Solar PV customers understand that they can generate cheap electricity with rooftop solar. That electricity is good for lighting, appliances, air conditioning and other household uses. But homeowners often ask about heating their homes with solar. The answer used to be installing a solar thermal system with rooftop solar panels generating hot water (stored in a tank) or hot air (stored in a bed of rocks or other thermal mass). But now there is another option: heat pumps combined with rooftop PV.

Two trends are making this type of system cost effective. First, rooftop PV systems now generate electricity inexpensively, often much less than what you would pay from your local utility. Second, there is a new generation of smaller, modular heat pumps called "mini-split systems" that allow you to heat and cool a few rooms at a time, instead of your entire house. The combination of cheap PV electricity and a zoned approach to heating and cooling are often less expensive than natural gas heat and central air conditioning.

Heat pumps draw on existing heat reservoirs, usually ambient outdoor air, underground water sources or pipes buried outdoors. When these heat reservoirs are in the range of 45 to 55 degrees F, heat pumps can be quite efficient. So they work best in temperate climates -- not in cold areas of the U.S. Nevertheless, even in cold climates a ground or water source heat pump with PV can be more efficient than gas or oil heat (and certainly cleaner). As PV costs continue to decline and split systems proliferate we can expect to see more and more homes relying solely on rooftop PV for their energy use. Please join me on this week's Energy Show on Renewable Energy World as we talk about the perfect match between heat pumps and rooftop PV.