Greenhouses as Power Producers
commercial costings are hard to define.
The best way to assess costs is to speak
to specialist VF suppliers and put your
situation to them. Nonetheless, several
VF suppliers have been kind enough to
provide price guidelines.
Static VF systems, on a full commercial
scale, vary between £40 - £80/m2
depending on the type of crop, crop
density and how many separate
hydroponic systems are required (source:
Saturn Bioponics Ltd.)
Some systems could cost even more.
Does VF pay?
Growing in three dimensions undoubtedly
increases production per square metre of
ground area and offers potential savings in
labour, water and fertiliser costs too.
In the past, these advantages have
not been sufficient to justify the high
investment, but with newer VF system
designs, and with the game changing
application of LED lighting, there is
emerging potential for VF and we are
bound to see more of it.
(For more information see the GrowSave
website http://bit.ly/2k9d5Xv)
We all recognise greenhouses as great collectors of heat and light from the sun
for growing. Could they be used to generate electricity too?
Over the last few decades, Photovoltaic (PV) cells have taken centre stage in
renewable electricity production. Invented over 60 years ago, they have continued
to improve in efficiency and reliability; costs have fallen dramatically as well. To date,
they have taken the form of opaque panels, ideally suited to being located on rooftops
or in fields as large arrays. Now, an interesting development offers a potential new
opportunity for greenhouses.
Enter the see-through photovoltaic panel, where a transparent solar cell is sandwiched
between two panes of glass. This potentially allows a structure to produce energy
through its windows.
Will this work in greenhouses? Or would such a device sap so much energy from the
light, in the form of electrical generation, that nothing is left for the plant? American
firm, Solaria, claim to have solved this problem by developing a proprietary technology
optimised for greenhouse applications. Solaria’s PV module, or ‘solar glass’, is able
to convert part of the sunlight into electricity, while transmitting quality light for plant
production. They achieve this with a luminescent backing on the panel to convert green
light to red light, which can be used by plants more effectively.
Although having improved over the years, the
efficiency of solar cells remains relatively low
at around 20%. Solar glass is likely to be less
efficient still, as transparency is traded-off against
electrical efficiency. In fact, the transparent cells
operate at less than one third of the efficiency of a
normal, opaque panel, outputting about 50 W/m2.
Nevertheless, this does not need to be a problem,
as utilising very large areas of greenhouse roof
glass could still make it a worthwhile investment.
One hectare of
greenhouse with a
solar PV glass roof
could generate an
output of around
500 kW.
At the moment, solar glass looks like costing five to seven times as much as
conventional greenhouse glass, but good returns on investment could still be possible.
Power generation can be expected for 25+ years, offsetting on-site electricity usage.
Furthermore, there is the potential for additional revenue through incentivised schemes
for renewable energy generation. Heating costs could be reduced, as PV glass has
better insulating properties than standard greenhouse glass and increased crop yield
may also be possible, for example, with the use of light quality enhancing panels.
As development of the technology continues and more companies get involved, it is
reasonable to expect prices to drop and for some applications, where the numbers
work, we may soon be seeing the first power producing greenhouses.
March 2017
Photographs in this article have been used with the kind permission of Soliculture
At the other end of the scale, computer
controlled containerised systems
with fully automated handling require
investment of around €200/m2 (racking,
control software, containers and internal
transport, (source: Logiqs.nl)), plus the
cost of irrigation and lighting - leading
to typically €1,000/m2 overall.