This article explores the important role of energy balance in the greenhouse and how the crop and greenhouse release the large amounts of energy they receive from sunlight and artificial lighting.
Empower plants through balanced climate control
Crops self-cooling strategies
The sun can bring 800 W/m² into a greenhouse. That is a huge amount of energy, especially considering the total size of greenhouses nowadays. However, only 2% is converted by the crop canopy for growth. The other 98% will leave the greenhouse. In that sense, plant production is not very energy efficient.
Artificial light
What is true for sunlight is also true for expensive artificial light. However, lamps bring less energy into the greenhouse. For example, to produce 200 µmol/m²/s, high-pressure sodium lamps bring in 114 W/m² of energy, while LED lamps bring in 74 W/m². When LED fixtures are water-cooled, this energy is reduced to 48 W/m².
What consequences does this have for the crop and the greenhouse when most of this energy must be released again? This article explains the important role of energy balances in a greenhouse and how we can support the crop and the greenhouse in releasing these large amounts of energy.
What is energy balance?
Greenhouse production is bound by the rules of physics, and one of the most important rules is that energy never ‘disappears’ but is usually converted into different types of energy. For a greenhouse, energy input and output are always in balance (for more, refer to the first article in this series).
The amount of energy absorbed by the plant is less than the energy entering the greenhouse, as part of the radiation is reflected. The plant can actually control that reflection by turning its leaves or by changing the shine of the leaf.
The amount of energy absorbed by the canopy can be measured with a device known as a net radiometer. It measures the light energy that has entered the greenhouse in the visible and infrared (heat) ranges, then subtracts the energy reflected by the canopy. The resulting measurement is the absorbed energy that must be converted by the plant to maintain its energy balance. So, the plant has its own energy balance to maintain.
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