Miniature Turbines for a solar collector

[Christo Fourie]

I have a satellite dish converted to a solar collector. It isn't very big, just a small scale prototype at the moment. I have measured just over 300 degrees Celsius at the focus point. I am considering either using a sterling engine or a steam turbine to generate some electricity.

The problem is hobby sterling engines are somewhat expensive in South Africa and turbines seam to not exist in these small sizes. Should anyone know of turbines smaller than 1kW I would love to hear about it.

If not, any tips on manufacturing one myself?

 

[anorlunda]

I'm skeptical that steam turbines would be less expensive. For example here.

I assume that you have looked at the non-electric uses of that heat such as hot-water, cooking, desalinization, distillation ...

 

[jrmichler]

Look into the Tesla Turbine. It's simple enough that you could build one yourself.

Suggestion: If you tackle this as a senior design project, team up with at least one other person, limit it to just the turbine, and test the turbine with compressed air. A solar steam generator would also be a good senior design project by itself.

 

[jim hardy]

Check junkshops for vacuum sweeper "Turbo" accessories.
Many have a small plastic turbine inside to drive the brush..
I don't know if they'll withstand 212 degF , but it'd be easy enough to find out.

 

[Deleted member 656102]

I'm skeptical that steam turbines would be less expensive. For example here.

I assume that you have looked at the non-electric uses of that heat such as hot-water, cooking, desalinization, distillation ...

I am thinking about making a molten salt insulated tank to use for cooking, maybe get a little bigger dish to get some more celzius.

You could design the system so the collector is at high altitude, higher than your house, then the hot molten salt falls into the tank, and the tank is above your kitchen. And then when the molten salt cools you just pump it with a regular pump back into the system. I don't know is this logical or possible, but this is what i think.

If you can use molten salt for cooking, just put one more solar collector for producing hot water for washing aand for hot water for cooking so you use less molten salt. Hope you got some new ideas.

 

[anorlunda]

I am thinking about making a molten salt insulated tank to use for cooking, maybe get a little bigger dish to get some more celzius.

You can do that. Some salts are molten at temperatures not much more than boiling water. But high temperatures, high pressures, caustic chemicals, and fire, are all hazards you need to avoid.

But what is the advantage of molten salt over water? https://en.wikipedia.org/wiki/Sous-vide is a warm water cooking technique popular in recent years. It should be ideally suited to solar heating. You could make a sous-vide cooker big enough to cook for hundreds of people rather than just one family. You could also make warming trays for storing cooked food at safe temperatures for many hours; think of buffet tables and cafeterias.

 

[Deleted member 656102]

Actually, not a bad idea, much easier than with molten salt.

I prefer Stirling engine anyway when it comes to solar, because it has efficiency more than 90 percent.
I know its a bit hard to get a stirling engine, but there are lot of simple diy instructions of making one yourself, and you could make a small power plant with water steam and couple of diy stirlings and combineing them into one system. I saw some of them being made out of aluminium cans and common household items.

I personally would prefer taking some serious money and designs to a "mechanic" and building a stirling engine capable of producing serious electricity, and then combining 3,4 solar dishes to produce steam and heat the stirling with produced steam.. Its complicated but it pays of if you can do it.

But if you have money for one big stirling, than you can easily build 3 smaller stirlings and simplify everything :D

 

[anorlunda]

I would much prefer to invest my serious money in solar photovoltaic panels. I'm an engineer and I worship the KISS principle.

 

[Deleted member 656102]

Don't know if its true but i heard that photovoltaics use more energy to produce (heating the glass or something) than they make in a lifetime.

 

[jrmichler]

Search EROEI (Energy Returned on Energy Invested) for some good information. According to Wikepedia, the EROEI for photovoltaic ranges from 8.7 to 34 depending on assumptions: https://en.wikipedia.org/wiki/Energy_returned_on_energy_invested.

 

[Deleted member 656102]

Search EROEI (Energy Returned on Energy Invested) for some good information. According to Wikepedia, the EROEI for photovoltaic ranges from 8.7 to 34 depending on assumptions: https://en.wikipedia.org/wiki/Energy_returned_on_energy_invested.

Parabolic dish with a stirling engine over 90 percent.

 

[Deleted member 656102]

@jrmichler it doesn't say about parabolic stirling but interesting fact, says that the most efficient battery is compressed air.

 

[Rive]

I have a satellite dish converted to a solar collector. It isn't very big, just a small scale prototype at the moment. I have measured just over 300 degrees Celsius at the focus point. I am considering either using a sterling engine or a steam turbine to generate some electricity.

The problem with this kind of small size - high temperature collectors is the unavoidable heat loss. With all the thermodinamics involved and the insulation problems due the size, the expected electric power from 1m² collection surface is ~ 70-150W at most.

With a simple PV panel 1m² will deliver ~ 150W and you don't need all that complicated mechanics (tracking, turbine, pipes and stuff).

People tends to be awed by the temperatures available with this kind of CSP dish. But in small size, it just does not worth it. Scale it up to 10m² and it might be comparable to some worn-down second hand PV panels (at far higher price, of course). But 10m² will just cook you alive if you are careless.

 

[OmCheeto]

Parabolic dish with a stirling engine over 90 percent.

For the record...

The best numbers I can find are 25 - 30%. [ref: Azelio]
And their dish size indicates a similar output to solar electric panels:

55 m^2 dish yields 12000 watts --> 218 watts/m^2​

"The most efficient solar panels on the market today have efficiency ratings as high as 22.2%" [ref]

1 m^2 panel @ 1000 watts/m^2 @ 22.2% efficiency --> 222 watts/m^2​

Solar panels have no moving parts, so I'm siding with Anorlunda.

ps. I could not find a price for the Azelio Stirling unit.

pps. Since the OP hasn't been here since last July, I'll not respond to their questions, but will instead post this most awesome reference:

Stirling Engines are Cool and Efficient
So, Why Aren’t They More Popular?
Stirling engines are efficient, environmentally-friendly, and clean running. Well, if they’re so great, why aren’t they used in cars, boats, and airplanes?​

ppps. Note to my future self; "You saved the web page to a folder titled: 'Why Stirling Engines Are Not More Popular_files' "

 

[dLouie]

Look into the Tesla Turbine. It's simple enough that you could build one yourself.

I've read some about Tesla Turbine and seems one good project indeed especially for beginners.

 

[rxyzm]

You can do that. Some salts are molten at temperatures not much more than boiling water. But high temperatures, high pressures, caustic chemicals, and fire, are all hazards you need to avoid.

But what is the advantage of molten salt over water? https://en.wikipedia.org/wiki/Sous-vide is a warm water cooking technique popular in recent years. It should be ideally suited to solar heating. You could make a sous-vide cooker big enough to cook for hundreds of people rather than just one family. You could also make warming trays for storing cooked food at safe temperatures for many hours; think of buffet tables and cafeterias.

Not sure whether the sous-vide cooking method will be useful for ingredients such as rice, legumes etc. where the boiling water is required for cooking them thoroughly., else, it will take much longer to cook them. As I understand, in sous-vide method, a. one needs to seal the ingredient (such as steak, chicken etc.) in a plastic bag and remove air from that bag; and b. to immerse that sealed bag in a water-bath that is maintained at 63 C temperature.

Warm Regards,