Heating Your Homemade Greenhouse With Active Solar Energy - Part I

If you had a large commercial greenhouse, you'd probably heat it with natural gas or propane in the winter, and write off the expense as part of doing business. This just isn't feasible with a homemade greenhouse. The cost of fuel would be prohibitive.

Let's discuss greenhouse heating in the winter with active solar energy that can be stored for release when the sun isn't shining.

First of all, a homemade greenhouse is usually much smaller than what you might find in a commercial operation. This makes it more difficult when it comes to regulating heat. Any heat that you get built up can quickly be released through leaky seams and doors that are opened too frequently and for too long.

Second, it is typical for a homemade greenhouse to be made of a single layer of plastic film. This provides little insulation value, so when the sun goes down, the temperature drops like a rock and quickly matches outside temperatures, or only a degree or two warmer.

Now, add a couple of days with limited sunshine, and you have a cold greenhouse that probably is the same temperature as outdoors. It only offers protection from the wind and snow, but doesn't have the ability to release stored energy to help moderate temperature swings.

One way to tackle this problem is an active solar heating system that makes use of solar energy during the day, and stores it for use when the sun isn't shining. Here is one approach.

Bury hot water piping under the floor of the greenhouse walkways and beds, and pipe warm water through it from one or more solar collectors. This warms the floor and allows the soil to act as a "thermal battery" to keep greenhouse temperatures elevated during the night and when the sun isn't providing warmth during the day.

In my first greenhouse, I buried hot water piping about one foot deep in all areas where it was possible to lay a trench. A foot or more deep protects the piping from shovels and roto-tillers, and gives you plenty of moist soil above for storage of energy. If you can keep the piping a foot or closer together, the heat will have a good chance of saturating the soil with heat on its way up to the surface. Use smaller piping, like one half inch or three quarter inch to provide lots of surface area for releasing heat.

The next step is to create an insulated reservoir about 4 to 5 feet deep. The reservoir needs an inlet near the top for adding water, venting, and to allow water to return from the circuit. It also needs an outlet near the bottom for the pump that will circulate water through the system. I used a stainless steel tank as the reservoir so plumbing fittings for the pump would be secure.

I attached the temperature probe from an indoor/outdoor thermometer low on the side of the tank so I can keep an eye on tank temperatures using the remote display mounted on the greenhouse wall. The tank was then placed inside of a 55 gallon plastic barrel and insulated with paper and fiberglass material.

The pump was mounted outside the plastic barrel and plumbed through to the steel tank. The pump was covered with a 5 gallon bucket mounted horizontally. Everything was strapped in place and sealed against dirt and water intrusion.

This deep reservoir design allows warm water from the system to drain back into the reservoir after the system is shut down. This large volume of warm water provides freeze protection to the reservoir and pump.

The system can be operated manually or set up with a high temperature switch to activate it when the sun is shining. All said and done, the system heats the ground to about 106 degrees in the spring over several hours of operation. It has worked flawlessly, and clearly showed its benefits once when nighttime temperatures dropped to just below freezing and the inside of the greenhouse stayed at 43 degrees.

The system costs about $450 to construct, using a pump, insulating materials and about 150 feet of three quarter inch Pex piping that were new from the home improvement store. The balance of the system was used or obtained at the scrap yard. There is no fuel bill for this heating system, and the electricity costs for the pump are about 20 cents a day. That's a cheap way to use active solar energy for greenhouse heating.

Clair Schwan is an experienced vegetable gardener with three greenhouses that are all heated with active solar energy systems. These solar energy systems help him make his vegetable gardening a year round adventure. See details of his greenhouses and heating systems, and vegetable gardening tips at http://www.frugal-living-freedom.com