use in my solar trough power plant. It should be good up to 300 degree C or 572 degree F with a minimal expansion.

 

[anorlunda]

molten salts are often used for that.

https://en.wikipedia.org/wiki/Molten_salt
https://web.archive.org/web/2011101...pdfs/2007/koning_molten_salt_applications.pdf

 

[FarmerFred]

Yes, you are correct, but this is a system I am building myself using an organic rankine engine generator. This will be a lower capital, lower tech and lower temperature system. The organic rankine engine uses a refigerant that can operate at temps from 170 to 240 degrees F rather than a steam turbine generator at 660 degrees F. I was hoping to use a high temp. thermal liquid in the solar field and storage tank, then run hot water under pressure thru a heat exchanger in the storage tank to the engine with a VFD pump for control. But it is looking like the cost of the thermal liquid is prohibitive. I need 10,000 gallons. I am probably just going to use water and something else to get my boiling point up above 240 degrees F and then pump straight to the engine. I was thinking magnesium chloride.

 

[berkeman]

Welcome to the PF, @FarmerFred -- since this introduction thread has grown beyond just a brief introduction, we've moved it to the ME forum where you can get more feedback.

 

[jrmichler]

Water can work very well in the range of 170 to 240 deg F. The saturation pressure of steam ranges from 6.0 PSIA at 170 deg F to 25 PSIA at 240 deg F. You can use steam down to almost any temperature that is greater than your cooling media. Lower minimum temperatures equate to higher efficiency, at the expense of larger condensing heat exchangers.

Have you looked at Paratherm (www.paratherm.com) heat transfer fluids? Their Paratherm NF is a food grade mineral oil, so should not be too expensive. I have used their Paratherm NF, and it performed as advertised.

 

[FarmerFred]

Yes I did, they were one of the first, because I call out transformers with mineral oil and it was still really expensive. Of course I need 10,000 gallons, maybe I'm just being too cheap. I was thinking of water with something that would raise the steam or boiling point. You mention 25 PSIA, my system can probably handle that, but I would rather not go that high because people will be taking tours and maintenance workers will be there cleaning panels and the chance that because the panel will rotate to follow the sun leaves a high chance a leak could spring and I'd rather not have someone sprayed with that.

 

[anorlunda]

I regret that I did not realize the safety considerations, before replying.

Even if you use different words, you are making a boiler. If you take a closed container holding water under pressure at the boiling point, then if the container splits, some of the water instantaneously flashes to steam. Even without the steam, it sprays boiling water. It could kill everyone nearby.

Ever since numerous boiler explosion deaths in the 1800s, all countries have strict codes for boiler design, construction, and operation. You have little freedom to design it yourself. You must comply with the codes. Most such codes also say that the design must be signed off by a licensed professional engineer. If you have workers, there are additional OSHA codes. If you have tourists, then even more safety codes apply.

I think you have no choice but to hire professional engineers to design the whole system. Certainly, asking strangers on the Internet for advice is not the way to go.

Thread closed.