I found myself wondering if there was any real benefit in fitting solar panels to our boat. The reason I pondered this was because of a trip we made three years ago to Boston in Lincolnshire. We had decided to take three weeks holiday and a good long trip would probably be appreciated by the boat's engine and transmission. In fairness we had a really good trip and enjoyed it.
The only fly in the ointment came when we stayed anywhere for more than one night. We found that we were having to run the boat's engine for several hours a day to 'top up' the leisure batteries. Our engine, despite in excellent condition, is almost seventy years old. It is quite noisy, which made it somewhat irritating. Also of course, with the engine running we could not leave the boat unattended. Not ideal.
I did a lot of research before finally making the decision to go ahead and install solar.
We already had an almost new set of four Trojan deep cycle batteries fitted and I can not impress upon the reader enough that genuine deep cycle batteries are essential if you want success with a solar setup. Please be aware that batteries sold as starter / leisure batteries are generally anything but and are destined to be a highly costly mistake. Deep cycle batteries have much thicker internal lead compound plates than starter batteries and are specially designed to be discharged on a regular basis. Our Trojan batteries are very commonly fitted to electric golf carts, and are charged at night to provide motive power on the golf course for hours at a time the following day. A starter battery would be fatally damaged if used in this way.
The next thing to consider is how to regulate power from the solar panels to get the absolute maximum into the batteries without damaging them. There are many options available and it is a big subject. The reason a good quality solar controller is essential is because standard 12-volt solar panels do NOT produce 12 volts. It is common for solar panels to produce up to 22 volts each and this voltage will fry your batteries if not controlled properly. For this reason, we chose a Victron MPPT controller. Victron is universally accepted as a market leader renounced for its quality products and we have been delided with ours. I'll begin another paragraph to explain why I am recommending this controller.
The Victron MPPT controllers are extremely cleverly programmed. They are fully functioning 'smart' chargers, and can also act as a direct power supply. The latest ones have a Bluetooth connection that allows charging regimes to be adjusted to suit all battery types. This is useful because our Trojans require a bulk charge higher than that available from a standard engine alternator. They utilize 'Maximum Power Point Tracking' technology (hence MPPT) to scrape every available electron from the solar panels. Now the best bit. We have three solar panels, each producing 22 volts in sunshine, and we have wired them in series. This has the effect of adding the voltage of each panel together. This means that we are often putting 66 volts into our controller! Far from doing damage, this is advantageous. The Victron cleverly takes the voltage from the panels, which is DC current, and turns it into AC current. The AC current is then reconverted to DC at the voltage required by the batteries and leftover power is converted into extra amperage for the batteries, speeding battery charging. Impressively clever in my opinion.