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Oude versie 60

changes.mady.by.user Gert-Jan Swinkels

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Nieuwe versie 61

changes.mady.by.user wur.gknwiki@gmail.com

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Sleutel

  • Deze regel is toegevoegd.
  • Deze regel is verwijderd.
  • Formattering is gewijzigd.

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Uitvouwen
titleGreenhouse climate

First, let’s look at the realized greenhouse climate.

  • Lighting with 180 µmol/(m² s) allows for a Daily Light Integral between 15 and 20 mol/m², which is roughly 60% of the light availability in summer in the Netherlands. This gives of course a higher production, but also a much more constant production level.

  • Because of the RTR temperature control the average air temperature is higher for the illuminated scenarios because of the higher PAR sum.

  • Of course the PAR sum of the illuminated scenarios is higher

  • Because of the increased crop transpiration when the lamps are on, the average RH is higher for illuminated scenarios.

  • The difference between HPS and LED is of course the lower electricity consumption of the latter, but LED also leads to a lower radiation load on the crop, leading to a reduced transpiration.

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Uitvouwen
titleElectricity

Because of the higher efficiency, LED consumes significant less electricity than HPS at the same illumination intensity. LED produces less heat which means that the CHP runs for more hours compared to HPS. The minus-sign in the table means that the CHP produces electricity instead of consumes electricity.

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titleHeat
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Uitvouwen
titleSources

In the table below the consumption of different sources is shown. Because of the higher greenhouse temperature in combination with a higher PAR sum, the water use is higher for the illuminated scenarios, but when using LED instead of HPS, the water use is a little lower. This is because the LED does not emit Near Infra Red radiation to the crop, leading to crop temperatures a little lower and hence less transpiration.
The scenario with LED + CHP has a net negative electricity use, which means that on a yearly base the greenhouse sells more electricity to the grid than in buys. This is partly because LED’s require less electricity and partly because the greenhouse needs somewhat more heating compared to an illumnated greenhouse with HPS-lamps.

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Performance

The overall performance is expressed in terms of economical feasibility and sustainability. The greenhouse without illumination has the lowest energy costs, but has also a substantial lower production.
When comparing the the illuminated greenhouses, the cases with LED lighting clearly have lower costs than the greenhouses with HPS lighting. This is of course to be expected and has to be weighed against the higher initial investments for LEDs compared to HPS-lamps.
Under the assumed economical conditions, options with CHP lead to lower costs, but higher CO2 emissions.

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Conclusions

  • Using illumination increases both costs and crop production significantly

  • The scenario with the highest electricity consumption (HPS and no co-generation) has the lowest CO2 emission. This is because it is assumed that the electricity from the grid is all coming from sustainable sources. In case the average CO2 emission of electricity in the public grid of the Netherlands (350 gram per kWh in the early twenties) is assumed to be associated to the bought electricity, the HPS greenhouse without CHP becomes the greenhouse with the highest CO2-emission, although the largest emission is then produced elsewhere. The CO2 emission of option 2 would then be 56.3+233.7*0.35 = 138 kg/(m² yr).

  • Assigning this 350 gram CO2-emission to public grid electricity would mean that the CO2-emission associated with option 4 would increase with 83.7*0.35 = 29 kg/(m² yr), whereas the CO2-emission associated with option 5 would decrease by 33.8*0.35=11.8 kg/(m² yr).
    This shows that LED-lighting is always to be preferred compared to HPS-lighting.

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