Photovoltaic Power Generation - Renewable Energy: Technology, Economics and Environment - page 281

efficiency. However, also inverters of nominal powers from 150 to 500 W are
used. The benefits are that virtually any kind of commercial consumer can be
connected and that batteries are effectively protected against misuse, since di-
rect connection of consumers to the battery is impossible. The technology of
such applications is largely available and reliable, provided that high quality
components are used. The spread of these technologies is rather impeded by
socio-economic and socio-technical problems hindering the wider use of such
systems.
− Village power supply systems. So-called village power supply systems repre-
sent an alternative to solar home systems. A central power supply systems pro-
vides electric energy to households that are connected to a mini-grid. Central
systems are easier to maintain and each household can be supplied with more
power while the energy consumption is similar to that of decentralised power
supply systems. Central power supply systems are usually hybrid systems that
include often all possibilities promising for a site-specific power generation
(e.g. micro-hydro, wind, Diesel generator).
− Energy supply of residential buildings and service stations in recreation areas.
Even in highly industrialised countries there is still a series of residential build-
ing, service stations for leisure activities and alpine huts that are still not con-
nected to the mains, due to the long distance and the related connection costs.
Within the EU-15 countries, for instance, about 300,000 houses do not have
access to the grid. To date, the only solution available is the installation of a
generator (i.e. Diesel generator) for direct power supply of consumers. Diesel
generators are thus often operated at partial load, and at disconnecting times,
electric energy is usually unavailable. Continuous operation is virtually impos-
sible, not only because of the problems of low partial-load efficiencies, noise
and exhaust gases, but also due to the limited technical lifetime of combustion
engines under such operating conditions. The example of the "Rotwandhaus", a
service station in the European Alps, has shown that a hybrid system, consist-
ing of a photovoltaic generator (5 kW), a wind energy converter (20 kW) and a
Diesel generator (20 kW) can provide reliable power supply of approximately
11 MWh/a at an installed capacity of 10 kW to this mountain hut equipped
with restaurant and sleeping facilities for 100 people, open year-round. When
the available wind speed is sufficient, the wind energy converter contributes to
power generation. As soon as the battery is recharged to the maximum voltage,
the power output of the wind turbine, the photovoltaic generator and the Diesel
generator must be reduced accordingly. An inverter serves for converting the
direct current (DC) of the battery into alternating current (AC) of 230 V, so
that common electric appliances may be used. The Diesel generator ensures un-
interrupted service even in case of extremely unfavourable weather conditions.
To utilise the available energy resources as well as possible, a computer moni-
tors and controls the overall system.