I should add, the most sensible way to get winter solar gain but good summer ventilation is to have removeable panels. Frame with 2x4 or such, cover with Suntuf or similar greenhouse-type plastic product. Bolt on (using wingnuts) for winter; remove when nice weather arrives. Have permanently-installed 1" welded wire mesh underneath.
Have a cleverly-calculated amount of roof overhang can also help a bit, but only in deeper sunporches, not for a very shallow or lean-to one.
I think you will need to have it clear in your mind whether you are trying to get actual solar heating -- in which case you want a SHALLOW sunporch, backed with a dark-colored wall with minimal mass -- or just a sheltered sunny protected area for chickens to hang out in January, in which case deeper is better because it gives them more room, and maximal thermal mass (possibly as a half-height wall partway back, near the limits of where sunlight goes in Jan/Feb) will help mediate temperatures night and day.
Just some thoughts,
Pat
Have a cleverly-calculated amount of roof overhang can also help a bit, but only in deeper sunporches, not for a very shallow or lean-to one.
I think you will need to have it clear in your mind whether you are trying to get actual solar heating -- in which case you want a SHALLOW sunporch, backed with a dark-colored wall with minimal mass -- or just a sheltered sunny protected area for chickens to hang out in January, in which case deeper is better because it gives them more room, and maximal thermal mass (possibly as a half-height wall partway back, near the limits of where sunlight goes in Jan/Feb) will help mediate temperatures night and day.
Just some thoughts,
Pat