An open design aids heat and light distribution. They work well on sunny days and in cloudy climates by collecting and using every bit of energy that passes through the glazing, direct or diffuse. Masonry thermal storage materials include concrete, concrete block, brick, stone and adobe. Indirect gain is when sunlight first strikes a thermal mass, located between the sun and the living space, commonly called a Trome wall. An attached greenhouse is a combination of direct and indirect gain.
Isolated gain is when collector and storage are isolated from the living space.
Temperature fluctuation can be controlled by operable windows or vents, shading devices, and a backup heating system. Incorporating solar design into a new structure is fairly simple and low cost. There are no special materials required-just a rearranging from typical design. Looking at ordinary homes, I usually see picture windows facing the road, when it would have been a simple change initially to orient to the south, providing a lasting energy gain in winter, instead of a loss. Also, many homes are built with brick or stone on the outside of the insulated shell, when a reversal of positions, with insulation exterior to the thermal mass, would greatly improve the homes' thermal stability and comfort at little or no added cost.