Solar heat, be it active or passive, worth a look

I just stacked a cord of firewood this past weekend. Not a big deal, but it makes you think about solar heating. Burning wood is an indirect form of solar heating, but not as efficient a converter of solar heat as a solar heating system can be.

I have been knocking around the solar heating business for a while, and as you might imagine, I have a couple of thoughts on it.

First, let’s look at the basics: If you put something dark-colored in the sun, it gets hot. Wow, that’s the gist of solar heating.

We can use that heat in several ways. Passive solar heating is a concept that uses a building as the solar collector.

A passive solar structure might emphasize some south-facing windows and let the house heat up on sunny days. If there is adequate mass in the house, it will hold the heat for a while and keep you warm after the sun sets. This all pre-supposes that you have a well-insulated home (note that ongoing theme in everything I write here).

A passive home should have no more than 6 percent of its floor space in south-facing glazing. More than that, and the house will overheat during the sunny times and lose excessive heat during the night. And it will overheat in the summer.

The other form of solar heating is active solar heating. Active solar heating uses solar collectors to heat air or water. A solar collector is usually a very thin version of a house with a lot of glass. It consists of a big window that allows the sun into an insulated box. It is like a passive solar house for tiny people that is one-half glass. It gets superhot in there very quickly. You can remove the heat by either moving air through the box and shunting it into your house or into a heat storage area for later use.

The heat can also be removed by heating water. A water collector usually uses a flat panel of conductive metal such as copper or aluminum with water tubing attached to it.

Sometimes, the panel is composed of fins of metal with the tubes attached to them. The metal plate or fins are called the solar absorber. The absorber is usually painted black or plated with a black covering. In either case, the black coating allows the radiant energy of the sun to be absorbed and converted to heat energy. That heat energy is then picked up by the water in the tubes, which is acting as a coolant. That coolant is stored in a tank for later use, for either domestic hot water or space heating.

There are variations on the theme, but these are the basics.

Now for the money part: A square foot of solar collector, facing south, will produce 1 to 2 gallons of oil-equivalent energy a year. With today’s oil prices, that is impressive. You do need to buy the solar collector and attendant hardware. That’s the rub! Today, a solar hot water system that will produce about 50 percent of your domestic hot water needs is averaging $9,000 in the U.S.

That’s a lot of scratch, whether you are eligible for tax credits or not. There is a lot more to this story, and we will have to sort through that in the next couple of columns, including low-cost ways to get there.

Questions for Tom Gocze should be sent to homefront@bangordailynews.net or mailed to The Home Page, Bangor Daily News, P.O. Box 1329, Bangor 04402-1329. A library of his practical home-improvement videos, reference material and a home-project blog are at bangordailynews.com/thehomepage.