Ground Solar, Part I

Recently, power went out for three days during and after Hurricane Matthew. Fortunately, we’ve been working with solar for a while. To keep our freezer and refrigerators running enough (about 12 hours per day) to keep things cool, we set up a ground-mounted solar system. This is a fancy term for “we just put the parts on the ground”. A shot of this deployment in action on day three is shown below:

Those are nine 265 W poly solar panels, arranged in three strings of three each. We’ll get into much more detail about that later, including the economics versus alternatives.

We also prioritized the loads; the freezer stayed shut the whole time, had more run time than either refrigerator, and we shuffled the contents around so that one refrigerator had the more perishable items in it. Butter, eggs and orange juice don’t need much cooling for a few days in a pinch, and milk isn’t that far behind; it can sour a little and still be fine to drink. Raw bacon can take getting a little warmer, also. All of those items, orange juice excepted, were, after all, pre-refrigeration staples (although today’s bacon probably has a lot less preserving salt than it once did). We made sure all the deli meat, leftovers (which were stone-souped pretty early), condiments and working supplies of the staples were all concentrated into what we called the working fridge. The working fridge received the second highest allocation of available electricity.

When opening the refrigerators during use, we also took temperatures. The highest refrigerator temperature we recorded was 59F in the staples fridge. The working fridge hit about 52F, and as I said before, the freezer stayed shut, so we have no temperature measurements for that. These highs were recorded early on the second day, after each refrigerator had only received about four hours of run-time over about thirty hours of power outage. After that point, we had so much available power that the temperatures, using good door discipline, were indistinguishable from normal operation with high door use. None of the food has been thrown away; we’ve been using all of it afterward as if nothing happened. The first thing to come out of the freezer about an hour after grid power was restored was a roast lying on top. It was a brick, as you might expect, with no softness anywhere.

So why put the panels on the ground instead of having them mounted beforehand? Several reasons. First, you might live in an area, such as a snooty subdivision, where solar installations are frowned upon. Second, you might not have had time or budget to install them. Third, you might be concerned that high winds or vandals might damage them. Whatever the reason, the economics of solar panels today means that emergency ground mounting, even though the angles aren’t optimal, isn’t a bad choice given the alternatives.

That’s enough for now. Future installments of this series will drill into the details of each portion of the system, practical tips for getting things done, some gaps between theory and practice, and things we could have done better.

Before then, the first old school homework assignment on this topic is to visit the Off-Grid Solar Design Guide put together by one of our sponsors, SoftBaugh. This guide contains a lot of background information about solar, and has some helpful calculators for designing panel and battery arrays. We’ll often refer to this guide in future installments, so it would be good to know what kind of information is there, and the general flow of information before we dig into the details.