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Sizing a Solar Hot Water System
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?Replies
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 ( http://www.nrel.gov/docs/legosti/fy96/17459.pdf ) 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
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