How to Size Solar Hot Water Systems

Learn how to size solar hot water systems for every region, climate and family size.

| April 14, 2014

Homeowners scramble to cut utility bills and find alternatives to fossil fuels as the prices of oil and natural gas continue to rise. The Homeowner’s Guide to Renewable Energy (New Society Publishers, 2011), by Dan Chiras, offers excellent ways to improve energy efficiency by making the switch from fossil fuels to clean, affordable, renewable energy. The following excerpt examines one practical option for utilizing solar energy and details how to size solar hot water systems for any climate and family size.

You can purchase this book from the MOTHER EARTH NEWS store: The Homeowner’s Guide to Renewable Energy.

Things to Consider: Sizing Solar Hot Water Systems

Sizing a DSHW 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.

In his excellent article, “Solar Hot Water: A Primer,” published in Home Power magazine Issue 84, Ken Olson recommends the following steps to make your home more efficient:

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

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