All greenhouses use the warmth and light of the sun to grow crops. However, a solar greenhouse further harnesses the energy of the sun, not only to grow crops but also to heat and ventilate the greenhouse.
Where traditional greenhouses rely on external heating sources to keep the temperature up during the night, cloudy days and during winter, solar greenhouses rely solely on the heat provided by the sun.
By carefully designing, orienting and choosing materials, solar greenhouses make use of natural processes to store heat during the day and release heat during the night. A solar greenhouse is really a solar-powered greenhouse.
Since solar greenhouses retain solar heat better than a regular greenhouse, these types of greenhouses allow gardeners to grow a large variety of plants that are out-of-season; even year-round.
Solar greenhouses are more cost-efficient than regular greenhouses, especially if you intend to grow fruits and vegetables out of season or all year round. It’s not uncommon for solar greenhouses to grow citrus, avocados, and tomatoes using a lot less energy and water than regular greenhouses.
Why are solar greenhouses better than regular greenhouses?
Solar greenhouses achieve all this by adhering to the basic principles that make them different from regular greenhouses:
While it is possible to buy pre-made solar greenhouses, it doesn’t have to have to be too difficult to build your own. Keeping in mind the five basic principles or solar greenhouses, as listed above, let’s look at some tips and tricks to keep in mind when designing your own solar greenhouse:
In solar greenhouses, it’s important to reach the right balance between high insulation and the ability to let enough light through.
In most cases, gardeners choose to add an extra layer of insulation to the glazing by way of a special polyethylene film (IR films or Thermal Films) that helps reduce heat loss. Consider ways to increase the insulation of your glazing, for example by working with a double air-filler layer.
In either case, look for a material that allows for at least 70% or light transmittance (or VT) and a solar heat gain of 0.6 or higher, while at the same time having a low ratio of heat lost to an outside or high insulating ratio.
As a rule of thumb, the long side of your greenhouse should face due south to catch the most amount of sun. This sun-facing side will most likely be completely covered in transparent glazing to maximize heat absorption.
The glazing on this south-side of your solar greenhouse should have a slope compatible with your latitude to help catch the most sun during winter. To calculate the degree of slope, figure out the latitude of the area where you will place the solar greenhouse (you can easily find this online) and add 10 to 15 degrees.
For example, the latitude of Tannersville, Pennsylvania is 41 degrees, so the slope of the glazing on a solar greenhouse placed in this area should be somewhere between 51 and 56 degrees.
After having put thought into how to insulate the most vulnerable part of your solar greenhouse; the glazing, it’s time to think about how to insulate the rest.
Since the north-facing wall will only get little sunlight and energy, it’s best to insulate it as best you can. Remember to also insulate the floor. If you live in a particularly cold area, you can also add a layer of pressed grass or straw during the winter months.
You might also want to consider burying part of your greenhouse in order to maximize insulation. Underground greenhouses have excellent insulation against both the cold of winter and the heat of summer. As an alternative, you could place bales of straw against the unglazed outside walls.
The whole point of all the glazing, orientation and insulation is to allow the heat-storing materials in your solar greenhouse to absorb the most heat possible, store that heat, and then release that heat when the temperatures drops (like during the night).
In a conventional passive solar greenhouse, the heat storing material (thermal mass) will be provided by water. The water is stored in dark, non-reflective plastic containers.
As a rule of thumb, you can use this equation:
Extending the growing season: 2.5 gallons of water for every 2 feet of glazing
Growing year-round: 5 gallons of water for every 2 feet of glazing.
If you live in a particularly cold region, you might need to use a solar greenhouse heater during the harshest part of the winter, especially if you live in an area that is usually overcast or cloudy.
When designing your solar greenhouse, remember to think about ventilation. Not only do you need a way to regulate heat during summer, but a healthy air flow also helps regulate moisture and provides plants with much-needed carbon dioxide.
There are three types of ventilation:
Finally, remember that venting, insulation, thermal mass, glazing and orientation all interact to create an environment that will boost plant growth. Once it’s set up, you will be able to enjoy your favorite fruits and vegetables all year-round!