Watered by the Sun

Innovation / by Maywa Montenegro /

Linking the efficiency of drip-irrigation to the reliability of solar panels, a new technology—and a creative science-development partnership—is helping women to grow more food in rural Benin.

If you’re like most Americans, you spend about 12 percent of your annual income each year in grocery stores and restaurants. It may sound like a lot, but now imagine shelling out 50 to 80 percent of your hard-earned cash each year just on food and drink. That’s commonplace in sub-Saharan Africa, where per capita income is much, much lower than just about anywhere else on Earth, and a huge chunk of it is spent on staple nourishment.

Lessening the food-related financial burden that many Africans bear is a multi-layered problem—spanning global trade, market access, and gender politics, to name a few. But given that most sub-Saharan communities rely on rain-fed agriculture, and given that it only rains between three and six months out of the year in that part of the world, better irrigation is emerging as a simple method for combating poverty and malnutrition.

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The Kalalé  district of Benin is a poor, dry region in the northern part of the country, with approximately 100,000 people—none of whom have access to the electricity grid.  A 2.1kW solar electric power supply, like the one shown here, can provide 100 percent of the energy for a drip irrigation system. Credit: Solar Electric Light Fund

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Malnutrition in Benin is widespread, as evidenced by the many children with distended bellies—a telltale sign of kwashiorkor, a condition largely caused by lack of protein and micronutrients. Credit: Solar Electric Light Fund

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As a result of the new solar-powered drip irrigation systems, not only are women better fed, but so are their children and the rest of the villagers. In 2009, SELF executive director Bob Freling visited two villages in Benin and was delighted to see women marching proudly into town with baskets filled to the brim with vegetables. Credit: Solar Electric Light Fund

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A pilot study led by Stanford researcher Jennifer Burney showed that solar-powered drip irrigation significantly boosted women’s nutrition and income—benefits that spilled over to all members of the community. Credit: Solar Electric Light Fund

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Women are earning an extra $7.50 per week form the sale of fresh produce at the local market, and several are using that income to launch other small entrepreneurial ventures. Credit: Solar Electric Light Fund

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A diagram of the “Solar Integrated Model” shows that local microgrids can power water pumping for irrigation and drinking, lighting and computers for schools, refrigerators and lab equipment for health clinics, a local Wi-Fi network, and more. Credit: Solar Electric Light Fund


Irrigation schemes come in many flavors, of course. Giant traveling sprinklers lavish water over fields in the US midwest, for instance, while rice plots from southern Louisiana to the Philippines get the full-on treatment of flood irrigation. Drip, or “micro,” irrigation, as the name suggests, is stingier with the water, delivering it to the roots of plants drop by drop. And due to its efficiency, drip irrigation is now the most rapidly expanding model in sub-Saharan Africa—some studies show that it can double yields, deliver water savings of 40 to 80 percent, and reduce the need for fertilizers, pesticides, and manual labor. But a big obstacle to expanding the reach of drip irrigation in Africa has been a lack of reliable energy supplies; even frugal drip schemes need some sort of energy source to power a water pump.

Now an innovative research partnership spanning California, Washington D.C., and Niger, is testing a new way to bring water to thirsty plants: photovoltaic drip irrigation (PVDI). Linking the efficiency of drip irrigation to the reliability of a solar-powered water pump, the PVDI systems need no batteries, gas, or kerosene. And in places like rural Benin, where women and girls traditionally haul water by hand, often from very long distances, PVDI can free them from the backbreaking work of tending vegetable crops, especially during the dry season.

“Our case study on women’s farming groups in rural Benin showed that solar-powered drip irrigation significantly improved nutrition as well as household incomes over the course of a year,” says Jennifer Burney, a post-doctoral student at FSE.

In 2007, Burney and her colleagues partnered with the Solar Electric Light Fund, a D.C.-based NGO, to install irrigation systems in two villages in Benin’s Kalalé district. In both villages, the systems were used and maintained by a group of about 30 women, who collectively grow vegetables for their own families’ consumption and for sale in local markets.

The team also set up control plots in both villages, where women hand-watered their vegetable plots, the traditional practice in the region.

What the researchers found, after just one year of monitoring, was striking: As Burney’s team reported earlier this year in PNAS, the solar-powered drip systems supplied an average of 1.9 metric tons of produce per month—a cornucopia of peppers, tomatoes, okra, eggplants, and carrots—without cutting into the women’s continued cultivation of major staples like corn, sorghum, yam, and cassava. And the women started piling more veggies onto their families’ plates. Usually, during the rainy season, overall vegetable consumption rises by about 150 grams per day. According to household surveys Burney’s team distributed, women tending the test plots were able to feed their families about 500 to 700 grams per day—the equivalent of three to five servings. They also started selling more vegetables on the market, which in turn gave them more money for other types of food, such as meat, milk, and cheese. Several women also earned enough extra cash to begin diversifying. “We saw anecdotally that a lot of women have invested some of the earnings into other small businesses: Some have devoted a portion of their plots to producing seeds to sell to others, some have invested in things like ingredients and bowls to sell prepared food in the market—they’re making a variety of little capital investments.”

Solar-powered irrigation systems are but one way that captured sunlight is slowly transforming the developing world. In rural regions, where millions of people have no access to a centralized power grid, photovoltaic micro-grids are beginning to bring electricity to town—and along with that, the chance for computer power, Internet access, and the simple luxury of reading after dusk. Recognizing this enormous potential, the Solar Electric Light Fund has been working since 1990 to raise funds for photovoltaic systems, partnering with companies like Dell and Infosat to donate PCs and satellite uplinks.

The Benin project, however, represents a unique NGO-academic merger. A great deal of non-profit developmental work takes place in a vacuum, without controlled monitoring or scientific evaluation. In partnering with Burney’s group at Stanford, SELF set out to design randomized, single-test treatment projects that could be rigorously studied and analyzed.

That kind of setup enabled the researchers to put some dollar figures to solar-powered irrigation systems. Each system, they found, costs about $18,000 to install and requires about $5,750 to maintain. Based on farmers’ projected earnings, the systems should pay for themselves in less than two and a half years. Compared with irrigation schemes that rely on gasoline, diesel, or kerosene, PVDI certainly has higher upfront costs, but in the long run, they end up being more economical, says Burney. Not to mention their added benefit of being emissions-free.

Other results were less quantifiable. “In most cases, these women never earned any income before—so there was an overwhelming sense of pride in the new systems,” says Burney. Now headed back to Benin for phase two of the project, which includes four more villages, Burney hesitates to use the buzz-word “innovative” about her work, but acknowledges a burgeoning interest in linking hard science to development practice at the very early stages. After all, she says, “Everyone wants to know what works.” 

What does solar irrigation look like? Jennifer Burney takes us on a visual tour.

Originally published April 5, 2010

Tags development food innovation technology

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