Metrics for plant lighting - ag.purdue.edu energy... · Metrics for plant lighting •...
Transcript of Metrics for plant lighting - ag.purdue.edu energy... · Metrics for plant lighting •...
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Reducing Energy Costs Associated with Supplemental Lighting in Controlled Environments
Cary A. Mitchell Department of Horticulture & Landscape Architecture
Purdue University, West Lafayette, Indiana USA
Indiana Hort CongressIndianapolis Marriott East Hotel
January 10, 2017
Metrics for plant lighting
• Photosynthetically Active Radiation (PAR, 400‐700 nm)
• Photosynthetic Photon Flux (PPF, μmol∙m‐2∙s‐1)
• Daily Light Integral (DLI, mol∙m‐2∙d‐1)
• Lux and foot‐candle units are less useful
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Relative quantum efficiency (RQE) according to McCree, 1972; Sager et al., 1988
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Avg. greenhouse DLI across the contiguous US
December June
2.5 ‐ 55 ‐ 7.57.5 ‐ 1010 ‐ 12.5
12.5 ‐ 1515 – 17.517.5 ‐ 20
20 – 22.522.5 – 2525 – 27.527.5 ‐ 30
After Korczynski et al., 2002
Supplemental light (SL)(supplemental photosynthetic lighting)
Frequently perceived as too expensive!
Important PAR source in Northern latitudes
Additional DLI needed to enhance canopy photosynthesis and crop growth
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Perspective
• US, second largest fresh‐market tomato producer in the world with 1.7 MMT
$1.4 billion
40% greenhouse (GH)‐grown
can gross $1.5 million per ha ($600,000 per acre) compared to $10,600 per ha for field vegetables
• In the last decade, GH production increased two‐fold (from 0.13 MMT to 0.27 MMT)
Still, US imports one‐third of its supply!
Greenhouse (GH) tomato industry in North America
84%
16%
Southern States
Northern States
42%
30%
28%2003
8%
3%
89%2011
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High‐wire GH tomato production
• Warm season crop
• High light requirement:
DLI of 20‐30 mol∙m‐2∙d‐1
• Indeterminate
• Long cropping cycles
• Labor intensive
Mature crop
New crop
Old crop
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Variable costs
1. Labor
2. Energy, 10 to 30% of total production cost• 60% lighting
• 40% heating
3. Production• Seedlings, fertilizer, substrate, pest‐control, etc…
4. Sales
5. Maintenance
Sweet pepper
Eggplant
Cucumber
Other high‐wire crops…
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Ave
rage
gre
en
hou
se D
LI
(mo
l m-2
d-1
)
0
5
10
15
20
25
30
35
40
45
Glass-glazed, 2012Polyhouse, 2013Glass-glazed, 2013
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
DLI inside a greenhouse in West Lafayette, IN
Higher DLI in 2013
Solar daily light integral (DLI) measured inside greenhouse
2014
Ave
rage
gre
enho
use
DLI
(m
ol m
-2 d
-1)
0
10
20
30
40
Above raftersAbove plant canopyMid-plant canopy
Month
Jan Feb Mar Apr May Jun Jul
Monitored with LI‐250A quantum sensors
Supplemental DLI: 9.5, 13.0, 8.8, 3.8, and 3.8 mol∙m‒2∙d‒1 for Feb.,
Mar., Apr., May, and Jun., respectively (at plant height).
Target DLI
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High‐Pressure Sodium (HPS) Lamp
Overhead (OH) high‐pressure sodium (HPS) lampscurrent standard
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Current standard: overhead (OH) high‐pressure sodium (HPS) lamps
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Mutual shading within foliar canopies
Leaves under direct light
Shaded leaves
LEDs a viable crop‐lighting option?
• Solid state
• Low volume & mass
• Long lifespan: 5 x 104 h (electronics) to 105
h (diodes) if heat sinked / not overdriven
• Waveband selectable
• Operate at low‐voltage DC
• Emitter surfaces relatively cool
• Potential for placement near plant tissues negates the inverse square law (I d‐2)
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Disadvantages of LEDs?
• Initial capital investment is high
• Need to be close to plants for best efficiency
• Proximity limits coverage area for lighting
• Fixture blocks solar during close placement in greenhouse
• Dense arrays of high‐output types require active heat sinking
• Variable spectra required for different phases of plant growth?
