Sizing a SDHW system is pretty straightforward process. Before you get started, however, it is important to be sure you have a good solar site. That is, you need to be sure you can position solar collectors so that they’re exposed to bright sunlight from 9 a.m. to 3 p.m. every day of the year. Fortunately, most homes, and even many apartments in cities, have good solar access somewhere on the site. Roofs are often free from obstructions that can shade solar panels.

If you have a good site, your next task is to scour your home for ways to make it more efficient with respect to hot water use. Remember: efficiency is the first rule of renewable energy system design! Make your home as efficient as possible, then size the system.

What do you do to make your home more efficient?

In his excellent article, “Solar Hot Water: A Primer,” published in Home Power magazine Issue 84, Ken Olson recommends the following steps, all of which were mentioned in Chapter 2 on home energy conservation:

1. Turn down the thermostat on your water heater to 120° to 125°F (48° to 51°C). “Many water heaters,” says Olsen, “are set between 140° and 180° F (60° and 82°C),” but much lower temperatures are just fine.

2. Wrap the water heater with an insulated water heater blanket.

3. Fix drips in faucets in the kitchen and bathrooms to prevent the waste of hot water.

4. Install water-efficient showerheads and faucet aerators to reduce hot water use.

5. Insulate hot water pipes in unconditioned space.

Once water and energy conservation measures are in place, it is time to size your solar hot water system. The size of a system depends on many factors, the most important of which are (1) your climate — how hot, cold or sunny it is, and (2) your family’s water consumption. It also depends, in part, on your solar exposure. Will your system have unobstructed access to the sun from at least 9 a.m. to 3 p.m. each day? If not, you’ll need a larger system.  ....read more