Page 180 - Applied Photovoltaics

9.1.3 Consumer education
To use a RAPS system effectively will involve:
x modified and disciplined living habits to minimise energy use and to
synchronise usage with solar and wind conditions and with diesel operating
times
x a basic appreciation of levels of energy usage of different appliances
x a superficial understanding of the RAPS system and its electrical generating
components
x evening out maximum loads supplied by the generator and also general loads
to be supplied via the inverter.

Probably the most common failure mechanism or cause for dissatisfaction with RAPS
systems results from inappropriate use of the system, rather than poor system design
(Lloyd, 2000; Krauter, 2004).

Difficulties in adjustment can often be experienced by families and individuals
moving from grid-connected areas to locations where RAPS systems are necessary.

9.1.4 Photovoltaic-diesel/petrol generator hybrid systems
The most common configuration for RAPS systems currently being installed is a
photovoltaic-battery-inverter system, with a diesel or petrol generator for emergency
use or for peak loads. Such systems are commonly used where availabilities near
100% are required, which would be prohibitively expensive using photovoltaics
alone, and in residential or commercial applications where diesel generators
previously dominated and were therefore already available. In the latter cases, once
the basis of the RAPS system is added to the generator, photovoltaics can be added
incrementally, as funds permit, gradually reducing the diesel requirement. Fig. 9.3
gives the electrical block diagram for a typical photovoltaic-diesel RAPS hybrid
system. The vast majority of such systems use fixed-tilt arrays but some use single- or
two-axis tracking or even concentration, as in the dish-concentrator systems in the
north-west of South Australia (Australian Greenhouse Office, 2003b).

Despite the high initial costs, where diesels are currently used, the addition of solar
panels, batteries and controller can greatly improve the efficiency of generator usage
as well as substantially reducing system operating costs. Conversely, a diesel
generator removes the need for oversized photovoltaic arrays, which would be both
costly and poorly utilised.

Conventional diesel generator system design simply involves selecting a locally
available unit that is closest to the peak load requirements of the application. By
comparison, hybrid system design is complex, requiring expert assistance in
component selection and interaction with the user to determine priorities. Guidance
on the interconnection of generators and renewable energy sources is provided by the
Australian Standard (Standards Australia, 2002).
Some of the costs that need to be considered include system components—
photovoltaic array, batteries, inverter, tracker, generator, wiring, control boards and
regulators. In addition, the fuel costs for diesel and petrol generators must be
estimated, as must the installation costs, maintenance costs and lifetimes for all
components, which will vary.

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