DIY Solar Hot Water – Building the Solar Panel


Welcome to the third article in our new DIY Solar Hot Water Heater series.  In this article we will walk through the building of a low cost and very functional solar panel for a DIY Solar Hot Water Heater.

Build Overview

The solar panel build is perhaps the most time consuming part of the entire project, but it is rather easy.  Expect lots of repetition and take your time.  The most important parts of the build are the solder joints on the pipe grid.  Be sure to make good, clean joints with plenty of solder by ensuring that each joint has been cleaned, deburred, fluxed and fully heated prior to wicking the solder into the joint.  After the pipe grid is complete, you will want to pressure test it to ensure there are no leaks.  I had a couple joints leak which were only discovered by performing a pressure test.

Materials Required

You will need the following materials:

Item Source Quantity Cost each Total Notes
4′ x 8′ sheet of 3/8″ plywood Lowes 1 15.52 15.52
2″ x 2″ x 8′ wood strip Lowes 3 1.72 5.16
1/2″ x 10′ Type M  (thin wall) copper pipe Lowes 10 10.48 104.80
Bag of 25 1/2″ copper couplers Lowes 1 8.38 8.38 Use leftovers for panel #2
Bag of 1/2″ copper T couplers Lowes 2 17.96 17.96 Use leftovers for panel #2
Bag of 1/2″ copper elbows Amazon 1 4.61 4.61 Cheaper on Amazon. Use leftovers for panel #2
Flat black spray paint Walmart 4 1.00 4.00
2′ x 8′ Polycarbonate sheeting Lowes 2 21.97 44.00
16oz. Lead Free Plumbing Solder Amazon 1 24.38 24.38 Cheaper on Amazon. Use leftover for panel #2
8oz Water Soluble Plumbing Solder Flux Amazon 1 7.59 7.59 Cheaper on Amazon. Use leftover for panel #2
Approximate Total 236.40

Tools Required

Hopefully you already have the following tools, but if not, here are some ideas…

Item Source Quantity Price Total Notes
Tubing Cutter Amazon  1  14.95 14.95 Useful for other projects too
Plumbing torch kit Lowes 1 35.00 35.00 Useful for other projects too
Drill with Phillips screw bit Lowes Hopefully you already have this
Box of 50 Phillips wood screws Lowes 1 5.00

Pre made modular hot water solar panels

Another approach to a DIY Solar Hot Water system is to purchase pre-made solar panels. This may be an option for someone who does not want to build the panel themselves… Here are some modular panel units.

Panel design diagram

The panel design is very simple and can be modified to fit the particular needs of your situation.  Here is the design I used:

Ensure that the grid is angled when mounted to the frame to allow for draining.

Building the Solar Panel Frame

The frame supports the pipe grid and provides the grid with structural rigidity, protection from the elements and moderate insulation.  Start the build by laying the plywood sheet out flat and then adding the side 2×2 strips to the edges of the top of the plywood sheet.  The side strips provide some structural support and the edge attachment points for the polycarbonate sheets.

Solar hot water panel frame with 2×2 spars screwed to the edges. Copper pipes and couplers strewn about for perspective…  Since the panel will be installed horizontally, the top of the frame is at the top of the image.


At this point, the frame will still be pretty flimsy and will flex when lifted by a corner.  To reduce flexing and increase the strength, you can attach four 2″ x 4″ x 4′ spars to the back of the frame, running from vertically at 2ft intervals.


Building the Solar Panel Pipe Grid

The pipe grid carries the heat transfer fluid (aka, the water).  The horizontal runners are ~90″ long so that they can fit within the frame along with the T-Couplers and vertical risers. Cold water enters the grid on the lower left side and exits the grid at the upper right side, with an extra runner returning heated water to the left side of the panel.

Building the left side riser. Test fit all of the pipes prior to soldering!Note that the lower 6 runners are made of of cutoffs from the upper 10 runners. Just use a coupler to make runners to length.

Test fitting the pipes while building. Leave about 1″ of room between the risers and the edge 2″x2″ strips.  You will use this space to angle the pipe grid in the frame.


Once mounted to the frame, the pipe grid will be angled slightly such that the upper right hand side of the grid is several inches higher than the upper left hand side of the grid.  This is to facilitate draining of the grid so that water does not pool in any of the runners.

After all of the pipes have been test fitted and you have ensured that the pipe grid will fit (and angle) in the frame, remove the pipe grid from the frame and solder all of the joints.

Pressure test the pipe grid by attaching a garden hose to the inlet and placing a cap over the outlet of the grid.  Take note of leaks and then fix any leaking joints.

Paint the pipe grid and the frame

Using the spray paint, ensure that the entire pipe grid is well covered by flat black paint.  Also, paint the front of the frame flat black.  The external portion of the frame can be painted to match your house color.  It is very important to paint the exterior of the frame as this will provide weather resistance to the wood.  I used exterior house paint for the frame interior and exterior as a first coat.  Then, I covered over the interior of the frame with the flat black spray paint.

Attach the pipe grid to the frame

Using copper pipe attachments, screw the pipe grid to the frame.  Ensure that the grid is angled such that the left hand side is lower than the right side to facilitate drainage.  You will have to drill several 5/8″ holes through the left side of the of the frame to allow the grid input and output pipes to extend out of the panel.

Cover the panel with Polycarbonate sheeting

Once the pipe grid has been mounted to the frame, attach the polycarbonate sheets to the frame edges using woodscrews.  Use a drill bit to make holes for each screw.  Be sure not to make the screws too tight to the sheeting as the sheets will expand and contract with the changes in heat.  Also, do not use plastic sheets as they will melt.

Mount the panel

Once the panel build is complete, mount the panel in it’s final location.  The panel may be mounted on a south facing roof, on a ground level frame or on the sidewall of a building.