by Guest Blogger H. Flint Ranney
Installing solar panels on your south-facing roof to heat your domestic hot water is a project that can pay for itself in less than four years.
I know, because we did it on our Nantucket house.
After battling with the HDC for a few months in 1980, we received a permit and put four panels on our roof. Pipes were plumbed down through the roof into the basement hot water tank, so that a mix of glycol and water heated by the sun in the roof panels circulated down through the tank in a closed loop and back up to the roof. Sensors turned on a pump when the roof was hot, and the system was entirely automatic. Glycol was added to prevent the fluid from freezing. It can’t contaminate our hot water because it is in a separate pipe in the water tank.
The system worked automatically for 26 years without a hitch, pre-heating the water in our hot water tank from the temperature of incoming Town water at 55 degrees, up to 80 or 90 degrees on a hot summer day. Even when it was foggy we had solar generated hot water. Even in the winter we could hear the quiet hum of the pump allowing the sun to save oil. How good is that?
The original cost was $6,500, but with tax credits in those days the net expense came to about $2,500.
In the 26th year one panel sprang a leak and we just closed it off, leaving three still operating. By the 28th year the plastic coverings had deteriorated from ultraviolet sunlight, had become somewhat opaque, and were no longer very efficient.
During those 28 years we saved an average of a gallon of oil every day. The estimate of total savings in oil not purchased was over $25,000 – a pretty good return on a $2,500 investment. About 32% per year!
We took those worn-out panels down and replaced them in 2008, with just two new panels because technology has advanced and the new ones are far more efficient. The piping and the tank were already generally in place but needed some work, and a new pump and sensors were necessary. While the roof was clear, we re-shingled it.
The total cost after a 30% Federal tax credit was $7,700. With these new panels, the inside tank sometimes reaches 130 degrees, and we have been saving two gallons of oil a day. The system has already paid for itself. At the current heating oil price of $4.26 per gallon, the cost of a new installation today would be covered in 2 1⁄2 years.
Project our experience to the rest of Nantucket: If a quarter of island homes have a south-facing roof, something like 2,500 houses could be fitted with rooftop solar panels at a total cost of about $20 million. If each home reduced its oil consumption by two gallons a day, the owner today would be saving $8 x 365 = $2,900 a year. The island would reduce oil bills by $7,300,000 every year. That $20 million would be repaid in three years. How
good is THAT? Maybe more popular than a wind turbine.