South African maize production: mitigating environmental impacts through solar powered irrigation
Agriculture is among the largest contributors to global greenhouse gas emissions. Clean technologies, such as renewable energies, have the potential to significantly reduce these environmental repercussions of agriculture. Countries like South Africa have a coal intensive electricity mix, as well as high solar irradiation and a dry climate which is why agricultural crops are produced under fossil energy intensive irrigation. At the same time, the high solar irradiation could be used for the generation of photovoltaic electricity as a renewable power supply for irrigation. A joint research project between the University of Cape Town and the Zurich University of Applied Sciences quantified the environmental impacts of South African maize production (Zea mays) and the improvement potential of maize irrigation with photovoltaic electricity by means of life cycle assessment (LCA).
The LCA includes the whole value chain of maize production from cultivation to storage in a silo for six months, respectively with a functional unit of one kilogram of maize at silo storage produced either on dry land or under irrigation. Electricity consumption for irrigation was identified as an environmental hotspot in the impacts related to greenhouse gas emissions from maize production. Therefore, clean electricity would be the starting point to reduce the carbon footprint of South Africa’s maize. We calculated that replacement of South African electricity mix with photovoltaic electricity in the maize irrigation can reduce environmental impacts by up to 47 %. The calculated greenhouse gas emissions per kilogram of maize on dry land without irrigation, under irrigation and under irrigation using photovoltaic electricity, are 0.50 kg CO2-eq. and 0.82 kg CO2-eq. and 0.54 kg CO2-eq., respectively, with a potential reduction of 33 % if the electricity is supplied from photovoltaics compared to the conventional fossil electricity mix. The analysis of further indicators reveals a reduction for non-renewable energy demand (nuclear and fossil), acidification, freshwater eutrophication and human toxicity of carcinogenic substances. The irrigation of a maize field of one hectare consumes 1'900 kWh of electricity per year, which, in turn, requires a solar power plant with an area of 9 m2. We computed that a total area of 199 ha of solar panels would suffice to produce the total electricity requirement of the current maize production area under irrigation. This corresponds to more than approximately 500'000 t CO2-eq. saved per year.
Compared to data representing maize production in the United States and in Switzerland, South African maize production has a higher global warming potential per kilogram of maize due to lower yields in South Africa.
The replacement of the South African electricity mix in the irrigation with electricity from photovoltaics has proven to be an effective clean technology to reduce environmental impacts associated with maize production in South Africa. Compared to the irrigated field area, land use for PV panels is almost negligible and is therefore no limiting factor in the implementation of irrigation using photovoltaic electricity.