We are going to draw up a balance sheet of the electrical consumption of our boat. To do this, we will have to establish a list of the main consumers. Their average duration of use will determine the capacity of the fleet, while the power of the most consuming appliances will determine the instantaneous power to be supplied. For an accurate estimate, we will also have to take into account the efficiency of the appliances and the electrical losses.
List the main energy consumers
With the help of a spreadsheet, we gather information on the devices on board requiring electricity . Among the main consumers, we will find the navigation instruments, such as the VHF, AIS, radar or the pilot and the on-board computer, which consume little, but serve a lot. Other devices related to safety and comfort, such as pumps or lights, will have an episodic operation. Finally, the large optional consumers dedicated to comfort, such as the fridge, hot water, washing machine, for example, depend a lot on the need, the navigation program and the budget allocated to the equipment.
It will be necessary to evaluate, for each device, their maximum instantaneous power and an estimate of their average duration of use. This last parameter is important to evaluate the future capacity of the battery park.
What voltage for my circuit?
A 12V circuit has the advantage of being simple. When in doubt, it is a good choice.
A 24V solution is interesting if a large number of devices operate with this voltage and more instantaneous power is needed. This will save on the size of the cables.
Finally, for even more comfort, a 48V circuit is possible, with the advantage of being compatible with a large number of devices dedicated to land autonomy.
In our example, we have chosen a 24V circuit that supplies 12V appliances with low power consumption, 24V and 230V.
Consider energy efficiency and losses
Consumers who operate on 230V will need a converter, whose efficiency should not be neglected. For example, a 1500W appliance may end up consuming 1700 to 2500W at the battery terminals, depending on the performance of the converter, the ambient temperature and the losses generated by the cables. To a lesser extent, low voltage converters, for example 24V to 12V, also have losses that must be taken into account.
In our spreadsheet, we will therefore have to specify whether the consumers require voltage conversion and estimate the total power required. Our example proposes a page of parameters allowing to vary the estimates according to the yields and the losses.
What are the important values of our energy balance?
The two most important values to consider are the instantaneous power to be supplied, expressed in watts, and the consumption, in watt-hours. If the first one is high, you will need a battery capable of supplying a lot of power as well as large cables. If the second one is high, you will certainly need a well sized battery pack, to be combined with the production capacities of your installation, such as solar panels, wind turbines and other sources.
It is also interesting to separate what is important from what is less important. If the balance seems too important, we can cut back a little on the devices dedicated to comfort while maintaining the power and capacity necessary for vital devices. However, it will be necessary to integrate some important details, such as the total consumption of the cycle of use of an appliance that one wishes to use at sea.
An essential prerequisite for the facility layout
Once the list of consumers is complete, we can move on to the next step: the choice of batteries, charger/converter and production systems for the most important elements. We will be able to build an electrical diagram adapted to the needs of the boat.
