How to recharge the batteries on board? The secret weapon is the charge controller, word from the super-expert

Photovoltaic panels used in marine applications deliver electricity at a voltage that, depending on the type of panel and the number of cells in it, can range from 5 to 30 volts, or even more.
To charge service batteries quickly and effectively without running the risk of damaging them, the current and voltage applied should be varied according to the state of charge, and in any case the voltage should never exceed 14.7 volts for 12-volt systems, and 29.4 volts for 24-volt systems. The task of regulating panel voltage and current to values compatible with fast and safe charging of the battery bank is entrusted to the charge controller.
It is easy to see that this is therefore a key component of our photovoltaic system and must be carefully chosen according to the panel it is combined with. Choosing an inappropriate charge controller will, at best, result in you losing a good portion of the valuable (and expensive) energy produced by the panel. In other cases of manifest incompatibility, however, your system will not work at all. Here are the three types of charge controllers found on the market:

PWM (Pulse Width Modulation)
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This is the simplest and least expensive type. Its electronic circuits can only lower the panel voltage to a value suitable for battery charging. Therefore they can only be used with panels that have a voltage higher than 15 volts (in 12-volt systems), and higher than 30 volts (in 24-volt systems).

MPPT (Maximum Power Point Tracking).
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Also called “Tracer.” These regulators have more sophisticated, and for this reason more expensive, circuits that not only lower the voltage as in PWMs, but also increase the current sent to the batteries so that the total power generated by the panel remains unchanged. If you remember, in the first installment of this series of articles we had seen that the power (Watts) was given by the voltage (Volts) multiplied by the current (Amps) and that is W = V x A. Now let’s take an example: a 100 Watt panel at 20 Volts, in full sunlight delivers a current of 5 Amps (100 Watts = 20 Volts x 5 Amps). If this panel is combined with a PWM regulator, the current flowing into the battery will always be at most 5 Amps, because this type of regulator, as mentioned, merely lowers the voltage from 20 Volts to about 14 Volts. Thus, only 70 watts of the 100 delivered by the panel will go into the battery (14 Volts x 5 Amps = 70 watts), resulting in a 30% loss of power! If, on the other hand, the same panel is combined with an MPPT regulator, the 5 Amps delivered by the panel is increased to about 7, thus conserving the total power (100 Watts = 14 Volts x 7 Amps). It is clear from this example that if the panel has a significantly higher voltage than that of the battery, the use of a PWM regulator is always possible, but an MPPT regulator will be able to avoid wasting a substantial part of the energy supplied by the panel.

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Step-Up
Also called “boosters.” These are somewhat special regulators, which should only be used in cases where the panel voltage is less than what is needed to charge the batteries (example: using a 10-volt panel in a 12-volt system, or using an 18-volt panel in a 24-volt system). In fact, the technology used in these charge controllers allows the voltage of the panel to be raised to a value suitable for charging. Generally these types of regulators will not work with panels at a higher voltage than the batteries, but this should be carefully verified by reading the technical specifications.

WHO IS ROBERTO MINOIA

Roberto Minoia is involved in software design in his life, but as soon as he can he devotes himself to sailing in the Tyrrhenian Sea aboard his Dehler 41 CR. His passion for sailing and technology, combined with a penchant for popularization led, in 2008, to the birth of the Blog Della Vela (www.blogdellavela.it) where, consistent with his free time, he writes technical articles, reviews boating products that he himself uses, and publishes diaries of his sailings.

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