ASK THE EXPERTS: Off-Grid Planning

Intermediate
Sometimes, siting PV modules to receive adequate sunshine requires ingenuity.

I’m interested in using off-grid systems on some property my brothers and I purchased. The problem is, my part of the property is in a valley, and surrounded by trees. I’m concerned about how far up the mountain I will have to go to clear land for either a PV system or a wind turbine. I don’t want to lose the beautiful forest.

The house I would like to build on the property will be no more than 500 square feet, but I have to use medical equipment, so it needs to be all-electric. Last year, I used 1,097 kWh for my electric loads in my existing home, which is about 1,000 square feet. I have a gas water heater and floor furnace—my gas bill is about $37 per month.

Also, can the electricity from a wind turbine or solar-electric array provide power for multiple small homes?

Tom Baldwin • Saint Albans, West Virginia

Solar-electric modules need sunshine—there’s no way around that. Looking at your property with a solar siting tool such as a Solar Pathfinder will give real data on how much sunshine a given spot receives. Either buy or borrow such a tool, or hire a professional to evaluate your site and compare the various options.

Selectively harvesting a few trees to create a solar window can be a worthy trade-off between generator run time and preserving the forest. In the tall-tree country of the Pacific Northwest where I live, resourceful folks sometimes put solar-electric arrays on high roofs, on towers, or even in trees to capture more solar energy. I have a 450-watt array that is at 125 feet on a tower, and even being half the size, it still gives me two-thirds as much energy as the 900 W array on my roof—there’s a lot more solar exposure up there.

Wind generators also need to be well above the trees and surrounding landforms. The standard rule is to site them at least 30 feet above anything within 500 feet. Pay attention to how tall the trees will get over the years—because towers don’t grow.

In addition to determining your resources, analyzing your loads is crucial to good system design. In your current home, 1,097 kWh per year is very modest usage—are you sure it’s accurate? If it is, taking this electricity thriftiness off-grid will make a system less expensive. You’ll also need to figure out how you’re going to heat water and provide space heating. In the early days of off-grid living, many people used propane for refrigeration, water heating, space heating, and even lighting. As prices for solar-electric systems have come down, off-gridders have shifted more loads to electricity. I’ve been using PV power for refrigeration for more than 30 years now, and recently installed a minisplit heat pump for opportunity heating using my surplus wind power. Exactly what loads you run—and how much you’ll need to rely on a generator—depend on your energy resources and your willingness to adapt your loads to the available resource.

Certainly, more than one home can share a renewable energy system, though there may be technical and social issues. Systems can be designed to power whole communities, in fact. The sizing issues are the same—how much energy potential does your site have, how much energy-capturing equipment will you invest in, and how much energy will the homes use? Multiple families on one system means either sophisticated controls and automated backup or very good awareness and communication between all of the users.

Ian Woofenden • Home Power senior editor

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