I can grow all year round?
What is a Solar Greenhouse?
Aren’t all greenhouses solar greenhouses?
Today you and I are going to answer these questions and talk about how you can use a solar greenhouse on your homestead to grow even more food for your family. But first I have a story for you.
My Dream Greenhouse
When it came to adding a greenhouse to our homestead here in Wyoming, I knew I was going to need to find something completely out of the box.
Our season is, at its max, only 115 days. That doesn't give us much time to get a large harvest for our family. And things like sweet potatoes, some varieties of squashes we can't grow because our season is too short.
My greenhouse would need to be able to extend our growing season, be low cost, energy efficient, and low maintenance. And above all, supply our homestead with more. More abundance, more fruits and vegetables, and even more meat. I will share more about that later.
But we have a philosophy here on the homestead: we don't build something unless it can pay for itself in some way!
That meant we could not build a conventional greenhouse. We needed a greenhouse that would not take loads of electricity or fuel to heat in the winter. Here in Wyoming, we can get temps in the negatives. We needed a greenhouse that was low cost and efficient enough to grow year round in. I mean why else would you invest in a greenhouse if it can’t help you grow more. We need a greenhouse that would be low maintenance too. There are only five of us after all.
With all of these expectations, I went looking for a solution and it wasn’t until I came across the Solar Greenhouse that I knew we found the solution. I have spent years researching, drawing up plans, and squirreling away every penny I could to try to make this greenhouse of my dreams come true. We were set to break ground on it this Spring, but with the sky rocking lumber prices of 2021, we had to hold off.
But let me tell you, every fiber of being can not wait for this greenhouse to be built. We plan to break ground in 2022!
Let me tell you more about this greenhouse and how it may just become your dream greenhouse too.
What is a Solar Greenhouse?
All greenhouse use the sun, but the Solar greenhouse uses thermal mass and other energy save techniques to harness the sun to not only grow delicious produce but to also heat the greenhouse. Most greenhouse needs other means of energy like, fossil fuels or wood burning stove, to heat the greenhouse at night or thru the winter.
That is just the basic difference between a conventional greenhouse and a solar greenhouse. Let's dive in just a little deeper.
Differences between a Conventional Greenhouse and Solar Greenhouse
A Conventional Greenhouse use of glass or polycarbonate and shape does not help trap the sun's warmth but instead spends most of its energy trying to cool itself with large fans during the day and heaters at night to keep it warm.
A Solar Greenhouse on the other hand is completely opposite. Its design tries to trap as much solar energy as possible with its southern exposure and insulated northern wall. The north wall is insulated to reduce heat loss at night and on cold days. Vents are placed strategically to promote natural ventilation to keep the greenhouse cool when needed. A thermal storage mass is added to help store the sun's energy, usually in the form of natural heat storing objects. Like large amounts of water in black barrels, and stone that naturally holds the sun’s heat during the day and then releases it at night. This is called passive solar energy. And what gives the solar greenhouse its name.
The advantage of passive solar heat is that it can be built right into a solar greenhouse. The passive design will use little maintenance, compared to conventional greenhouse systems often do. A solar greenhouse must contain the following parts to be considered a complete passive solar heating system:
A collector: such as the double layer of greenhouse window glazing (glass, polycarbonate, acrylics, fiberglass or Poly plastic) that is faced to the south.
An absorber: usually the darkened surfaces of the north wall, floor, and water-filled containers inside the greenhouse.
A storage mass: normally the concrete, brick or water that retains the heat after energy has been absorbed. The distribution system: is the means of getting heat around the greenhouse using fans and natural circulation.
A control system: such as a movable insulated curtain or blanket used to prevent heat loss from the greenhouse at night. Roof overhangs that block the summer sun through the summer when the sun is at a higher angle.
The main difference is that the Passive Solar Greenhouse stores its own heat. Let’s talk about the two different types of solar energy system you can use in your solar homestead greenhouse!
