dry t/ha/y of woody biomass can be produced in Northern Europe... .
Thus an area of 1 km2 will produce 1000 dry t/y – enough for a power output
150 kWe at low conversion efficiencies or 300 kWe at high conversion
efficiencies.” This means 0.15–0.3 W(e)/m2.
See also Layzell et al. (2006), [3ap7lc].

283Oilseed rape. Sources: Bayer Crop Science (2003), Evans (2007), www.defra.

Sugar beet. Source: statistics.defra.gov.uk/esg/default.asp

284Bioethanol from corn. Source: Shapouri et al. (1995).

Bioethanol from cellulose. See also Mabee et al. (2006).

Jatropha. Sources: Francis et al. (2005), Asselbergs et al. (2006).

285In America, in ponds fed with concentrated CO2, algae can grow at 30 grams
per square metre per day, producing 0.01 litres of biodiesel per square metre
per day.
Source: Putt (2007). This calculation has ignored the energy cost
of running the algae ponds and processing the algae into biodiesel. Putt
describes the energy balance of a proposed design for a 100-acre algae farm,
powered by methane from an animal litter digester. The farm described
would in fact produce less power than the methane power input. The 100-
acre farm would use 2600 kW of methane, which corresponds to an input
power density of 6.4 W/m2. To recap, the power density of the output, in the
form of biodiesel, would be just 4.2 W/m2. All proposals to make biofuels
should be approached with a critical eye!

286A research study from the National Renewable Energy Laboratory predicted
that genetically-modified green algae, covering an area of 11 hectares, could
produce 300 kg of hydrogen per day.
Source: Amos (2004).

Elean power station. Source: Government White Paper (2003). Elean Power
Station (36 MW) – the UK’s first straw-fired power plant. Straw production:

287Landfill gas. Sources: Matthew Chester, City University, London, personal
communication; Meadows (1996), Aitchison (1996); Alan Rosevear, UK Rep-
resentative on Methane to Markets Landfill Gas Sub-Committee, May 2005