# Solar PVC Efficiency vs Solar Thermal Efficiency



## Warwalk (May 25, 2011)

I believe that currently PVC panels operate at about 20% efficiency currently, but what about the arrays set up designed to focus the sun on one central point? I've seen some of the large solar collector arrays set up, but I've also seen home-made varieties where either reflective metal or basic mirrors were used. 

I don't even know if I'm comparing these two items correctly or not, but has anyone seen any cost analyses of these systems side by side? Would a person compare overall surface area for the PVC vs the Thermal, or would it be more like "A $30K system of PVC vs a $30K system for Thermal". Any thoughts on this?


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## Warwalk (May 25, 2011)

This was one of those solar collectors I was talking about... don't know if anyone's seen much done yet with these or not, or what the drawbacks would be. 

[ame]http://www.youtube.com/watch?v=jTvAL7ty53M[/ame]


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## Warwalk (May 25, 2011)

Any thoughts on the solar thermal shtuff?


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## artificer (Feb 26, 2007)

What are you trying to do? If you want electricity, photo-voltaic is the way to go. You don't get more power with reflected light, especially now that solar cell prices have gotten so cheap. Maybe in winter when its cold, the heating/lowering of efficiency will not be a problem. In summer, however, more light means more heat, and less efficiency. Cheaper to just add more panels.

If you want heat, then PV panels don't make sense.

If you want electricity, and are thinking of some heat-to-electricity method, you can compare them on a $/watt basis. On a small scale, I find it hard to believe the thermal energy to electrical conversion is going to be any where near as cheap as PV panels. Stirling engines are always brought up, but I have yet to see a commercial unit available for a reasonable price. ($1000-$2000)

Michael


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## Warwalk (May 25, 2011)

@Artificier ~ Huge thanks for the response! =) The system in question is basically the mirrored array focused on a single point, either heating water or some other medium to power a generator. In the case of the water, the water is turned to steam and vented (not recirculated) from "exhaust" pipes. 

In the video above there's an example of where a guy does this with a relatively small amount of mirrors and powers a pretty large generator. One of the difficulties ~not~ discussed in the video is the fact that the guy is using water... in Arizona. I'd think that having a plentiful supply would be difficult! Still, to me, the technology has an appeal. I could picture a series of very lightweight plastic plates with a reflective coating, each the size of a cafeteria tray, all pointed toward some central post some 20' off the ground. At that point, there would simply need to be an appropriate collector attached to an appropriate generator. Sure, the plastic reflectors might wear out in a third the time that standard PVC panels would, but they might cost $20 apiece in bulk... maybe less. Or, at least, that's what I picture, lol! Heck, even polished metal could work I'd think? 

I've seen the types that place their focus on a Stirling engine like what you talked about, but in the video the power goes to a standard generator.


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## Warwalk (May 25, 2011)

@Artificier ~ Here is a wikipedia link to commercial style towers currently in place. According to the wiki article, there's a belief that by 2020 this technology could be producing power at about 5 1/2 cents a kilowatt (which is so much nicer than the dollar or so that PVC seems to be running!). Still, it doesn't seem like this technology is readily available to small consumers. I read the thread on here about the dangers of steam, and I could see how a system such as this could quickly overheat the water, or how a blockage in the water line could cause a catastrophic failure. Still, it's interesting!


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## SolarGary (Sep 8, 2005)

Warwalk said:


> @Artificier ~ Huge thanks for the response! =) The system in question is basically the mirrored array focused on a single point, either heating water or some other medium to power a generator. In the case of the water, the water is turned to steam and vented (not recirculated) from "exhaust" pipes.
> 
> In the video above there's an example of where a guy does this with a relatively small amount of mirrors and powers a pretty large generator. One of the difficulties ~not~ discussed in the video is the fact that the guy is using water... in Arizona. I'd think that having a plentiful supply would be difficult! Still, to me, the technology has an appeal. I could picture a series of very lightweight plastic plates with a reflective coating, each the size of a cafeteria tray, all pointed toward some central post some 20' off the ground. At that point, there would simply need to be an appropriate collector attached to an appropriate generator. Sure, the plastic reflectors might wear out in a third the time that standard PVC panels would, but they might cost $20 apiece in bulk... maybe less. Or, at least, that's what I picture, lol! Heck, even polished metal could work I'd think?
> 
> I've seen the types that place their focus on a Stirling engine like what you talked about, but in the video the power goes to a standard generator.


Hi,
One thing to keep in mind is that all of those mirrors have to be tracked to stay on your collector pot as the sun moves. And, its not as simple as just aiming the mirror at the sun -- it has to be aimed at a point half way between the sun and the collector. Or, if the boiler and mirrors are all mounted on the same structure, then that whole thing has to be tracked on the sun.

When you couple the mirror tracking with taking care of a steam boiler and steam engine with all safety issues and need constant attention issues, I think you have your work cut out for you.

There is some stuff on the collector end that might be good for some ideas here: http://www.builditsolar.com/Projects/Concentrating/concentrating.htm

Concentrating solar thermal collectors can be pretty efficient if done well -- of the order of 60%, but regular piston type steam engines are inefficient, so even though PV has poor efficiency (system efficiency around 12%), I'm not sure you can beat it with the solar thermal system.

I don't mean to be discouraging, but it seems like a pretty challenging way to go.


Gary


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## Warwalk (May 25, 2011)

@SolarGary ~ Huge thx for the reply! For me this is really more about brainstorming as much as anything else. At this point, I've looked at solar, I've looked at wind, I've looked at the microhydro, I've thought about a wood fired system, and just recently thought about the solar power tower (solar thermal) technology. It's a good point too, about all those moving parts, as even if you could get the mirroring for relatively inexpensive, on a small scale it could get awful pricey having each mirror on it's own self tracking and adjusting armature.


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## artificer (Feb 26, 2007)

Be careful of the cost numbers you use. The 5.5 cents/kw is probably per kw-hr of produced electricity. I can't see any mechanical system being built for 1/20th of what solar panels are selling for. 

I agree with Solargary about the problems with a dynamic system. Lots of moving parts if you want high grade heat energy. With stationary systems, you're stuck with low grade heat, which makes it hard to convert it efficiently. Maybe if you used a liquid with a lower boiling point, like one of the refrigerants, you could make a closed loop system that would work with the lower temps. Either way, its not going to be easy, or a simple system.

PV is just so much simpler to do. Reliable, easy, proven... it works. It would be really easy to burn through $10k getting a system up and running. Same amount would give you 40kw-hrs of pv electricity a day with little maintenance or monitoring.

Michael


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