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.
Step 1: Approach for Mounting
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.