In this article, I will explore what you need to know about building a solar powered greenhouse.
Several years ago, I decided to build my first greenhouse. Prior to the DIY project, I had been growing herbs in a window garden and fresh veggies hydroponically in a small grow room. However, I wanted to grow crops on a widescale but I lived in a region with a noticeably short growth cycle so I decided a year-round solar greenhouse would provide me with produce even during the bleak days of winter, but I needed to learn how to build a solar greenhouse. Luckily, with a little ingenuity, the process was remarkably easy to accomplish. Initially, I used plastic sheeting to cover the structure, but in a few years, I upgraded by doing away with the sheeting and attaching translucent PVC panels to the exterior.
What is a Solar Greenhouse
A solar greenhouse is a type of greenhouse that uses the sun’s energy to grow plants. It has a wall that faces south, and that wall must be built from a translucent material (clear plastic or glass). It also uses a thermal mass and is ventilated. Basically, except for the thermal mass, it’s a design that most people would build regardless.
Learn How to Build a Solar Greenhouse
Being self-sufficient by growing your own fruits and veggies is remarkably rewarding. Gardening is the number one hobby in the United States and the UK because it’s so relaxing. Imagine what it’s like to enjoy your passion year-round. The greenhouse will quickly become your retreat. If you are like me, it will be a place to heal your body, spirit, and mind.
Not only does a greenhouse provide you with fresh produce for your own personal use but you can even make a little extra money selling the items directly out of your greenhouse or a local farmers market. One year I grew so many zucchinis in my greenhouse and pumpkins in my pumpkin patch beside the greenhouse that my children sold the veggies at a small stand at the end of our driveway.
1. Pick Your Greenhouse Location
A successful year-round solar greenhouse requires sunlight, which means you won’t want to construct your greenhouse by large trees or structures that can block out the sunlight. If you live in a region with mild winters and hot summers, then you’ll want to choose a location that exposes the greenhouse to the morning sun. However, if you live in an area with severe winters then you should pick a location that affords both morning and afternoon sunlight exposure to help keep the plants warm during the dark days of winter. With a solar greenhouse, you want to utilize the sun to your benefit.
A traditional greenhouse often relies on the use of fossil fuels to heat its interior during the harsh, chilly winter months. However, a solar greenhouse uses sunlight to create a warm interior environment year-round. If the greenhouse receives sufficient sun exposure, then you should not need an extra heat source.
Try to situate the greenhouse so it faces south with an east orientation. You’ll maximize the morning sun but also enjoy a little protection in the later afternoon when the summertime sun can become intense. Also, maximizing sun exposure will keep the greenhouse warm in the winter by quickly making use of the morning sunlight as the sun rises and onward into the afternoon hours.
2. How to Design and Build a Net-zero Energy Greenhouse
A net-zero energy greenhouse is a passive greenhouse which means it uses only the sun for energy. As I mentioned, location is everything but design matters too. You must determine the square footage you need for your greenhouse garden. Think about what you will be growing and the space you need to move around between the plant’s rows, potting bench, and more. You need to be honest with yourself about the amount of space you need to grow the crops you desire. A standard-sized greenhouse will often measure 30 feet wide by 96 feet long.
With a net-zero energy greenhouse, many growers place barrels of water in the corners of the greenhouse which heat up during the day from the sunlight exposure and then help keep the greenhouse above freezing at night when the mercury dips. I have personally used with remarkable success dark-colored water barrels that I placed by the north wall of the greenhouse and filled with water to help keep the plants warm.
When designing the greenhouse remember that you want to maximize the sunlight in the winter so ensure that the walls and roof are south-facing. They should be made of glass, polycarbonate, or plastic sheeting.
To minimize heat loss, cover the north-facing wall and roof with nontransparent material such as siding or shingles.
3. Selecting the Greenhouse Materials
With a solar-powered greenhouse, you’ll need to pick material that allows at least 70% of the sunlight to pass through into the confines of the greenhouse, which is a process called transmissivity. You’ll also need to minimize your energy loss which is referred to as (R-Value).
My first greenhouse design used plastic sheeting (polyethylene film) which has an R-value of 0.85. The R-value of the plastic sheeting is the same as a sheet of translucent fiberglass. I doubled the sheeting to maximize the R-Value. To increase the R-value, I made sure there was a layer of air between the two layers which gave me an increase of 50% which brought the R-value from 1.25 to 1.50
When I upgraded my greenhouse, I used double poly which is like putting together two layers of polyethylene. I was not gaining any more R-value, but I was gaining greater durability by investing in the double poly versus the plastic which started to break down after a couple of years. Double poly has an R-value of 1.50. It is considered one of the best materials you can use for a greenhouse (if not the best material).
You can also construct a glass greenhouse. A 3mm sheet of glass has an R-value of 0.95.
4. Insulating the Greenhouse
Above I mentioned that you can garner some nighttime heat by placing large barrels of water in the greenhouse to absorb the sun’s heat which the water will release during the night.
Using two layers of sheeting with an air pocket increases the insulative value of the greenhouse or using double poly is another option.
You can use bubble wrap inside the greenhouse to get an even greater R-value. Use 20 mm big bubbles for the best results.
I lived in a region with heavy snowfall so I would regularly shovel snow around the base of the greenhouse to use the natural insulative factors of snow.
5. Ventilate the Greenhouse
Your plants need air in the greenhouse. You’ll want to have a ventilation system in place to help cool down the interior of the greenhouse during the height of summer. Also, fresh moving air helps prevent diseases and pest infestations.
Use intake vents placed down low and exhaust vents up high to effectively ventilate the greenhouse interior. Cool air will flow through the intake vents and then rise as it warms to exit through the exhaust vents which are positioned high in the greenhouse.
Install automated solar-powered vent openers or exhaust fans to better control the conditions in the greenhouse.
With my personal greenhouse, I used exhaust fans to maintain airflow and control the interior heat. The exhaust fans would pull the heat out of the greenhouse while keeping the air moving in a healthy fashion. Plants thrive with air circulation.
6. Add Thermal Mass
Many materials naturally store heat. Adding thermal mass to your greenhouse will help keep it warm at night. Concrete, cob, stone, and water are all ideal for thermal mass. You can easily spread a layer of cob across the floor. Using pebbles or stones on the ground or even concrete stepping stones can help collect heat during the day and release it when the sun sets.
My personal favorite remains 55-gallon dark drums of water which have saved my greenhouse plants on many cold nights. I stacked them along my north wall, and they would collect heat during the day to release at night. I always positioned my tender plants closest to the water barrels to maximize protection.
In addition, to my water barrels, I laid a flagstone walkway down the center of my greenhouse and near my potting table to further absorb heat during the daylight.
7. Consider Soil and Irrigation
A greenhouse helps plants grow faster and larger year-round by creating its own ecosystem. You want to foster those growing conditions for the best results. Never build your greenhouse on a concrete slab. The greenhouse needs to be positioned directly on the ground. You can then add compost and mulch to the soil to create a nutrient-rich solution.
In my greenhouse, I used a remarkable rainwater drip irrigation system that worked well. I would collect the water in barrels outside the greenhouse and then have the drip irrigation system slowly water my plants. I prefer rainwater because it’s free of the chlorine that drinking water so often contains if you don’t have a well.
Learning how to build a solar greenhouse isn’t hard. Your first greenhouse can be basic, and you can add to it as you learn what works for your area – as I did. A year-round greenhouse is a remarkably rewarding investment. During the winter months, the price of produce at a grocery store starts to skyrocket, but with a year-round design, you can enjoy your favorite fruits and veggies that you lovingly cultivated.