Solar powered offgrid greenhouse grows food faster using less water

A pilot structure built in California has shown that ‘wavelength selective’ greenhouses can be designed with solar panels that feed crops enough sunlight, while also powering the structure. In the greenhouse, 20% of crops actually grew better – while overall, plants used about 5% less water.

The broader goals of the project were to lower agricultural co2 emissions with sustainable energy generation, while exploring how to increase our food security with offgrid greenhouses.

The research was done at the University of California, Santa Cruz by Michael Loik, professor of environmental studies at the school.

The main challenge was to determine how the plants would perform under different lighting conditions – one in which certain light wavelengths are absorbed to generate electricity. It turned out that 80% of plants grew unaffected by the change in the lighting. A few plants actually grew better – C. annuum (peppers), Citrus aurantifolia (limes), Fragaria × ananassa (strawberries) and L. esculentum (tomatoes) – under the meganta panels.

In email response response to Electrek from Professor Loik, on why red as a color, “its absorption spectrum (green plus some of the blue) and the photoluminescence spectrum (red) were about as good a match to the absorption spectrum of chlorophyll as one could find.” That means, the light that the solar cells needed compared to the light that best drives plant photosynthesis were different enough that both could be used for their own purpose concurrently.

The magenta dyed panels are defined as ‘wavelength-selective photovoltaic systems’ (WSPV). Per the project, they field tested at 4% efficiency. Cutting edge standard solar panels are pushing past 22% in commercial laboratories. Looking closely at the header image – you’ll notice that there are black strips within the red plastic material. These are the actual photovoltaic cells. The solar panels are suggested to cost about 65¢/W.

In another email question – ‘Were the red panels above or below the solar cells?’, the Professor responded:

Above. Our design is unique because prior LSCs placed the solar cells on the ends of the panels; the current design has them facing up toward the sun. So the solar cells are illuminated by sunlight, plus the energy delivered within the plastic by resonance transfer between dye molecules.

Also from the Professor – “In terms of electricity loads, there are temperature and humidity controls, lighting, irrigation, etc. Things that draw load in a greenhouse: fans, louvers, rooftop windows that automatically open and close, blowers, coolers, humidifiers, condensers, lights, high-pressure sodium lamps, pumps, analytical lab equipment (balances, drying ovens), monitoring sensors and data loggers.”

About 37% of earth’s land – 49m km² is used for making food. In comparison, about two times the land of New Jersey is under greenhouses – about 36,400 km² globally. There is currently 15.5m km² of farmland being used at any point within five years. This represents 31% of all land that is used for food production (the rest is pasture land – 33.5m km²). Land under greenhouses represents 0.2% of all land being used for crop production within the last five years (which itself is only 31% of land for all food production).

Electrek’s Take

I really like the concept of an offgrid greenhouse. On some level it makes me think of the greenhouse as being a cell in a body – a mitochondria. And the organism being the human species across the planet. We have these independent, sustainable and self managing greenhouses around the world significantly protected from the complexity of the world around them.

Seeing these units, it makes me think of shipping container farming systems. The main differences I see are that the shipping container can be delivered easier – but the greenhouse feeds itself electricity, whereas the container needs a grid (or accompanying solar array). Seems the military could deliver these two solutions to areas in need during different times – longer term production locations might get a solar powered greenhouse, while an under duress situation might get pre-grown shipping containers.

While these greenhouses won’t be able to feed the power grid any significant amount of electricity they do parallel the use of solar power as a building material – called building integrated photovoltaics (BIPV) – and as part of combined revenue projects – called infrastructure integrated photovoltaics (IIPV). We get to grow the list of many creative ways we’re starting to use solar power outside of fields and rooftops. Our collection includes:

• Solar powered highway sound barriers in the Netherlands
• Chinese built solar farm atop a fishery
• Japan mushrooms underneath solar farms
• Indian solar panel covered water canals
• Minnesota integrating flowering plants and natural grasses
• The Carolinas researching integration of sheep grazing and solar
• The Netherlands bike path with solar panels
• And a huge 700MW Chinese solar farm with grapes growing underneath

and of course…

• Solar freaking roadways man – which may or may not come to be ‘roadways’, but instead sidewalks, parking lots or public space

Any to add here?

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