Can I charge my trolling motor batteries with a solar panel?
Unfortunately, this simple question doesn’t come with a straight forward yes or no answer. When a customer asks this question, we find that there are three situations they are trying to accomplish. So let’s rephrase the questions:
Can I maintain my trolling motor batteries with a solar panel while the boat is not being used?
Yes, it is possible to attach a small 12v or 24v solar panel to your trolling motor battery pack. A small 6-watt to 12-watt panel can, in most situations, keep an already fully charged battery pack maintained while you are not using them. BatteryStuff.com carries low wattage solar panels meant for this purpose. They will typically output appoximently 750 mA to 5 Amps a day depending on the size you pick. In most situation these type of solar panels can keep a fully charged battery pack topped off and maintained for future use if there is no parasitic load coming off the battery. If there is a parasitic load coming off the battery, we recommend that the panel outputs more than double that load in a 24-hour period. So, if your parasitic draw is 2 amps a day, then your solar panel should be capable of outputting 4 amps a day on the low side.
Can I recharge my trolling motor batteries with solar panel after I’m done using them?
Yes, it is possible, but most of the time we find most customers don’t find it feasible. It is possible to recharge your trolling motor battery pack with a solar panel after use, but it does come with some limitations. A higher wattage solar panel is larger in size, so typically most people don’t have enough space for mounting the solar panel. In general, most trolling motor manufacturers typically recommend that a customer use a group 27 to group 31 size battery for their trolling motor. This means they factor you are going to discharge the battery at least 50% per use, which means a solar panel is going to need to make up for 50 to 65 amps if the battery is 50% discharged.
While a lot of our customer’s don’t care how long it takes to recharge, we believe that a battery should be brought back to fully charged as quickly as possible. If a battery sits too long, the sulfation within the battery can harden causing the battery to have a shorter life. For this reason, our recommendation may seem high, but they are aimed towards keeping your batteries in good condition.
For 12v trolling motor batteries, using batteries that range from 75 (group 24) to 120 AH (group 31), we would recommend a solar panel no smaller than a 12v 70 watt Solar Panel. Ideally, we would like to recommend a 12v 100 Watt or 150 Watt Solar Panel. The 12v 70 watt can output 16 to 24 Amps a day, while the 12v 100 Watt can output 20 to 31 amps a day, with the 12v 150 Watt offering 32 to 48 amps a day. As you can see, the 12v 70-Watt panel may take 3 to 4 days to charge the battery completely with a battery that is discharged 50%. The larger panel may be able to do it in just over a day depending on sunlight conditions. If you go with the smaller 70 watt panel you just need to know that you cannot expect it to keep up with back to back days of using your trolling motor.
For 24v trolling motor batteries it becomes even more difficult to recharge the battery pack with a solar panel. If you are using a group 27 to 31 battery, you need a panel double the wattage of the 12 volt solar panels mentioned above. So a 24v 140 Watt solar panel at minimum up to a 24v 300 Watt solar panel ideally is what would be needed. This can be accomplished using two of the 12-volt panels put in series or getting a single 24-volt panel. We find that customer with a 24-volt trolling motor simply won’t have the room on their boat or dock for these size solar panels. In the end it is possible, but most find it not feasible given the space required.
Can I power my trolling motor with a solar panel?
While anything is possible given the right amount of space, the answer to this question is no. The amperage requirements of a small 30 lb thrust Minn Kota trolling motor draws 30 Amps at Max Thrust! Our largest 12v 150 Watt panel outputs around 8 amps an hour in direct sunlight, so it cannot keep up with that kind of draw. If you have a large pontoon boat and want to make a canopy of solar panels, then sure it may be possible, but most customers don’t find this feasible.
While we wish every example here was possible, we hope you at least found our answers helpful. Not every situation is alike and there are situations where any one of these is possible. If after reading this post you still want to proceed, then we would invite you to read our article Solar Systems the Right Way, which will link to calculators to help you size your system.
The examples used above are based on our most frequently ask questions. If your question wasn’t answered above, or your situation is unique to what we described above, then feel free to reach out to our Tech Support for assistance.