Solar-Powered Drip Irrigation
Solar-powered drip irrigation is the marriage of two systems that have been shown to have an enormous independent impact, but have rarely been used together in a well-documented fashion. Drip irrigation is an extremely efficient mechanism for delivering water (and fertilizer) directly to the roots of plants. It increases yields and allows for introduction of new (potentially high-value) crops in regions where they could not be sustained by rainfall alone. Solar-powered (photovoltaic, or PV) pumps save potentially hours of labor daily in rural off-grid areas where water hauling is traditionally done by hand by women and young girls. They are durable and immune to fuel shortages, and in the medium- to long- term cost less than traditional diesel-powered generators (e.g., Kohle et. al., 2002). When used in tandem, these technologies allow for production of market garden vegetables during the dry season, providing a much-needed source of both income and nutrition.
As shown in the cartoon schematic above, a PV array powers a pump (either surface or submersible, depending on the water source), which feeds water to a reservoir. The reservoir then gravity-distributes the water to a low-pressure drip irrigation system. Sizing of pumps, reservoirs, and fields is done based on water availability and estimated evapotranspiration needs for the region.
From a technical standpoint, solar-powered pumps and low-pressure drip irrigation systems make an ideal pairing. First, drip irrigation applications in the developing world have been limited by reliable access to water (e.g., ICRISAT Briefing Note 7, 2007). Solar-powered pumps provide a low-maintenance, long-term solution. Additionally, they can be used together in a direct-power system (no batteries) because the solar radiation (which governs pump speed) is also the main driver of evapotranspiration (how much water crops need). Thus, the pump works faster when it is sunny and the plants need more water, and vice-versa. While training is necessary for use and maintenance, the systems are simple to operate and repair.
This design is an expansion of the African Market Garden, a low-pressure drip irrigation system developed by the International Program for Arid Land Crops Center (IPALAC) and disseminated by the International Crops Research Institute of the Semi-Arid Tropics (ICRISAT). As part of the pilot phase of this project, three half-hectare systems have been installed -- one in the village of Dunkassa (sumbersible pump) and two in the village of Bessassi (surface pumps). Please see the photo gallery to get a better idea of what these actually look like!
Sources and Suggestions
African Market Garden (AMG) press release.
"Solar (Photovoltaic) Water Pumping," Technical Brief, Practical Action (http://www.practicalaction.org). [.pdf]
Kolhe M., et. al. "Economic viability of stand-alone photovoltaic systems in comparison with diesel-powered systems for India," Energy Economics, 24, 2002. [.pdf]
"Can Drip Irrigation Improve Food Security for Vulnerable Households in Zimbabwe?" ICRISAT Briefing Note No. 7, February 2007. [.pdf]