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Issue #211 February 2008
Intelligent Energy Solutions
Solar-Powering the Circuit Cellar
Part 3: Wiring & Electronics
by Steve Ciarcia
Installing a major renewable energy source like Steve’s home photovoltaic system is no small feat. It requires intelligent planning, technical know-how, and the ability to think outside the box. This month, he describes the last leg of this long technical adventure: wiring and electronics.
Start | Back to the Solar Panels | Wiring and Inverters | It's All About Architecture | Maximum Power Point Tracking | So, Does It Work? | Conservation | Soaking Up Some Photons | Sources & PDF
For the past 2.5 months, I’ve been installing a 10.76-kW net-metered photovoltaic (PV) electric power system at my house in Connecticut. Way back in the beginning of this series, I predicted that building this system would be an adventure. Because of the lead time associated with presenting all of this in print, I decided to describe it as a work in progress rather than wait until the entire system was finished and all of the inspections and approvals were concluded. That’s why this series presents subjects primarily in the order in which you have to configure and install a PV system. First, you think about how much power you need and where to put the panels. Then you do the site preparation and install everything. Aside from a bit of paranoia and calculations about wind loading on the two pole-mounted arrays that resulted in a Rock of Gibraltar support base, there haven’t been a lot of engineering issues. It isn’t until you have panels installed and you start wiring and configuring the inverters that you have to think about the engineering aspects of the system again. Before I jump into that, however, let me continue where I left off last month.
At the end of last month, I had 20 solar panels on the solarium roof, two 11¢8² diameter schedule 80 poles sticking out of the ground, and a backyard completely destroyed by cement trucks and heavy equipment. Just so I don’t keep you in suspense any longer, Photo 1 shows what the completed arrays looked like when mounted on the poles and their location compared to the roof array. Because the picture was taken from about 100¢ away and the pole-mounted arrays are angled at 35°, dimensions can appear deceptive. The total area of the three solar arrays is almost 700 square feet, and those “little” pole mounts in the background are 20¢ high and over 200 square feet each.
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| Photo 1—This is my finished PV installation. |
While fixed-angle roof-mounted solar arrays are the least expensive to install, you are typically stuck with whatever direction and angle the roof happens to be. In Connecticut at least, if it is due south and pitched at about 35° then you pretty much have an optimum fixed-angle system. Of course, the best solar generation comes from two-axis tracking systems that have pole-mounted motorized arrays that keep the sun perpendicular to the panels all day. While such systems do exist, I concluded that I didn’t have enough available ground area for the poles and that they would have been prohibitively expensive for an 11-kW system. The next best solution was a pole-mounted single-axis adjustable system like mine. Using the arrangement I’ve described, I can adjust my 6.5-kW pole-mounted arrays within a range of 15° to 65°. All it takes is a quick visit to the PVWATTS energy calculator to determine the optimum monthly solar angle for any location (http://rredc.nrel.gov/solar/codes_algs/PVWATTS/).
Assembling the pole mounts was not an insignificant task. This is one of those places where having a professional installer like Sunlight Solar Energy comes in handy. The first task in completing the pole mount was to hoist the strongback to the top of the 11¢ schedule 80 pipe and attach it to the mounting sleeve pivot bolt. Estimated as about 300 lb, it took the whole Sunlight Solar Energy team plus Bob Kuca and Floyd Palmer to get it up there (see Photo 2a).
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| Photo 2a—Bob and Floyd help the Sunlight Solar Energy crew hoist and bolt the 300-lb strongback to the top of the 11' 8" schedule 80 mounting pole. b—Tom Smith and Jason Ross bolt the module rails and rail brackets to the strongback. c—Tom and Jason start attaching the SunPower SPR-205 solar panels. d—Tom, Jason, and Ian Applegate add #6 braided copper cable to each panel to properly ground the entire array. |
Once the strongback is attached, module rails and rail brackets are bolted to the strongback (see Photo 2b) and then solar panels are attached (see Photo 2c). A bunch of panels later, the structure starts looking recognizable (see Photo 2d). The finished arrays were angled at 35° for the particular time in Connecticut (see Photo 3). Take a look at the different colors in these photos and perhaps you’ll understand why I chose SunPower SPR-205s for the pole mounts that I can see from the house and the deck. They are much more pleasing to the eye than the SunPower SPR-210s on the roof.
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| Photo 3—The finished pole-mounted arrays are set at 35° for a final test. |
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