Q: I have just had a solar thermal system installed. The PV pump was described as making a “soft whirring noise.” Mine makes an annoying whine, varying with the cloud cover. Is there any way this can be ameliorated?

Also the installer suggested that the system should provide “about 100 percent” of the hot water in the summer months. The furnace (hot water) comes on several times even in direct bright sun. This was excused as the water in the furnace cooling off, requiring the furnace to ignite and heat it. How can this be called providing 100 percent of the needed hot water?

Thanks for your help.

– Roberta Goodell

A: The pump should not make significant noise. The system may have air entrained, or the flow may be restricted, causing cavitation. Either of these events will force the pump to growl. The storage tank for the solar system should be large enough to shut off the boiler during the summer season. Is the boiler in series with the solar system? Is it in parallel with the solar system? If either answer is “yes,” the piping should be changed to isolate the solar system from the boiler, and the boiler should be shut down. The plumbing for the solar system should bypass the boiler. This means that on cloudy days, or on days of high hot water demand, the valves must be changed and the system put back on the oil burner.

Answer provided by Richard Hill, retired professor of engineering at the University of Maine.