A Modest Solar Panel Setup And How Well It Performs

Editor’s Note: EarthTechling is proud to repost this article courtesy of Do The Math. Author credit goes to Tom Murphy.

I have made repeated references in past posts to the modest off-grid photovoltaic (PV) system I built to cover a large share of our—again modest—electricity usage.  By popular demand, I’ll take you on a tour of the system: it’s history, its composition, and adaptation to my house.

In 2007, I acquired a single, second-hand solar panel—intent on doing something useful with it. Confronted with a variety of options, and eager to explore multiple paths, I purchased a second panel and proceeded to set up a dual system: two stand-alone off-grid PV systems mounted side by side. It was really cool. I was able to power my television console and living room lights off of the two systems, while experimenting with different components and learning to live (part of) my life on natural power. I wrote a comprehensive article about how to size and design such a system, which may be worth reading first. Since that initial success, I have incrementally expanded my system so that I now get more than half of my electrical power from eight panels sitting in the sun. This is their story.

I have enough to say about my solar setup (and PV systems in general) that I must break this topic into multiple posts. In this, the first, I will describe the components, functions, and evolution of the system. In a future post, I will present system performance data and an assessment of efficiency of the various components. Perhaps even later I can explore the impacts of panel orientation, tracking, horizon obstructions, and geographic location.

Beginnings

I was teaching a class at UCSD on Energy and the Environment (for the second time), and was about to get to the part where I described solar power and photovoltaics when I happened upon an Earth Day demonstration on campus. Some guy had a truck decked out in solar panels, and was thumping out youth-magnet music on large speakers. I chatted with him for a bit about practical issues of PV panels and systems, which led to his giving me a sweet deal on a spare panel he had. I figured I owed it to myself and to my students to transcend the theoretical and learn more about the practical side of an apparently important player in our energy future.

To develop an idea of how to put a PV system together, I turned to the Solar Living Sourcebook (12th edition, in my case). This book—a mixture of tutorial and catalog—allowed me puzzle out the components I would need, conveniently interspersed with parts selection and prices. The book also offered an appendix on the National Electrical Code (NEC) suggested practices for photovoltaic installations, compiled by J. Wiles and also available here.

Even then, I was surprised at how difficult it was to find a definitive, comprehensive wiring diagram for an off-grid system. Picking up tidbits from a variety of sources (including helpful diagrams from Outback, and referring to the NEC standards), I was able to cobble together a code-compliant schematic, and proceeded to buy parts and build up my system.

Because the endeavor had a large educational focus for me, I was willing to: purchase asecond panel and build two independent systems; try out multiple charge controllers; and spend money on monitoring/data collection. So my expenses are not representative of an installation where saving money on electricity is the primary focus. A small scale (few-panel) off-grid system is bound to come out less favorably than a large grid-tie system from a financial point of view. The latter type can certainly accomplish a financially-motivated quick payback, but my entry was more of the hobby variety.

The two panels I started out using in my dual PV system. At left is a 130 W polycrystalline panel, and at right is a 64 W thin-film flexible panel. Both are mounted on frames allowing tilt adjustments to follow the seasons.

First cut at the electronics for my dual PV system (June 2007); keeping it simple at first. Two golf cart batteries are in the back, and mounted on the plywood are two different charge controllers, two 400 W inverters, a couple of shunts (for current measurement), and fuses here and there. The class-T 110 A fuses for the batteries are hidden on the back of the plywood.