Since diving into the deep end when it comes to energy issues, almost every day sees new concepts, approaches, and technologies — fascinating, exciting, even hope-inspiring at times. And, to top it all off, so many of these are truly Energy COOL as well.
Innovative combinations of rather straightforward, well-in-hand technologies can offer real solutions to problems while creating new opportunities.
Several weeks ago, a group of researchers published an article in the Proceedings of the National Academy of Sciences documenting how relatively low-powered solar systems offer the potential to increase food supplies in impoverished arid regions while reducing demands for fertilizers and other costly (in fiscal and other terms)additives.
Solar-powered drip irrigation enhances food security in the Sudano–Sahel documents a field research project which found that:
Solar-powered drip irrigation significantly augments both household income and nutritional intake, particularly during the dry season, and is cost effective compared to alternative technologies
Over the decades, irrigation has been shown to greatly increase agricultural productivity. Drip irrigation is spreading rapidly in Africa, with significant benefits.
Drip irrigation delivers water (and fertilizer) directly to the roots of plants, thereby improving soil moisture conditions; in some studies, this has resulted in yield gains of up to 100%, water savings of up to 40–80%, and associated fertilizer, pesticide, and labor savings over conventional irrigation systems
The solar-powered systems, however, look to offer the potential for even better results. From the study on impacts of photovoltaic drip irrigation (PVDI) systems it was reported:
The women’s agricultural group members utilizing the PVDI systems became strong net producers in vegetables with extra income earned from sales, significantly increasing their purchases of staples, pulses, and protein during the dry season, and oil during the rainy season.
Finally, survey respondents were asked how frequently they were unable to meet their household food needs. Based on the frequency and most recent incident, households were assigned a food insecurity score ranging from zero (no problems during the previous year) to one (perpetually unable to meet food needs). This score changed significantly for project beneficiaries, as they were 17% less likely to feel chronically food-insecure. In short, the PVDI systems had a remarkable effect on both year-round and seasonal food access.
One of the basic design characteristics is a “battery-free configuration, thereby avoiding one of the major pitfalls of photovoltai use in the developing world.
In a photovoltaic- (or solar-) powered drip irrigation (PVDI) system, a PV array powers a pump (either surface or submersible, depending on the water source) that feeds water to a reservoir. The reservoir then gravity-distributes the water to a low-pressure drip irrigation system.
This arrangement leads to a benefit that provided one of those ‘head-slapping of course’ moments.
No batteries are used in the system: The pump only runs during the daytime, and energy storage is in the height of the column of water in the reservoir. Sizing of pumps, reservoirs, and fields is done on the basis of water availability and local evapotranspiration needs. The system passively self-regulates: Because solar radiation is the main driver of both pump speed and evapotranspiration, the volume of water pumped increases on clear hot days when plants need more water, and vice versa.
Now, clearly solar systems have higher upfront costs – but so does any sophisticated irrigation system (what, after all, are irrigation ditches but ‘upfront costs’?). Even so, rather astonishingly, the scientists conclude a 2.3 year payback on the installation of a PVDI system. Their research led them to the conclusion that:
solar-powered drip irrigation significantly augments both household income and nutritional intake, particularly during the dry season, and is cost effective compared to alternative technologies.
Leap frogging past fossil-fueled systems into PVDIs looks, based on this research, to make sense for areas home to the world’s poorest citizens. And, this tool for increasing wealth and improving food security has another benefit:
When considering the energy requirements for expanded irrigation in rural Africa, PVDI systems have an additional advantage over liquid-fuel-based systems in that they provide emissions-free pumping power. Assuming that a similar size pump set (0.75–1.5 kW) would replace the solar-powered pump and would require 0.15 L of fuel per cubic meter of water pumped, we calculate that each garden avoids a minimum of 0.86 t of carbon emissions per yr (12.9 t over a 15 yr lifetime) in comparison with the liquid-fuel alternative.
Each PVDI system would, over 15 years, cut carbon emissions roughly equivalent to 60 percent of an average American’s annual emissions. (Hint — another way of realizing that we need lots of silver dust rather than seeking an elusive silver bullet.)
Article by A. Siegel appearing courtesy Celsias.
photo: Elsa Wenzel
