Siting a Ground Mount System

The Hack My Solar Podcast

Yesterday we spoke about different options for mounting a solar array. Today we are going to dive deeper into ground mount systems and talk specifically about some of the considerations one would need to take when siting a ground mount system in order to get the most optimum solar exposure. The nice thing about ground-mounted systems is they can be optimally-aligned with respect to both their southern orientation and their tilt angle. I use a tool called PVWatts in order to look at the different options for azimuth and what kind of impact that will have over the course of the year. In my area, a more Southwesterly orientation is better than due south when looking at overall system production. Where I live, if I were grid ties, I would have my panels facing about 220 degrees, or 40 degrees off due south. However since I am more concerned with when I get my energy than squeezing every watt our of daily production, we aren't pointing at 220 degrees. When I get up in the morning I work many times from my upstairs office or my front porch. I need energy in order to run my office machinery to include my routers as well as a fan to keep me cool during the summer, where mornings are pleasant but still hot and muggy. If I were maximizing the daily output, it would be 11 AM before I was getting any real production from my panels. Lets talk for a inut about reducing the amount of shade on the panels. Lets say I have an array of three solar panels. And each of those panels has 72 cells...thats 216 total cells Now if a few of those cells are shaded, they reduce the amount of current that can pass through the system by the proportion of shading on those cells times the total number of cells. So lets say one cell is 50% shaded, now I have the equivalent of 1.5 panels worth of energy coming from my three panels. In other words by shading one out of 216 cells, I have erased the generation of 108 of those cells. That's not a good utilization of my investment at all. The reason for this is that every cell in the string has to operate at the current set by the shaded cell. One strategy for mitigating this issue is to place panels that may recieve shading on a parallel string, so that only the string the shaded cells are in is affected and all the parallel strings are not. This is how our system is set up in that the eastern most string which receives early shade, and the westernmost string which receives evening shade, wont impact the other two respective strings. An interesting emergiung tech is Module Level Power Electronics which are essentially microinverters that operate on the individual module level and therefore limit shading losses to a single panel. These are initially more expensive but in the right environments can pay for themselves over time. I plan to do a stand alone show on microinverters in the future. Some panel manufacturers are also looking into in panel electronics that may act as microinverter for each cell, limiting the shading losses to the individual cells that are shaded and not impacting any of the other cells on that panel. As with any solar project, ground-mounted PV systems must be designed with care to meet your individual goals and address practical issues. Siting issues for ground-mounted systems are different than for roof-mounted systems and include such things as property boundaries, terrain, soil properties, the location of electrical interconnections and potential permitting issues. But in addition to these general siting concerns, energy generation optimization in a ground-mounted system (or, for that matter, on most flat-roof installations) must address the unique issue of how to space the rows of solar panels to maximize energy harvest while preventing the panels from shading one another. This issue can of course be avoided by simply keeping the rows of panels sufficiently far apart, but generally one needs to minimize this inter-row spacing to most efficiently utilize the available site.