What is “passive” solar?

We’ve focused on three major ways of using sunlight to generate energy: solar thermal for heating water, photovoltaics that turn sunlight into electricity, and large systems that make use of concentrated solar power. These are all forms of what we call active solar energy, because they require systems that actively convert sunlight into other forms of energy. But if you get involved in architecture or construction, you will also hear a lot about passive use of solar energy.

Generally speaking, passive solar refers to techniques that take advantage of sunlight without converting the energy into other forms. These techniques are used to improve the energy efficiency of a building. As a simple example, imagine planting deciduous trees (those that shed their leaves in the fall) that can shade a building. During the summer, these trees will provide shade to the building, helping to keep it cool. During the winter, when their leaves are gone, they will allow most of the sunlight through, helping to keep the building warm.

Architects and builders have developed many innovative ways of taking advantage of passive solar to reduce energy demand. In some cases, these techniques have been found to reduce the energy use for a building more than 75% compared to what it would have been without those passive solar innovations. It is worth learning more about passive solar techniques, so that if you are ever involved in a building project of any kind, you can make sure that passive solar methods are used to their fullest, making the building as energy efficient as possible.