Modular Solar Setup Question

[SurlySailor]

Hi All,

Hoping someone here can help/ suggest there best way forward for us.

So our current set up is 1) Renology 100 Watt Panel, 1 MPPT 75/15 solar controller (pre Bluetooth), and two Trojan 12V Lead Acid Batteries.

We have a Racer Cruiser and spend a majority of our summer doing weeknight and assorted weekend racing as well as cruises lasting up to 2-3 weeks. We’re planning a 3-4 week cruise for this summer and Generally try to anchor out or grab a mooring vs tie up and use shore power.

Current power consumption is pretty limited. It’s running our fridge while cruising (it pulls about 3-4 amps per hour), and running an inverter to charge iPads, iPhones, etc. I have everything converted to LED including the masthead anchor light and all NAV lights. I also have to turn on the diesel daily for about an hour for hot water while cruising. Aside from that I like keeping the batteries charged so we can sail and have all the instruments.

Our current set up is not really working... the 100 Watt panel is too big and I have been taking it in while sailing and then tying it to the rail when at anchor to recharge the batteries. We’re finding we pull to much power when the solar isn’t rigged and have to run the engine more than we want especially if we’re on a longer overnight sail.

We are also limited because due to racing I don’t want to mount a permanent solar arch or Bimini with panels. I know I’m looking for a silver bullet here.....

So here is what I was thinking. Sell the 100 watt panel, and replace it with two smaller 50 Watt panels, attach it to the rail with removable rail mounts. When out sailing for the day, or when I’m at my mooring I could keep one of the 50 watt panels onboard and charging the batteries. While on a longer cruise I could add the second panel. Seems like the best of both worlds working in my constraints. I also looked at the lighter flexible panels but it seems they aren’t good for unsupported installations.

Now to the questions:

1) is this a sensible approach? Or am I not thinking about this problem the right way.
2) if I move forward with this. The easiest way to pull this off would be to wire the panels in series. Can my mppt 75/15 handle two 50 watt panels in series, and will it auto convert the 24 volt output to 12v? I ask this because when I remove the one panel I would then be sending it 12v.

Thanks for any advice on this. I’m a relatively visual person so I have a hard time reading all the documentation and working this out on my own.

[smac999]

realistically you need 400w+ to run a boat with a fridge.

Weather you have 50 or 100 you still need lots of engine running.

Do you have a battery monitor on the boat?

[Dusty Mac]

You don't say where you are, so this may not apply as it is a different approach but what about a methanol fuel cell like the efoy? (I have no connection) Small, out of the way, not interfere with racing and enough power to keep the boat charged up for an extended cruise.

[SunPoweredYachts]

I would look at maybe first cutting down how often you are using the inverter. It sounds like you could be charging most of those devices (phones and tablet) from a USB/12V cigarette lighter plug. That will help reduce power consumption.

With regards the solar, do you have a dodger you could install a flex panel onto? If not we have seen some custom aluminum frames made for flex panels (50W and 110W) and then rail mounted.

You have a good size controller (75|15) that could take up to 220W at 12V. So you would be fine with 2x50W panels wired in series. The controller will handle any voltage on the input side up to 75V. It auto-detects 12V or 24V when connected to your battery so that won't change.

You could always add a Victron bluetooth dongle to the BlueSolar controller if you want to connect to the app and monitor the system in detail.