Now, if we want reduce power consumption, the first step, if airco is a must, is reduce it to the minimum, and also to replace the water maker by the more efficient (and much less noisy) DC water-hydraulic type. The result is as follows:
Consumers
Consumption
Time / 24-hours
Consumption / 24-hour period
Watt 1500 2000 6000
Amp
Hours
kWh Ah (24 V)
Microwave oven
0.25
0.4 0.6 1.2
16 25 50 (9) 33 56 42 10
Kettle, 6 litres per day
Electric stove, 4 persons on board
Heater
3
6 x 0.5 = 3 12.x 0.5 = 6
Air conditioning, cooling capacity 2 kW
700
29 10
4.2 1.4
175
Watermaker, 200 litres per day
3.3
Small washing machine, once every 2 days
2000 2000
0.5 x 2.7
Small dishwasher, daily
1.0
More pumps
Consumption per 24-hour period
9.6
407
Together with the basic consumption on a sailing boat, consumption per 24-hour period now adds up to:
- with air conditioning:
min. 160 + 407 = 567 Ah and max. 160 + 609 = 796 Ah
at a current of, on average: min. 567 Ah / 24 V = 24 A and max 796 Ah / 24 V = 33 A total energy consumption per 24-hour period: min 567 x 24 = 13.6 kWh and max 796 x 24 = 19.1 kWh
- without air conditioning: at a current of, on average:
160 + 232 = 392 Ah per 24 hour period
392 / 24 = 16 A. total energy consumption per 24-hour period: 392 x 24 = 9.4 kWh.
10.6. Energy generation
10.6.1. With alternators on the main engine
This is certainly possible, see chapter 9.
10.6.2. Alternative sources of energy
As explained in chapter 9, solar cells can be an excellent means to recharge the battery when the boar is left in the slip for a week or more.
When sailing, solar cells (1 m 2 ), a wind generator (1 metre diameter) and a water generator (say 60 W at 5 knots speed through the water) together deliver almost 2.4 kWh (= 100 Ah in a 24 V battery) per 24-hour period. In other words: the contribution of alternative sources of energy can reduce engine hours substantially if not much more than the basic equipment is on board.
But when the daily energy needed increases further, other means of generating electricity are needed. The alternatives will be discussed in the next sections.
10.6.3. With an AC generator
The time-honoured method to cope with the high power demand of for example a washing machine or electric stove is installation of an AC diesel generator, to be started when power demand is high. The generator would for example run every evening for 2 to 4 hours during cooking and until the dishwasher has finished. During these same 4 hours one could run the washing machine and dryer, the water maker, the battery chargers, and heat-up the boiler (either electric or with cooling water from the generator). If needed, one could have a second generator period of 1 or 2 hours during breakfast in the morning.
In general the generator period is kept as short as possible, for the following reasons: - noise and vibration - wear and maintenance -
preventing operation with insufficient load, as this will increase wear and maintenance
-
fuel consumption
55
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