Page 178 - Applied Photovoltaics

General appliances
Grid-connected households use a wide range of electric appliances in the kitchen,
laundry and generally. These include toasters, electric jugs, vacuum cleaners and
washing machines, all of which typically draw large amounts of power, albeit for
only short periods. If a diesel or petrol generator is incorporated into the RAPS
system, it is advisable to synchronise use of such appliances with the generator run
times.
Front loading washing machines are considerably more energy and water efficient
than the top loading agitator type. Never use the electrical heating elements, and if hot
water is necessary, use water heated by other means, such as via a solar water heater,
rather than via electricity.

Electric motors often require very large starting currents (up to five times the rated
power use for normal operation) and hence, where possible should not be driven
through the inverter but rather directly from the generator. This will allow
considerable cost saving through a smaller inverter. However, inverters commonly
have a rating for a high transient load that may accommodate motor starting.
Appliances with motors that start automatically, such as refrigerators, should be
tolerated by the inverter. Battery charging should also occur while the generator is
running.
In general, the most important design criterion for a RAPS system is to avoid the use
of electrical appliances wherever possible, in favour of non-electrical substitutes.
Table 9.1 gives a typical load analysis of appliances in a home using a RAPS system.
Further information on typical lighting and appliance energy use is tabulated by
Castañer et al. (2003) and Lawrence Berkeley Laboratories (2004), while Fig. 9.2
gives a schematic of such a home.

Figure 9.2. A typical hybrid RAPS system (Department of Primary Industries and
Energy, 1993).

165