Pilot Project at the Institute for Crop Science and Plant Breeding
Low-Energy Greenhouse with conceptional LED Plant Lighting

Greenhouse with LED plant lighting switched on
Together with the State Building Construction Department Freising, a greenhouse planner and a structural engineer, the Bavarian State Research Center for Agriculture has realized a pilot project according to ZINEG criteria, to test (effective) solutions for the energy-efficient modernization of existing research greenhouses. The Future-Initiative Low-Energy-Greenhouse (ZINEG) has won the German sustainability award, in the category research, in 2014.
Moreover, for plant lighting inside the new greenhouse, energy-efficient wideband LEDs of the newest generation are being tested.
The location of the new greenhouse was chosen within the Institute for Crop Science and Plant Breeding, as plant cultures on site have a very high heat- and light demand (>10 klx), and because a later comparability of the results can be ensured.
This first pilot project has been launched in September 2014, and was completed in March 2015. It already provides important findings, concerning the used materials and their properties, the strategy of the reconstruction measures, and first energy efficiency measures based on manufacturers specifications.
Consumption measurements, with caloric and electric energy meters, are intended for ongoing operation and deliver reliable data for comparison with existing greenhouses.

Features and energy-efficient Construction Measures

Dimensions

Wide-span greenhouse, three equally big compartments

  • Total ground area: 284 m²
  • Usable ground area: 255 m²
  • Subdivision in three separate (and separately controllable) compartments
    • Cost-effective big space partitioning
    • In efficiency-orientated plant breeding, these greenhouse compartments are an important connective link between laboratory/climate chamber and field
  • Ridge height: 7,2 m
  • Side wall height: 5 m
    • High side walls and high ridge enable very good possibilities for climate control in the plant area
    • In these spacious compartments, suffused with light and air, realistic observations for breeding research can be conducted

Greenhouse Shell

All around isolated greenhouse shell through isolated base, double glazing and thermally separated glazing bar profiles

  • Base: perimeter insulation 80 mm EPS (=expanded polystyrene hard foam)
    • Heat conduction group: 035
  • Roof covering: insulating glass “Consafis ISO LE 9000”
    • Insulating glass (construction: 4mm ESG extra white – 18mm air – 4mm ESG extra white)
    • Highly transparent, ironless flint glass
    • Light transmissivity: 84 %
    • UV transmissivity: 68%
    • Thermal transmission coefficient (U-Value): 2,7
  • Side walls east/west and southern gable wall: heat reflecting glass “Consafis neutral LE 9000”
    • Insulating glass (construction: 4mm ESG coated with precious metal – 18mm argon fill – 4mm ESG)
    • Light transmissivity: 80 %
    • UV transmissivity: 37 %
    • Thermal transmission coefficient (U-Value): 1,1
  • Northern gable wall: isolation panel sandwich elements “Kingspan KS1150 FR FireSafe®”
    • Insulation core made from mineral fibres, core thickness 150 mm
    • light transmissivity: 0 %
    • UV transmissivity: 0 %
    • Thermal transmission coefficient (U-Value): 0,28
  • Glazing bar profiles “SAPA Variolux Thermo 26”
    • Special aluminum profile for greenhouse insulation free of thermal bridges
    • Thermally separated through insulating profile made from special polyvinyl chloride (rigid PVC)
    • Putty free glazing (dry glazing) through EPDM seals
    • Thermal transmission coefficient (U-Value): 3,2

Energy Screens

Two separately controllable, tightly closing, hanging, energy/shading screens at eaves height, for achievement of a thermos flask effect

  • Lower screen layer (daytime screen): “Svensson XLS 30 Harmony Revolux”
    • Hardly inflammable (B1), polyester tissue for shading and energy saving, with closed structure and white polyester stripes for good scattering of daylight
    • Light transmissivity: 64 % (diffuse light) to 71 % (direct light)
  • Upper screen layer: “Reimann PyroSilver ultra weiß”
    • Hardly inflammable (B1), white, acrylic tissue for shading and energy saving, with open structure, thin aluminum stripes and good scattering of daylight
    • Light transmissivity: 32 % (diffuse light) to 40 % (direct light)
  • Rolling screen at southern gable wall: “Svensson ILS 50 Harmony Revolux”
    • Hardly inflammable (B1), polyester tissue for shading and energy saving, with closed structure and white polyester stripes for good scattering of daylight
    • Light transmissivity: 46 % (diffuse light) to 51 % (direct light)

Heating System

Use of district heating with high-efficiency circulation pumps for adjusted supply of heat energy

  • Undertable heating pipes for delivery of heat directly to the plant area
  • Fan heater in the roof area “COSMO Classic 45”
    • External-rotor axial fan with EC motors (variable-speed) and hydraulic compensation (max. air flow: 3900 m3/h, heating capacity: 33,4 kW, power consumption: 170 W)

Irrigation- and Fertilization Technique

Watering of planting tables is possible using ebb and flow irrigation as well as drip irrigation

  • Water supply through existing water pipe
  • Fertilizer supply through mobile fertilizer dispense trolley

