Environmental Engineering Reference
In-Depth Information
of fossil fuels is unstable (Germany relies heavily on Russian gas, while Italy has imported
a lot of its oil from Iran). In Germany's case it has also bolstered the ambitious national
commitment to an 'energy transition' from fossil and nuclear energy to renewables.
The growth of solar PV has also had an unexpected positive effect on the entire
electricity system in both countries, smoothing the peaks of electricity demand during
midday. Before the PV boom in Italy, there were two price peaks in the power market,
one during the day (around 11:00 AM) and another in the evening (between 6:00 and
8:00 PM). The eleven o'clock peak has now almost disappeared, as during central daytime
hoursPVcompeteswithfossilfuel-basedpowerstations,restrainingthepriceofelectricity
How Many Panels Would Each Roof Need?
The market conditions for PV varies considerably from country to country. This is
attributable to three main factors: differences in state energy policies, differences in public
enthusiasm for renewable energy, and differences in the amount of available sunlight.
As with wind power, some regions are far more suited to solar energy than others.
Unfortunately, those countries with the highest levels of industrialisation and the greatest
energy demand tend not to be those with the highest incidence of solar radiation. Average
solar radiation varies from about 250 watts per square metre at hot spots such as the Sahara
Desert,theArabianPeninsula,andcentralAustraliatoabout50wattspersquaremetrenear
the poles.
Theaverageefficiencyvalue(fromsuntoelectricity)ofsolarPVcellsisjust10percent.
This is because most PV panels have conversion efficiencies of 20 per cent or less, some
energy is lost through inverters and cables, and about 15 per cent of the area of a panel is
not covered by solar cells. In Germany, for example, the average solar radiation measured
over a period of a year (including nighttime) is about 150 watts per square metre. We can
thus calculate an annual energy output of 131 kilowatt-hours per square metre per year.
Considering that the average German household consumes about 5,000 kilowatt-hours of
electricity per year, that household would require 38 square metres of solar panels to meet
its electricity needs. The productivity of solar PV systems also depends on a few other
factors, most importantly the orientation of the panels (the optimal tilt depends on latitude
and time of year) and shading from trees, chimneys or other objects.
The Potential of Solar Photovoltaics
In the last ten years, the solar PV market has seen extraordinary growth, from 1.5 GW of
installedcapacityin2000to70GWin2011.Thetopcountriesfortotalinstalledcapacityin
