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Effects of electric power supply for artificial illumination
of greenhouse crops at volatile current supply
Method
The photosynthesis of a tomato crop is estimated by a model (Kläring et al., Agric.
For. Meteorol. 143: 208-216) from data of a reference year of Grossbeeren,
Germany (52 N, 13 E) using the following parameters:
•Leaf Area Index: 3 m2m-2
•CO2 concentration: 400 ppm
•Transmission of PAR radiation: 75 %
Simulated scenarios are compared under:
•Artificial illumination: 200 μmol m-2s-1
•No illumination (only solar light)
Heat energy savings (Schuch, PhD Thesis
HU-Berlin, 2014: pp. 22-25) are estimated
considering:
•Heating set points: 19C/17C day/night
•Power of HPS lamps: 160 W m-2 (75% heat efficiency)
•Price of heat produced from oil: 0.04 € kWh-1
•Average tomato price: 2 € kg-1
Objective
In Germany, the increasing generation of electricity based on
renewable energy is accompanied by a high volatility in the
availability. Greenhouses could be such flexible users of volatile
current supply. They can use it for heating the greenhouse and/or
illuminating the crops. The present model study evaluates the
potential benefit effect of illuminating a tomato crop. The
photosynthesis and the potential yield are simulated in the course
of a year. In addition, the savings in heat energy consumption due
to the heat by the lamps released into the greenhouse is estimated.
Results
Artificial illumination has a high positive impact on photosynthesis during nights and winter time. As complement, the energy savings due to the heat released
from the lamps are higher in winter than in summer. The benefit from using artificial illumination is more affected by the surplus in photosynthesis and yield
than by the heat energy savings (data not shown).
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PAR [µmol m-2s-1]
Discussion
During the winter, using electricity for illuminating plants would be profitable if prices are in the range below 0.15 € kWh-1. In summer, illumination may be
profitable only during the night hours. However, the estimated effect must be proven in experiments, because a feedback inhibition of assimilates on
photosynthesis could be possible due to a very high source/sink ratio. During summer other options could be much more profitable such as using the electricity
for cooling the greenhouse in the (semi) closed operation mode.
This study considers only the operation phase, thus investment costs are not included. It also does not take into account the possible effect of a 24-h light phase
which however, will rarely happen in the investigated conditions of volatile current supply.
T. Ramirez and H.-P. Kläring, Leibniz Institute of Vegetable and Ornamental Crops, Grossbeeren, Germany
contact: ramirez@igzev.de
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T [C]
This project is supported by funds of the German Government's Special Purpose fund held at Landwirtschaftliche Rentenbank
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Photosynthesis
[g CO2 m-2h-1]
No illumination Artificial illumination Outside PAR
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Energy savings [kWm-2]
Energy savings Outside temperature
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Profit difference [€ kWh-1]
Profit difference of illumination and no illumination