A news item I contributed to the August issue of tED Magazine. Reprinted with permission.
According to Technavio, the global greenhouse horticulture market is expected to grow at a CAGR of nearly 11 percent from 2017 to 2021. Estimated at 1 billion square feet of growing space in 2017, the horticultural market includes supplemented greenhouses, which use electric lighting to supplement, extend, or replace daylight; non-stacked indoor farms, which use ceiling lighting on plants grown in a horizontal area; and vertical farms, where plants are grown stacked on shelving that typically includes integrated lighting.
For many utilities, horticultural facilities are one of their fastest-growing loads, with lighting constituting the largest portion. As a result, the DesignLights Consortium (DLC) produced a specification for inclusion of LED horticultural products in the Qualified Products List, expected to be released in September. This recognizes the energy-savings potential of LED horticultural lighting and will qualify LED horticultural products for utility rebate programs. Currently, LED lighting has a high penetration in vertical farms but very low penetration in the other two types of horticultural facilities. Initial cost is a significant factor, which often requires justification based on satisfactory energy savings.
Young plants in a greenhouse in the Netherlands
In May 2018, the Lighting Research Center (LRC) released a cautionary report evaluating potential energy savings for LED horticultural lighting. The LRC found that energy savings is possible with LED, but one should evaluate products based on application efficiency rather than simple luminaire efficacy. In short, rather than generalizing about energy efficiency, the lesson seems to be that some LED products save energy compared to some traditional products, depending on the product and the application.
The LRC conducted photometric testing, application simulations, and life-cycle cost analysis for 10 LED horticultural luminaires and 4 traditional luminaires including high-pressure sodium (HPS) and metal halide (MH). The evaluation included 11 luminaire-specific metrics and 5 application-specific metrics, focusing on photosynthetic photon flux density (PPFD), which measures light energy the plants need to grow and is analogous to footcandles in a commercial application.
The LRC discovered a wide variation among products, resulting in some of the tested LED horticultural products saving energy while achieving the same PPFD. The LRC also found that an average three times more LED luminaires were needed to produce the same PPFD as a typical 1000W HPS layout. The number of luminaires and their size produces shading. The LRC found the tested LED luminaires reduced daylight by 13-55 percent compared to 5 percent for HPS.
“Upon analyzing our data, we were intrigued by how intensity distribution and layout emerged as key factors in system performance,” LRC Research Scientist Leora Radetsky stated in an LRC press release.
As a result, the LRC concluded that three of the tested LED luminaires produced a lower life-cycle cost while the remaining seven had a higher life-cycle cost than the two tested 1000W HPS systems.
The findings contradicted a report by the U.S. Department of Energy (DOE) published in December 2017, which claimed potential energy savings of up to 40 percent if all horticultural lighting switched to LED today. The DOE analysis was based on an assumption of a 1:1 replacement of luminaires, which the LRC disputed, and a focus on luminaire rather than application efficiency.
Click here to download the LRC report.
You must be logged in to post a comment.