Don’t all greenhouses use solar sunlight? Yes and no. Many greenhouses use sunlight to grow plants, but add electricity, gas, and other power devices during cold winter months to keep the plants from dying. Growing crops in northern latitudes where winter months freeze, and sunlight is minimum, is traditionally done by installing light fixtures and/or greenhouse heaters. This may sound like a simple solution, but when you get the monthly electrical bill, you’ll find it’s no solution at all.
Fortunately, growers have developed greenhouse designs that get around this problem- We call it the Solar Greenhouse (AKA, passive solar greenhouse). A pure solar greenhouse creates energy by optimizing sunlight and positioning (facing) the grow-plant wall toward the south. This way the greenhouse will capture heat during the day, then let it back into the environment at night when it’s cold. Along with the orientation positioning; proper insulation, thermal mass, and clever glazing practices combine to creates a greenhouse that uses little if not any outside power .
- Orientation is positioning the greenhouse plant area wall towards the south to maximize sunlight. Pointing it directly at the sun can overheat the building and harm plants, especially in the summer. It’s best to alter the south-faced wall marginally to the east at roughly 45° due south. This provides plenty of sunlight for plants with morning sun, and avoiding the heat that increases in late afternoon.
- If you can’t point southeast for whatever reason, orienting slightly to the west will suffice, though you may have to shade the plants in midday when the heat rises. *Tip, For optimum sun exposure, build the south-faced wall sloping at 45°. The north facing wall will be sloping at roughly 80° giving the south wall an expansive surface of sunlight.
Your greenhouse needs a way to control the fluctuating temperatures and humidity to provide an optimum environment for your plants. That’s where energy-efficient insulation comes into play for your crops and the fish tanks. Using the proper insulation, and where to install it, can also save you money by reducing use of energy.
Greenhouse Insulation is essential for minimizing the heating expenses, especially if you live in a cold region. Maintaining high temperatures in your greenhouse during the winter months is crucial to health of your plants. How can you get around excessive costs, and keeping your plants healthy at the same time? Simple, install insulation.
Types of Insulation
- The plants in aquaponics grow beds need protection from fluctuating temperatures, so it’s important to insulate the south facing wall of the greenhouse. The insulation should surround the wall up to the height of the plants, safeguarding them from hot temperatures in the day, and cold at night. This can be done using reflecting foil wrap, or even covering the wall with white paint.
- An inexpensive material that many greenhouse owners use is good old bubble wrap, not the type used for packing, but horticultural bubble wrap. This not only stabilizes the temperature but allows light with UV filtering.
- To insulate the cold north side wall with its limited sun exposure, use bubble wrap wedged between 2 layers of thermal insulation foil. This will induce a reflection of both light and heat back into the greenhouse.
- Recycled plastic bottles can be used as a portable plant cover as an insulation. This doesn’t cost anything and acts as a miniature greenhouse capturing warm air and even protects against insect pests.
- Recycle used Polystyrene boxes and insulate by wrapping around trays of plants to keep the roots warm in cold weather
- Rigid Foam board is often used in walls and underground. It’s moisture resistant and inexpensive. Polystyrene (blocks of Styrofoam) is a good insulation for walls, and humid areas underground. Polyiso is a plastic insulation that’s inexpensive, absorbs moisture, and can help insulate walls.
Insulation is also used to keep cool air in the greenhouse during hot summer months. There are several ways to cool down the plants including:
- Install vents- ventilation moves air-flow to cool the plants.
- Blinds can be installed outside the greenhouse windows to filter out the the sun exposure.
- Shade cloths can be used to decrease the sun’s radiation but be sure these knitted or woven cloths are of 40% or less blockage. Otherwise they will shade the plants into wilted unhealthy vegetation.
- Damping down water on hard surfaces that raises the humidity in the building. This helps plants deal with heat by increasing moisture in the air.
- Depending on the plants you’re growing, and the temperatures in your region, you can create a cooler environment by using bright aluminum as a reflector.
When Warmth is Needed You Can Insulate to Avoid Heat Loss
- Heat up Areas by painting dark colors near the plants.
- What about the very top of the roof? Due to the angle of the sun, this area has minimal effect on the plants. It makes sense to insulate this portion of the roof and add to the overall energy efficiency of the greenhouse.
