Solar system planning questions

[rslifkin]

I'm currently working on planning out a solar system for my (power) boat. I'd also like to add an inverter to the system, although I haven't decided yet if that'll happen this winter along with solar or if the inverter will wait.

I think I've decided on going with Victron gear for pretty much everything. Inverter will be a Multiplus 12/2000/80. And I'm thinking of going with the Cerbo GX + touchscreen to tie it all together. And a smartshunt for monitoring (to replace my current Blue Sea SoC meter). The house bank is currently 2x L16 AGM 6 volts (400ah at 12 volts). I think I'll be up for new batteries next season, but I don't expect to change the basic design of the house bank unless I can somehow stomach the (almost double) cost of 3 of the L15+ 4V Firefly batteries (and then have to rebuild my battery mounts for them).

The big question is around how to configure the solar panels. I have a slightly awkward space for solar panels (on the cabin top forward of the windshields). The space is basically 90" x 100", but the catch is that I need to maintain a walkway up the center and across the windshields to access the windshields for cleaning, etc. So I've figured I basically have a pair of 36" x 84" spaces to fill with panels. This unfortunately restricts me from just using a pair of big 300+ watt panels, as they're all too wide to leave an adequate walkway. And the 200-ish watt panels are all too big to fit 2 of them per side, but just 1 leaves a good bit of space un-used.

Within the available space, it seems like the most solar I can fit is 600 watts, in the form of 6x 100W panels. The 100W poly panels from Newpowa are 35.83" x 26.57", so I can fit 3 per side, basically consuming a 36" x 80" space.

So the question comes down to how to wire the panels and what charge controllers to use (definitely MPPT). I've come up with a few choices:

• 2 series strings, each with a Victron 100/30 controller
• All 6 panels in series on a single Victron 150/45 controller
• 2 series strings in parallel on a single Victron 100/50 controller
• 3 series strings, each with a Victron 75/15 controller

The last 2 options are a little cheaper than the first 2, but we're only talking about a $100-ish spread between the cheapest and most expensive option, so cost isn't a big driver.

Shading isn't a significant concern. The forward pair of panels on each side should never experience shading other than from a person walking past (unless we're at a dock with tall stuff around us, but then we're probably plugged in anyway). The panel on each side closest to the windshield may get some shading at very low sun angles, but will be un-shaded through most of the day.

Based on those controller and wiring layout options, what does everyone think the most effective option will be?

[sailorboy1]

This basic question comes up alot. The higher number of individual strings are always best. But I feel overall it just doesn't matter once it all gets averaged out (assuming the wire sizes are correct). I personally would go the route that installs easiest and neatest.

[rslifkin]

I think 2 series strings (either separate controllers or paralleled to 1 controller) are the easiest options to wire, as they'll only require 1 cable coming down from each panel group. All in series or 3 strings of 2 will have more wiring involved.

I'm personally leaning towards the 2 series strings each with a 100/30 controller option, but I figure it's a good idea to see if anyone has any better suggestions.

[Chotu]

I’m thinking 2 strings and 2 controllers for redundancy purposes even if shading isn’t an issue.

However, you’re bouncing around the Erie Canal and the lake in a powerboat so in a lot of ways, you don’t need that “in the middle of nowhere “ level of redundancy.

Go with the single controller.

I read somewhere you want to keep the input voltage as high as easily possible (wiring wise) which allows better efficiency. That means series wiring. But there will be a limit on your controller as yo what you can send it, voltage wise, so you’ll need to stay under that.

[rslifkin]

Massive redundancy is definitely not a big concern, as there's no way we'll ever be more than a day away from somewhere to find parts or power. I've got an generator and 2 engines, so even if I lose the solar system entirely, I'm ok, it just means more generator runtime until I can fix the issue. The single vs 2 controller setup is more a question of ease of wiring and performance than one of redundancy. With a series string of 3 panels, I'd be looking at 65 volts open circuit, or 130 for all 6 panels in series.

