Science & Tech

'Power Plant' Greenhouses Are Coming

A magenta greenhouse at the University of California, Santa Cruz, is paving the way to a whole new idea of what greenhouses can be.

At first, the greenhouse concept developed by Michael Loik, a professor of environmental studies at U of C, Santa Cruz, and his colleagues appears to be similar in many respects to conventional greenhouses.

Loik’s greenhouse is set out in the sun and acts as a hothouse location for raising plants. The plants grown in recent experiments using this greenhouse were tomatoes and cucumbers. The vegetables were as healthy and delicious as any other greenhouse-grown ones.

What makes this greenhouse concept unique, however, is that it is a dual-use greenhouse designed from the start to keep the heat from the sun within the structure, so the plants can grow, while also making it possible to capture and convert some of that solar energy into electricity.

This electricity-generating solar greenhouse uses what is known as Wavelength-Selective Photovoltaic Systems (WSPVs). These systems, which can be optimized to respond to a specific wavelength of light, are able to generate more electrical power at a lower cost and with higher efficiency than ordinary “broad-spectrum” photovoltaic systems.

This solar greenhouse has transparent roof panels that have been soaked in a bright magenta luminescent dye. That dye absorbs a high percentage of the solar energy that hits the roof and then transfers energy – via luminescence – to narrow photovoltaic strips. These strips then convert the resulting light into electrical power that can be passed on and/or stored in battery power banks.

Part of the unique greenhouse design involved with WSPVs is that this specific one at U of C, Santa Cruz, absorbs some of the blue and green wavelengths of light while naturally passing the rest through. The light that gets through allows the hothouse plants to grow, while the light that is absorbed allows the hothouse to efficiently produce additional solar-powered electrical output.

Loik – along with Catherine Wade, a graduate student; Carley Corrado, a post-doctoral researcher; and undergraduates David Shugar and Devin Jokerst, all of Santa Cruz – conducted most of the experiments. Carol Kitayama, a senior grower at Kitayama Brothers, also participated in the research efforts.

What Loik and the rest did in evaluating the dual-use design was to look at how well photosynthesis and fruit production worked with the dual-use system and the WSPVs. The plants studied eventually broadened to a total of 20 different varieties of tomatoes, cucumbers, lemons, limes, peppers, strawberries and basil. Each of the batches was grown in a dual-use magenta greenhouse either at the university facility or in nearby Watsonville, California, one of the most important growing regions in the state.

Originally, the researchers were not sure what might happen and were expecting negative results. As Loik said, “I thought the panels would grow [plants] more slowly, because it’s darker under these pink panels. The color of the light makes it like being on the Red Planet.” Yet despite those plants being sensitive not just to light intensity but also to color, the researchers discovered that “it turns out the plants grow just as well” in this unusual greenhouse.

In fact, in 80% of the plants evaluated, there was no negative impact of putting them in this new growing environment. Some 20% grew even better under the light of the magenta windows.

Loik also discovered that the “plants required 5% less water to grow the same amount as in more conventional greenhouses.”

The ability of the greenhouse to generate its own electricity is also important, since most commercial greenhouses use electricity to maintain temperatures as well as power fans, lights and other electrical monitoring systems. With the WSPV-technology panels costing only 65 cents per watt of energy generated – this is a big win. As Loik, a specialist in climate-change studies, plant physiology and sustainable technologies, points out, “This technology has the potential to take greenhouses offline.”

In all cases – especially considering that tomatoes and cucumbers are some of the highest-volume greenhouse-produced crops worldwide – the results could mean big wins as a business opportunity too. This comes as very good news for U of C, Santa Cruz, physics professors Glenn Aers and Sue Carter, who invented the WSPV technology and then, in 2012, founded a company called Soliculture to bring it into broader markets and crop use.

All of this points to the sprouting up of more of these dual-use magenta greenhouses in the future, perhaps eventually for use throughout the world.