Renewable Gossip

Homemade Solar Parabolic Trough Hits 300 degrees.

This weeks project was building a Solar Parabolic Trough.
First Attempt:

140.7 degree solar reflector

I first came up with the idea of building my own Solar Trough while researching a topic for a client on youtube.  The video I found suggested cutting a piece of 8″ pvc tube in half, lining it with a reflective surface and aiming the concentrated sunlight at whatever you wanted to heat.   I had everything I needed sitting in my garage and following the directions from youtube,  I had one constructed in less than half an hour.  Initial testing resulted in a maximum temp of 140 degrees.  Not bad, but nothing  spectacular.  As a test I also spray painted a 2 liter soda bottle black and filled it with water.  In the same sunlight in less than an hour it achieved a maximum temperature of 120 degrees.  For all the effort of building the PVC reflector I was only getting 20 degrees hotter than I was by heating up water with sunlight in a black bottle.  After going back to the drawing board I realized the PVC tube is a circle (duh) and what I really wanted was a parabolic shape (thanks for wasting my time youtube guy!)
Second Attempt:

300 + Degree Homemade Parabolic Solar Trough

My math is a little rusty but a quick search on the internet revealed a number of sites that provided me with the proper calculations to draw a parabola. Rather than bore you I’ll cut right to the chase. Again I had everything I needed in my garage to construct my new design.  The 4′ x 4′ Parabolic Trough took me about an hour to build and initial testing provided over 300 degrees in less than three minutes of direct 10:00am sunlight.   That’s enough to boil water (212 degrees), cook a hamburger or provide all the hot water a family could ever need as long as the sun is out.

Conditions on the test date:  90 degrees ambient air temperature, clear and sunny.  Location – Lewes Delaware USA.  Date August 12 2009.

300 Degrees is a good deal more than 140 degrees so I would consider this second test a huge success.  With some slight modifications I should be able to reach somewhere between 400 and 500 degrees.

Materials:
4′ x 4′ piece of plywood $12.00
three  2 x 4’s $9.00
1 box of 2″ screws – $5.00
4′ x 4′ piece of 1/8″ wall paneling. Lowe’s or homedepot sell them for about $10
4′ x 4′ sheet of mylar $5.00
Can of spray glue $5.00
4′ length of 1″ Copper Tube $5.00

Grand Total $51.00 ( I had all of these items lying around as scrap so it cost me nothing. )

Possible Improvements:

High Temp Thermometer. Currently my thermometer maxes out at around 300 Degrees.
High Temp black paint for the Copper tube.
Better Mylar reflector. My Mylar was very thin and difficult to attach without creating wrinkles.

Coming Soon:
I plan on adding a pump and some plumbing to this design to see how quickly it can heat 30 gallons of water.
If stationary testing provides the desired results I may add solar tracking to it at a later date.
In the winter months  running glycerin through the plumbing to a small radiator could easily heat a small cabin while the sun is out.

To do List:
Search Ebay for high temperature pumps.
Search the web for a tempering valve to control  water temperature.
Search the web for solar tracking devices.
Search the web for a long Pyrex tube to encase the copper tube inside of to trap generated heat.
Locate insulation that will not melt at 500 degrees.

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