Two Types of Solar Energy Systems
The two types are referred to as active and passive, the best system for a simple homestead solar greenhouse would be passive. But I am going to explain both and let you decide what works for you.
In a passive system, a thermal mass such as rocks, concrete, or water filled drums captures heat during the day and releases it back at night.
The active system is just that it needs action and requires electricity or another conventional source of energy to pump heated air into a storage area such as a basement filled with rocks or water drums. This system is more efficient than passive solar heating but is more expensive and more complex.
Both types of solar heating systems of course use the sun so work best in areas with a higher percentage of sunny days even if the days are cold compared to overcast days. Here are the more technical definitions of each.
Passive System: The sun's warmth is deposited and held in the thermal-mass heat sink during the day. At night this heat radiates out and keeps the greenhouse warm.
Active System: The sun's heat warms the transfer fluid (water or air) in a solar collector, it is pumped to another location and stored for redistribution as heat later or when needed.
Solar Heat Sinks (thermal mass) are materials used for capturing & storing solar heat usually in the form of water in containers; stacked water filled steel drums; concrete-filled cinder or pumice; brick, stone or adobe wall; masonry floors and walls; concrete slab on top of a bed of rocks; bin or loose pile of rocks or rock wall held in place w/wire-mesh are used in passive solar houses to store heat during the day and emit it into the living space at night.
Storage mass is also used to regulate heat inside your greenhouse so that it is not too hot during the day or too cold at night. The large areas of south-facing glazing on a passive solar greenhouse create a large amount of heat loss during the night. This can be compensated for with thick thermal curtains that are closed at night or a ventilation system that blows warm air in an active system from the bank and between the two layers of glazing.
Which Energy System is Best for the Homestead
The passive solar greenhouse would be the most efficient and low cost of the two systems. But I think the better question to ask would be which would be better for your situation. If you live in a place that has a high amount of cloudy days then an active system will be more beneficial for you. And if you live in a climate like mine, cold but lots of clear days, then a passive system would work best. I will also depend on what you plan to grow!
If you want to ensure year round growing so that you could grow plants that would not normally grow in your growing zone then you may need to invest in the active system so that you can have a more constant and continuous heat. But if you are thinking that you will be just using your solar greenhouse to extend your season but still grow cold hardy plants in the winter then a passive system would be best for you.
The point is you do you but be sure to look at the goals of your greenhouse first to help you decide what is best!
And don’t decide just yet as it is also going to depend on the design you chose to use too. I will share the three different designs in a moment. Each can use both passive or active solar systems but each will prefer one over the other. But before we get into designs I want to discuss how a solar greenhouse can help you grow year round.
How a Solar Greenhouse Can Help You Grow Year Round?
You and I have talked about the parts and pieces. But how does the solar greenhouse work to give you the benefit of growing year round?
Here is a brief explanation that covers the basics how a solar greenhouse operates:
The sun shines through the clear south facing windows in short waves. These waves strike objects in the greenhouse and are reflected as long waves.
The long waves cannot escape because of the glazing, this is a good example of the greenhouse effect.
Large objects in the greenhouse such as brick walls, rocks, water drums, concrete absorb heat during the day and return heat to the structure at night. The most efficient heat sink is water in a barrel.
The warm air (80-90F) from the greenhouse rises. And with proper ventilation that has both high and low openings, the vents establish a natural air circulation system.
The overhang and insulated greenhouse roof will keep it warmer in winter and cooler in summer. And how well the greenhouse retains heat will be subject to air leaks and drafts.
A well constructed greenhouse and has all windows, side walls and joints insulated and caulked to prevent heat loss.
By harnessing the sun’s rays a solar greenhouse can heat and cool itself through all seasons! Isn’t that amazing?
Let’s talk about the different design options you can choose from.
Three Different Solar Greenhouse Designs
Each of these designs have unique qualities and downfalls. But I am sure you will find one that is right for you and your property. Because no matter which one you pick you need to have a side that is directly south facing.
