How to Mount a Solar Panel

We recently purchased a 45 watt solar panel kit from Harbor Freight.  This kit ranges in price from $259 down to $159, depending on week and the special being offered.  We got it at the lower price.  This kit contains three 15 watt solar panels, a stand for mounting the three panels, a regulator box, and two 12 volt DC lights.  The the three panels each have 11 foot power cables that you attach to the box in parallel.  The box has a place to attach a storage battery, a cigar lighter port where you can attach an inverter, and outputs for 3, 6, 9, and 12 volts DC,  There is also a USB port with 5 volts. You get a lot for the $159.  Note, a recent check at the Harbor Freight store had on  display a much simpler regulator box. 

The downside of this unit is that if you try to use the rack that they give you for mounting, it will have to sit on the ground in a place that would be temporary.  The wind could easily knock over the panels.  There are no instructions in the package to mount the panels permanently and calling the support number got me nowhere.  After considerable thought and experimentation, I have come up with a solution that works.  The purpose of this instructable is show how I did it.

The goal was to mount the solar panels to the roof of a shed out in a country garden which does not have electrical power.  The system would generally be used to charge battery-operated tools but other AC tools could probably be used via an inverter.

The back of each solar panel has a channel that runs around the perimeter.  Half-way down each the two long channels is a piece of metal that has slot for receiving a knob protruding from the mounting frame.  This piece of metal is trapped inside the channel and is held in place with two set screws. 

Based on what I saw in a 5 watt panel that I had bought from Harbor Freight, I realized that if I could get a nut inside the channel, I would have a way to screw a matching bolt into it.  The 5 watt panel used a metric nut called an M8 (the 'instructions' for that unit were printed on the back of the box).  After a long search for an M8, I gave up (the US doesn't do metric) and chose a 5/16th inch nut.  However, a regular nut won't do due to the vertical clearance of the channel.  I went to Ace Hardware and found a half-height 5/16th inch nut.  The guy at Ace pointed out that since the frame was aluminum, I should go with a stainless steel nut because, otherwise, the steel will interact electrically with the aluminum.  From that point, I purchased only stainless steel hardware for any piece that would make contact with the panel. 

The overall approach that I followed was to slide two nuts down each side channel and then bolt three inch aluminum plates to these nuts.  The plates would then be used to anchor the panel to wood rails that ultimately would be mounted to boards screwed into the joists on the roof. 

The following are the materials that you will need:

12 half-height stainless steel 5/16ths inch nuts (possibly a metric M8 nut)--sometimes called 'jam nuts'
12 stainless steel 5/16ths inch lock washers
12 stainless steel 5/16ths inch bolts (3/4ths inch long or half inch if you can find them)
12 stainless steel normal height 5/16ths inch nuts
12 zinc-coated lag bolts 1/4 inch diameter  by 1 1/2  inches long
 6 zinc-coated lag bolts 1/4 inch diameter by 2 inches long
2 boards 1x3 inch by 8 foot long
1 board 1x4 inch by 8 foot long
1 strip of of aluminum 2x36 inches (1/8th inch thickness)
Sealer for the holes drilled into the roof
12 volt deep cycle battery

The most expensive item is the battery.  The strip of aluminum is also fairly expensive (around $10).  I would stick with stainless steel nuts, bolts, and washers.  You can can find alternate solutions for the strip of aluminum.  The critical issue in this instructable is the nut that will fit in the channel.  After you have that in place, you can come up with all kinds of alternate solutions.

The half-height 5/16ths inch nut must be inserted into the channel.  It took me quite a while to figure out how to do this.  It turns out that the way to do this is to remove screws from the end of the frame that doesn't have the power output wire.  To do this:

1. Remove the two screws from the top corners of the panel. 

2. Loosen the set screws in the corner brackets that hold the corner brackets into the top and side channels.  (these screws are very small so make sure you don't lose them)

3. Pull the top channel away from the panel.  One of these was caulked in pretty tight, so you might have to use a little force.  The other two came right off.

4. Slide out the corner brackets.

5. Loosen the set screws in the mounting brackets that are located half way down in each of the side channels.  Slide out these brackets.

