Food Plus Electricity: Solar Cells and Crops can Share the Sun

August 8, 2013


UC Santa Cruz

Santa Cruz.Com:

Truly renewable resources and self-sustaining systems are few and far between.  But what if you could have one in your garden? Imagine strolling through your back yard, past the calming sound of your cherub fountain, breathing in the smell of fresh earth. You enter your greenhouse, and a fan gently blows air into your face. Your spinach and lettuce are looking good, and even the artichokes are coming along. Languid ladybugs and fragrant flowers live in happy harmony.

In this near-future scene, you’ll be happy with your power bill, too. The fountain, the fan and the pumps watering your garden will all be powered by the greenhouse itself.

A team of scientific innovators from UCSC has created a self-sustaining system like this, using a new generation of solar panels. These devices trap just part of the sun’s light to produce electricity. The rest passes through, nourishing the growing plants underneath.

Solar energy has a promising future, but it fights for land with threatened species, agriculture and California’s natural landscape. The UCSC team—boosted by support from NASA—aims for a more cooperative way to extract power from the sun.

“Much of the current solar development in California scrapes away plants and flattens the habitat, then solar farms are installed,” says environmental studies professor Michael Loik, a photosynthesis expert at UCSC. “I want to install our technology in a way that is compatible with the native vegetation.”

On a large scale, solar “farms” seem like a good source of clean energy. However, the bulky installations require development that can destroy ecosystems and drive away animals. What’s more, Loik says, today’s solar panels use rare Earth metals, the ingredients of smart phones and LED televisions and hybrid car batteries. “These materials are not very sustainable in the way they are mined or disposed of,” Loik notes.

The UCSC team hopes to coax part of the solar industry in a new direction with its twist on solar panels: Wavelength Selective Photovoltaic Systems, or WSPVs.

Photovoltaic systems use the photoelectric effect, a basic process in physics, to convert light energy into electricity. If it exceeds a certain energy level, incoming light can excite and set free the outermost electrons of the atoms in a chemical element. That critical wavelength, or color, of light varies from one element to the next. Traditional solar panels capture these electrons ejected from unsustainable rare earth metals, such as cadmium and special forms of silicon. In contrast, the photovoltaic generators in WSPVs absorb light that travels down what could be called a “pigment highway.”

A Glowstick on Steroids

It all started in a physics lab on the UCSC campus. Physics professor Sue Carter works with Luminescent Solar Collectors—LSCs for short. These special panels use pigments to absorb sunlight. Like a glow-stick on steroids, a fantastically vibrant pink-orange color explodes from the panels as soon as sunlight touches them. The result is nearly blinding, leaving blotches in your sight if you stare at the edges for too long. The pigment, scattered throughout the collectors, traps incoming light energy and guides it to electricity generators.

The key to this innovative form of solar energy is that physicists can control the wavelength of light that the pigment traps. “I started looking closer and closer at the spectrum of luminescent materials,” says Carter. “I realized that the most efficient color nearly aligned with what plants wouldn’t need.”

WSPVs use a pigment called LR305, which catches only green and blue wavelengths. Plants do not absorb green light. Instead, they reflect it, which is why they appear green. By taking light that plants don’t use for photosynthesis to generate electricity, the panels allow plants underneath to grow, flower and fruit.

Carter knew her panels had the potential to change the outlook of the solar energy field. However, a big question loomed: With some colors subtracted, how would plants react to the altered light quality? “For certain species,” Loik says, “seed germination, or the decision to make flowers or leaves, is controlled by the color of available light.”

Loik and several undergraduate students are running experiments on campus to test the effects of changing light quality on photosynthesis, fruit production and plants’ abilities to capture and hold the carbon they need. On top of UCSC’s Interdisciplinary Sciences Building on Science Hill, a normal-looking greenhouse offers peaceful views of the surrounding redwood trunks. But inside, hidden behind foggy windows, sit what appear to be futuristic teepees. Shining scarlet panels laced with LR305 house small clusters of lettuce, spinach and tomatoes. The team’s latest results show that tomato plants grown under the teepees produce more fruit than the plants grown in normal light conditions. However, the tomatoes are a tad smaller.

“Different species of plants respond differently to the changing light environment,” Loik says. Lettuce and spinach, for example, are unaffected by the altered light. Unfortunately, in recent tests, strawberries seemed to dislike the light under the panels.

“We can’t solve every puzzle,” says Carter. “But we can get a good idea on how to proceed forward and how species interact in different environments. This will help make better greenhouses for those plants.”

What’s more, this new technology will not negatively affect the existing solar market, says James Allen, CEO of Allterra Solar, a design and installation company based in Santa Cruz. There will still be a market for traditional solar panels, he explains, in rooftop installations where all of the available light can be harvested. Far from competing with traditional solar panels, WSPVs broaden the marketability of solar energy as a whole.

Allen says his company is always enthusiastic about any advancement in renewable energy. He considers WSPVs a perfect solution for farmers who need the power source, but can’t sacrifice their land.

“This technology allows farmers to get the best of both worlds. We are always excited when new innovations can be integrated into the field of solar energy,” Allen says.

If the team can demonstrate that their WSPVs are more cost-effective than traditional solar panels, the UCSC scientists believe this project will open other gates in alternative energy. The venture already has spawned a company: Soliculture, founded in 2012 in Scotts Valley by Glenn Alers, a physicist and computer engineer at UCSC, with Carter and entrepreneurial lead Carley Corrado. The company is working with greenhouse growers and farmers to test the feasibility and commercial application of WSPV technology.

All the panels Soliculture installs for its customers are built in research labs at UCSC. However, the team has made sure that the WSPV panels can fit into the preexisting solar manufacturing market, because they aim to contract out the production process in the future. Soliculture now supplies nearly 100 customers with electricity generated from panels covering productive crop land near the central coast.

Loik hopes to carry out the same experiments in the desert or in grassland ecosystems—ultimately, on a larger scale.

“Windows are everywhere,” Loik says. “Why not utilize all that glass surface to generate electricity at the same time?”

3 Responses to “Food Plus Electricity: Solar Cells and Crops can Share the Sun”

  1. petersjazz Says:

    US is a strange country. I live in Sweden and have setup solar panels but the sun is a lot more intense in US and you have a lot of air condition. Air condition and solar panels is a great combination, the more sun, the more air condition you want. I guess theres something wrong in the political system, otherwise US should have been before Germany in solar energy. By far.

    • jcl64 Says:

      I agree. Also, all cars should have been fitted with solar roofs so that they can bring the temperature of the inside without having to use a lot of fuel to cool it down. Ofc an electrical car is a better option in all cases, but still these should have solar powered aircondition imo.

      Seriously tempted into getting a solar panel myself in spite of my region having more than 200 rainy days a year. 🙂 – If not only to try it out and see what I can run on a battery pack. A Raspberry Pi surely dont take much power to run – although the problem next then is to find a low power monitor for it. 🙂

      • MorinMoss Says:

        I keep saying it and will keep on saying it until I start reflecting blue light – carports with solar panels EVERYWHERE – schools, stadiums, shopping malls, parking lots.

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