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diy solar

Help to plan new system for boat

UK boat

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Joined
Oct 8, 2022
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Hi everyone,

New member here. Have been reading through some of the threads here over the last few days and thought I’d introduce myself ?

My name is Will, based in the UK and am trying to design/plan a small solar system to charge leisure batteries for occasional use on a modest size 30ft boat (leisure use - mainly the odd evening/weekend maybe a little more often in the summer).

Currently the boat has three regular lead acid batteries - one for each engine starter and a 100Ah leisure battery, charged via a split charge system off the port (Left) engine. Also has a 230v AC hook up (shore power) when available.

The boat has a 12v electric system for the usual stuff - lighting and water pumps etc. There is also a warm blown-air diesel heater that is connected to the other engine starter battery (not the leisure one) - I assume as it is fitted on that side.

Moving on, I have a 2kW 230v pure sine wave inverter to install that seems to work well - runs an LCD TV and a microwave etc nicely, which are the main things we use when on the boat. Using a 100Ah leisure battery it seems to run the TV (c. 100W load) for several hours which seems enough for a typical evening’s use plus a few minute’s microwave etc. I think 200-300Ah would be a nice amount for the inverter to run off to allow for headroom and prevent discharging too much in normal use?

So I’m trying to plan a relatively simple/budget friendly solar system, along with a bit of extra battery capacity to run the inverter and keep the rest of the 12v batteries topped up whilst the boat is not in use.

My logic is that even a relatively small system may be enough to charge the batteries for a few hours a day over the course of a week to to replace what is used over an evening or two at the weekend? That’s without running the engines of course.

There is probably room for 4 extra batteries in the engine compartment and solar panel wise I have two ideas:

1) There is quite a large area under the wrap around windscreen that would fit one or two typical 100W panels or maybe one larger and one smaller panel? The glass is flat and not tinted. I know that the output is said to be greatly reduced through glass but could someone advise by approximately how much (ball park?) - 50%? The boat gets quite a good amount of sunlight so I was wondering if this was a reasonable consideration? Positives I can think of would be that it would be more discreet than mounting panels on the outside (security) and simpler to install (no holes to cut etc. Would also keep the panels clean and dry if that helps anything.

2) Second option is to mount some panels on the outside. Two or possibly three areas (roof tops and potentially rear deck/roof) would mean that I could add quite a few panels if needed. I would think 4x 100w panels wouldn’t be too difficult, maybe overkill for my needs though? I guess it could be handy though and if I’m able to store the energy efficiently could mean a few more options and better flexibility. Eg could help to run some ventilation or security whilst not in use, as well as charging quicker if using the boat more in the future.

3) Any advice on equipment most welcomed. I’m leaning towards maybe a few low cost lead acid leisure batteries just to begin with (£100 each, or £50 used), a reasonable quality (MPPT?) charge controller (£100-150?) and what about panels? Seems as though there’s quite a few cheap options on Amazon - ‘Renogy’ and ‘Eco Worthy’ or is it worth paying more and if so what would people recommend? 100w panels seem to be around £100 a piece. I would need cables and other bits like terminals and brackets etc I guess.

Are Victron the go-to brand for a charge controllers or any other suitable options? Seems like they have several different models and it’s confusing as to what to go for.

I’m not against buying used items, is there anything to be wary of here - panels or controllers?

I’d like to use Lithium batteries in future but just don’t think I’d have the budget for what I need right now, so a possible future upgrade here or keep an eye out for offers/deals locally in time. My thinking was to buy a good quality MPPT controller and sort the panels out for now and then go for better batteries when budget allows.

I also need to think about how to charge not only the planned additional batteries for the solar kit/inverter use but to connect to also charge the existing 12v leisure battery and ideally trickle charge the engine start batteries too.

Any advice would be welcomed, especially as I have a blank canvas at the moment.

Thanks again and kind regards ?
 
Probably best to post this in the marine area, where marine-specific concerns might come into play.
 
I have 260 watts of solar on my boat and 240 Ah lead acid.

Hence you need two pv panels , a victron mppt solar controller and an extra 100AH battery , about £400 or so ex fitting
 
As others mention above, Victron is a pretty good bet.
There is a wide enough range of MPPTs to choose from in your case and their equipment is pretty efficient.
You can easily add to the system over time, and most of their equipment can communicate for better integration.
I have installed one of their Pheonix inverter/charger units on a sailing yacht for somebody before, and it worked really well.
It also had a charge output for both the main battery bank, and the starter battery.
My little sister has just finished building a 60' canal barge which is a Hybrid. It has electric motor propulsion from a large 48v AGM bank (forklift truck 2v cells), a diesel generator, and 800W of PV on the cabin top. They chose to use Victron themselves and are very pleased so far (Quattro 5000VA)
 
Thanks for the input guys.

Have picked up a few parts already to begin work on this project.

- Renogy 200Ah LiFePO4 battery w/Bluetooth

- Ordered 2x conventional mono 100W panels and 2x flexible 100W panels (again Renogy products). I’m pretty sure these will both fit where I have in mind but either way it gives me the flexibility to check what works/fits and can go from there.

