RES Scenario in the European Union - The Sustainability of Renewable Energy in Europe - page 36

etc.). The stand-alone PV systems are the best solution to address the lack of
electricity network. This technology can be very useful in developing countries
that have problems of energy supply to hospitals, schools, and kindergartens, and
also in remote areas (in the mountains or countryside) not served by the national
grid.
• PV plants connected to the grid: they have the feature to work on an interchange
with the local power grid. In particular, during daylight hours, the user consumes
the electricity produced by his solar system, and when there is no light or it is
not sufficient, or if the user requires more energy than the plant can provide, the
electricity network will ensure the supply of the electricity needed. On the other
hand, in the case, the plant produces more energy than required by the user, such
energy can be fed into the network. Solar installations connected to the grid thus
represent an additional source, because they provide a contribution for a differ-
ent amount depending on the size of the plant, the building's overall electricity
balance that uses them. There are also power stations connected to the network
in the medium or high voltage.
• “Anti-blackout” PV systems: they are hybrid systems which provide electricity
during power cuts by taking energy from the battery (as in systems for isolated
users), while working as normal systems to connect to the network when there is
electricity.
Of all the energy that hits the solar cell in the form of light radiation, only a portion
is converted into electric energy available at its terminals. The conversion efficiency
of commercial silicon cells is generally between 13 and 20 %, while laboratory cells
have reached values of 32.5 %.
A PV system produces electricity for 20-25 years, with few maintenance require-
ments and a good resistance to atmospheric agents. Disposal at the end of life does
not have any particular problems: a PV module is in fact more than 90 % recyclable.
The most significant cost item for the construction of a solar system is certainly
made up of the purchase cost of PV modules that affect the total to 40-60 % (de-
pending on power). The PV modules are the most long-lived component of a plant,
as designed and manufactured to produce electricity for more than 50 years (some
researchers claim that they can work for over 100 years). The design and installa-
tion together range from 30 % for smaller plants to about 15 % for the major power
plants. The remaining cost items are almost always below 10 %. In particular, the
inverter is at most 10 % of the total cost of the system for a power range of 20-
100 kWp, which declined gradually to 7 % in the case of plants from 3 kWp. The
support structures of the modules instead vary from 5 to 8 % for traditional struc-
tures depending on the size of the system.
In 2012 there have been installed 31.4 GW worldwide, an increase of 14 % com-
pared to 2011 and in 2013 the PV has grown more than 13 %. The EU accounts for
the predominant share of the global PV market, with 55 % of all new capacity in
2012 and about 70 % of the world's cumulative PV capacity with more than 70 GW
of cumulative installed capacity in 2012. China is the second largest producer of
PV with cumulative capacity amounts to 8.3 GW in 2012, followed by the USA