System Sizing

Just as conventional water heaters come in different sizes, so too do solar hot water heaters. Sizing a solar hot water heater properly requires determining the total number of solar collectors needed, as well as the storage volume of the water tank. Solar hot water heater professionals can assist you best in determining a system size that will meet your hot water needs.

Here are some general rules of thumb to consider before speaking with a professional.

1. Sizing the solar collector: Allow 20 ft2 collector area for each of the first two household members and a 14ft2 area for each additional household member.
2. Sizing the storage tank: The size of the storage tank is related to the solar collector area. Thus a larger collector area requires a larger storage tank. Typically, in Humboldt County, a ratio of 1.5 gallons of storage capacity is needed for every square foot of collector area. This ratio both meets the hot water demands of an average household in this area, while at the same time preventing the system from overheating when the hot water demand is low.

These sizing guidelines usually supply 90-100% of an average Humboldt County household’s hot water. Many solar hot water heating systems also use a gas or electric backup system to compensate for cloudy days or above average hot water use by the household.

Rooftop Considerations

The same considerations mentioned in the Solar Works Guide for a photovoltaic system should also be followed for installing a solar hot water system. Experienced and reliable installers and contractors can determine if your roof will need additional framing or if it already has enough support for the solar hot water collectors. It’s important to note that solar hot water collectors are heavier than photovoltaic panels, and so require a roof or mounting structure with a greater load-bearing capacity than do photovoltaic systems.