Solar Charging for small boats, Pitfalls and Problems 

What a kind remark, Wyatt. Thank you. Likewise, I always get fresh insight from your automotive videos.

Thanks, man. Inline is better but I have a habit of messing up. Inductive is safer if you can accept poor sensitivity for low numbers. Scotty Kilmer (grin) had another strangely creative idea, for those who have already fried the ammeter side of their DVOM. Use an inline 1 ohm 10 watt resistor, inline with the circuit you want to measure. Measure the voltage drop across that resistor and simply recognize that drop to be equal to DC current going through the resistor (V=iR=i*1). Anything slightly more than ~3 amps will fry the resistor (sqrt(10 watts)= max current), so set up the multimeter before, then just touch it inline to get a reading, then remove it. Leave it in place with more than 3 amps and your car or boat may burn to the ground, ha ha.

Thanks, Shawn!

I was thinking the same thing about voltage. This made me wonder if adding another panel might help. My first thought was to add another panel in series, to boost voltage, but I'm told that series installations can make the whole unit prone to being taken down by one bad cell. What do you think? I really liked the idea of flexible panels, because we always remove them and put them downstairs while racing, but their survival after three years is doubtful. Then I wondered why spend more money on a system that is so fragile.

​@@spelunkerd I'm not sure and it has been a while since I looked at this kind of problem. The thought that comes to my mind is that, depending on what the MPPT controller likes to see on its inputs, adding a series panel and bypass diodes might be worth looking into. I selected the components of the solar system of my boat before MPPT controllers were available (1999) and went with a parallel system (even the panels had parallel groups of cells internally -- 4 x Kyocera -85) at least in part for shade tolerance. Even with "shade tolerant" panels, a single line of shade across any panel makes a significant difference to the power output. I'm aware of the shading implications of how I make up halyards and such. So, clearing the way for good light is my first priority.

@@tsmwebb I think the problem is not so much open circuit voltage as it is the big drop of input voltage when the controller begins to draw current from the panels. Near the end of the video on the Victron app I show a real time graph of battery voltage in blue and solar voltage in red. They show big rhythmic swings in voltage, which I think is a sign of suboptimal consistency of power input from the panel. According to the Victron manual, the controller requires a 5 V difference between input and battery voltage before it will start using power, and once it begins to draw power it will continue until the difference is 1V. Also in the manual they say that the controller will be most efficient if two 12V panels are used in series. Clearly I don't have much input reserve in this system but for the moment I don't see an easy answer that fits in a boat used for racing. Thanks for your input!

@@spelunkerd Space, weight, money and time budgets and the need to easily stow the panel do make it a hard problem. What you've done looks good to me and may be as good as can be done. I think that if it were mine I would take the lines that you have crossing the panel off, place the panel in good light and test the system to see if that didn't make a difference. My guess it that even though the panel has deteriorated that the OC voltage, SC current and Vmpp would all go up from what you're seeing now. If so then revisiting the panel attachment system might worth something. I believe the Victron controller is a buck type (as opposed to SEPIC). So, as the manual says it needs a bit of voltage headroom. I've heard reports of the Victron MPPTs not working well with small panels. I have some suspicions about why that might be but, regardless, if the panel that fits in the space can not provide the voltages the controller requires then controller isn't going to work well. It could well be less efficient than a controller system that doesn't use a switch mode converter. For the absolute minimum running and quiescent current and for simplicity a controller that's just a reference and a comparator with hysteresis is hard to beat. PWM has the potential to be light on resources too and it seems to have become the standard option to MPPT in the marine market. To be clear, that's all a very hypothetical first guess on my part. I don't want to mislead anyone. Thinking about it again was a pleasure though. Thanks for making such an informative and thought provoking video!

Great point. I was shocked to see what starter (and windlass) batteries need to put out. On a car, it's not uncommon to draw 150+ Amps, on top of about 30 amps for the signal wire. So house batteries can tolerate much more sulphation, while the starter battery really needs to have fitness to do the quick and heavy lifting. The other thing is the way the curve of Amps vs Resistance is hyperbolic, and for the low resistance of a starter circuit the slope is nearly vertical. This means a tiny increase of line resistance has a profound effect on current and power delivery. So, although corrosion happens everywhere, the most vulnerable circuits are the high current ones. Thanks for dropping by!