Passive solar heating is a design approach that uses the sun's energy to maintain comfortable indoor temperatures without mechanical systems. It involves strategically placing windows, walls, and floors to capture and store sunlight during the day, which then radiates heat into the living space at night. Key elements of passive solar heating include thermal mass materials, such as concrete or brick, that absorb heat, and south-facing windows that maximize sunlight exposure. This method is energy-efficient and can reduce heating costs, making it an environmentally friendly option for home design.