Realistically, even with no solar we did 8 days of no shore power a few weeks ago and only put 16 hours on the generator (never ran it just for battery charging and about 6 of those hours were for A/C on a hot, rainy afternoon). However, we didn't stay anywhere for more than 2 nights without moving at least a few hours, so we got some engine charging in there. And I think we PSOC-ed a set of house batteries to death, as they performed fine on the trip, but seem noticeably down on capacity since we got back. Having an inverter and solar would cut the generator runtime down by about 30 - 40%, as currently I need the generator in the morning to make coffee if we're not plugged in. I'll still need it in the evening for galley power and hot water, but 1 run per day is better than 2.

[Chotu]

Ahhh. So it’s an auxiliary solar installation. I can’t think of anything to add. You have it all dialed in provided the controller matches the panels and is located near the batteries for most efficient charging.
Having been on a generator based boat all summer, I can definitely understand this installation. I’ll be a nice relief to have to use the generator less.

[Apollo366]

I'd recommend the 3 series strings as this will keep the voltages down and have less of a chance of breaking down insulation and electrocution from the panel voltages.
Also the 3 Victron controllers is more redundant in case of problems down the line.

Just my thoughts,

Capt Wayne

[waterman46]

Originally Posted by Apollo366

I'd recommend the 3 series strings as this will keep the voltages down and have less of a chance of breaking down insulation and electrocution from the panel voltages.
Also the 3 Victron controllers is more redundant in case of problems down the line.

Just my thoughts,

Capt Wayne

Yep, 6 panels in series do create lethal voltages, be very careful with that. My view is that its enough to have one system already carrying lethal voltage (AC from inverter). I would avoid connecting 6 panels in series since parts of these wires are exposed to the elements and being "just DC" someone working on it may forget and assume it's only 12V.

Worse case, you get a short from the hot side to the aluminum frame on the last solar panel in series. Somebody touches that frame with a wet hand or foot.

[Mark Thurlow]

And without migrating the thread; give a thought to replacing your AGM with LiFePO4 batteries. Space for space you should triple your usable battery power, reduce weight and in the long term get lower costing watts.

I mention it now so you set your charging capacity now for Li in the future and get a Li profile charger; pretty sure the Victron meats the criteria.

[rslifkin]

Originally Posted by Mark Thurlow

And without migrating the thread; give a thought to replacing your AGM with LiFePO4 batteries. Space for space you should triple your usable battery power, reduce weight and in the long term get lower costing watts.

I mention it now so you set your charging capacity now for Li in the future and get a Li profile charger; pretty sure the Victron meats the criteria.

Any of the gear I'm looking at could support a future swap to lithium. But honestly, I don't know if I'm quite comfortable with lithium yet, and it's also still pretty expensive. I could probably drop down to 300ah with lithium, but that's still $3000+, compared to about $2500 for firefly or $1200-ish for AGM. Or even less for flooded.

[coopec43]

Have you had a look at this site?


12 Volt, 24 Volt or 48 Volt - Summary

https://www.rpc.com.au/information/f...2v-or-24v.html

[rslifkin]

I had not seen that link, I'll give it a read.

But I do have some good news. I did some measuring and I have 101 inches between the hand rails on the cabin top. I did some testing both in the house and on the boat and determined that 3" of clearance inboard of the handrails is enough that I can grab them quickly without looking and without hitting my fingers on the object inboard of them.

Based on that 101 inches and 3 inches to each handrail, I have 95 inches of width to work with. If I figure 16 inches as a minimum walkway up the center, I can fit a pair of solar panels up to 39.5 inches wide. That gives me a lot more options and means I should be able to fit a pair of 400 watt panels. That makes wiring easy too. 2 panels, 2 controllers, done.

Below is a picture of the mounting space. The center walkway will include the horns, which I've already confirmed are easy enough to step over (I don't need to walk up there in anything other than dead calm conditions).