Tuesday, April 18, 2017

reader questions - concentrator versus flat plate

Re article Summary/Conclusion - DIY Flat Plate vs. Concentrator Performance

On 4/17/2017 8:29 PM, Paul Arnold wrote:
> Hi. I came across your website via builditsolar.com and was interested in your comparison of the flat plate collector vs concentrator. You don't mention cost and ease of construction factors. Could you say which is cheaper to build on average? You built both. Which would you say would be easier to construct? What about speed of construction when attempting to build a large array?
> I am also intrigued by the idea of running a steam engine with your concentrators. Would you be able to guess the cost comparison per watt of useful energy with solar panels? I'm assuming you would capture the exhaust from the steam engine for space and water heating so it might be close. I'd love to hear your thoughts on this.
> -Paul Arnold

Hi Paul. Thanks for your interest and your good questions.

Originally I built a concentrating pool heater array which was un-insulated. It worked well for that application for five years (until I had to move and I took it down).

In that situation, I thought the concentrator was less expensive than flat plate although more complex, especially since I would be doing it for the first time. I could not find a suitable design for a concentrator so had to come up with a design myself. (This resulted in my first book "How to Build ...").

For pool heating, I was trying to heat a huge quantity of water by only a few degrees which the concentrator did admirably. Insulation was not required for the pool heater application, so lower cost.

I continued to work on a set of improvements which I called Gen2 which is an insulated version. This second version of the concentrator with the insulated collector (The Home Experimentor's Manual) would be more expensive. The added insulation (primarily the glass evacuated tubes) would not be required for a pool heater but made possible higher temperatures and higher latitude use in winter.

I publish cost estimates for both my parabolic designs although these are only for guidance. Your approach may differ from mine. See Bill of Materials here.

The cost of building a flat plate will depend on the design and materials you use. Whether it will be insulated, for example. You will find many versions and Gary's recommendations at his site builditsolar.com. Determine your cost of making a flat plate after you decide on your favored approach for your application.

About making electricity from steam, I am not currently pursuing this nor do I know anyone who has demonstrated a durable, safe, long term approach. Since the price of PV solar panels has plunged over the past ten years, it seems that interest in doing the alternative, with solar generated steam and some sort of turbine/generator, has faded. Are you clear that you cannot make steam with a flat plate? You need a concentrator for that. The two are not interchangable.

Best of luck with your efforts. Let me know if you build something that works for you. If trying steam, be SAFE!


George Plhak

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