To avoid buying a television working on DC (there is very little choice in this area), a commercial 230 V AC model will be used with a power of 90 W. It is planned to connect it via a small inverter, with 90% efficiency, which will only be switched on at the same time as the television. For a projected use of 4 h/day, consumption will therefore be
90 W x 4 h/0.9 = 400 Wh or 33.3 Ah at 12 V
Summary of consumption
Table 5.23 summarises the consumption, by season. To obtain average consumption over time, which will enable us to size the panels, we need to take account of the fact that the chalet is only occupied 2 days/week:
• average daily consumption in summer: 75.3 Ah x 2/7 = 21.5 Ah;
• average daily consumption in winter: 63.3 Ah x 2/7 = 18.1 Ah.
Table 5.23 Electrical consumption of the chalet
This is a domestic application, subject to possible variations. It is quite different from our telemetry case study (see Section 5.6.1) where consumption was programmed and unlikely to vary. The users must therefore be careful in their energy consumption. But they will learn by experience and should be able to balance their consumption conveniently without exceeding the possibilities of their system. Accurate monitoring of the battery voltage is important as it enables one to keep track of the actual situation (with the help of an 11-14 V voltmeter on the regulator, for example).
To size the regulator, the peak current of the appliances must be calculated. If all the appliances are working at the same time, it would give 28.8 A. In practice, the load will be at its maximum when the refrigerator, television and two lamps are all on at the same time: it is easy to arrange not to operate the pump at the same time as the television. Thus, the peak power load will be: 70 + 100 + 26 = 196 W, which represents a current of 16.3 A.