- Another obvious heat loss, but easily solved, are cracks and gaps in the walls. Use silicone caulking wear ever you can and monitor it at least twice a year. You can’t block them 100% with all the gaps that open during temperature fluctuations, but it can be reduced significantly.
- Greenhouse covering- Also called floating row covers, these inexpensive sheets can save your plants if freezing temperatures are forecast, just be sure you remove them when the freeze is gone. You can find them online as horticultural fleece or cover sheets.
- I know we said our aquaponic greenhouses don’t need soil, but if necessary, staging a pile of compost in the middle of the building will warm up the area very nicely.
Thermal Mass Materials
These are insulation elements that have the capability to capture heat during the day. When temperatures plummet at night, the trapped heat is used to warm up the greenhouse. These passive thermal mass substances (AKA Heat sinks), are media that absorb heat. They can be tanks or barrels that hold water, or even stone, and concrete.
Since we’re using an Aquaponics system in our greenhouse, the tanks are already in place, and are positioned adjacent to the north-face wall. These medium size systems typically hold 55 gallons of water and can serve as a heat sink capturing warm air during the day.
For smaller greenhouses, you can use plastic jugs containing water. The one-gallon jugs are placed throughout the plant beds and can be painted black to strengthen the heat absorption.
Greenhouses have always provided various amounts of sunlight and warmth but gave little importance to the performance of energy efficiency in the system. Nowadays, with our smart phones, smart homes, and smart teenagers (lol); we also have smart greenhouses. Solar greenhouse designs can now balance glazing materials against insulation elements, raising energy efficiency to another level.
When I first saw the word “glazed” way back when I was first interested in building a greenhouse, the only thing I knew about glazed involved Donuts (lol). The Unabridged Dictionary quotes glazing as “the act of furnishing or fitting with glass”. The word “glaze” when referring to a greenhouse, is defined as a transparent material integrated into its walls and roof, whether the wall be glass or any plastic covering.
In order to understand why glazing works, let’s start with the influence it has on plants. Just like us humans, plants are only affected by a small portion of the sunlight spectrum. Plants grow best when exposed to the red and blue segments of the spectrum.
Plants need sun exposure as a source of light and heat in order to grow properly. How are you going to control heat and sunlight year-round, especially during winter? As mentioned before, position your Greenhouse glazing in the direction of the sun, that means towards the south if you’re in the Northern Hemisphere.
Since we can’t see these portions of sunlight, we can’t evaluate the glazing material by simply looking at it. For example, common residential window glass is often coated with tints that block out large portions of the spectrum that plants need. We need to go over the different types of cover materials available before we know which will work best for our greenhouse.
Picking the Right Materials
The glazing material you choose determines the level of sunlight exposure allowed in, the durability of the material, it’s weight in relation to the type of frame you’ll need, solar energy efficiency in the panels/sheets, and translucent compared to transparency .
These materials are great at stabilizing the sunlight so that plants get what they need, but without getting too much exposure. However, they’re not particularly good at keeping heat in, that’s where insulation comes in (see in Insulation section).
Here is a brief check list to consider for your glazing material choices:
- Is it Tough against rock, hail, and snow fall?
- Is there a guarantee that it lose its clarity over a reasonable amount of time ?
- What about its longevity overall?
- Simplicity of installation?
- Energy efficiency?
- Light diffusion?
- Light transfer level?
- Operating costs of glass panels?
Glazing materials come in 3 basic categories:
1. Glass (Type 111 glazing material)
- Glass is pretty much old school, being the traditional option before technical advances developed other choices. In my opinion it’s still has the better appearance over other glazing types. Many greenhouse growers still consider glass to be their favorite because of its enduring long-term investment.
- The Pros: durability and long life span, commonly available, aesthetics, and recyclable.
- Cons: Brittle, most expensive to acquire (or replace) and install, excessive humidity between panes, heavy so requiring stronger frames, inadequate thermal efficiency
- Tempered or laminated glass (safety glass) are used in greenhouses because of their shatter-resistant attributes. Maximum sunlight is allowed through
2. Rigid Plastic Covers (Type 11 glazing material)
- These include polycarbonates, fiberglass, and Acrylic (PMMA Poly methyl methacrylate). Rigid plastics are much lighter than glass, and the Transmission of light is very good. However, plastics tend to yellow over time from UV in the sunlight, limiting the amount of light entering the greenhouse.
