New materials for greenhousecovers on the

horizon

Energiek event 11-04-2019

Bram van Breugel

On energy saving efforts in the past

● VenlowEnergy Greenhouse

Without emittance to a high transmittance

Low-e materials

Interference for anti reflective coatings

Processing conditions

Upcomming project on emerging (semi) transparent energy

generating technologies

Outline

2

Light is (almost) never too much:

yield increase per% light increase

Crop % Yield increase

Lettuce 0.8

Radish 1

Cucumber 0.71

Tomato 0.71

Rose 0.81

Chrysanthemum

0.6

Pointsettia 0.50.7

Ficus benjamina 0.6

Source: Marcelis et al.,

2006

Goal: Greenhouse concept with highest energy saving and good tomato production

● Double glass with low u-value and high light transmission

● Mechanical dehumidification with heat-regain

● “Next Generation CultivationStrategies” (climate control)

VenLowEnergykas

● Double glass

● low u-value due to low-e coating

● high light transmission due toAR coating

VenLowEnergykas – double glass

Glass Coating Th U-value

Single - 82 6.7

Single AR-AR 91

Single AR-Low-e 81

DoubleAR-AR-Low-e-AR 79 1.2

Hemming et al. 2012

VenLowEnergykas: energy consumption

Kempkes et al. 2014

50% saving

VenLowEnergykas: crop production

tomato (cv. ‘Komeett’)

Kempkes et al. 2014

0

10

20

30

40

50

60

70

80

121416182022242628303234363840424446485052Prod

ucti

on

to

mato

cv.

'Ko

meett

'[kg

m-2

]

week number2011 2012 2013 2014

Prediction: 70 kg m-2 y-1

Comparable to

commercial growers

VenLowEnergyKas conclusion: ~50% energy

saving with normal tomato production

8

The reference used

to be simple single

glass

This now has to

compete with AR

coated single glazing

With the use of AR coatings

similar light transmittance

can be reached for DGU’s

Glass Coating Th U-value

Single - 82 6.7

Single AR-AR 91

Single AR-Low-e 81

DoubleAR-AR-Low-e-AR 79 1.2

Can improved optical quality save energy and

compete with AR glass?

9

Without emittance to a high transmittance

Why do we lose 5% for the Low-e and gain 5%

for AR? Low emissivity requires free charge carriers with

high mobility

Either extremely thin 5~12 nm metal layers

Other option is transparent conducting oxides (TCO), common types are:

● Indium Tin Oxide (ITO)

● Fluorine doped Tin Oxide (FTO)

● Aluminum doped Zinc oxide (AZO)

● n >> 1.5 usually 1.7~2.1

● n heavily depends on processing

Currently used AR coatings

consist of quarter wave layer

of refractive index between

that of air and glass

This makes the materials

used in low-e rather different

from those used for Low-e

10

Glass

λ/4 (n≈1.22)

Alternative (more complex) antireflective coating

options which could incorporate Low-e materials

11

Double quarter wave AR stack

Allows n>1.5

Quarter wave, halve wave,

quarter wave AR stack

N in range of common TCOs

Modelling antireflective coatings – weighing

factors NEN2675

12

Solar photon flux from

400 to 700 nm sin(cos(Angle of Incidence))

Modelling antireflective coatings

13

Glass

λ/4

λ/4

Python package tmm* - (transfer matrix method)*S.J. Byrnes. 2016. Multilayer optical calculations.

Some preliminary modelling antireflective

coatings

14

Refractive index data from

refractiveindex.info

● No idea how realistic

this data is or how this

will be influenced by

processing!

Data from refractiveindex.info

Al2O3: I. H. Malitson and M. J. Dodge. Refractive Index and Birefringence of Synthetic Sapphire, J. Opt. Soc. Am. 62, 1405 (1972) AZO: R. E. Treharne, A. Seymour-Pierce, K. Durose, K. Hutchings, S. Roncallo, D. Lane, Optical design and fabrication of fully sputtered CdTe/CdS solar cells, J. Phys: Conf. Ser. 286, 012038, (2011)ITO: T. A. F. König, P. A. Ledin, J. Kerszulis, M. A. Mahmoud; M. A. El-Sayed, J. R. Reynolds and V. V. Tsukruk. Electrically tunable plasmonic behavior of nanocube-polymer nanomaterials induced by a redox-active electrochromic polymer, ACS Nano 8, 6182-6192 (2014)SiO2: L. Gao, F. Lemarchand, and M. Lequime. Exploitation of multiple incidences spectrometric measurements for thin film reverse engineering, Opt. Express 20, 15734-15751 (2012)Ta2O5: L. Gao, F. Lemarchand, and M. Lequime. Exploitation of multiple incidences spectrometric measurements for thin film reverse engineering, Opt. Express 20, 15734-15751 (2012)MgF2: M. J. Dodge. Refractive properties of magnesium fluoride, Appl. Opt. 23, 1980-1985 (1984)

Double quarter wave AR stack

15

Glass

λ/4 = Al2O3

λ/4 = MgF2

λ/4 ; n=1.32

Glass

λ/4 = Al2O3

λ/4 ; n=1.32

λ/4 ; n=1.32

Glass

λ/4 = AZO

λ/4 ; n=1.32

λ/4 ; n=1.32

Glass

λ/4 = ITO

λ/4 ; n=1.32

λ/4 ; n=1.32

• From Fresnel reflections

can be minimised via

destructive interference

• Materials absorbing in

PAR range need to be

simply avoided

• Definitely some

variations in this range

Transmittance loss – actual data from different

processes

16

Still a long road ahead

• Finding out and understanding

how processing conditions

influence the optical properties

• Not all processes are

scalable to an industrial

size

• Integrating TCO’s with other

layers taking into account

process compatibility

• Durability

17

Upcomming project

• Investigating the performance of

energy generating materials for

greenhouses

18