The primary components of a drainback-type solar hot water system include:
- Solar collectors – typically installed on the roof, the solar collectors gather heat from the sun.
- Storage tank – residential storage tanks are generally 65-120 gallons, depending upon the number of people in the household. Hot water flows from here to the fixtures in your home or business.
- Drainback tank – this small tank provides freeze protection, and holds the liquids that circulate through the solar loop when the pump is off.
- System Controller – The system controller is a small, sophisticated computer. This computer is attached to temperature sensors on the roof and in the storage tank, as well as the circulating pump. When the collectors are warmer than the storage tank, the controller switches the system on.
- Circulating Pump – The circulating pump runs the solar loop. Water circulates through the collectors on the roof and gets hot. From here, the water flows down to a heat exchanger where it heats the water in your storage tank. Cooler water then circulates back up to the roof, where the cycle begins again.
- Flow meter – The flow meter is used to attain optimum circulation, so that heat is transferred efficiently to your storage tank.
- Pipes and Insulation- Because of the heat generated by the solar collectors, we recommend copper pipe. PVC piping, particularly near the solar collectors, will not withstanding the high temperatures generated. High quality insulation surrounding the copper pipes in a solar hot water system generates heat loss and makes the system more efficient.
How to choose the system that's right for you
If you're interested in a drainback-type system, you'll want to consider the following.
- Where should I put the collectors? If you have a south-facing (or near-south) roof that's unshaded, this is often the ideal location. For a drainback system, the collectors need to be above the level of both the drainback tank and storage tank.
- What type of collector should I use? There are many options out there. Sustainable Future offers two types, flat plate collectors manufactured by AET and evacuated tubes manufactured by Sunda. For some people, it's an aesthetic decision. Flat plate collectors look more like skylights if they are flush-mounted. You'll need slightly less surface area if you use the evacuated tubes. For residential systems, the cost of using one versus another is very similar.
- Do the collectors need to be tilted at an angle? Ideally, yes. However, if you prefer the look of flush-mounted collectors, this can be done with a small decrease in the efficiency of the collectors. If efficiency is of primary importance, we suggest tilting the collectors approximately 10 degrees more than your latitude (for customers in the northern hemisphere). This gives a "winter bias" and makes your collectors most efficient during the winter months when the sun is low in the sky.
- What happens at night or when it's cloudy? A well-insulated solar hot water system will retain the heat in the tank overnight with no problem. If, for example, it's cloudy for a week in December and you're using your hot water each day, most systems have either a gas or electric backup to provide supplementary heat if enough solar energy is not available. We can also retrofit your old hot water system.
- What size storage tank do I need? This depends upon how much hot water you're using per day. For 3-4 people, we recommend an 80-gallon solar storage tank. If you have teenagers who like long showers or a larger family, you may need the 120-gallon tank.