While a greenhouse may look like a self-sustaining structure, you will need to monitor its energy use to manage its efficiency. You will have to factor in light consumption since the plants you decide to grow in there will require several energy sources to thrive, including heat. I almost lost my plants when I made my first greenhouse because I didn’t factor in some critical energy consumption and heating elements. It all comes down to temperature control and efficiency. Get these two things right as an agriculture buff and you can create and maintain a sustainable environment.
The Importance of Controlling Photosynthesis
You cannot expect to place a seed from a plant in the hot sun, water it and expect it to grow well all the time. The environment has to provide the right blend of conditions for each to survive and thrive. This is why the ancient Romans created artificial environments to grow vegetables year-round for their agriculture needs. (https://www.rimolgreenhouses.com/blog/the-first-greenhouses-from-rome-to-america). These consisted of beds that were mounted on wheels and which were moved into the sun and wheeled back in during the cold days to protect the seedlings. Each was glazed with transparent gauze or mica for maximum energy efficiency and heating.
In other words, the ancient Romans understood that while plants need light to grow, they require it in moderation. How they grow depends on how each plant undergoes photosynthesis. It is basically an energy transfer reaction during which carbohydrate is synthesized into carbon dioxide and water via an energy source. The reaction only occurs in the green parts of plants and only when there is sufficient light, water, and CO2 to facilitate the process in the greenhouse
During the winter, CO2 levels can drop, which can prevent the process from taking place unless that supply is supplemented somehow. Many growers even starve their plants of carbon dioxide to conserve heat by reducing air exchange in the greenhouse. You need at least two full air exchanges per hour to ensure your plants thrive in that environment. Plus, if you are circulating cold air, it has to be heated. The sunlight will be too weak during this time.
Measuring Light Quantity for Photosynthesis
Humans and plants perceive light in different ways. For example, we can see green light clearly at about 550 nm and we don’t need a lot to see well. For photosynthesis to occur, the light consumption of plants lies between 400 to 700 nm and the more light they get, the better the process. The amount of light the sun provides varies by season and according to cloud cover. For instance, your greenhouse can get about 2,000 μmol/m2/second of light on a sunny day. At noon or during winter when sunlight is weak, that amount can be reduced to 50 μmol/m2/second in a day