Climate Control and Measurement Technique

  • Sensors for light, temperature und air humidity, two climate areas per greenhouse compartment
  • Electricity meter and heat meter for precise analysis of energy consumption
  • RAM climate computer for exact control of light, air, heat, water and nutrients

LED Workplace Lighting

Manufacturers designation: Trilux Nextrema 4000 – 840 ET+ LV TWW
Lamp type: moisture proof LED ceiling lamp
Dimensions: 1045 x 92 x 85 mm
Weight: 1,934 kg
Degree of protection: IP 66
Cooling: passive
Power consumption: max. 45 W
Correlated colour temperature (CCT): 4000 Kelvin
Colour rendering index (CRI): > 80
Luminous flux: 4500 lumen

Further Construction Characteristics

  • Cable routes separated at table- and eaves height for less shading of planting tables
  • Door threshold and gutter system designed barrier-free for good trafficability of the greenhouse
  • Access roads made of turf pavers for backing of surface water
  • Rolling tables for small share of pathways
  • Latest generation wideband LED plant lighting

Savings Potential compared to existing Greenhouses

A lot of light, air and free space for healthy plant growth and comfortable work experience. Saving energy without trade-offs? The technical data situation shows very high saving potentials on the way to CO2-neutral greenhouse production. How much of this technical potential can be implemented in practice, strongly depends on the demands of cultures in plant breeding.
Basically, set point limits shall be fulfilled. Light, air, heat, water and nutrients shall be adjusted to the natural needs and development progress of plant cultures.

Lighting Concepts and Wavelength Ranges

Conventional plant lighting with high pressure sodium lamps

Plant lighting in greenhouses is generally used in addition to natural daylight to achieve certain day length or light sums. Thereby, so far mainly high pressure sodium lamps are being used. Their spectrum seems very bright to the human eye, as light is emitted mostly in the middle of the wavelength region, in between 550 and 650 nm (yellow and light red) and as the sensitivity of the human eye is highest in this region.
However, plants have other demands for light quality and use light in a substantially bigger wavelength region for photosynthesis (PAR = photosynthetic active radiation = 400-700 nm).

Conceptional LED Plant Lighting

Steering plant physiology and morphology by means of light spectrum
However, light is not only energy source for photosynthesis, but also serves as signal transducer for various physiological and morphological processes, involving different photoreceptors. Spectral demands of these photoreceptors partly differ considerably from photosynthetic active light spectrum. So one also speaks of the “photobiologic active light spectrum” (PBAR = photobiologic active radiation = 280-800 nm).
By using latest wideband LED technology, different photoreceptors can be specifically addressed, so morphologic and physiologic processes can be controlled by choosing different light spectra.
Furthermore, the light spectrum can be adjusted to developmental stage of plant life.
Employed wideband LED grow lamps
Plant lighting in the three compartments is done by different wideband LEDs from the Finnish and Danish manufacturers “Valoya” and “Fionia Senmatic”.
Thereby, lighting regimes in the three compartments are adjusted to developmental stages of plant life.
While high pressure sodium lamps employ much of the used electric energy in narrow banded peaks in the yellow to light-red wavelength region (see “Conventional plant lighting with high pressure sodium lamps”), wideband distribution of photon flux over a great wavelength range is a common feature of all three employed LED spectra. Therefore the designation “wideband LED lamps”.
LED Valoya NS1
The light spectrum of “Valoya NS1” is especially suitable for germination and juvenile plant development, as 31 % of the photons emitted have a wavelength between 500 and 600 nm. As the sensitivity of the human eye is highest at medium wavelength, the emitted light has a bright, whitish colour to human eyes.
LED Fionia FL300 grow white
The spectrum of “Fionia FL300 grow white” is especially suitable for vegetative growth of many plant species, as 50 % of emitted photons are in the range of 600-700 nm. Especially tillering and branching shall benefit from the emitted spectrum.
LED Valoya AP67
The relatively high proportion of far red (15 % of emitted photons) in the spectrum of “Valoya AP67” supports flower formation, elongation growth and seed production in many plant species. Thus the spectral distribution is mainly suitable for generative plant development.
Technical specifications of employed wideband LED grow lamps
Manufacturers designation: Valoya R300 NS1 Fionia Senmatic/DGT FL300 grow white Valoya R300 AP67
Designation of spectrum: NS1 grow white AP67
Lamp type: wideband LED grow light wideband LED grow light wideband LED grow light
Dimensions: 340 x 400 x 167 mm 550 x 230 x 160 mm 340 x 400 x 167 mm
Weight: 14,5 kg 12,4 kg 14,5 kg
Degree of protection: IP 55 IP 54 IP 55
LED-lifetime: 35000-50000 operating hours 35000-50000 operating hours 35000-50000 operating hours
Cooling: passive, cooling fins active, fan + cooling fins passive, cooling fins
Power consumption: 276 Watts variable, 100-600 Watts 276 Watts
Variable light spectrum: no yes, variable share of blue 2-14 % no
Correlated colour temperature (CCT): 4800 Kelvin depends on setting 2500 Kelvin
Colour rendering index (CRI): 80 depends on setting 70
PAR (photosynthetic active radiation): 94 % depends on setting 83 %

