Solar Energy: Understanding Active and Passive Solar Heating

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  • 0:07 Solar Energy
  • 1:15 Passive Solar Heating
  • 2:57 Thermal Mass
  • 4:17 Active Solar Heating
  • 5:47 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Solar energy is the energy we harness from the sun. We can use this energy to heat our homes. Learn about the design elements needed for passive solar heating and the equipment needed for active solar heating.

Solar Energy

Step outside on a cloudless summer day, and you will experience the power of the sun. In fact, the sun provides enough energy in just one hour to power the earth for an entire year. This energy obtained from the sun, or solar energy, is free for us to use, environmentally friendly and essentially never runs out. It sounds like the perfect solution to ending our dependence on dirty and expensive fossil fuels. The trick is discovering efficient and practical ways to harness the energy from the sun.

Now currently, solar energy only meets a small portion of our energy needs; however, thanks to growing concerns about the cost and environmental impact of burning fossil fuels - such as oil, coal and natural gas - harnessing usable energy from the sun is getting a closer look. One of the great things about solar energy is that we can use both simple and complex strategies to capture it and use it for heating. In this lesson we will take a look at two strategies for capturing the power of the sun: active and passive solar heating.

Passive Solar Heating

Passive solar heating, as you may have guessed, is passive. In other words, it takes advantage of the existing heat generated by the sun to heat living spaces. We have all witnessed passive solar heating when we climbed into a car on a sunny day. Rays from the sun entered the car windows and were absorbed by the car's seats, panels and floor, and this heat got trapped in the car and warmed the interior.

Passive solar heating is also what makes greenhouses effective at growing plants all year round. When the sun's rays penetrate the windows of the greenhouse, the items inside the greenhouse absorb and then release the heat, providing a nice environment for the plants to grow.

Passive solar heating can be used in your home to cut your wintertime heating bill and improve comfort. But to fully take advantage of solar energy in this way, some planning is required. Because passive solar heating does not involve any mechanical devices, a home designed for passive solar heating will need to be positioned in a way that allows heat from the sun to enter in the winter and be rejected in the summer months. This positioning will vary by local climate conditions, but in the Northern Hemisphere, a good passive solar design uses south-facing windows to capture the sun's rays. In the winter, when the sun is positioned low in the sky, the southern-facing windows allow the sun's rays to enter through the windows and heat the home. In the summer months, when the sun is positioned high in the sky, a passive solar home will use a large overhang for shade. This prevents the sun's rays from entering the window, keeping the home cool.

Thermal Mass

Beyond being positioned correctly, a passive solar heating design will also depend on thermal mass of the walls, flooring and other objects within the home. Thermal mass can be defined as a material's ability to absorb, store and release heat.

When the sun's rays enter the home in the winter months, the heat energy is absorbed by the materials inside the building that have a high thermal mass. This would include materials that are dense, such as stone, brick, concrete or ceramic tile. These materials absorb and hold onto heat during the period of time that the sun shines on them and then slowly release that heat throughout the nighttime, keeping the home at a more stable and comfortable temperature.

If you live in a climate that has regular snowfall each year, you can get a good idea of how thermal mass works by thinking about the first snowfall of the season. What you likely notice is that snow easily melts on the road surface, but it clings to the grass and the trees. This is because the dense material that makes up the road has a high thermal mass, and it has held onto the sun's heat, causing the snow to melt on contact. The grass and trees are less dense and have a low thermal mass, so the snow does not melt.

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