A house that has any of the following characteristics which hurt a solar power system installation and investment: a shaded roof, small roof spaces, multiple roof vent pipes, expired roof material, breakable roof material, northern roof orientation, south, west or east chimney location, numerous roof lines, low dead weight tolerance, multiple floors, steep roof pitch, receives less than 5 hours of direct sunlight per day, absence of a utility net-metering program, monthly electric bill under $100, and less than a 200 AMP electrical service box.
Person 1: A tree shaded 800 squarefoot multi-level house built in 1970 with clay tile shingles, 100 AMP electrical service, a chimney on the west side with bathroom and attic vent pipes on the south facing roof in the front is totally solar coal.

Person 2: That's solar coal for sure!
by Sheldon's Solar, LLC November 29, 2010
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