How Energy Is Produced - The Renaissance of Renewable Energy - page 118

2011 were Germany, Italy, Japan, and Spain, followed closely by the United States, China,
Japan and Australia. The leaders for solar PV per inhabitant were all in Europe: Germany,
Italy, the Czech Republic, Belgium, and Spain (REN21 2012 ) .
MostinstalledPVcapacitytodayisgrid-connected,andsmall-scaleoff-gridapplications
account for a declining share of overall capacity. This is linked to the fact that most of
the incentives offered for PV installation are available only for grid-connected systems.
However, with time and as new funding models emerge, off-grid solar PV is likely to
expand, particularly in developing countries or remote locations that lack an extensive grid
network. Just as mobile phone technology has revolutionised communications in many
parts of Africa, Asia, and South America, small-scale off-grid solar PV plants have the
potential to bring electrical power to communities that have lacked electrical power up to
now.
Estimates for the annual total technical potential of solar energy (not differentiated
by conversion technology) vary widely between different studies, from roughly 1500
to 50,000 exajoules per year (Arvizu et al. 2011a ; IEA 2012a ). The main difference
between the studies arises from assumptions about the power conversion efficiency of the
technology and the allocated land area availabilities. A recent comparative study estimated
future technical potentials of photovoltaics at roughly 1,700 exajoules per year in 2050 for
photovoltaics (Arvizu et al. 2011a ; Krewitt et al. 2009 ) . This represents more than three
times the current global primary energy production (530 EJ).
4.6 Concentrating Solar Power
Archimedes' Mirrors
In 212 BCE, Syracuse, the last of the Hellenic colonies in Italy, fell to the Romans after
a long siege. That this city held out for sixty years after the rest of Magna Graecia had
capitulated was largely thanks to its excellent defences, designed in part by the inventor
and mathematician Archimedes. Among the many impressive weapons he is reported to
have devised were giant mirrors that concentrated sunlight on the Roman ships, causing
them to burst spontaneously into flame. Early modern scientists, including Leonardo
da Vinci, Descartes and Kepler, were both fascinated by and sceptical of the accounts
of Archimedes' mirrors, 14 and modern reconstructions have cast further doubt on the
feasibility of such weaponry with the limited means available to Archimedes. Had the
discoverer of the principle of floatation not perished on a Roman sword at the end of the
siege, perhaps we would know more today about his 'burning mirrors'. 15 Whatever its
veracity, this story advanced the idea that the sun's rays, if concentrated, were a powerful