Solar Energy Perspectives - IEA

Solar Energy Perspectives: Rationale for harnessing the solar resource
average around 15°C; evaporating water; nourishing crops and trees; drying harvests and
clothes; illuminating our days; making our skin synthesize vitamin D3; and many others. But,
even overlooking these factors, the question remains: Why are free and renewable energy
forms still largely outpaced by costly fossil fuels, which are less widespread and are exhaustible?
Figure 1.2 Renewable electricity generation in 2007
Total renewables: 3 546 TWh
Renewable municipal waste
Solid biomass
Biogas
Liquid biomass
Geothermal
Solar PV
Solar CSP
Ocean
Wind
Source: IEA, 2010a.
Other 13.2% Hydro 86.8%
Key point
Direct solar electricity still pales next to other renewables.
For millennia, solar energy and its derivatives – human force, animal traction, biomass and
wind for sailing – were the only energy forms used by humans. Coal and (naturally seeping)
oil were known, but played a very small role. During the Middle Ages, watermills and
windmills became more common, so renewable energy was still dominant. From around
1300, however, the use of coal for space heating increased, and became dominant in the 17 th
century in the British Isles. Steam engines and coal-based metallurgy developed in the 18 th
century. Town gas, made from coal, was used for lighting in the 19 th century, when subsoil
oil, primarily to be used for lighting, was discovered.
At the beginning of the 20 th century, while incandescent bulbs and electricity from
hydropower and coal burning began displacing oil for lighting, the emergence of the auto
industry provided a new market for oil products. Nowadays, fossil fuels – oil, coal and gas –
provide more than 80% of the world’s primary energy supply. By contrast, all renewable
energies together comprise about 13%.
This domination of fossil fuels needs an explanation. Year after year, decade after decade, the
fossil fuel industry has maintained dominance and resisted competition by new entrants. Its
advantage is built on two practical factors: density and convenience.
Fossil fuels are very dense in energy. One litre of gasoline can deliver 35 megajoules of
energy – twice as much as one kilogram of wood. This is the amount of energy one square
metre of land receives from the sun in the best conditions in approximately ten hours. Plus,
gasoline is easy to handle, store and transport, as are all fuels that are liquid at ordinary
temperature and pressure.
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© OECD/IEA, 2011