The first thing to understand about a passive solar system is that it traps and stores energy, but it doesn’t generate electricity. So, while it can greatly improve your home’s energy efficiency, it’s not a replacement for active solar.

The sun produces both heat and light, and passive solar uses the sun’s heat to warm a house. That’s different from active photovoltaic (PV) solar systems, like those produced by SunPower, that use the sun’s light to produce electricity and power household devices.

How does passive solar work? Picture a sunlit room on a winter’s day. Even though it’s cold outside, the sunlight coming through the windows warms the room. That “greenhouse effect” is passive solar. And it’s important because the correct use of passive solar can cut a home’s electricity use.

To do that, homeowners have to boost the amount of passive solar their house collects and retains. First, that requires plenty of south-facing windows to let in as much sunlight as possible each day.

Also, homeowners need to use building materials that hold in the sun’s heat, including concrete, brick, stone, and tile. These materials are called “thermal mass.”

Distributing the heat these materials collect is important. In most cases, the heat will naturally spread throughout a house. However, small fans can help the process along.

Finally, homeowners need a way to control how much heat is being generated, especially in the summer months. This can be done with removable blinds, shutters, awnings, or roof overhangs that cover or shade the windows. These vital pieces keep down the need for air conditioning when it’s hot outside.

Good insulation also is vital to making passive solar work. All that heat energy needs to be held in for as long as possible.

The effectiveness of passive solar depends a lot on geography. Many homes are not properly oriented toward the sun to make it work. Others have been built in regions with lots of clouds or rain, and that limits the impact of passive solar.

Passive solar usually requires homeowners to invest time and money upfront, but the long-term payoff can be tremendous. The energy it harnesses lowers energy bills while reducing your home’s carbon footprint.

Passive solar is a great way to improve your home’s energy efficiency. However, it’s not a replacement for an active solar system that generates its own electricity and can power your home even in the event of a grid outage. Active solar systems are more versatile and reliable and harness the same clean, free energy. If you're considering going solar, get a free quote.