Thursday, February 09, 2006

Renewable energy and food supply: will there be enough land?

Today, land is used for living, working, recreation and most importantly, food production. A relatively new use is growing biomass for energy use, which requires vast areas of land because of the diffuse nature of sunlight, and the low efficiency of plants capturing it. There is a direct competition for agricultural land between energy and food. Land requirements for both uses depend on consumption and production per square meter, 2 parameters which vary widely. In this paper, S Nonhebel estimates land requirements based on today's consumption patterns and production efficiency, providing a basis for the construction of scenario's.

How much land?

Total land available is 13 Gha (13 billion ha or 130 million square km). Arable land (1.5 Gha), pastures (3.5 Gha) and forests/woodlands (4 Gha) provide total 9 Gha for growing biomass, which in a world of 6 billion people means 1.5 ha (15,000 sq.meter) per person (under the untenable assumption that humans are entitled to 100% of available land).

How much energy?

In 2003, the world consumed 435 EJ of primary energy, or 70 GJ/pp/year. Developing countries use about 35 GJ/pp/year, whereas developed countries consume 200 GJ. Within developed countries, consumption varies significantly between Japan (100 GJ), Europe (150 GJ) and North America (350 GJ).

How much food?

Just like we express energy use in primary energy equivalents expressed in Joules or tonnes of oil equivalent (toe), food consumption can be expressed in kg grain equivalent. A basic menu requires 200 kg/pp/yr, while rich countries consume more like 800 kg (including fooder required for secondary foods such as beef, porc, ...).

Food and energy production

The paper below mentions following conversion factors:
'rich' 'poor'
Grain yield (kg/m2) 1.0 0.2
Energy yield - photovoltaics (MJ/m2) 780 780
Energy yield - biomass (MJ/m2) 27 1.8

Using these ratio's in combination with today's energy & food diets yields following land requirement per person:
  • developing countries, biomass energy: > 20,000 m2
  • developed countres, biomass energy: 8,200 m2
  • developed countries, photovoltaics: 1,000 m2 (of which 256 m2 PV)

Conclusion

The author concludes that for developing countries, the use of biomass points to a critical situation. For developed countries, PV-systems are the only long-term option, though biomass may function as a transition fuel.

S Nonhebel, Renewable energy and food supply: will there be enough land?, Renewable & Sustainable Energy Reviews, 9(2005) 191-201

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