Harvesting the Sun

A new generation of farmers may soon reap crops and electricity.


Solar panels
Nellis AFB

In a video posted this spring at Newsweek.com, a third-generation almond farmer in California's Central Valley explains how the state's longstanding drought has necessitated a shift in strategy. "We have land, we have lots of sunshine, but we have no water," he says. "So we better think of something else to use the asset for."

The answer he came up with was solar farming. As the camera pans a dusty array of photovoltaic (PV) panels, the man notes that almond orchards and solar farms have similar lifespans of around 20 to 25 years. "When it's up, you can pull it out," he says of the latter. "If we have water at that time, and an almond orchard is still viable, we can replant that, or some other kind of crop. Or we could put new-technology solar in."

With its lingering close-ups of parched soil and its sad-keyboards soundtrack, the video strikes an emphatically declinist note. The bounty of yore, it suggests, is a distant Eden, and our future is one of compromise and diminishing returns—not as fertile as the past, not as lucrative, not as fulfilling.

The farmer himself buys into this proposition: He presents a future of either crops or panels. But recent research suggests the choice may not be so clear-cut. That's because a new hybrid innovation called agrivoltaics is allowing farmers to raise crops on the same land that solar installations occupy.

The idea of doubling down in this manner was first proposed by a couple of German scientists in a 1982 research paper called "On the Coexistence of Solar Energy Conversion and Plant Conservation." In 2010, a French agronomist named Christian Dupraz decided to put the theory into practice.

Along with his colleagues at France's National Institute for Agricultural Research, Dupraz divided a small field in Montpellier into four plots. Two of the plots remain fully exposed to the sun; two others are covered by PV panel arrays. In one of these plots, the arrays were constructed at full density, or what Dupraz described as "optimal spacing for electricity production."

In the other, the arrays exhibit only "half-density." That is, there was more space between the panels to allow for greater sun exposure. In both instances, the arrays were mounted 13 feet above the ground via support pillars spaced approximately 20 feet apart—this way, farm machinery could still operate in the plots.

Dupraz's general hypothesis was that the lack of sun would inhibit crop production but that the shade provided by the PV panels might also increase water efficiency and thus make up for some of the reduced sun. In a series of experiments conducted over the course of several years, Dupraz, Helen Marrou, and others grew and carefully monitored a variety of crops at Montpellier, including wheat, cucumbers, and several kinds of lettuce.

What they have found to date is that crops grown under the full-density arrays fare less well than those receiving full exposure from the sun. But those grown under the half-density arrays do surprisingly well—essentially equaling the productivity of the control plants, and in some instances, even exceeding them.

One reason for this is because of the phenomenon Dupraz had hypothesized about: The shade created by the panels allowed the plants to utilize water more efficiently than those that were fully exposed to the sun. But as Marrou described in a 2013 research paper, the plants also increased their leaf area and altered the arrangement of their leaves. Faced with less sun exposure, they adapted to become more efficient light harvesters.

Courtney White, founder of the nonprofit Quivira Coalition, writes about agrivoltaics in his 2015 book, Two Percent Solutions for the Planet. "It was the Goldilocks principle at work again: Too much shade hurt the crops, too little hurt electricity generation. Everything had to be just right."

What makes agrivoltaics especially compelling is how this balancing act increases overall productivity. According to Dupraz's calculations, combining solar and farming can potentially make the land 60–70 percent more productive.

For that third-generation California almond farmer, agrivoltaics is not a viable option at the moment: His farm lost its access to water after a shift in federal policy earlier this year, and attempts to drill wells on his land came up dry. Thus, he currently lacks the ability to hydrate any kind of crops, even ones not quite as water-dependent as almonds.

But the idea behind agrivoltaics—that land need not be reserved for one use at a time—will be essential in coming decades. Over the next 35 years, global population is projected to grow from seven billion to nine billion. And around 2.5 billion people, mostly in China and India, will enter the middle class. This growth—in both population and wealth—will put even more pressure on scarce natural resources and already-straining social institutions.

And yet, in their 2014 book Resource Revolution, former McKinsey consultants Matt Rogers and Stefan Heck see opportunity where others see looming catastrophe. "While labor productivity has improved almost 100 percent over the last two decades," they write, "resource productivity has increased only 5 to 10 percent—and it's not because there isn't room for improvement."

In their estimation, the vast new coming market of global middle-class consumers gives entrepreneurs an incentive to use information and industrial technology to extract far more value from existing resources.

As the world urbanizes, many observers have come to believe in the virtues of increasing density. While cities were once equated with disease, crime, and vice, they're now associated with higher wages, more jobs, expanding innovation, and greater environmental sustainability.

"The average Vermonter…consumes more than four times as much electricity as the average New York City resident, has a larger carbon footprint, and generates more solid waste, backyard compost bins notwithstanding," writes David Owen in his 2009 book Green Metropolis. "In terms of sustainability, dense cities have far more to teach us than solar-powered mountainside cabins or quaint old New England towns."

Intensifying land productivity—especially by combining agricultural with industrial uses—goes against the vogue for free-range, organic farming practices. High-efficiency agriculture doesn't create the best optics for attracting well-heeled Whole Foods customers seeking heirloom tomatoes raised in 18th century–esque settings. But switching to agrivoltaics makes financial and environmental sense. Not only does it extract greater productivity from a given piece of land via multitasking, but these simultaneous uses are designed to complement each other in synergistic ways. In a world where water is only going to get scarcer, turning to growing environments with built-in shade is itself a form of conservation.

A Stanford research scientist named Sujith Ravi has noted another way agriculture and photovoltaics can complement each other. Currently, many California solar farms are located in desert habitat. But when dust and dirt accumulate on the PV panels, their efficiency can drop substantially. So operators often use water to both wash panels directly and to dampen the ground underneath them to mitigate dust. Ravi theorized that that water would go to better use if there were crops there to take advantage of it. Using computer models, he explored the feasibility of growing agave—a crop with low water requirements and the potential to be used as a biofuel (or to make tequila).

Ravi has yet to test this approach in the real world. And Dupraz's own experiments have been relatively small. But if agrivoltaics is feasible at scale, it could play an important role in California's economy in coming years. In 2008, Governor Arnold Schwarzenegger signed legislation that California's public utilities must serve at least 33 percent of their load with renewable energy by 2020. Utility providers are looking for ways to reach this goal, and one possible route is through large-scale solar projects.

It's not necessarily that easy to find the land for such projects. Frequently, permits have to be procured and environmental analyses conducted before construction can begin on wild lands. In such instances, there are typically questions about displacement of sensitive species, objections over the loss of open spaces, and other similar concerns.

Agrivoltaics presents an opportunity to place large-scale solar installations on flat, sunny, privately owned land near existing electrical grid infrastructure. And increasing the productivity of land that's already in use gives farmers an added revenue stream while minimizing new development of wild spaces. It suggests a future where sustainability arises from innovation and the pursuit of plenty, not from privation. Let the carbon-neutral margaritas flow!