Our solar water heater is a Radco DBHX, rated as one of the highest efficiency systems on the market. Not like we really need high efficiency in the summer, but this system will be able to provide hot water even in the winter months. For example, on a sunny December day, with an outside temperature of 50 °F, this collector will still output 150 °F water. It does this with only 40 sq. ft. of collector area, using diffusive glass to catch sunlight better at all angles, and an “infrared black” coating to absorb heat. During the summer, an automatic mixing valve keeps the hot water supply at a safe temperature.
The collector is permanently set at 51°, the optimum winter angle. Unlike photovoltaic panels, sufficient energy will be absorbed from the high summer Sun without lowering the tilt angle. You can see there are shadows cast on the collector by both the roof lights and weather station (not in photo). On a photovoltaic panel this would create problems. With a solar water heater it’s not really an issue, as the hot water output is directly proportional to the area not shaded.
The inside part of the system interfaces with our electric hot water heater, a Rheem model 81 VR80U-1. with 80 gallon capacity, specifically designed for use with solar water heating systems. It has all the extra connections needed, as well as super-insulation. Immediately to the right is the drain-down storage tank. The other two appliances to the right comprise our water softener, not part of this solar heating system.
During a potential freeze situation, water from the rooftop collector will drain to the storage tank to prevent damage to the collector. We get occasional freezing temperatures up here at 2200 ft elevation — maybe 2-3 days a year. During normal operation hot water from the collector delivers its heat through a heat exchanger inside the electric water heater. If needed, an electric heating element tops off the temperature to 120 °F.
Unlike a purely convective system, this unit requires two small pumps to move the fluids. Of course this uses electricity, but the overall increase in efficiency is worth it. The system is estimated to save 3000 kWh each year over a conventional electrical water heater. The federal 30% tax credit applied to this system, further sweetening the deal.