- Also ordered a Renogy 40A MPPT charge controller with BT-1 module.

I need to source cables and brackets for the rigid panels, but wasn’t sure on what the best options here were? Have seen a 4-into-1 branch set for £20 but also need to source cables from this to the charge controller. Any recommendations, cable size (4mm vs 6mm) etc?

Once I get the kit and can plan the install, I will also need to think about how to work out what I’m doing battery wise.

Would it be best to run the solar unit into the 200Ah LiFePO4 battery and then some kind of DC-DC charger to feed into the 3x lead acid batteries? I do have a 2Kw pure sine inverter and could in theory run a regular (AC) battery charger to top up that engine starter and regular leisure battery otherwise.

Thanks again in advance for any suggestion or feedback ?
 
Was also going to say, any suggestions for other good kit would be welcomed - eg displays for battery voltages or state of charge (I know you can see this on the Renogy app, but thinking of convenience), mounting/wiring tips etc.

Would it be even worth considering seeing how many watts the panels would get through the windscreen even if just to trickle charge over the winter whilst boat isn’t really being used etc? Appreciate it’s dark and short days now though.

I think the battery I have has built in low temp protection, does it need a temperature probe also?
 
Would it be even worth considering seeing how many watts the panels would get through the windscreen even if just to trickle charge over the winter whilst boat isn’t really being used etc? Appreciate it’s dark and short days now though.
Remember that PV panels do not like shadows across them. Many of the cells are in series, so that whole string is only as good as the one being shadowed. Unless a panel fits in the window area and can be positioned to avoid shadowing, its not going to do well. Also do not forget that a PV panel needs ventilation (convection) around it to lose heat.
 
Thanks for that. I guess it’s a probable no then, but I wasn’t sure even if with minimal lighting/some shadows or whatever it may give a fraction of the 100W output (even say 10-20W or something) for a few hours a day in the winter.

The plan I was thinking of was just to maintain/float/trickle the various batteries whilst the boat is winterised, but sounds like it wouldn’t be worth it.

Any suggestions for maintenance charging the 3x lead acid batteries on a long term basis using the main LiFePO4 battery as a source?

Again appreciate the input ?
 
Okay so having sourced most of the main parts for this project, I’m starting to question a relatively important part that I need to plan what’s best for.

So the boat has 3x 12v lead acid batteries - one for each engine starter and an Aux. All three batteries are circa 100Ah, and one of the engine batteries actually feeds some other stuff (power for the diesel heater)

The 200Ah LiFePO4 battery which I plan on using as the main system battery for the solar charge and inverter will obviously get charged from the solar charge controller.

But I’m starting to wonder more about how best to charge the 3x lead acid batteries.

I mean, options I can think of:

- Buy a different MPPT with DC to DC charger built in

- Run a regular AC to DC battery charger when needed

- Or even a different inverter with a built in charger?

- I guess the AC to DC option also allows charging from shore power too, so that has an advantage there?

How can I connect the 3x lead acid batteries to charge them all up but obviously they need to be isolated from each other. I was thinking also of some kind of monitor/status indicator for the lead acid batteries (Renogy has BT app which sort of covers that?)

Suggestions for the easiest/simplest option would be really appreciated. I can work with what I have but sometimes a fresh look over a design helps :)

Thanks in advance :)
 
But I’m starting to wonder more about how best to charge the 3x lead acid batteries.

Suggestions for the easiest/simplest option would be really appreciated. I can work with what I have but sometimes a fresh look over a design helps :)

Thanks in advance :)
It sounds like you need to look at your Pb battery system and perhaps simplify.
At the moment you have 4 separate battery banks (3 Pb and 1 LiFePo ).
The engine starters need to be there for the usual reasons.
Why are you not getting rid of the other Pb, you now have the LiFePo?

Because of the efficiency of modern MPPTs and the Lithium battery you could consider a DC to DC charger from the Lithium to the Pb.
You would need to have control over the charger and be able to cut it off if the Lithium bank reaches a settable lower SOC threshold.
Longer term I would be inclined to do away with the Pb batteries with the exception of the starter battery.

Health and Safety
This should only be done by the technically competent, working with high current battery systems is a risky endeavour and should be treated with much respect. The low voltages lure people in to a false sense of security, and they forget there is a lot of energy stored.

As long as the negatives of the batteries are common and of similar Ah rating, you can charge them from the same charger unit. Lead acid batteries have a charge voltage characteristic that makes them balance as they get closer to full charge. This can allow the ability to split the charger through high power Schottky diodes. You would need to find some good quality diode modules that can handle the charge current and each output from diode to battery should have a protection fuse (protection in case of a diode failing, Semi Conductors tend to fail short circuit). With an isolator switch on each leg of the charge split after the fuse, you can manually set which battery can receive a charge.
With this arrangement the charge current will go to which ever Pb battery is lower in SOC. As it reaches the level of the other batteries the current will start to balance across the batteries being charged.
I attach a quick sketch.
 

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