Passive solar energy systems, utilize solar energy with out use of any mechanical components. these include building design, building materials, building orientation and shadings etc.
Passive solar energy systems are those using the sun's energy directly for either heating or cooling purposes. Unlike photovoltaic or other technological solar power applications.For using in building one design the building to perform the function of heating, cooling or transferring the heat or the radiation from one part to the other in the building to the other for sake of distribution.
So, one exploit the building design and material to more or less condition it without use of air conditioning.
As for the equation above it represents the heat Q stored in a body having a mass m and specific heat Cp under constant pressure, T2 is the final temperature and T1 is the starting temperature of the body. So, it is the heat gained by a body when its temperature is raised from T2 TO T1. Q itself will be acquired from the absorption of the solar radiation.