Connected to the Home
This first is the solar greenhouse that is attached to your home. There are many benefits to this design if you can make it work for you.
The lean-to type solar greenhouse is attached to your home by windows, a sliding door, or just a door. But in one way or another you have a place where air can move freely from the home into the greenhouse and vice versa. One huge benefit of this design is that the greenhouse can help lower heating bills for your home and vice versa in the cool of the night the house can heat the greenhouse. The other upside is you have a greenhouse connected to your home, where you can visit anytime you want without having to go outside first. This is amazing in the winter months when you want to harvest a little salad for lunch and you don’t have to put on 5 layers of clothing or tread through any deep snow. Plus all the fresh air plants made through photosynthesis will fill your home and the air won’t become stale through the winter months.
The only downside of this design is the ease of using your house’s heater for heating the greenhouse in the winter, which will surely raise your heating bill. Yes, the greenhouse will supplement some heat during the day. But not enough to counter the heat needed if you do not build any passive thermal heat systems in the greenhouse. Which is harder to do without a solid back wall and limiting growing area. As these greenhouses are limited in size. You can’t make one that is taller or bigger than your house.
Free Standing
The biggest benefit of a free standing solar greenhouse is that you can make it any size you like. You just need to keep the basic principle in tact. But remember the bigger you make it the bigger the thermal mass will need to be.
That is why most free standing solar greenhouse use the active solar system. Where there is a solar collector, and heat is pumped to another location and stored for redistribution as heat later. And this system is more expensive to run and build.
You would need to build a climate battery.
“A climate battery is a ground to air heating system consisting of a series of underground tubes that circulates air several feet below the soil surface. The circulating air helps regulate temperature and moisture in the greenhouse, minimizing (or eliminating) the need for propane heat in winter as well as helping reduce disease pressure by keeping air moisture low. The climate battery is a unique system built using low-cost materials, requires minimal maintenance and can be fitted to any size tunnel.” nofamass.org
The expense of this system would be the digging of the large climate battery. Its size will depend on the size of your greenhouse. And the electricity you would need to use pushes the hot air down into the battery and pulls it out in the winter.
The other down size would be the amount of insulation you would need for the walls. Remember this system only works if the greenhouse has enough insulation to trap the heat and distribute it to the passive or active solar system.
This is where that R-value can really make a difference. You will need to select the level of thermal resistance you need based on the number of growing seasons you plan on using the greenhouse for. For example, we would have to not grow much in January and February because the amount of R-value for those below zero temperatures would be too great. The northern wall needs to be fully insulated — but if you’re in a colder climate, you will need to insulate the east and west walls as well as the floor and the perimeter.
In the Ground or Hill
That is where the “In Ground, Sunken, or In the Hill” solar greenhouse can help with this problem. There is nothing better insulation than the earth!
The earth below the frost line stays at a constant temperature. Which makes the temperature of the solar greenhouse more stable than a Free Standing Solar Greenhouse. And plants love it when there are no drastic changes in the environment.
It also means that in winter, the underground structure will already be warmer than the surrounding area, even before the sun starts pouring in. The sun can work much more effectively than it does in conventional, surface-built greenhouses because it has a lot less work to do to heat the greenhouse to ideal growing temperatures.
The cons of this design are the labor or equipment that you would need to dig out a pit or hillside. And you will have to be extra careful with water drainage off of a hill or on your property so that your pit doesn't end up a swimming pool. Also you will have to invest in underground wall structure like cement or masonry so that your greenhouse doesn’t cave in.
Also you are limited to size as well you will need a greenhouse at least 8 ft by 12 ft. or the greenhouse will be too small and the amount of heat that can be stored in the ground will be too much. Resulting in a greenhouse with unstable temperatures, or just too warm.
With specs of our property and our climate we have voted to go with this design for our homestead. But again you must do you. Be researching other solar greenhouses in your area.
