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May 22, 2023

Michigan not best locale for solar heat, using the sun to heat water is more practical

Q: I live in a rehabilitated farmhouse near Kalamazoo. Although well-insulated,

Q:

I live in a rehabilitated farmhouse near Kalamazoo. Although well-insulated, it uses more gas and wood energy to heat than I would like. One roof is south-facing. Several decades ago, solar power in cloudy Michigan was not a feasible economic option. Now that technology has advanced, what is the feasibility of solar-powered generation in Southwest Michigan?

A:

It seems as though you might be asking about two different things. "Solar-powered generation" implies producing electricity from the sun. But the reference to your house using more heating fuel than you would like speaks more to space heating. So let's talk about solar space heating in this column and electrical generation in a subsequent one

Frankly, on a purely economic basis, it would be difficult to justify installing a solar space heating system on an existing home in this part of the state. As you said, Michigan is notably cloudy.

Worse, trying to extract heat from the sun gets harder in the winter. As the earth tilts on its axis, the sun's rays lose their energy-producing power. So, coupled with short and often cloudy days, there is just not much heat potential to be had.

You could spend quite a bit of money and not lower the heating portion of your utility bill very much.

If you still want to pursue this idea, the most cost-effective option would be to build some solar collectors and mount them on the side of your house. There also are commercial versions of this product available.

These simple devices consist of a thin, insulated box that is painted black on the inside. A clear cover on the top allows solar rays to enter the box and heat up the air inside. A small fan moves indoor air into the heated chamber through an intake port while simultaneously blowing warmed air into the house. On warm, sunny days, air movement and exchange can take place without the assistance of the fan.

These types of collectors also can be mounted on a roof. However, inefficiencies in transferring warmed air through a cold attic reduce their effectiveness. Also, snow can collect on top of the unit, cutting off solar gain.

Because this type of collector typically doesn't have much surface area, it doesn't produce much heat. Think "room heater" rather than something that can boost the indoor temperature of an entire house. And they only work in daytime when the sun is shining.

A more effective system, though much costlier, would be a heat-transfer evacuated tube solar collector mounted on the roof. With this setup, copper pipes containing a refrigerant are encased in sealed glass vacuum tubes. The sun shines through the glass, heats the copper piping and the refrigerant inside.

Connecting pipes transfer the refrigerant to the furnace, where a heat exchanger installed inside the warm air plenum allows heat to be extracted when the blower activates.

Again, such a system is entirely sun-dependent, and can be ineffective for days if snow shades the collector.

A more practical way to use the sun to reduce your energy bills would be to install an evacuated tube solar system to heat water for domestic use. It would help cut cost year-round, reducing water heating bills in the winter, and possibly eliminating them entirely in the summer.

Zolton Cohen is a Kalamazoo-based newspaper columnist and former American Society of Home Inspectors-certified home inspector. Write to Zolton B. Cohen, Around the House, P.O. Box 2007, Kalamazoo, MI 49003.

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