Solar Energy Perspectives - IEA

Chapter 2: The solar resource and its possible uses
A recent special report on renewable energy published by the Intergovernmental Panel on
Climate Change (IPCC, 2011) provides estimates of the global technical potential of renewable
energy sources from a wide number of studies (Figure 2.2). They are shown on a logarithmic
scale, due to the wide range of assessed data. Biomass and direct solar energy are shown as
primary energy due to their multiple uses. Interestingly, the lowest estimate of the technical
potential for direct solar energy is not only greater than the current global primary energy
supply; it is also greater than the highest estimate of any other renewable energy potential.
Figure 2.2 Global technical potentials of energy sources
Global technical potential (EJ/yr, log scale)
Maximum
Minimum
Electricity
100 000
10 000
Heat
Primary energy
1 000
100
Global Heat
Demand, 2008: 164 EJ
Global Primary Energy
Supply, 2008: 492 EJ
10
Global Electricity
Demand, 2008: 61 EJ
0
Geothermal Hydropower
energy
Ocean
energy
Wind
energy
Geothermal
energy
Biomass
Direct solar
energy
Notes: Biomass and solar are shown as primary energy due to their multiple uses; the figure is presented in logarithmic scale due to
the wide range of assessed data. Technical potentials reported here represent total worldwide potentials for annual RE supply and do
Figure 2.2
not deduct any potential that is already being utilised. 1 exajoule (EJ) ≈ 278 terawatt hours (TWh).
Source: IPCC, 2011.
Key point
Solar energy potential by far exceeds those of other renewables.
Since routine measurements of irradiance began in the 1950s, scientists have observed a 4%
reduction of irradiance. This was named “global dimming” and attributed to man-made
emissions of aerosols, notably sulphate aerosols, and possibly also aircraft contrails. Global
dimming may have partially masked the global warming due to the atmospheric accumulation
of greenhouse gas resulting from man-made emissions. It could be responsible for localised
cooling of regions, such as the eastern United States, that are downwind of major sources of
air pollution. Since 1990 global dimming has stopped and even reversed into a “global
brightening”. This switch took place just as global aerosol emissions started to decline. In
sum, neither dimming nor brightening should significantly affect the prospects of solar
energy.
Other variations in solar irradiance are even less relevant for energy purposes. Short-term
changes, such as those linked to the 11-year sunspot cycle, are too small (about 0.1% or
1.3 W/m 2 ). Larger foreseeable evolutions linked to astronomical cycles are too slow (in the
scale of millennia). On a local scale, however, weather pattern variations between years are
much more significant. Climate change due to increase of greenhouse gases in the atmosphere
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© OECD/IEA, 2011