A solar hot water system was recently installed at my family’s house. The government incentives which accounts for about 30% of the system and the fact that the old hot water heater was broken were the main drivers of the project. The system is designed to provide hot water for four to six individuals which equates to 75 square feet of solar panels on the roof. We are using a dual tank solution since this is more efficient, but more expensive than just using a single tank. With the dual tank solution, one tank acts as a preheat tank which preheats the cold water from the street while the other tank is the hot water tank which keeps the water at a constant 120F. Since the water from the street is between 40-60F, a great deal of energy is required to heat this to 120F. n With the preheat tank, the solar panels heat the water from the street before it enters the hot water tank so less energy is needed to heat the water to 120F. The hot water tank has two backup sources in case the preheat tank is feeding water colder than 120F. During the winter the backup is a tankless coil in the boiler and during the summer it is electric which allows the boiler to be turned off.

We have only had a couple days of sun and the rest has been snowstorms. On a 30F sunny day, the preheat tank started at 58F in the morning and at the end of the day was 82F which isn’t bad considering it is 105 gallons (double the size of an average tank). The glycol (water freezes) which flows through the panels was a constant 140F which is incredible if you think of the low UV radiation that the sun produces during the winter months. Hopefully there will be a couple sunny days in a row to get the big preheat tank over 100F.