Hey everyone! I'm setting up three 500W solar panels for my narrowboat and I'm pretty new to all this, so I could really use some advice. I used the Victron MPPT calculator, which suggested the Victron SmartSolar 150/85, but I'm running into issues with cable sizes. With a Vmpp of 34.44V and an Impp of 13.56A, I'm facing long cable runs of about 12m, and the calculation came out to needing 35mm² cables. That's pretty pricey at around £250, and I'm not sure I can even attach MC4 connectors to them. So, I have two main questions: 1) Is my cable size calculation correct, or can I go with thinner cables? 2) Would it be better to wire the panels in series through one MPPT or use separate MPPTs for each panel? I'm concerned about the shading I'll experience on my boat, which is why I considered going parallel, but I'm open to suggestions. Any help would be greatly appreciated!
3 Answers
If your panels are all facing the same direction, series is usually the way to go. Separate MPPTs are primarily for when panels are angled differently. If shading is a big issue, consider optimizers instead, since they are cheaper than using multiple controllers.
A good approach might be to run three standard 4mm² wires to the back and combine them with a fuse box there before heading to the main MPPT. This cuts down on costs and is simpler to manage.
Great idea! I didn’t realize I could do that; I'll definitely consider it!
It sounds like there might be a mistake in your cable size calculation. Since you're dealing with three panels, the total current could go up to 39A. But a 35mm² cable can handle way more than that—around 240A! Just make sure your setup is safe above all else.
Thanks for the clarification! I thought I needed to keep the voltage drop under 2%, but maybe I don't need to worry since rare high power scenarios are tolerable, right?
Yeah, they’re all aligned, but I’m still worried about shading from trees quite often.