Environmental Engineering Reference
In-Depth Information
Direct current (DC) generators may be connected to the DC bus-bar of such
power supply systems or may be connected via inverters directly to the alternating
current AC bus-bar. For hybrid systems, for instance, also mini-hydropower sta-
tions or even fuel cells may be applied besides motor or wind generators. Whereas
Diesel generator operation only achieves medium efficiencies (scarcely above
15 % measured on an annual basis) and has high maintenance requirements, fuel
cells are characterised by low noise emissions, zero-emission local, higher effi-
ciencies, particularly when operated at partial load, and the availability of virtually
any nominal power; however, their still high cost and the too low lifetimes are
their major disadvantage.
For system designs as shown in Fig. 6.26 a unidirectional or a bi-directional in-
verter can be applied. Within the former design the motor generator feeds via an
inverter the bus-bar; by this the battery is loaded. According to the system layout
shown in Fig. 6.26 the windmill can provide only as much power as directly used
by the AC-consumers. If instead a bi-directional inverter is used all systems can
be created that are provided with only one alternating current bus-bar. Under these
circumstances the inverter attached to the motor generator is not needed any more.
Additionally excess power can be used for recharging the battery. The integration
of bi-directional inverters allow also for the design of systems with only one al-
ternating current bus-bar and no direct current bus-bar. For such systems also
batteries and photovoltaic generators are directly connected to the alternating cur-
rent bus-bar via an individual inverter (unidirectional for the photovoltaic system,
bi-directional for the battery).
The voltage on the direct current side is mainly determined by the electrical
power of the connected consumers and the power supply from the generators. The
resulting currents determine in turn the requirements in terms of cabling, and, in
particular, of the required direct current switches and fuses. Especially for high
amperage, the latter components are highly sophisticated and expensive. For in-
stance, for systems supplied with alternating current amperage of 100 A at the
direct current side represents a reasonable upper limit.
Examples. As follows, some typical applications of autonomous, grid-
independent photovoltaic power supply systems, currently in use, are discussed.
House number illumination. A lot of information should also be legible at
night. For instance, emergency rescue services, the police, and emergency re-
lief organisations have for a long time been claiming lighted street names and
house number panels. For this purpose, house number illumination supplied by
photovoltaic power has been developed. Energy generated during the day is
stored in a NiCd or lead-acid accumulator. Such a system allows attaching the
house number to virtually any spot of the building without having to lay out-
door cables. House number illumination turns on automatically at the onset of
twilight and turns off again the next morning. The entire sequential control as
well as load status monitoring of the accumulator is performed electronically,
so that the system is nearly maintenance-free. The illuminated surface consists
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