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New study highlights southern Africa's impressive sugarcane bioenergy potential

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A recent study by the International Renewable Energy Agency (IRENA) has found that there is significant potential for an expansion in sugarcane bioenergy production in seven southern African countries.

The study estimates that the available growing area for sugarcane in Eswatini, Malawi, Mozambique, South Africa, the United Republic of Tanzania, Zambia and Zimbabwe is substantially larger than the 544,000 hectares currently covered by the crop.

The authors also assess how the use of higher yielding “energy cane” cultivars, optimal growing practices and integrated 1st and 2nd generation ethanol production would impact both the volume of ethanol produced and the electricity available from cogeneration.

Southern Africa is unusually well suited to sugarcane cultivation. Average yields of 70.6 tonnes per hectare are well in excess of the global average of 38 tonnes.

As sugarcane is one of the most useful bioenergy crops, with a photosynthetic efficiency of 1% to 2%, the region holds great promise for enhanced bioenergy production.

The IRENA study divides land into three categories: land currently under sugarcane cultivation, land in which sugarcane can be watered through rainfall alone, and land where irrigation would be required.

Including each of these three land types and excluding lower quality soil, the authors find that there are 3.7 million hectares of “very-suitable land” available for sugarcane cultivation.

This figure – already well in excess of the current area under cultivation – is more remarkable because it represents only 7.4% of the total area in which sugarcane could be grown in Southern Africa (exclusive of forested regions).

To maximise the value of this land, the authors advocate partnering with local smallholders, rather than direct ownership by mills or contracts with commercial farming operations.

Taking this approach would ensure that the rewards of increased bioenergy production are more evenly spread whilst respecting existing land tenure structures.

Southern Africa’s bioenergy output could be further enhanced through the use of new cultivars of energy cane, say IRENA.

These cultivars have been developed primarily through hybridisation with wild species. Their sucrose content is lower than conventional crops, but is balanced by higher fibre content and higher yields.

The economic value of switching to energy cane would be considerable. The study cites previous research which estimates that energy cane could raise the yearly energy output per hectare from an average of 628 GJ (in 2010) to a projected 1228 GJ by the year 2030.

Coupling energy cane cultivation with integrated 1st and 2nd generation ethanol production would bring the greatest overall increase in energy output, say IRENA.

Plant sugars represent only one third of the bioenergy content of sugarcane, with the rest contained within the leftover plant fibres (bagasse), and the leaves and stalk of the plant (the straw).

2nd generation production processes allow both bagasse and straw to be used as ethanol feedstocks. This increases the volume of fuel produced per hectare, albeit with an associated rise in production costs.

Bagasse and straw are also burned by sugar mills to generate heat and electricity for industrial processes. With the appropriate regulations and infrastructure, excess electricity can then be sold to the power grid.

The study concludes that Southern Africa’s potential bioenergy production amounts to 128.6 billion litres of ethanol production per annum and 158.9 TWh of cogeneration capacity. These figures assume cultivation of energy cane on both rainfed and irrigated land, subject to 1st and 2nd generation production processes.

By comparison, the region’s­ gasoline demand is expected to reach only 22 billion litres by the year 2030. Nearly all the ethanol produced would be cost competitive with gasoline at crude prices of USD 75 per barrel or higher.

On the other hand, 158.9 TWh of cogeneration capacity would cover 43% of projected electricity demand in the region by the same date, at a cost of USD 0.054 per kWh.

The full study is available to download for free on IRENA’s website.

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