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

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

Jan Hassing, Gartneriernes Fjernvarmeforsyning,

(organization of producers with district heating) •

Jan Strømvig, FjernvarmeFyn (Funen district heating), •

Jens Rystedt, AgroTech,

Energy extraction

from greenhouse

nurseries with

district heating

A research project is focusing on how

it is possible to use the surplus energy

from greenhouses thus making the

greenhouse nurseries energy producers

rather than energy consumers

Over a single year, a greenhouse

receives more solar energy than it

needs for heating and controlling humidity.

So, every year there is an energy

surplus in a greenhouse. The problem is

just that so far it has not been possible to

extract the surplus energy and store it for

later use, for example from day until night,

or even better, from summer until winter.

In recent years, new technologies have

made it possible to extract surplus energy.

The energy conditions in an “average

greenhouse” can be outlined as below:

When the energy is extracted, it must

be possible to either use it immediately

or to store it, for example in a groundwater

aquifer or energy storage ponds.

The investment required for storage is very

high, however, and not all locations are

suitable for underground storage.

The district heating area around Odense

Energy conditions in an “average greenhouse”

has 151 greenhouse producers with a total

of 1.8 million m² under glass. These greenhouses

are all connected to the district

heating network.

An obvious question is whether it is possible

to send the surplus energy directly

out to the district heating network, instead

of storing it in expensive seasonal storage


Energy for 20.000 households

This year, the district heating company

on Funen, (Fjernvarme Fyn), Gartnernes

Fjernvarmeselskaber and AgroTech are

looking at the possibilities of exploiting

the surplus heat from nurseries. Preliminary

calculations show that the total potential

energy extraction from the nurseries

amounts to about 2.2 million GJ per year,

corresponding to the energy consumption

of about 20,000 households. However,

KWh per m2 Radiation out

greenhouse per year


Radiation influx to a greenhouse 900

Energy consumption in a greenhouse (standard year) 400 – 450

Energy surplus 450 – 500

Potential energy extraction 350 - 400

this assumes that all nurseries extract all

their surplus energy and that the district

heating network can take all the energy.

The calculations show more realistically

that if 25 percent of the nurseries practice

energy extraction, the district heating

network will immediately be able to take

all the energy without storage for longer


Before this can become a reality, however,

there are some technical challenges to

be overcome - most importantly that the

temperature from the energy extraction by

the nurseries is too low to be immediately

sent into the district heating network. The

temperature must be increased from 35°C

to about 70°C, using either solar heating

plant, heat pumps or the existing boilers at

the nurseries.

The whole issue of financing, costs and

taxation has not yet been resolved.

Nevertheless, the greenhouse companies

do have an energy surplus which could

be recovered and which could transform

greenhouses from energy consumers to

energy producers.

The project is being funded by Gartneribrugets

Afsætningsudvalg, a foundation to

enhance development of the horticultutral

sector, and will be completed with an

overall analysis at the end of 2009.


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