10. Up to 14 kWh required per day (600 W average)
10.1. Introduction
In chapter 9 we saw that up to 4 kWh of electric energy required per day, a relatively simple DC system is perfectly adequate. Next to the basic consumers, for which about 1.5 kWh was required, 2.5 kWh was available daily to operate additional equipment, increasing safety and / or comfort on board. The required battery capacity did range from 250 Ah / 12 V for the “basic” yacht to 600 Ah / 12 V, for a “full featured” yacht. Even above 4 kWh per day, a system with powerful alternators on the main engine is feasible (and the main engine will be more reliable than a small 3000-rpm genset). For reasons of noise, redundancy, and efficiency it is, however, certainly worthwhile to explore alternatives.
The available alternatives are: -
An AC diesel genset to directly supply AC consumers: the AC concept. A (smaller) battery assisted AC genset: the battery assisted AC concept.
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- A DC genset: extension of the DC concept of the previous chapter to higher power ratings.
A daily energy consumption of 14 kWh is quite substantial and could very well be the average consumption in your land based home. Check your electricity bill! In terms of boats, we are looking at motorboats and catamaran sailing yachts of up to 15 metres (49 ft) or monohull sailing boats of up to 18 metres (59 ft).
The calculations that follow are based on a 24 V house battery. To convert to 12 V, simply double current and Ah required.
To start with, the list of standard electric equipment:
10.2. Equipment: the minimum
10.2.1. Navigation equipment
A navigation computer is almost standard on bigger boats. Including GPS, VHF, SSB, radar, Inmarsat, average current consumption rises to between 2 A and 5 A at 24 V.
10.2.2. Navigation light and anchor light: 25 W
10.2.3. Autopilot
Power consumption depends on model, the seas, trimming, etc. Average: between 5 A and 10 A when on, with 30 % duty cycle.
10.2.4. Refrigerator and freezer
We assume an installation with two 50 W compressors and water-cooled heat exchangers. Furthermore, we assume that in order to keep consumption low, specific attention has been paid to insulation. This can limit the duty cycle of the refrigerator compressor to 25 % and of the freezer compressor to 50 %.
10.2.5. Cabin lighting
More light fittings and less thrifty usage than on smaller boats. Average: 20 Ah per 24-hour period.
10.2.6. Radio
More power and more loudspeakers than on smaller boats: approximately 2 A
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