It is at least somewhat commonly understood that a solar thermal system will save you money over the long run. But what people are most aware of are the checks they’re writing to the utility every month. So what we want to know most of all is what monthly difference a solar thermal hot water heater will make.

That, of course, varies. It depends on location, energy costs, system size, family size, hot water consumption, and other factors. Hot water heating comes in second on the average energy bill (behind space heating) and is responsible for roughly 30% of monthly consumption. While specific energy costs will vary, it is easy, based on some generally accepted data, to calculate savings for the average family of four.

This average family uses about 70 gallons of water per day and a solar hot water heater can replace up to 80% of their water heating needs. At average electrical rates (roughly 10 cents per kWh), a solar hot water heater will save about $300 annually–roughly $25 per month. That is a pretty decent amount, especially when you dig a little deeper to determine the payback period for a solar hot water heater. (more…)