Solar Power & Energy

Solar heating by convection is a natural process which involves trapping air and letting it warm up before releasing it back into a given space.

Convection heating is often used as a solar heating source because the two naturally go hand in hand. By trapping air into a confined space which has sunlight hitting it, the trapped air is heated up naturally by the solar power of the sun. This same type of natural heat transfer is also used for solar water heating too.

Now you may or may not already know that hot air rises, and this is a key component to solar heating with convection. Inside your home, the coldest air is closest to the floor and the warmest is up high along the ceiling. As the warm air at the top of the room cools it drops lower, and as the cooler air is warmed up, it rises.

Now, to use this process naturally in your home - and particularly to make use of the warming power of solar energy - you need to find or create a way to have the cool air go into a space that is warmed up by the sun. That same space usually allows the warm air to escape once it has reached a certain point.

In many cases, all you need is some sort of confined area to direct and control airflow. If you have a sunny window for example, you could put a piece of black fabric, wood, plactic or metal against that window frame to trap the air in for a short period of time. There needs to be a space between the black material you choose to use, and the glass window pane itself. Usually this space is at least a few inches, but there can be as much as 5-6 inches between your window glass and the black material.

This black material is going to be used to draw heat more efficiently and effectively from the sun. When direct sunlight hits dark colored objects, those objects absorb heat quite quickly. And it’s this heat that you want to absorb, because that will in turn heat up the air between your dark backing and the glass window pane.

You’ll need a small airflow opening at the bottom and top of your black window covering object. The opening at the bottom will allow cool air to enter from near the coolest floor areas of your home. The cool air will enter the space between the window glass and black object naturally, and once it’s in there it will begin to warm up because of the warm solar sunlight.

As that air warms inside the window space it will start rising upwards naturally, and this is why you need open space at the top of your solar heater enclosure too. The warming air will continue to rise up until it escapes out of the open space at the very top.

You’ve probably realized by now that this solar heating process helps create an air circulation flow in your home naturally. Because the cool air is naturally down low, it will easily enter the open space at the bottom of your solar window heater. And because it naturally escapes out the top at a much warmer temperature, it will begin to drop towards the floor as it cools to room temperature. As this circulation continues, the overall air in the room becomes warmer and more comfortable naturally.

Be aware that convection heating works exactly the same way as convection cooling though. If you don’t block the lower air vent at night time when there is no sunlight to provide solar power within your little window heater, then your air flow circulation will reverse. The warm air will start going in at the top, the window will cool the air quickly, and that cold air will be released out of the bottom of your heater. This is excellent for solar cooling in the summertime but it’s not what we want for solar heating in the winter.

Some people have a difficult time believing that a simple solar heater like the convection window technique noted above will actually do much good at heating up a room or home. You may be surprised at just how well this works though. If you were to take a measurement of the air temperature going into the window heater and then measure the output, you can see the full effectiveness of this natural solar heating technique. It’s not unusual to have cold air going in at fifty degrees, and have it coming out at over 100 degrees or more.

The larger your convection solar heater is, the more change the air has to accumulate heat as it travels upwards. Some people like to put a small fan at the top vent so they can pull the warmer air out more quickly. There’s nothing wrong with this of course, but keep in mind that the faster you pull the warm air out, the less chance it has to gather solar heat. So if you’re going to use a fan to force the warm air to circulate, you’ll have better results with a larger version of this type of solar heater.

I should also note that you don’t have to build a convection heater yourself either. You can actually buy solar home heaters ready made from commercial sources. Many of these heaters can be mounted to a wall or awning, and have just the in airflow vent and out airflow vent coming into the house. Ready made solar convection heaters are convenient, and prices are coming down quite quickly these days so they’re nicely affordable in most cases.