Thursday, April 21, 2016

reader projects 4

Occasionally I hear from readers who have built the unique parabolic solar heater in my book. I also receive interesting questions. Here are some recent examples for your inspiration.

(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!


Ravindra Pardeshi commented: "Hello George, Is it possible to make superheated steam with the drawings in your latest book. I am interested in making steam type community kitchen in India."

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.


Guillermo Sivori writes: Hi George, I am interested in your book to built a concentrated solar collector. I just wanted to know if the collector pipe in your project is a vacuum glass pipe or a different pipe.

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 Your purchase of my book helps support my work.

Thank you for your interest,

George Plhak
Lion's Head, Ontario, Canada

Friday, November 06, 2015

compost temperature

Knowing the temperature deep in my compost pile gives me an idea of how well decomposition is going. This is a fresh pile about a week old made mostly of moist chopped up leaves (mostly maple) along with some other plant materials roughly mixed in.

The outside temperature is in the low 13C/55F. As shown by a thermocouple 24 inches into the pile, roughly in the center, temperature is almost 127F!

I will come back to the pile throughout the next few weeks to record the internal temperature. I won't leave the expensive thermocouple and meter outside. I will bring the two out when I want to check, inserting the thermocouple like a probe into two hollow tubes I have embedded in the pile.

I wonder about the amount of heat produced by the pile and how long it lasts? Would it be possible to extract from the pile to, for example, heat the shed nearby?

click pic to enlarge The pile is about 1 meter wide at the base, two meters in length and about 24"/60cm high about a week after being initially piled up.

The height of the pile is about 10cm lower now than a week ago. I expect that the pile will continue to fall as decomposition proceeds but less quickly. The pile will also be packed by the snow cover. The snow cover will act to insulate the pile. I don't plan to turn the pile until Spring.

I am using plastic electrical conduit for tunnels into the core of the compost pipe. I have measured off from the end with the distance (in inches) to the end of the pipe. There is a wooden plug hot glued into the inner pile ends.

The tubes were difficult to push to the desired depths. The cut up leaves had already compacted enough to make for heavy pushing. I will insert corks into the outer ends to keep the water and bugs out of the tubes when they don't have a thermocouple in the and will also avoid some heat loss.

Thanks for your interest. George Plhak, Lion's Head


Sunday, August 23, 2015

pool heating 2

Hello George,

I just stumbled across your blog on solar heating water using parabolic concentration. I am interested in heating my pool this way. The pool contains about 15,000 gallons of water and is 16 feet wide and 32 feet long and about 4 feet deep. How many of the of the units would I need to build in order to heat the pool in the summer months. The pool normally without heat would sit in the low to mid 70s and I would like to keep in in the mid 80s most of the time. I live in the pacific northwest near Bremerton, Washington.

Very Respectfully,


Hello Robert and thank you for writing.

Here are a few articles that may help:

My original book on the solar pool heater is still available as a download for only $10!

Thanks for your interest.