By Kaare   |   2022-11-14

Solar Panels

As you have guessed by now everything on a cruising yacht evolves around two things: water and electricity. You might have heard sailors complaining about a lot of things, however, you have never heard of anyone complaining about having too much water or too much energy.

On IRIS we have mounted 3*200W of solar panels on our targa arch. We have also 2*35W on the roof, but they do not yield very much because they are often partly in shadow, so in this context I will not dwell on them.

Solar panels are very sensitive to shadow. Even if only a very small part of a panel is in shadow, the output from that panel is severely reduced. The technology is still evolving, and there are measures in place which In part mitigates this effect, but it is still something you have to take into account.

The shadow effect influences where you can place the panels, and how to connect them. We have chosen to install the solar panels on top of our targa arch. That way they are as much clear of shadow as possible. We will mostly be sailing on a westerly course. Therefore, by having the panels astern, the mast and sails will not cast a shadow on the panels until late in the afternoon/evening. The panels are almost horizontal. There are different thoughts on the optimum angle for the panels, but trying to mount them on an angle is really over-engineering things. The panels are on a boat, and a boat moves. Therefore you should mount them horizontally (potentially very slightly angled to the rear in order for rain to drain away from the boat).

Next discussion is how to connect them: in parallel or in serial configuration . Placing them in series will result in higher voltage and lower amps, and in parallel you will get lower voltage and higher amps. The charger cannot send energy to the batteries unless the panels generate sufficient high voltage. This advocates for a serial configuration, however, if one panel in a serial configuration drops out because it is partly in shadow, then the entire serial set drops out. If one panel in a parallel configuration is partly in shadow, that will only influence that particular panel, you will still have the other panels to generate full power. Since the issue with a too low voltage is only relevant early in the morning and late in the evening, it becomes clear that a parallel configuration is the way to go on a boat.

One can argue that with the lower voltage and higher amps you will need bigger cables in order to avoid loss of energy. That is absolutely correct, however, do not save on cable dimension. You spend a fortune installing solar panels, and in that context upgrading from 16 or 35 mm2 cables to 50mm2 is really nothing - don’t go cheap !

Our solar arch is so wisely built that I can run the cables inside one of the arch’s ø40mm legs, and from there through the deck into one of the cupboards In the port side of the aft cabin. From here it is relatively easy to find a good spot to mount the MPPT charger. Our charger have a Bluetooth connection, which allows me to monitor the output of the panels - that is nice.

From here on the installation is rather simple. The positive cable is lead to the battery plus, and the negative cable is lead to the battery minus. However if your electrical setup incudes a shunt the negative cable should be connected to the shunt rather than directly to the battery. That way your main electrical system (Mastervolt, Victron, or equivalent) will be able to monitor the input from the solar panels and act accordingly, I.e. show you a correct reading of battery status.

Do not forget to install a fuse on the positive cable AS CLOSE TO THE BATTERY AS POSSIBLE. Electricity flows from positive to negative, therefore you want to cut the cables with a fuse as close to the source as possible, and therefore you need the fuse as close to the battery positive as possible.

Finally you need to program the MPPT charger for the solar panels with the specifics of your batteries. No batteries are the same, and different manufacturers have different optimum parameters for charging their batteries. Slight changes to the charging parameters can mean the world to your system. Unfortunately these parameters for your specific batteries can sometimes be difficult to obtain. Our batteries are Exide marine dual purpose, and you should think that a major battery producer like Exide have published these parameters - sadly no.

On a final note: when you are working with the cables from the panels you need to ensure that the cables are voltage-free. The best way to do that is simply to cover the panels with a blanket, alternatively to work at night.