After getting this building in the shell last time in Enough Rest, Onward Ho, it is now time to think about having what “Tim Taylor” always wanted, more power!
We currently have one 130 watt solar module charging two automotive batteries, not the ideal arrangement. We have a car stereo, a 13 inch tv, and a toilet fan. We desperately need lighting. Natural light entering from the plexiglass at the top of the exterior walls is plentiful during the day, but at night we need some help. I am spending more time at the property as conditions improve. Also, all work thus far has been achieved by use of cordless tools, so charging capabilities would be very handy. It was time to add to the solar “array.”
I decided to use a pole mount for the array since I could save money by building it myself, and I had most of the material on hand. The previous winter, I had chosen the exact location for the mount and drove a stake in the ground to mark it. Starting around December 15th, I began looking for a clear day, as close to the solstice as possible. On the 18th, the sky was clear so I noted the exact time of sunrise and sunset on that spot, and divided the length of day by 2, to yield solar noon. Then, on December 21st at solar noon for that spot, I aligned another stake behind, and in the shadow of, the first stake. I now had the orientation of the array. Actually, a variation of 15 degrees east or west will be of little consequence. In hindsight, and for the main house, 15 - 20 degrees west of true will provide greater generation because the sun is slightly stronger a little later in the afternoon. A 2 ½ foot deep hole was dug to accept the pole, then filled with concrete. This arrangement has worked trouble free for ten years. If the mount is located in an open area not in the forest, the hole would need to be larger and deeper, to withstand wind loading.
In the state of Tennessee in 2003, the local power distributor required the electrical system inspection by a state licensed inspector. Not being connected to the local distributor, i.e. offgrid, an electrical inspection was not required. I’m “off the hook,” right? WRONG!
Do not, I repeat do not, think you can ignore electrical code. As I’ve stated previously, you do not want to spend the cash and labor to build a power system only to have your building burn to the ground. Sustainable, remember? Code details are safety details. Bearing this in mind, I began construction of the power system.
I built a frame to accommodate four 130 watt modules out of 1 inch aluminum angle, with gussets on the backside. I used 1 ¼ inch square tube steel for the pole. A length of round steel pipe, with gussets welded on, was attached perpendicular to the pole at the top of it. I inserted an aluminum tube, the length of the module frame, through the steel pipe at the pole top, and through the frame gussets, then welded the aluminum pole to the aluminum gussets. The module frame would then rotate in the pole mount. I researched the optimum seasonal tilt angles for the array (latitude for spring and fall, + or - 15 degrees for summer and winter), then positioned the array at these angles and drilled three corresponding holes through both pipes, on either side of the pole. I could then use a pin and clip in these holes to seasonally adjust the array for maximum output. Manual, but quick and easy.
I next mounted an Outback Power combiner box on the pole. The modules were wired individually through 15 amp circuit breakers, even though each module output rating was only 7.1 amps. I used one breaker per module in anticipation of expanding the array in the future. The 15 amp breakers would allow this expansion, with extra capacity as required by code. All ampacity ratings must be exceeded by a minimum of 10%. (A little more would be better, as I would later learn, and will discuss in a future article.) An extra breaker was installed to accommodate a small gas generator. A surge protection device was installed in the combiner to complete array construction.
Located in fairly thick forest, the optimum location for the array was about 90 feet from the building, not the best of circumstances. D/C power does not travel
distances well, being susceptible to line losses due to resistance. To keep line loss to a minimum, I had to use 1/0 (one ought) welding cable to transport electricity from the array to the building. In 2003, I purchased 400 feet of this cable at a cost of $500. Today, the cost would be much higher. The design needs to place the array as close to the battery bank as possible, to minimize losses and expense.
I now had to run the 1/0 cable “power lines“ to the building. Not wishing to deal with ice and fallen trees damaging the lines, I decided to run them underground. Since I had other excavation work to do, I rented a backhoe and dug a trench 2 feet deep, between the array and building. In the trench I placed a 1 inch layer of gravel, then 6 inch pvc pipe (to be discussed later), another 1 inch gravel layer, and finally a 4 inch pvc pipe to contain the power lines. The pole mount exit of the power line pipe, with cables protruding, was filled with expanding foam to keep out any critters.
To assure a good ground connection through the adjustable pole mount, I attached a #6 bare ground wire between the array frame and the pole, which I allowed to ground itself. A better idea, and to adhere strictly to code, a ground rod should have been installed at the pole mount, and a separate conductor included in the pipe to bond to a second ground rod installed at the entrance to the building.
Although I have had no problems thus far with my installation, I will do this properly next time. This was just a storage building, right? I keep referring to this, and will explain later. Even a storage building must be done correctly. For now, please reuse and recycle any and everything when possible.
All photos by Jeff & Kathy Chaney
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(This article is dedicated to my friend Scotty McGregor of Brunswick, Ga., who saved my life more than once and helped me maintain my sanity during a long, hot summer in the Persian Gulf in 1981. Rock on Bruce - Les)