Usually, the choice for solar photovoltaic (PV) systems is to have them face due south or mount them on trackers. There are other solutions for solar installations, however, and some are worth knowing about.
A building with a north-south roof ridge axis is not a readily workable place to mount a conventional south-facing rooftop system. In such circumstances, however, it is possible to install some panels facing east and some facing west. Power production is somewhat less than what it might be with a conventional system of the same size, but for some buildings, it may be ideal. PV panels have become inexpensive enough that east-west solar systems can be practical.
A good example of such a system appeared in the October, 2018 edition of Green Energy Times, in the article, “Solar is a Family Affair” (bit.ly/solar-family). That article describes a 27-kilowatt (kW) system Integrity Solar installed for EyeCare for You, in Bethel, Vermont.
Katrina Wilson, of Integrated Solar Solutions of Brattleboro, Vermont, said, “We started installing on the east and west roof as well as the south when we were introduced to SolarEdge Inverters back in 2015.” She also gave us some technical details. “The average home in Vermont without conventional electric heat or cold climate heat pumps is sized at 24 modules or 6.96kW with a south-facing array,” she said. She compared this with an orientation of either east or west, saying, “With the same system, with the same factors facing directly east or west is estimated to produce 7,270 kilowatt-hours per year. This is just slightly less than if it were facing south.”
Kim Frase of Frase Electric in South Tamworth, New Hampshire, has also had some experience installing east-west solar. He told us, “Depending on the roof pitch and how far west or east it is, it can be a 15-20% reduction from optimal orientation. But with limited shade, it can be as good as a true south installation if the true south installation has 20% shade.”
There has also been an increase of west-facing solar arrays, or more commonly arrays facing south-west, in some parts of the country. This happens when the array owner can sell electricity from the afternoon sun at a premium. On most days, peak grid demand is in the late afternoon to early evening. It has historically been taken up by power plants that charge very high prices. West-facing arrays can cover high afternoon demand when the sun is shining, and if they are associated with batteries, they can provide power at other times also.
Another non-traditional type of installation uses bi-directional solar panels. Bi-facial solar panels collect light from both surfaces to convert it into electricity.
Panels of this type have been tested at the United States Department of Energy’s Regional Test Center (RTC) in Williston, Vermont, one of five such centers in the country. The RTC is doing research on the panels to see how they could best be used. The data it gathers will be useful for making engineering decisions in the future, both for manufacture and use. The bidirectional solar panels they are testing were made by Prism Solar, in Highland, New York, SolarWorld USA, in Hillsboro, Oregon, and Tesla, of Palo Alto, California.
While some bi-facial panels can be installed vertically, with one side facing east and the other west, they are especially valuable for applications in northern areas, because they can be mounted in a couple of ways that ordinary panels cannot. They can be set up toward the noon position of the sun, much like other PVs. If that is done, and if their backs are unobstructed so as to receive light coming from the side facing away from the noonday sun, they can generate electricity from light reflected by snow, so they can produce added power from the less powerful winter sun.
Another mounting system for bi-facial panels is to install them above decks, car-ports and similar locations, where the floor or ground below them is of a color that can reflect a good deal of light. The panels have glass on both sides, allowing light to pass through them, producing a mottled pattern on the ground below. If the ground is reflective enough to send light back up to the panels, they generate light from both sides.
Clair Chang of the Greenfield Solar Store told us her business installs bi-facial panels made by Prism Solar for places that are demanding. “They are not for a roof or a similar situation, but they have a unique niche,” she said. The dappled shading they produce is very much appreciated in some places. The light reflected from the white gravel driveway of a carport, for example, can produce significant amounts of power.