Using Solar Energy to Heat Your Greenhouse

Heating your DIY Greenhouse, as we have previously covered, can be one of the most expensive parts of ownership. While there are many great potential heating systems available to the home gardener, not everyone can afford the expense of purchase and upkeep that those systems require. If you have already taken the time to calculate the heating needs of your greenhouse, and have reviewed energy costs in your area, you may already be aware of this fact.

Just by building a greenhouse you already have an understanding and appreciation for solar energy, you use it everyday to help your plants grow and have built a greenhouse to take advantage of it. While your first thought on hearing about the idea of using solar energy to heat your greenhouse may be one of expensive panels, batteries and heating elements; simple, cheap and time tested methods do exist to help out the gardener on a budget.

In order to build and plan for solar heating, you must first have a basic understanding of how solar energy works. Heat arrives through solar rays in short wavelength form. These short wavelengths come in contact with and heat objects within the greenhouse; the glazing of your greenhouse allows these short wavelengths to easily enter into it. Once the items inside of your greenhouse begin to radiate their warmth, they do so, but in a long waveform that does not easily escape your greenhouse’s covering. (The greenhouse effect works the same way with the planet and our ozone layer)

Using this principle we can create what are known as “heat sinks”. Heat sinks are nothing more than items that retain and then

Solar Heated Greenhouse

emit heat when needed. Inside your greenhouse, rocks, wood, benches and even concrete can act as a heat sink; absorbing warmth during the day and giving it back to the greenhouse at night when needed.

Your heat sinks can be inexpensive; rocks, bricks or even concrete blocks as mentioned above. If you happen to have some 55-gallon drums sitting around; paint them black, put them in your greenhouse and fill them with water. A 55-gallon drum of water heated to just 70 degrees Fahrenheit will have roughly 10,000 BTUs of energy to give back to the greenhouse at night. These barrels can be located under your planting benches or raised gardening beds to be out of the way.

There are of course more expensive options for having solar heating inside of your greenhouse. Several manufacturers produce stainless steel tubes that are filled with a special substance know as calcium chloride hexahydrate. This substance actually changes from a solid to a liquid around 85 degrees and can store a vast amount of heat energy.

As with any heating system, you need to consider its design and intended purpose. Passive solar heating such as a 55-gallon drum of water will not work in the dead of winter in Maine, but it will extend you growing season later into the fall, which is most likely what you are after. These types of small steps and areas of understanding can make your DIY Greenhouse even more enjoyable, while saving you money and improving your plant’s health.


Leave a Reply