Build your own flat panel solar thermal collector

Step 2 Tools and Materials

Tools

• Table Saw
• Hand Saw
• Drill press
• Power Drill
• 3/4" drill bit
• 1" hole saw
• Exacto knife
• Tape measure
• Screw driver
• Digital thermometer
• Caulking gun for silicone adhesive
• Coarse round file

Materials for collector (shown in image below)

• 1 - sheet of corrugated plastic (4'x8') cut to 22"x90" - $8.50
• 1 - 4' of 1 1/4" ABS tubing - $6
• 4 - 1 1/4" ABS caps - $10
• 2 - threaded 1/2" hose nipples - $1.00
• 1 - cartridge of silicone adhesive/sealant suitable for plastic - $3.50
• 1 - can of flat black spray paint - $5.00

Materials for frame

• 1 - 1/2" sheet of plywood (4'x8') cut to 24"x8' - $8.00
• 1 - 3/4" sheet of polystyrene (2'x8') cut to 22"x87.5" - $2.50
• 3 - 2x3 x 8' - $8.00 used.
• 1 - at least 4'x10' of transparent plastic sheet - basically $0
• misc screws and staples

Materials for tank / water circulation

• 1 - cooler (or other water tank, preferably insulated) - $20 but I had one already
• 1 - 15ft of 5/8" garden hose - $5.50
• 2 - 1/2" hose clamps - $1.50

Total cost of materials excluding tank = $59.50

Comments

[lucindanl]

Does the length of the hose make a difference? I want to build something to keep a worm composting bin from freezing this winter. My bin is a disused cement water cistern w/o access to AC power. It’s about 6’ x 6’ x 3’ and lined with plastic. I plan to surround it with hay and cover it with insulated panels, but I’ll need a heat source, beyond the composting itself, as I live in the northeast where we have substantial freezing. I’m wondering if the thermal siphoning would work if I used substantially more hose – like 75’ to 100’ – coiled on the bottom of the bin and buried under the compost. The tank and panel could be placed as high as needed as long as the hose could be lower. Do you think this would work? Also, would freezing during the night destroy the panel?

[Marcos]

What if you dug your bin into the ground, to insulate, and maybe even absorb any warmth from the earth? Then you'd need a smaller solar collector, if any.

I live in the SF Bay Area, where temps are moderate compared to the Frozen East. I keep my worm bin in an outdoor shed, raised slightly from the cement paver floor and it's fine.

[avid0g]

This sound really great.  If the collector is above the cistern, you will need a pump, so I hope you have a downslope to place the solar collector.  The length of hose will slow down the siphon but the biggest drag is elbows and collector heat loss; avoid them.  You need a low-pressure check valve to prevent back-flow and a water storage tank/bladder above the compost.

The cistern sounds like a great way of having Thermal Mass.  If you can keep the soil Under it away from moving ground water, sink the insulation deeper into the soil around it and use the additional mass of the soil underneath to ride through cloudy days.  The insulation and surrounding soil may need to be covered with tarp to drain away moisture.  It may take a while to heat the soil underneath, but the solar collector would eventually get there.  

Rigid hose under the compost sounds great.  Of course the plumbing and collector would need substantial insulation, since it will be out in the cold.  The water is in a closed loop and not used for drinking or for moisture, so you can load it with a non-toxic antifreeze and black dye for improved heat absorption.  (We are on a web page with a transparent absorber!)  

It is also a good idea to provide some heating from above.  This could be rubber hose and/or bladder on top of soil and/or transparent insulation (bubble-wrap or white closed-foam) above the rest to let in light.  

Good Luck!

[fbujold]

Build the same concept several years ago out of black coroplast and the only weak link was the PL adhesive sealant. Tried at least 7 or 8 different product and the final champion was marine goop. (http://www.eclecticproducts.com/ag_adhesives.htm) Available at home depot and other fine hardware strores. Make sure to sand the coroplast and pipe surface for improved adhesion.

[vinyard]

Where do you get the corrugated plastic sheet?

[iwilltry]

I got mine from Home Depot. $17 for an 8' x 4' sheet.