Building A Solar Greenhouse on the Homestead
Now what if you have decided this is the greenhouse for your homestead. You see all of the benefits and can deal with the cons. And you can wait to start well. Here is a step by step guide to follow so you don’t miss anything in the planning stage. Remember a well thought out plan can help you flatten out any wrinkles before you get started.
Pick the Right Spot- make sure the patch you pick receives optimal sun exposure.
Greenhouse Southern Orientation- Situate your greenhouse so that it faces south, with a slight orientation to the east. This helps maximize early morning sunlight and offers some protection from overheating in the late afternoon. It also ensures full sun exposure during the winter when the sun rises in the southeast.
Figure Your Workable Area- Take the time to draw your greenhouse to scale and have fun figuring out where you are going to put everything. This will help you determine the perfect size. One that will hold all you plan to grow but not be too big or small.
Find the Right Materials- you will need to take the time to find the right glazing, see through material. You want transparency for light and heat to enter. But you want it thick enough to be able to stop the heat from being lost at night through conduction.
Insulate the North Wall and Everywhere Else- you also need to insulate everywhere you can so that more and more of that heat can be held so it has time to absorb into your thermal mass system. You are going to lose heat through your glazing no matter what you choose to use. But you don’t want to lose it anywhere else.
Insulate Underground- Don’t forget that in a free standing greenhouse the floor can pull heat from your greenhouse if it is not insulated to below the frost line along the footers.
Use the Earth's Energy- Thermal mass is any material that has the capacity to store large amounts of thermal energy. All materials have some ability to store energy, but some have much more than others. Water for instance can store about 4 times as much heat as air, making it one of the more popular thermal mass materials (or heat sink) used in greenhouses. Other materials are concrete, stone, or the soil underground.
Maximize your Design for Heat and Light In the Winter- the sun lies lower in the sky in the winter so the angle of your glazing is important you don't want is so steep the low light can’t enter and two shallow that the low like reflects off of it. You can find more about glazing angles HERE.
Maximize your Design for Shade and Cool in the Summer- you will need to design an overhang in your roof design that will help block sun during the summer when the sun is high in the sky. Summer is when the sun is the hottest. So having an overhang can create more shade in your greenhouse in the summer but not in the winter when you need the extra sun.
Natural Ventilation is Key- design your ventilation to flow with natural air movement. Having vents up high and down low will force the air to naturally circulate. As hot air rises and cooler air sinks. The result is additional airflow, without added energy.
Use Automated Vents- this will take the guesswork out of ventilation. Having a system in place for ventilation is important because if it happens to warm up and you are not home to open the vent you will lose plants. The other way is true too. If you leave the vent open and run to town for a few hours and the temps drop quickly you will lose plants. Automatic vents work by using wax cylinders to open and close without electricity. As the temps rise the wax will thin and the vents will open and as it cools the opposite happens.
Soil and Water- lastly think about how you are going to water your plants inside your greenhouse. And if you are going to do raised beds you will need to think about the soil you will need to fill these beds. Greenhouse growing is year round so you will need very fertile soil to hold up to the abuse.
How to Grow Even More in a Solar Greenhouse
Another thing you can think about is if you have an area that is warm all year what all could you grow. One of things we are thinking of doing is growing fish in our thermal mass tanks. Water is the best source for storing heat so why can’t I grow something in the water too.
Our plan is to use Aquaponics to grow fish and use the fish poop to fertilize our soil to keep up with high demands “all year growing” needs.
Dream Big
A greenhouse can add benefits to a homestead but a solar greenhouse can add even more with its year round growing, low cost, efficiency, and self sustainability. With these great benefits the sky's the limit when it comes to growing healthy food for your family.
I give you permission to Dream Big. A Lot of the time on the homestead we focus on just the day to day needs. And don’t look to the future. What goals do you have for your homestead, say in two years, five year, or even twenty years. A solar greenhouse is an investment in your future. So have fun and Dream Big!!
Have a blessed day,
Crystal