6. Slide a half-height nut down each side of the side channels past the point where the mounting bracket had been. 

7. Slide in the mounting brackets to the position where they had been and tighten the set screws.

8. Slide in two more of the nuts, one on each side of the panel.

9. Insert the corner brackets into each end of the channel piece you had removed.

10. Push the end channel piece back on to the panel making sure the the corner bracket slides into the long channels.  Tighten down the set screws on the corner brackets.

11. Screw in the screws that you first took out.

The nuts that you inserted will slide back and forth and can be positioned later to where it makes most sense.

I used a 3 foot long piece of aluminum 2 inches wide and 1/8th inches thick to create mount plates.  In the photo you can see the label for the piece.  I purchased it at Lowes for about $9.00.  I decided to make each mount plate 3 inches long because I needed 12 of them (36/12=3).  To cut these, I used a jigsaw with a metal blade.  It cut right through.  Later I used a grinder to take off the sharp edges.

After that drilled two holes in each plate.  One was about an inch from the one end and it was large enough to insert a 5/16th inch bolt.  The other was about an inch from the other end and was large enough to insert a 1/4 inch lag bolt.

Take the two 1x3 inch boards and cut four 36 inch sections.  Paint these with some sort of outdoor paint for appearance and to make it weather proof. 

Put the panel right-side up and line each rail along the side of the panel under the mounting plates.  I placed and tightened down the plates to the channel about 9 inches from each end.  Mark where the lag screws are located.  Pre-drill the holes with a drill bit slightly smaller than the lag screws.  Attach the rails to the mount plates. 

You should attach rails on each side of two of the panels. The drop the middle panel into the middle of them to see where you should line up the mounting plates.  I lined up these mount plates about three inches from each end.  Do not attach the middle panel to the rails of the end panels at this time because the whole affair would be too heavy and unwieldy..  This will have to be done up on the roof.

Cut the 8 foot 1x4 board in half.  Paint it with the same paint you used on the side rails.
With the panels assembled upright, Lay the 4 foot boards across the panels.   Place a mark on the board over the center of each panel.  These will be where the lag bolts that attach the board to the roof will be driven in.  Of course, the panels will sit on top of these boards up on the roof.
Pre-drill holes where you made these marks. Use a drill bit that is a little smaller than the diameter of the 2 inch lag bolts.

The roof mount boards are 48 inches long and are attached directly to the roof.  I had predrilled three holes on each board that matched up with what will be the centers of the panels.  After finding the studs, we lined the board up along them and drilled through the hole in the board and then on through the shingles and into the studs.  The diameter of the drill bit has to be smaller than the lag screws that will  be used so that they will have some grip.

The panels go horizontal to the roof.  The side rails  are already attached to the two end panels.  Where these side rails cross the roof mount  boards you affix the side rails to the roof mount boards.  You need to predrill the holes and then drive in lag screws.  I had chosen 1/4th inch by 1 inch long.  It turns out that I really should have 1 1/2 inch lag screws but I went with what I had. 

First, mount the bottom end panel.  You won't be able to get to it if you do it last.

Then lay the middle and to top end panels into place.  Lag-screw the metal tabs of the middle panel into the side rails of the end panels that they are laying on.

Finally, lag-screw the side rails of the upper panel to the base boards. 

The panel is now mounted on the roof.  While you are up there, gather together the three power cords into a single bundle and tape them together.

We  dropped the power cables that came in through a side hole in the attic down to a shelf where I had placed the regulator and the battery.  We then connected the power cables to the regulator and the battery to the regulator.  The regulator will control the charge of the battery and will also output various voltages.  Notice the USB connection for 5 volts.

The display shows 12.6 volts.  This is the output of the battery.  If you disconnect the battery, you will see the actual unloaded output of the panels.  This will range from around 22 volts in full daylight to zero at night.

Note: The regulator that is now being included in this package is not nearly as nice.  It looks cheaper and does not have a display.  I don't think it even has a USB output.  I just checked in Harbor Freight today and that's what I saw. 

What are we going to do with this power?  We intend to charge things like battery-operated drills and other tools.  We will do this using a car inverter that will be plugged into the cigar lighter slot.  For a test, we connected a house fan to the unit and it ran fine.  Another idea is to run a laptop and WiFi router.  Maybe we will borrow a neighbor's signal (with permission)  and send out security images to post on our website.

Finally, I feel that the most significant point of this instructable is the technique I developed for inserting nuts in the channels on the back of each panel.  Without this, there would be no easy way to mount the panel permanently.