• Different spectra required for different species/cultivars
Discrete LED
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Luxeon Rebel LEDs
LED Applications for the Greenhouse Industry
Technologies, protocols, best practices, guidelines• For LED photoperiod lighting of ornamental crops
• To replace INC and CWF lamps for night‐interruption treatments• To determine R/FR ratios for efficient flower induction/crop development
• For propagation and finishing of transplants• Vegetable• Ornamental• End‐of‐day lighting• Daylength‐extension (DLI) lighting
• For supplemental lighting of vegetable crops• Daily light integral• Off‐season local production• Energy savings
• Designing arrays, fixtures, luminaires• Minimize blockage of sunlight• Apply supplemental LED light efficiently and effectively
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Image from the work of Gomez and Mitchell, Purdue University
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C.A. Mitchell: LED “Lightsicle” Concept, 1996
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Lightsicle design by ORBITEC
Massa&
Mitchell
PurdueUniversity
Each LED tower has a built‐in datalogger to record kW‐h of energy consumed
e2 classic 2.0 energy monitor
Large‐scale LED intracanopysupplemental lighting forgreenhouse high‐wire crops
Peak λ of red and blue LEDs were 627 nm and 450 nm.
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LED Intracanopy Lighting(from the work of Celina Gomez and Cary Mitchell, Purdue University)
Intracanopy lighting tower technology developed by ORBITEC
General results: SL increases yield
OH-HPS ICL-LED Hybrid Control
Fru
it y
ield
(kg
m-2
)
0
10
12
14
16
18
20
b
aa
a
Harvest parameters: no differences among SL treatments; all greater than control.
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Sink‐source relationship effects
The “source” is the net exporter/producer of photo‐assimilates and the “sink” is a net importer/consumer of photo‐assimilates
Flowering young tomato plants: Roots > young leaves > inflorescenceFruiting tomato plants: Fruits > young leaves > flowers > roots
Allocation of assimilates from the source to the sink are governed by:• Sink strength • Distance between sink and source • Plant developmental stage • Environmental conditions
Daily energy consumption
winter‐to‐summer
summer‐to‐winter
Expt. 1
DAT
0 20 40 60 80 100 120 140 160
En
erg
y co
nsu
med
(kW
h/d)
0
20
40
60
80
100
120
140
160
180
OH-HPSIC-LED
Expt. 2
DAT
0 20 40 60 80 100 120 140 160
Ene
rgy
con
sum
ed (
kWh
/d)
0
20
40
60
80
100
120
OH-HPSIC-LED
Expt. 4
DAT
0 20 40 60 80 100 120 140 160
Ene
rgy
con
sum
ed (
kWh
/d)
0
20
40
60
80
100
120
140
160OH-HPSIC-LED
Expt. 3
DAT
0 20 40 60 80 100 120 140 160
En
erg
y co
nsu
med
(kW
h/d)
0
20
40
60
80
100
120
140
OH-HPSIC-LED
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1. 600 W OH‐HPS lamps2. Hybrid lighting (OH‐HPS + interlighting) 3. Intracanopy‐LED towers4. Unsupplemented control
Image courtesy Philips Lighting
ICL‐LED with OH‐HPS lighting for tomatoes(supplemental lighting)
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Interlighting at mid canopy
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Current Situation
• HPS and LED fixtures have equal photon efficiencies, but the initial capital cost per photon delivered per unit area lighted from LED fixtures is five to ten times higher.
• Most presently available commercial LED fixtures have limited spectral choices, fixed‐color ratios, low output intensities, and are not specifically designed to maximize light distribution within GHs.
• PPF ≥ that of HPS lamps can be obtained for lower electrical power density (kW/m2) with LEDs.
• Light distribution from LEDs can be tightly controlled, leading to less waste of energy by not lighting areas not populated by plants.
• Continued improvement in LED efficiency + cost reduction from mass production suggest a bright future for LEDs in greenhouse applications.
Questions?
Dr. Cary A. MitchellDepartment of Horticulture & Landscape Architecture
Purdue University625 Agriculture Mall Drive
West Lafayette, Indiana 47907‐2010 USA(765) 494‐1347