Sunday, September 27, 2009

A Few Words About Solar Energy

A reader requested that I say something about solar energy and its applicability here in the Southwest. I’ll break it down into its main subcategories, and talk a little about my personal experience with each type of solar energy.

First, high-tech solar applications. These all convert solar energy into electricity with the aid of photovoltaic panels. These panels wear out over time, and have to be replaced every 20 years or so. Unfortunately, this requires an industrial civilization – the very civilization we’re trying to evolve away from. Talk about a conflict of interest! Also, I’m assuming that ultimately there will no longer be an industrial civilization capable of building photovoltaic panels.

The primary photovoltaic application is creating electricity for household use. There are two main ways of doing this: stand-alone, and grid-tie.

Stand-alone systems require batteries to store electricity for nighttime use. These batteries – which are essentially 19th Century technology – are expensive, very heavy, have to be replaced every few years, and have to be carefully tended by the owner. For this reason I have never considered installing such a system for myself.

A grid-tie system dispenses with the batteries by tying into the electrical grid. During the daytime, household needs are supplied by the solar array, and excess power is fed into the grid, reducing your electric bill. At night and during cloudy weather, the household runs on grid power.

One inhibiting factor of photovoltaic is the high cost of the panels. I’ve been following solar energy in a casual way for 40 years now. Invariably, there is always news of the latest technological breakthrough, which promises to offer solar energy at a revolutionary low price. Yet the cost of solar panels always remains high. When you consider that even a modest solar electric system can cost $30,000 or more, it’s no wonder they are so rare.

There is, however, one excellent application for photoelectric panels – pumping water. It’s an elegant strategy: during daylight hours when the sun is shining, water is pumped into an elevated storage tank. Water then flows into the household system, on demand, whenever you need it. No moving parts are required, because gravity does all the work. Except for the solar panel and electric pump, the system is elegantly cheap and simple. I used such a system for about 10 years starting in 1983, and liked it a lot. The system I used was already obsolete at the time I installed it, requiring a heavy flywheel and ancient windmill technology inside the well. This setup could now be replaced by a pump you could easily hold in one hand... which I’m now doing.

Moving onward to my favorite use of solar energy: providing heat. You can heat air, which can be used to heat your home, or a solar oven, or an herb drier, or whatever you need hot air for. (Solar-powered politicians, why not?) The other application is hot water, to supply your household’s hot water needs. These applications are both wonderfully low-tech, which is why I like them so much.

For hot air, the concept is simple: Take a surface, any surface. Paint it black, and aim it south. Voila, the black surface heats up! Then you cover the black surface with a transparent membrane -- such a glass – creating an air space. The glass simultaneously lets the sunlight through while trapping the heat in the form of hot air. This hot air can be blown anywhere you want via ductwork, or can heat your home using no moving parts – by putting a greenhouse on the south end of your house, for example.

This has always been my favorite use of solar energy. It’s so cheap, so easy, so obvious... yet I get to feel clever whenever I build a greenhouse or solar heat collector. I’ve built a couple of greenhouses, and half a dozen collectors since 1973. Also a couple of passive solar houses. One thing I’ve learned: use glass if you can afford it. Protect it from hail and kids throwing rocks, and it should last for a long, long time. Transparent fiberglass is quick and easy, but only lasts about 20 years, even if it contain a UV inhibitor.

The most elegant way to heat a home with solar is to design it properly in the first place. Consider the house to be a huge solar oven: put lots of glass on the south wall, and aim it south. This is called “passive solar” because no moving parts are required. No fans, no blowers, no ductwork, just the silent whisper of hot air warming your home. What could be simpler? Yet... at this late date, how many passive solar homes do you see? Very, very few.

Moving onward to hot water. Again, a very simple concept. Build an insulated box, with a glass wall aiming south to let in the sunlight. Paint a water tank black, and stick it in the box. Voila, hot water! The next time you’re driving around, keep your eyes peeled and let me know how many of these you see. I’ve built two of these during my solar career. The main thing I learned was in winter, to take a bath or shower during late afternoon when the water is hottest. But even after sitting overnight, the water is still hot enough for doing dishes.