Sizing a Solar Hot Water System

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  • Sizing a Solar Hot Water System
    Posted by Dan Henry | 1 reply |  Last reply about 6 years and 2 months ago by Solar Geek

    I’m considering installing a solar water heating system as part of a renovation in an old house. How do I figure out how to size the system? What if I plan on using part of my property as an apartment – how does that affect how the system is configured?

  • Dan,

    Solar water heaters are usually sized to the number of occupants and anticipated usage. Louisiana only allows “indirect active” type solar systems to be installed because of their redundant water safety features, so that generally means a certain amount of “collector” area on the roof, and a certain storage tank size.

    A nice old document from NREL ( ) says more than you’d ever want to know, including:

    “Solar storage tanks are usually 60-,
    80-, or 120-gallon capacity. A small (60 gallon)
    system is sufficient for 1 to 3 people, a
    medium (80-gallon) system is adequate for
    a 3- or 4-person household, and a large
    (120-gallon) system is appropriate for 4 to
    6 people.
    A rule of thumb for sizing collectors: allow
    about 20 square feet of collector area for each of the
    first two family members and 8 square
    feet for each additional
    family member if you live in the Sun Belt.
    Allow 12 to 14 additional square feet
    per person if you
    live in the northern United States.
    A ratio of at least 1.5 gallons
    of storage capacity to 1 square foot
    of collector area prevents
    the system from overheating when
    the demand for hot water is low. In very
    warm, sunny climates, experts suggest
    that the ratio should be at least 2 gallons
    of storage to 1 square foot
    of collector area.”

    Solar Geek posted on November 10, 2012
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