Plants grown in a luminescent-concentrator-equipped greenhouse fared as well or better than plants grown in conventional greenhouses. Research greenhouses at the University of California, Santa Cruz which were equipped with electricity-producing luminescent solar concentrators are growing tomatoes and cucumbers. The first crops grown in the greenhouses were as healthy as those raised in conventional greenhouses.

Shaped like a pane of glass, a luminescent solar concentrator is typically transparent, but contains a luminescent dye that absorbs light within a particular spectral range, then re-emits the light at a different wavelength. This light is reflected within the plate, traveling sideways until it is absorbed and turned into electricity by narrow strips of photovoltaic cells, which are either sporadically embedded in the plate or placed at the plate's ends. These luminescent panels can concentrate sunlight even on completely cloudy days, which is impossible for ordinary concentrating optics.

The luminescent solar concentrators on the UC Santa Cruz greenhouses have a magenta look. They pass the red and a bit of the green and blue spectral regions while converting the rest of the blue and green light to electricity. Red and blue light are uniquely important for plant growth.

Through a strategic collaboration, Solaria and Soliculture have combined their technologies to create PV solutions for greenhouse applications that allow growers to generate revenue on the existing footprint of their greenhouses without compromising agricultural productivity. Soliculture is a provider of Greenhouse Integrated Photovoltaics for commercial greenhouse growers. Its wavelength selective greenhouse panels simultaneously enhance light quality onto plants while generating power.

These companies address two of the most pressing issues of our time—food and energy. According to the World Bank, we need to produce at least 50 percent more food by 2050 to keep up with the world’s growing populations. Everyone realizes the grave importance of creating a more sustainable energy future. Being able to address both crop yields and climate change with one product could be revolutionary.

There is a unique technical synergy between Solaria’s proprietary cell processing technology and Soliculture’s luminescent solar concentrator technology. Combined, they offer a value of high efficiency, aesthetically attractive modules at a cost-effective price with an altered light spectrum optimized for plant growth while simultaneously generating electricity. This solution solves the unique needs of farmers and their businesses for a material that has neutral effects on plants but generates enough power to make it economical. Now greenhouse growers have a major incentive to incorporate integrated photovoltaics into their agriculture projects.

The LUMO solar panel is the result of this partnership. These transparent panels contain a low density of silicon photovoltaic (PV) strips arranged periodically on a panel of glass, allowing light to transmit between the strips. A thin layer of luminescent material is adhered to the backside of the glass, enhancing light quality by converting green light to red light. The optimized light spectrum enhances power production and facilitates plant growth. LUMO solar panels are ideally suited for crop production areas of a greenhouse, where maximum light transmission is desired.

The LUMO technology utilizes a light-altering dye that converts green light to red light. Red light produces the highest efficiency for photosynthesis in plants. The absorbance of chlorophyll a and b, two pigments found in plants that are critical to photosynthesis, highlights the fact that plants absorb in the blue and red portion of the spectrum, and not in the green. In extensive plant trials, crops under LUMO have experienced positive growth responses, including increased yield, faster time to maturation, and disease resistance.

Soliculture offers SD panels as a frameless, single pane glass module, allowing compatibility with many common glass greenhouse designs, such as wide-span and venlo styles. These solar panels can be customized to any greenhouse glazing dimensions. This design negates the need for costly solar panel racking materials. Installing SD solar panels into a greenhouse roof is the most economical solution for solar energy generation in agriculture.

Reducing the energy used by greenhouses is a priority as the global use of greenhouses for food production has increased six-fold in the past 20 years to more than 9 million acres today and it's getting bigger. Canada relies heavily on greenhouses for vegetable production.

Electricity-generating solar greenhouses utilize a unique technology that produces electricity more efficiently and at less cost than standard photovoltaic systems. This is achieved by concentrating sunlight on a small solar cell. Luminescent solar concentrators concentrate both diffused and direct solar radiation without having to track the sun. The concentrators are comprised of plates of a transparent format fixed with luminescent materials such as organic dyes, rare earth ions, or semiconductor quantum dots. This material absorbs light and emits it at longer wavelengths. Most of the emitted light is trapped inside the plate by internal reflection. Then, it is directed to the edges where solar cells convert the concentrated light into electricity, which is used to regulate the greenhouse’s temperature, as well as power lights, fans, and monitoring systems.

Luminescent Solar Concentrators have the potential of providing small scale farmers with an affordable means of sustainability, grid parity and energy independence, while large scale greenhouse producers can double as large scale renewable energy producers, at the same time enhancing their plant production within same footprint.  While standard PV panels cost $1.00 per watt and produce 200 watts per sqm, LSC panels can produce 50 watts per sqm at a $0.50 per watt cost.  

The payback period is said to be between 3 and 7 years, with a 20+ year electricity-generating life, which could lead to a 20-30% capital cost savings when compared with a conventional greenhouse.

In areas with a short growing season combined with high electricity rates, the need for LSC panels makes perfect sense. As the price of panels continues to drop, crops that were once too costly to grow in greenhouses, such as lettuce and other crops could soon find a place there.

In hotter regions, like California’s Central Valley, cooling is a concern. Growers use swamp coolers and blinds to block the sunlight. Here is where the color of the panels is advantageous. Not only do the panels provide electricity to power swamp coolers, but the colored shading of the panels keeps greenhouses cooler and can eliminate the need for blinds.

Soon, we will see magenta greenhouses dotting the landscape.

For additional information:

1. https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-20-S2-A157&id=226225
2. https://sacarter.soe.ucsc.edu/sites/default/files/Corrado_PowerGeneratingGreenhouse.pdf

The content & opinions in this article are the author’s and do not necessarily represent the views of AgriTechTomorrow

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