Given the current high cost of energy, the question, should I fit solar on the boat, hardly requires an answer. It’s a no brainer! Do it!

If your boat or R.V. has batteries aboard, it is always beneficial to have a level of solar charging if only to prevent battery degradation through natural self-discharge over time. This topic is covered fully in a previous post titled ‘How do you hook up a solar panel to a boat or R.V.’s starter battery.’ We’re going to discuss a simple starter battery only setup first and then move on to a meaningful leisure bank. Both are important.

Should I fit solar on the boat starter battery(s)?

Have you ever visited your boat only to find that your starter battery is flat? Many have, but it can be avoided as long as the batteries are actually servicable. Over time, all batteries self discharge, and they can get to the point where they can’t turn the engine through lack of charge. A simple way to solve this is to add a small solar panel and connect it through a charge controller to your starter battery. This will help keep the battery happy and should result in fewer dissapointments when you visit the boat. There is an article on this site that covers solar protection of starter batteries, click the link.

Should I fit solar on the boat domestic batteries?

To decide whether it is cost effective to fit solar to your boat’s domestic system, you need to ask yourself whether it will benefit you or not. If you have a boat that you love, but rarely use, you may wish to simply protect your batteries from losing their charge over a period when you are not there. If you use your boat more fully, or live aboard as we do, solar is more than welcome.

In October 2014 I installed a bank of Trojan deep cycle batteries on our boat. I did this after learning the hard way that not all batteries are suitable for the hard use that a domestic bank must bear. I am still using this same bank ten years later.

Why I added solar

In 2015 we embarked on a three-week cruise on the UK’s lovely inland waterways. We had a fun time but discovered a problem that we had not previously thought about. Cruising is great, but the idea is to travel from place to place, stopping and enjoying new scenery or a new town. The problem with doing this was that we still needed to run the engine for several hours a day to maintain the domestic battery bank. It was realising this that prompted me to consider solar power assistance. Should I fit solar on the boat? Definitely

Like you, I asked why should I fit solar on the boat? It was a no brainer really. A summer cruise with daylight from the very early hours until late at night – 16 hours of solar energy for free. Why would I not like that! Saves diesel too!

Make sure you use the right solar controller

As our boat is only thirty feet (9.2m’s) long, we have only enough roof space to accommodate a total of three x 100 watts of solar panels. Of course, we already had an almost new battery bank, so much of the cost of the solar installation was already covered.
The solar controller we have fitted is the Victron MPPT. This stands for ‘maximum power point tracking.’ Our unit is known as the 75/15. This signifies that the unit can deal with an input of up to seventy-five volts from the solar panels and can provide up to fifteen amps output to the 24-volt battery bank.

Each of the three solar panels we have, produces a maximum voltage of twenty-two volts at 6 amps. We wired the three panels in series, so the controller receives up to a maximum of sixty-six volts at six amps. If your system is twelve volts you would purchase the 12-volt version of the Victron MPP

The benefits of putting higher voltage through the MPPT

You may wonder why we are putting up to sixty-six volts into a controller that is only supplying a 24-volt system. here are a couple of reasons. One is that in low light conditions the controller can still operate. The second reason is one that involves an element of electrical sorcery! In bright conditions, when the voltage is higher than the battery requires, the controller takes the excess voltage and creates additional amperage for the batteries, cutting the charge time required. Even though our solar system has a rating of six amps, in bright conditions we regularly read up to just over nine amps. Magic!

I’ve just added the picture above as an edit, showing the amps we were collecting in late March on a bright sunny day. Just as interesting, is the 942 number bottom left. This is the total free kilowatts we have received so far. Usable electricity for free!

Although my current system is quite small, it is still very effective. It is also very scalable if you match your battery capacity to solar panel and MPPT. All this comes together and answers my original question ‘should I fit solar on the boat’.

More info about Lithium batteries

I am currently researching Lithium Iron Phosphate (LFP) systems for when my Trojans eventually fail. Look out for a future post on the subject. When I publish the new article, I will place a link on this page too.

Here is the link I promised – Lithium Iron Phosphate Batteries

Bottom line -‘should I fit solar on the boat’? Definitely!

If you want to know more about ‘photovoltaics’, solar energy and panels etc., click the link. Fascinating reading.