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Combined heating and power (CHP) systems consist of an engine, which drives uses natural gas as a fuel to drive a generator , to simultaneously produce heat, electricity, and CO2 using natural gas (hence the name ‘co-generator’).
The heat produced is used to heat the water for the heating pipes;
The electricity produced can be used internally, e.g. for supplementary lighting, or sold to the grid;
The CO2 produced is supplied to the greenhouse to be used by the crops.
The use of CHP can be optimized either based on maximizing the reduction of emissions ('Heat demand mode') or based on maximizing the economic gain ('Economic value mode').
Heat demand mode
The CHP is operational only when the produced heat can be used. This applies also for times when the crop is illuminated (lamps switched on) and/or at peak hours (which typically coincide with the times when electricity is used most, such as in the morning and evening when households and businesses are active), and also when there is a CO2 demand and the heat buffer is not full.
Economic value mode
The CHP is used when the revenues from electricity sales exceed the costs of fuel at any moment.
To verify the difference between dynamic prices and peak/off-peak such as used in the Greenhouse Energy Guide, historical hourly data on the electricity feed-in tariff are used in the model.
Contribution to energy balance and resource use of
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greenhouses:
The CHP supplies heat to the water running in the heating pipes, which adds energy to the greenhouse.
The electricity supplied by the CHP might also can be used for artificial illumination, which in turn will add further energy to the greenhouse.
Impact on resource use of greenhouse
The CHP process consumes natural gas.
As a by-product of the CHP process, CO2 can be supplied to the greenhouse.
, or to power heat exchangers or heat pumps. Electricity generated by the CHP can be sold to the grid, reducing the net electricity usage/expenses.
The CO2 that is co-generated is supplied to the greenhouse.
Possible steps towards
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sustainable fossil-free greenhouses
As the basis of the CHP process is fossil fuels, there is a limit on how sustainable this installation can be made. However, storing the energy heat generated in excess over the greenhouse energy demand can be stored in a buffer tank for later use, outside the CHP operating hours.
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