Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2018 / S4 / 3 / c

Compare average delivered electrical power per land area with consistent boundaries. Illustrative values are about $1000\mathrm{W}{\mathrm{m}}^{-2}$ for the compact plant site of nuclear generation, $5$-$15\mathrm{W}{\mathrm{m}}^{-2}$ for a UK ground-mounted photovoltaic site, $1$-$3\mathrm{W}{\mathrm{m}}^{-2}$ across a wind-farm lease area, around $0.5\mathrm{W}{\mathrm{m}}^{-2}$ for an energy crop after conversion, and perhaps $5\mathrm{W}{\mathrm{m}}^{-2}$ for a reservoir hydroelectric scheme. These are scale estimates, not universal technology constants.

At representative values $1000,10,2,0.5,5\mathrm{W}{\mathrm{m}}^{-2}$, one average gigawatt requires approximately $1,100,500,2000,200\mathrm{k}{\mathrm{m}}^2$ respectively. Biomass therefore has substantial land competition even when fuel can be stored. Solar development competes less with farming if placed on roofs or already developed land. Wind's large separation area is not entirely excluded from agriculture; its actual foundations and roads occupy a much smaller area. Reservoir impacts can be extensive and strongly site dependent.

A nuclear-site number excludes mining, cooling constraints, transport and exclusion areas; a wind lease number includes much land still usable for other purposes. Reporting them as identical measures of permanently occupied land would mislead. Deployment decisions need both the average energy yield and the consequences of the particular land boundary, ecology, food production and local acceptance.