Photovoltaic Power Generation - Renewable Energy: Technology, Economics and Environment - page 276

Further system components. Further photovoltaic system components, that are
by no means negligible cost factors, are direct current connecting cables between
modules, batteries and inverters. Additionally, usually also fuses, grounding,
lightning protection, energy meters as well as low voltage or overvoltage monitor-
ing protection is required. Some components are required to comply with legal
prescriptions, whereas others, such as lightning protection, are highly recom-
mended depending on the plant exposure. Photovoltaic power plants also require a
transformer to feed the electric energy into the grid with the required power char-
acteristics. Overall losses of these additional system components accounts for 5 to
12 % of the electric energy fed into the mains.
6.2.3 Grid-independent systems
Grid-independent applications are further distinguished into stand-alone and off-
grid applications /6-29/ (for examples see Table 6.2).
− In industrialised countries applications are referred to as stand-alone applica-
tions if photovoltaic energy supply is applied alternatively to power supply by
the power grid for reasons of cost-efficiency, handling, safety or environmental
protection; although the mains is available at close hand. If such stand-alone
systems are used indoors (at daylight or artificial light) they are referred to as
indoor applications; a classic example is the photovoltaic powered calculator.
Such systems may be further subdivided into consumer applications (e.g.
photovoltaic garden lamps) and industrial or professional applications (e.g.
parking ticket vending machines, city furnishings). The solar generator capac-
ity of these applications stretches from a few mW to several 100 W.
− Photovoltaic energy supply systems are referred to as off-grid systems, if the
power grid is inaccessible for technical or economic reasons because of the dis-
tance to the closest grid connection point (e.g. alpine huts or households lo-
cated in regions with a missing infrastructure for electricity supply). For larger
systems also the terms of "stand-alone applications" or "autonomous energy
supply systems" are commonly used. Also in this respect, the systems are fur-
ther subdivided into industrial applications (the greatest market share account-
ing for wire-less telecommunication systems) on the one hand, and household
supply on the other. Especially for developing countries, the borderlines are
loose since economic activities are often only permitted by the power supply to
households.
Photovoltaic pump systems receive an exceptional position within grid-
independent systems. Their main characteristic feature is their lack of electric
energy storage units. Pumped water is stored in an elevated tank when there is
sufficient solar radiation for pump operation available. Although there are also
pumps operated by direct current, the majority of such systems are equipped with
a special inverter, which enables optimum pump operation.