What Is Solar Heat Gain?

By Darrell Smith
If you have stepped inside a greenhouse, you may have experienced solar heat gain. The inside of the green house is noticeably warmer than when you were outdoors.

The sun’s infrared light, which is invisible to our eyes, is a form of radiation that creates heat. More than half of the sun’s output is in the form of infrared light.
While the sun rays hit the earth’s north and south poles at an angle, the same amount of sun rays hit the equator regions more directly and in a more concentrated manner. This is why locations nearest to the equator have generally hotter climates and it also why in summer months, when the sun is more directly overhead in relation to the earth, it is also much warmer in our Northern Hemisphere.

Clear glass transmits a high percentage of the sun’s energy indoors. With the sun’s infrared energy hitting the earth and our homes, objects inside a home, such as floors, furniture and nearly any material, when struck by it absorb the sun’s energy and increase in temperature. The absorbed heat energy is re-radiated in the room, making it warmer. As this is a continuing process the interior room space gets hotter and hotter. This is one reason why when you sit next to an unprotected glass window, your skin gets warm, or if you are wearing dark clothing, when you brush the surface with your hand, the material feels noticeably warmer, or even hot. These are all examples of solar heat gain.

When the sun’s heat energy goes to work it can heat up your home quickly, especially if the doors and windows are closed to the outdoors, such as when you are running air conditioning. The sun’s solar heat gain can have several negative impacts on your home’s interior, such as creating hots spots nearest to doors and windows, making your air conditioning system work harder and causing the system to use more power as it attempts to achieve your thermostat’s temperature setting.

Knocking down solar heat gain is one of window film’s best attributes. While window films differ in how they perform based on how they are manufactured, they can reduce solar heat gain in your home by as much as 80 percent. This means fewer if any hots spots, a more even interior room temperature and less power needed to help your air conditioning system keep up with the sun’s heat. This benefit is especially noticeable when the sun is at it’s peak energy transmittance during the day, which would be after 12:00 pm, and utility companies are having to produce more power to meet the increased peak demand from both homeowners and businesses.

Window film is a smart way to reduce solar heat gain and and save money on utility costs by as much as 10% or more, year in and year out. It may also reduce your overall carbon emissions and that’s good for all of us.