- Polypolycarbonate materials- This comes in double or triple layers that act to increase the insulation effect, but the more layers, the higher the price. It’s a strong sheet that last up to 15 years but tends to yellow around the tenth. There are some manufacturers that claim 100% UV blockage with panels that do not discolor.
- Polycarbonate is exceptionally flexible and shock resistance up to 200 times compared to glass. The multiple layered materials are terrific for diffusing light and increasing photosynthesis for plants. Keep in mind that the interior of the layers can cause condensation, but there are chemicals available that help reduce it. Also watch out for scratching of the surface
- Fiberglass-reinforced plastic- Fairly inexpensive and good for diffusing light, FRP’s come in both corrugated and flat. They are flexible and easier to cut and work with compared to other materials. Corrugated panels are usually placed on the greenhouse roofs for their rigidness and strength. Flat panels can be fit to windows and sidewalls, good for an inexpensive 2nd layer for insulation. Keep in mind that fiberglass plastics are very combustible!
- Acrylic- PMMA’s are commonly available in double layers and known for its exceptional light transmission and clarity. It’s fairly expensive in single sheets, and the price goes up with multiple layers. Acrylic panels are assumed to be the most suitable translucent glazing material for greenhouses for those who can afford it.
3. Thin Plastic Films (Type 1 glazing material)
Films included are Tefzel Film, Polyvinyl Chloride Film (PVC), Polyethylene Film, and Polyester Film. These plastic films currently dominate greenhouse covers because of their inexpensive films, of course this results in diminished longevity.
Tefzel Film has a 95% sunlight transmission, higher than any other glaze materials currently. There is also a double layer version that transmits light at a 90 % level.
- Polyvinyl Chloride Film (PVC) a widely used synthetic plastic polymer has an appealing variety of properties that make it a useful glazing material cover. It has an exceptional resistance to abrasion and fatigue. PVC film is unyielding to oxidation issues but will decompose with increased light and heat over 2 to 3 years. It also has characteristics that reduce heat loss at night when used as a covering.
- Polyethylene Film, like the other plastic films, are inexpensive in cost and installation. Because of its light weight it doesn’t need frame support. Polyester Film is higher in cost than the other plastic films but is a lot more durable. It is resistant to static electric charge that collects dust and other debris.
Additives That Enhance Performance
There are also Plastic Element Additives available you can form to employ and manage sunlight power and its heat. This can help you to control different wavelengths and absorption levels in the films, making it possible to create a broad range of micro climates using the film types I’ve gone over. These material additives include:
- Anti-Condensation Inhibiting
- Infrared Blocking Plastic Materials
- Light Diffusion Elements
- Anti-Dust Inhibitors
- Plastic Material Additives
- Anti-Condensation Inhibitors
- Infrared (IR) Blocking Plastic Materials
- UV-Blocking Materials
- Anti-Dust Inhibitors
- Light Diffusion Elements
Greenhouse Staging Plans
Staging a greenhouse, in short, is calculating zones of space in the building for all its components. Planning ahead the quantity and size of benches, shelves, fish tanks, pump(s), and other accessories, can save you time and money. There are questions that you need to address before moving forward:
- How about the plants? How many do you want? Are they small, large, both? You need to stage these before the growing season starts or you’ll wind up with a topsy-turvy system. A good practice to start with would be to separate your greenhouse into zones, for example:
- Where should you stage an Aquaponics system? Best Answer-> Place the grow bed plant containers near the south-face wall where they will get sunlight. Place the fish tanks near the north-face wall where the sun exposure can’t harm them.
- Staging the shelves and benches- As an example, if your greenhouse flooring space is 10ft X 6ft and you have to make room for a small aquaponics system, you’ll have limited space for shelving. The only way to get around this would be vertical multi-tiered shelves. If you have square footage of 10ft X 20ft and more, one level shelves may be enough. Still, this is all relative to the system verses the greenhouse sizes.
- What about greenhouse ventilation systems? The size and placement of the vents need to be decided ahead of time according to size of the greenhouse so hot and cold air are balanced.
- How about designating vegetables, herbs, and non-edible plants, in their own specified zone?