I am planning to install a solar water heater soon. Reading Home Power articles has me wondering which type I should buy. I live in Ohio near the Pennsylvania border, about an hour due east of Cleveland. Peak sun-hours average about 3.8 hours a day here. What’s your recommendation?

Frank Carradine • Fowler, Ohio

In a climate like Ohio’s, you can expect that a selective surface flatplate collector and evacuated-tube collector of equal size will produce about the same amount of domestic hot water year-round. But under more ideal solar conditions, a flat-plate collector will outproduce the evacuated-tube collector most of the year, except during the winter.

Be aware that snow and frost can cause performance drops in evacuated tube collectors. The super-insulation of the vacuum in an evacuated tube collector can prevent snow from melting off the tubes. The sun can penetrate the snow to heat the absorber, but the superior insulation in some tube designs prevents the heat from melting the snow off the glass. There is no independent test data on how much this affects evacuated-tube collectors in different climates but it does mitigate—and can eliminate—the performance advantage of evacuated tubes in areas with large snow loads.

Note the photo (above) of my home after a snow. The long collector on the left is double-glazed—the industry standard for air collectors in the early 1980s. Toward the back on the right is a smaller, more recently installed collector that’s single-glazed and has a selective-surface absorber—the industry standard today. You can see that the snow is already sliding off the collector on the right, while the snow remains on the better-insulated, double-glazed collector on the left. I would imagine the phenomena would be more pronounced with a tube collector since their insulation is superior to double-glazing. If frost and snow are an issue, which I believe they are in Ohio, I would choose a flat-plate collector.

If winter snow or frost isn’t a big issue, I would pick whatever collector has the lower cost (making sure to compare collectors of the same size)—unless you have an aesthetic preference.

Chuck Marken • Solar Thermal Editor