With the new WSPV solar technology developed at UCSC, it would take only 4 percent of U.S. agricultural land to supply the amount of energy used annually in this country.
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.”
New Wavelength
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.”
Future Slime
Beyond these common garden plants in Loik’s projects, Carter works with another species to see how it grows under LR305 panels: algae. “Algae are one of the main materials being considered for next generation biofuels, because they have much greater power output per acre than any other biomaterial,” Carter says.
Growing large quantities of algae is tricky. The plants usually cannot be grown outside because they easily get contaminated. One remedy is to grow algae in greenhouses, which protect them from foreign particles in the air, but this is expensive. Carter’s panels cost less in materials, and by yielding power they lower the overall energy costs.
These qualities piqued the interest of microbial biologist Leslie Bebout from NASA’s Ames Research Center in Mountain View. Bebout studies algae and its potential cultivation in outer space for future long-term missions. “I am very enthusiastic about the WSPVs,” Bebout says. “They are a smart and elegant solution to the challenges facing crop production in California, and we hope for algae also.”
Bebout is eager to see WSPV technology mature for our descendants to use in space or on the moon. There, she says, “the largest source of free energy is sunlight.”
Carter and Bebout met at a coffee shop in Felton to discuss applying WSPVs to research on algae and energy production. Bebout admits that growing algae in space is still beyond the horizon, but she believes today's studies can set the stage. In her own research, Bebout showed how well algae grew under the altered light of Carter’s panels.
“For five different commercial strains of algae, [with] the WSPVs selectively taking a full one-third of the incoming sunlight, the cells perform just as well, if not better than in full sunlight,” she says. “If this technology for algae can go up in scale, it could be a real game-changer.”
Carter’s team recognizes this potential, too. Carter protects her algae in a distinctly un-green greenhouse in the New Zealand Garden at UCSC's famed Arboretum. The shocking orange structure, in stark contrast to the various exotic trees, reveals that this building uses WSPVs to sustain itself.
“All the fans and the electronic instruments for monitoring conditions and entering data are powered by electricity that the greenhouse generates itself,” Loik says. The algae inside stay cozy and safe, and maintaining the greenhouse is cheap.
Market Forces
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?”
According to the team, at projected levels of efficiency, it would take only 4 percent of U.S. agricultural land to supply the amount of energy used annually in this country. Those lands, rather than lying in shadows under acres of panels, would yield crops in the warm pink light of WSPVs.
It might take time to get used to such a foreign glow among lush green crops. But a sustainable energy future may depend on this vision.
