Climate control & energy > Fuels
Greenhouse heating
Greenhouses use a fair bit of energy. By far the largest part is used for heating, or more accurately, for controlling the growing conditions in the greenhouse (temperature, humidity, CO2, possibly light). New fuels and innovative ways to use existing energy sources are being explored and developed, as conventional energy sources become more expensive.
Fuels
Traditionally, the fuels most commonly used in greenhouse horticulture are natural gas, coal and oil, and less common are diesel, LPG, propane and butane. Since some decades, waste heat from power plants or from industrial processes is used for heating large-scale greenhouses in several places in the world. Geothermal energy is used on some places in New Zealand and elsewhere. Wood-based products, including waste wood from forestry, is used in some places. More recently, biofuel and biogas are used or tested for greenhouse heating.
Combined heat and power (CHP)
CHP units (combined heat and power units, or co-generators) are engines that burn a fuel (e.g. natural gas, oil) to produce heat, electricity and possibly CO2 gas (albeit after purification). The use of a CHP allows getting more out of a fuel. Electricity is rarely used for greenhouse heating on a large scale as it is too expensive, but obviously electricity is used extensively to drive pumps, motors, lighting, etc.
Solar energy
The sun is an obvious source of heat for greenhouses, as greenhouses efficiently trap solar radiation in a direct way. To use solar energy for heating at night requires heat storage and heat retrieval, which proved to be difficult on a large scale. However, over recent years the Dutch greenhouse industry has developed a system where solar heat is harvested from the greenhouse itself in summer. The heat is stored in the aquifer as lukewarm water, and then used for greenhouse heating in winter by using effective heat exchangers. This requires new technology and very high investments.
The table below shows some details of the main fuels. Additional information can be found in the articles below.
Table. Attributes of the main fuels used in New Zealand Horticulture. Gross energy content in MegaJoule per unit energy. Source: ‘New Zealand energy information handbook’ by J.T.Baines (1993).
Note: Gross energy content is the upper energy value, based on the principle that also the energy of condensation of water is retrieved. In contrast, the net energy content is the lower energy value, which is about 6-8% lower than gross energy content for liquid fuels, and 10% for gaseous fuels.
* Average values for group of fuel oils. Specific weight 0.93 kg/litre
** Specific weight diesel 0.83 kg/litre
Further reading
The Barton Soot Collector for coal boilers (2005)
The costs of carbon tax for greenhouse growers (2005)
