Article. Energy in fokus - from Kyoto to Copenhagen. - AgroTech

Article. Energy in fokus - from Kyoto to Copenhagen. - AgroTech

Carl-Otto Ottosen, Department of Horticulture, Kirstinebjergvej 10, 5792 Aarslev, Aarhus University DENMARK,

Bo Nørregaard Jørgensen, The Maersk Mc-Kinney Moller Institute, University of Southern Denmark, Campusvej 55

DK-5230 Odense M, DENMARK,

Dynamic management

of supplemental light


Even the most advanced control in greenhouse

does not include species differences

adjustment. In terms of supplemental light

use, the plant species might differ dramatically

in terms of light response – both in

level and in time. In an attempt to address

not only the challenges of efficiency of

light use we have tried to combine physiological

knowledge, weather forecast

and actual energy prices to control the

light use.

The state-of-the-art dynamic climate

control system IntelliGrow is based on

the photosynthesis response of plants has

hitherto not included the control of supplemental

light control besides fixed set

points. While the initial aim was to reduce

the heating costs as much as possible,

so a natural step is find solutions to the

increasing use of electricity for the supplemental

light use in commercial green-

houses – both vegetables and ornamentals.

As the natural light even in darkest part of

the year on a sunny day might be enough

we have decided to combine information

about the weather forecasts, the actual

forecasted electricity prices and the photosynthetic

performance of the actual species

into one context.


To reach this target a software package has

been developed, that installed on a PC

connected to the Internet and with access

to a climate computer will calculate the

most efficient time to turn on the supplemental

light based on the weather forecast,

the energy prices and the photosynthesis

sum from individual plant species. In this

way we not only overcome the traditional

rather conservative set points for use of

supplemental light, but also secures that

The screen shows an example of supplemental light control, where the light is on 6 hrs

during the night (lower left). The graph shows times of light on (red), price of electricity

(light blue) and working light (yellow). The green line is natural light and light green line

is the photosynthetic activity.

the use of supplemental light takes place

in periods where the gain in terms of photosynthesis

per light hours are the best. The

control of supplemental light is predictive

rather than the traditional retrospect analysis

of light sums.


Experiments with different photosynthesis

sums using dynamic light control vs. traditional

light controls based of set point

of supplemental light has been performed

in Spring 2009. The dynamic supplemental

light control was use in combination

with dynamic climate control using potted

miniature roses, Hibiscus rosa-sinensis and

Euphorbia milii showed that a reduction of

more than 10% of the supplemental light

use was possible. If it was combined with

dynamic climate control both the cost for

heating and electricity was reduced with

an improved plant performance (often

more compact plants).

Photosynthesis measurements of the

species reveal large differences in response

times to light, which indicate several

additional possibilities for reducing electricity

costs using different igniting patterns

for the lamps. This knowledge will

be included in the software and on going

work on the software will include a better

prediction of the climate to improve

the photosynthesis calculation, but also

include suggestion for different uses of the

installed supplementary light in different



The software that enables the link between

actual costs of electricity and the weather

forecast is as such an effective tool for

greenhouse growers to reduce the energy

cost as it illustrates clearly the actual costs

for providing light for the plants. When it is

combined with the species specific information

about the required photosynthesis

and the response rates of the plants it will

enable growers to reduce the energy costs,

by moving energy use from peak to low

peak periods, which on the other hand is

beneficial for the energy providers.


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