Thursday, April 21, 2016
(click on pictures to enlarge)
Miranda writes: "I’m a physics major [at a college in Nebraska] and as part of our capstone experience we are required to choose an area that interests us and do a senior project that pertains to that area. I loved the idea of solar…I came across your book and chose to base my project off of it! I love the book and your clear writing style...I was just going to compare to your 90% efficiency by doing the same calculation for mine...I’m only 42% efficient at my boiling flow rate."
Miranda is asking about a performance measurement I made and wrote up in this early article based on the non-insulated design Performance of the DIY tracking solar parabola array which was updated and included in the book as the Performance chapter (p 131).
I wrote back: That's possible Miranda.
If you are boiling water you will have higher thermal losses which will reduce the efficiency. [The amount of loss] will depend on your insulation like the glass tube, fibre wrap or other techniques to reduce heat losses but that is the cause.
As you noticed, I was heating pool water at a high flow rate to only a few degrees above ambient. Life is much easier at lower temperatures. No insulation required. I got into the higher temp effort after that. Haven't measured my own efficiency at higher temps but I would expect it to be less.
Don't be disappointed by lower efficiency at higher temperatures.
It does sound to me like you understand what you are doing. Good luck!
I wrote back: Hello Ravindra Pardeshi. Please see this article how to make solar superheated steam
This work was all done with parts made from the design in my book.
I show how to make the solar collectors only. The balance of the system would be up to you. I show the temperatures and the amounts of steam that can be produced with even a small system.
Good luck with your project and thank you for your interest.
I live in Southamerica and I am not sure if glass pipes, used to isolate cooper pipes can be easily found.
I wrote back: Hello Guillermo and thank you for writing to me.
Yes, the vacuum glass tubes can be difficult to find, particularly in Canada! I first saw the tubes in Mexico where the roof top solar heaters are very common, much more common than here. Short tubes are available with mail order but for the longer tubes, you must find an installer of the heating systems and convince them to sell you a few tubes of the spares they keep in case of breakage, or you will need to import a box of the tubes from a manufacturer. I wrote an article about the tubes here: more about evacuated tubes for parabolic troughs
I did find the tubes, even in Canada and with some research, I think you should be able to find them also.
Good luck and let me know your progress.
You can see previous reader project articles: 3, 2 and 1.
I am very interested in hearing from you if you have built one of these systems and used my book for inspiration.
You can see background on my project diy solar parabolic trough gen2 intro and you can buy my book at georgesworkshop.ca. Your purchase of my book helps support my work.
Thank you for your interest,
Lion's Head, Ontario, Canada