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Table 8 Suitable/available area for electricity generation by technology. Area (million km2)

Period

Building-integrated

Land-based

PV on roofs

PV on land

PV on facades

Country level

Methodology

Off-shore CSP on land

Wind on land

Wind on sea

GIS level

Total (excl. Antarctica)

2010 2030 2070

0.13 0.17 0.21

0.19 0.25 0.33

146 (134)

361; EEZ:148 (140)

Suitable area (before resource cut-off)

All

n/a

n/a

81

65

97

21

Suitable area

2010 2030 2070

0.04 0.06 0.07

0.02 0.02 0.10

n/a

41

35 37 37

13 13 13

Available area . . . % of suitable area . . . % of total area

All All All

n/a n/a 33%

n/a n/a 10%–30%

0.6–5.0 0.7%–6.2% 0.4%–3.4%

0.4–3.1 0.9%–7.5% 0.3%–2.1%

0.5–3.9 1.4%–10.4% 0.3%–2.6%

2.4–8.1 18.8%–62.2% 0.7%–2.2%

PV: photovoltaic; CSP: concentrated solar power; EEZ: Economic Exclusion Zones, i.e. zone denoting areas of the ocean attributable to a country.

land use beyond technical limitations or economic attractiveness. Based, where possible, on an assessment of the difference between existing and maximum penetration levels, we developed cases covering a range of values (denoted Low, Medium, High), from 0.1% for PV on available agricultural land to 80% for offshore wind far from the coast (see Table 2). For comparison, if the $33 GW of PV installed in Germany today was entirely from solar farms it would cover around 0.64% of the suitable country area (or 0.31% of total land area). After establishing the area available for energy harvesting, the resource intensity incident upon this area was calculated and converted into ﬁnal useful electric energy. We used conversion factors which account for expected technological progress. The largest improvements are expected in solar PV technologies, and we have assumed a module efﬁciency which increases from around 16% today to 35% by 2070 with additional increases in the net conversion efﬁciency from increasing packing densities on the ground. Note that even this doubling of efﬁciency for PV has only a moderate impact on the ﬁnal results: the largest uncertainty stems from the availability factor which spans a range of up to a factor 20 for some land types. In wind and CSP the gains are expected to be smaller (see also the approach to availability factors in Section 2 and the Supplementary Information). The total long-term potential for renewable electricity onshore, offshore and on buildings is calculated to be between 730–3700 EJ/ a depending on the availability case. An estimated additional potential of 50–110 EJ/a could be contributed from geothermal and hydroelectricity. The latter two technologies were assessed through a meta-study with additional extrapolations. Table 9 summarises the results for potentials and shows a comparison with previous studies. Ranges indicate: range found in literature for literature studies (Edenhofer et al., 2011; de Vries et al., 2007); and cases for all other results. We ﬁnd global single technology potentials are largest for the land-based solar resources (ground-based PV and CSP), ranging between 130 EJ/a and 2800 EJ/a in 2070. The total land-based potential is estimated at 320–2800 EJ/a. Note that the potentials are not additive across technologies as they can originate from the same area. Our GIS-based approach allows an assessment of this overlap when reporting total potential. We have chosen the potential in a given grid cell to be that of the single technology with 3

The total potential on land was calculated by summing the potential of the best technology on those available areas where more than one technology was suitable. If the lowest yielding technology is used instead, then the total land potential ﬁgure in the Low case changes from 320 EJ/a to 199 EJ/a, and the total solar and wind potential from 728 EJ/a to 606 EJ/a.

the largest potential in that grid cell.3 In practice some of this potential could be additive locally, i.e. solitary wind turbines could co-exist with PV installations meaning our approach may lead to a slight underestimate of the total cross-technology potential. Note also that we have used ﬁxed land-use through time. Expansion of cropland, whether for food or biomass energy use, could overlap with long-term PV and CSP potentials. However, at an aggregate level, the overlap is likely to be small, and, in our view, the availability factors should easily accommodate it. The land type which is most likely to be affected is ‘grassland’; the potential on this land type represents around 4–8% of the total PV and CSP potential. Fig. 3 shows the results in graphical form, for the single technologies as well as the total potential, accounting for overlaps. The main driver behind the increase in the PV potentials for both, buildings and on land, is the increase in net conversion efﬁciency. A further important factor in both cases is the increase in area used for PV. The available roof and fac¸ade area is expected to grow substantially with population and housing growth, while on land, we assume a rising ground coverage level. Global electricity demand (65 EJ/a in 2010) may increase by a factor 2–5 by 2050, as a result of increased per capita energy use in developing regions and an increased shift from fuel to electricity (IEA, 2012a; GEA, 2012; Lund and Mathiesen, 2009; Deng et al., 2012; Shell, 2013). To illustrate this, Fig. 3 also shows a range of future electricity demand estimates for comparison with our 2070 potential estimates. These demand estimates are based on a long-term global population of 10 billion (reached in the 2080s in the UN mid-case projections (United Nations, 2011) and a range of percapita electricity demand projections of 24–40 GJ/cap/a (IEA, 2012a; GEA, 2012; Deng et al., 2012; Shell, 2013). These per-capita demand projections include transmission and distribution losses and are driven by an increasing demand for energy services (primarily in developing regions) and continuing electriﬁcation of demand, and are only partially offset by energy efﬁciency even in high efﬁciency projections. For comparison, current levels in developed regions are around 30 GJ/cap/a. At a world level, this increased demand would not exceed the global resource base, even in the Low case. However, country or regional constraints may occur within this. 4. Discussion 4.1. Comparison with other studies As shown in Fig. 4, our results fall within the ranges of (constrained) technical potential reported in the meta-analysis for individual technologies of the IPCC’s Special Report on Renewables