In most of the country, heat is a bigger energy problem than electricity, and it cannot be solved with more panels. Wood is the classic answer where there is wood; propane is the clean, quiet one; a heat pump works in the shoulder seasons; electric resistance heat is impractical as primary heat on almost any off-grid solar system. The right answer is usually two of these: one primary, one backup.
The number that sizes all of them is the building's heat loss in BTU per hour at the design temperature, which is mostly about insulation and air sealing. A tight 800 square foot cabin in a cold climate heats on half the wood of a drafty one. Spend on the envelope before the stove.