Effects of particular Wavelength Regions on Plant Physiology and Morphology

A complex network of photoreceptors provides for different morphologic and physiologic plant reactions in response to different wavelength regions
Plant reactions on different wavelength described below have no general validity, as involved photoreceptors, their absorption spectra and triggered reactions can differ widely between plant species. Therefore, the prediction of reactions of different plant species on the three employed LED spectra is only possible to a very limited extent.
UV (<400 nm)
Is DNA degrading in high doses, in low doses UV-light increases stress tolerance, leads to thick leaves and short internodes. Photoreceptor UVR8 reacts specifically on UV-B (290-320 nm). Additional photoreceptors involved in UV-sensing are Cryptochromes, Phototropines and ZEITLUPE, but also Phytochromes absorb light in the UV region of the spectrum.
Blue (400-500 nm)
Leads to stomata opening (Zeaxanthin, Phototropines), hence to effective transpiration, low leaf temperature and efficient photosynthesis. Phototropines make sure chloroplasts are adjusted in the right way to incident light, depending on irradiance.
Coaction of Cryptochromes, Phototropines and Phytochromes prevents elongation growth and ensures short internodes.
Green (500-600 nm)
Opposes the effects of blue light by converting Cryptochromes and Phototropines into their inactive forms. Leads to longer internodes as well as to higher leaf temperatures due to partly closure of the stomata (Zeaxanthin).
Red (600-700 nm)
Is especially registered by the Phytochrome system. The inactive form of Phytochrome is called Pr and has an absorption maximum at 660 nm.
Radiation in the red region of the spectrum leads to conversion of Pr into its physiologically active form Pfr. The latter is converted back into Pr (= photoreversibility), either in darkness (slow reaction), or by exposure to light in the far-red region of the spectrum (faster reaction). As mentioned, this phenomenon is refered to as photoreversibility. Thereby, the absorption maximum of Pfr is at about 730 nm.
Red light in the region of 600-700 nm impedes elongation growth of the hypocotyl and leads to compact growth with short internodes.
Far-red (700-800 nm)
Opposes the effects of red light by converting the Pfr form of Phytochrome back into the inactive Pr form (see above).
Plants react with so called „shade avoidence symptoms“ (= elongated petioles, long internodes, enhanced elongation growth, premature flowering).
Red / Far-red ratio
The ratio of red to far-red influences the ratio of inactive Phytochrome Pr and active Phytochrome Pfr (see above). Direct Sunlight has a red/far-red ratio of about 1,2. Under a dense canopy however, driven by shading through other plants, the ratio can get as low as 0,1.
When exposing plants to radiation with high red/far-red ratio, reactions on red light are predominant (short internodes, compact growth). Conversely, a low red/far-red ratio leads to the so called „shade avoidance symptoms“ described above.
Blue / Green ratio
As green light opposes the effects of blue light, the blue/green ratio of a light spectrum provides information about the intensity of the blue light reaction. A high blue/green ratio usually leads to short internodes and leaf petioles; conversely, with increasing the green component of the spectrum, these plant reactions are weakened.

Tasks

  • Ecologic and economic assessment of conducted measures
  • Identification of cost factors and saving potentials
  • Life Cycle Assessments (LCAs)
  • Conceptional use of energy-efficient LED-lighting systems in plant breeding
  • Photomorphogenic investigation (plant reactions on light) of new breeds
  • Reduction of maintenance costs for plant lighting

Open Questions

  • Are the measures in line with breeding work and growth success at the institute?
  • Can the construction measures be adopted for other research greenhouses?
  • What are the future priorities?
  • Does high humidity harm elite plants?
  • Can new control strategies reduce humidity in a way that makes good sense?
  • Considerations about climate protection and CO2-footprint of greenhouses

The Future

Very tight, highly insulated greenhouses can lead to undesirably high air humidity. Clever strategies are needed when under these conditions, plants reduce transpiration and as a consequence uptake of water and nutrients is limited. Then, water and fertilizer should be adjusted, metabolism can be stimulated using fans and air humidity can be limited by ventilating before nighttime eventually while energy screens are closed.
The new model project shall not only provide important details for further restructuring of greenhouses, but also work on open questions of the ZINEG-projects, like for example the smart use of highly efficient full-spectrum LED lamps in new light concepts, or the employment of intelligent dehumidification strategies.
New knowledge and experience values will take on our understanding of plants and Photomorphogenesis and will lead breeding research into the future.

Low-Energy Greenhouse at night, view from southern side

Impressions from ongoing greenhouse trials

Soybean variety "ES Mentor" under different lighting regimes

Chronological sequence of cultivation under LED Valoya NS1
Chronological sequence of cultivation under LED Fionia FL300 grow white
Chronological sequence of cultivation under LED Valoya AP67
Project Information
Project leadership: Dr. Peter Doleschel
Project team: Rudolf Rinder, Maximilian Neumair
Duration: 01.10.2013 - 31.07.2018
Financing: Bavarian State Ministry for Food, Agriculture and Forestry
Project partner: State Building Department Freising Weihenstephan
Funding code: EW/13/64