Solar Panel to Top Up Batteries

[comino]

A bit of help and advice please. I intend to put a temporary solar panel on my boat in Greece to top up the batteries during the winter months whilst we're back in the UK. I've got three batteries, but unfortunately I don't have details of their output. Is there a rule of thumb about the KW panel I might need to do the job - not too little charging ability and not too much I guess????? Much appreciated.

 

[Graham376]

25w will maintain batteries if no loads but if you're buying one, go as large as you have space for and fit a regulator.

 

[sailaboutvic]

" I've got three batteries, but unfortunately I don't have details of their output." As in AH ? It doesn't matter for what you want to use the panel for.

If you just want to use the panel over the winter months 50/100₩ will do the Job but get a good mppt to Control it.

But as said you better off getting a large panel which you can use in the summer moths too .

 

[comino]

Thanks for the replies - really helpful. I've already got a 50w solar panel, but since getting an all-over winter cover it isn't doing its job!!!

 

[Graham376]

Thanks for the replies - really helpful. I've already got a 50w solar panel, but since getting an all-over winter cover it isn't doing its job!!!

Can you mount it on the guard wires outside the cover?

 

[comino]

It's very neatly screwed flat (no aluminium frame) to an ideal area on coachroof, with the wires invisibly built into the boat - it was a professional job done at some considerable expense. It would be a shame to lift it and in any event, when we're at anchor it keeps the engine battery topped up. We use a generator to run all the other essentials (cold beer in the fridge). I'm now trying to establish if the existing regulator is OK to deal with another 50w panel.....in which case I won't need another one.

 

[sailaboutvic]

It's very neatly screwed flat (no aluminium frame) to an ideal area on coachroof, with the wires invisibly built into the boat - it was a professional job done at some considerable expense. It would be a shame to lift it and in any event, when we're at anchor it keeps the engine battery topped up. We use a generator to run all the other essentials (cold beer in the fridge). I'm now trying to establish if the existing regulator is OK to deal with another 50w panel.....in which case I won't need another one.

You just as well to buy a cheap panel and temp wire it to the same reg if you don't want to buy a new reg if you do I would buy a mppt one that will take descent amount of W ,
Believe me when I say if your paying out money then buy a good mppt as once you start using solar you soon fine you be wanting to go bigger especially if you a full time liveaboard .

We started many years ago with 100w panel ,
It wasn't long before we brought a second one .

We now have 4x180w panels

 

[PetiteFleur]

You can get Dual Battery charge controllers from Photonic Universe - pwm or mppt. The Photonic Universe ones you can alter the charge to each battery.

 

[comino]

Thanks for feedback. I guess the question for me is a simple one. Will my Morningstar 12 V Sunsaver Duo Regulator already installed be OK to take another 50 w panel without the need for additional kit or adjustment. I had an input socket fitted in the cockpit allowing us to plug in another panel in an instant. It's just a question of whether the regulator is fit for purpose and, as I've now mentioned a new issue.......will the regulator require adjustment in any way? I've tried to contact the original suppliers and fitters many times, but with no reply.

 

[Mistroma]

The Morningstar 12 V Sunsaver Duo Regulator is a 25A max. PWM regulator capable of charging 2 batteries.

The reference to buying a 2 battery model in one post is not relevant. It is already capable of that and you are asking a different question anyway.

It would seem to be way over-specified for a 50W panel and adding another 50W panel wouldn't be a problem, even in summer. However, you state that the existing panel is covered anyway during winter.

Options are to fit a temporary "winter panel" outside the cover and:

1. Connect it to the regulator with the existing panel still connected
2. Disconnect the original panel at the regulator and connect a temporary "winter panel" to the existing regulator
3. Connect it via a new cheap regulator

Option 1:
Should be fine as long as your existing panel doesn't take power out. The regulator will almost certainly not allow that at present but the panel may not have a blocking diode and both panels will be connected. Power possibly drain back from a new panel to the covered panel during the day.

Option 2:
No problem at all, just a matter of swapping over the wires (follow instructions for your regulator).

Option 3:
I imagine it would be cheaper to buy a slightly larger panel than paying for an MPPT regulator. The MPPT will probably give a good percentage gain over winter. However, the panel size is quite small and actual gain won't be great. A cheap PWM regulator should be fine as long as it is reliable. Your existing regulator is quite an expensive model and should be well built.

You are going to have to run wires from your temporary "winter panel" for all three options. I would have expected your existing panel to have connectors close to the panel to make it easy to remove. Are you certain there aren't some quick release connectors underneath? I have them on my system and that makes it really easy to disconnect and add a different panel.

You didn't give battery type or size and that makes it difficult to work out the smallest acceptable panel. I can give some rough figures for daily Ah for Greece and assuming a 50W panel.

Ah/day for a panel lying flat on deck:
Oct. 10
Nov. 7
Dec. 5
Jan. 6
Feb. 8
Mar. 11
Apr. 15

Ah/day for a panel angle at about 45 degrees in the best direction:
Oct. 14
Nov. 12
Dec. 11
Jan. 11
Feb. 11
Mar. 13
Apr. 15

You can see that angling the panel helps a lot in winter. However, it pretty much guarantees a lot of shading from nearby boats, trees, buildings etc.

The Ah/day actually required to keep your batteries topped up will depend on type and capacity. I only used a 50W example as you have that size already and van easily scale to smaller sizes.

 

[comino]

Thanks Mistroma.......that's really helped me. Option one seems easiest, but how do I know if the existing panel has a blocking diode. It is a Solara SM200S Solar Module 55 Wp. Thanks again.

 

[sailaboutvic]

Thanks Mistroma.......that's really helped me. Option one seems easiest, but how do I know if the existing panel has a blocking diode. It is a Solara SM200S Solar Module 55 Wp. Thanks again.

If you open the connector box you see your diode ,
Most will have diode

 

[Mistroma]

You

Thanks Mistroma.......that's really helped me. Option one seems easiest, but how do I know if the existing panel has a blocking diode. It is a Solara SM200S Solar Module 55 Wp. Thanks again.

You'd need to check documentation for the model you have. I think most Solara panels have blocking diodes in the junction box but some have them in an additional external box. Probably just as easy to look as Vic suggests.

Battery type will determine the self-discharge rate and hence the daily Ah to maintain a charge. AGM are usually OK for 6 months as long as they are completely disconnected. Deep cycle such as Trojan 6V batteries really must be given a charge over the winter months and leisure style/ low maint. batteries are somewhere in the middle.

Nothing is risk free with batteries these days.

People who left their AGM batteries isolated at end of 2019 wouldn't expect they might not return until 2021 due to Covid.

I had my Trojan batteries on a decent charge regime with a monthly eq. charge to stir up the electrolyte. I slightly overfilled in Oct. 2019 but never imagined they'd need to last until Sept. 2021 without a top up. They were OK but only just.

Quite a few people had ruined batteries on a nearby yard when power failed due to condensation in distribution points. Nobody noticed for several months.

I spoke to one person with a failed solar regulator and ruined batteries. However, I think a reasonably sized panel with a decent regulator is probably the safest option if you can't visit for regular checks.

 

[comino]

Thanks again. One thing I've learn't from this is to take copies of all the manuals and instruction documents that are kept on the boat. Like so many others, I hadn't intended to be away for so long and in the past I used to nip back quite frequently to do a bit of maintenance (sit in the cockpit with a cold beer more like).

 

[Chris_Robb]

One word of warning to anyone using un monitored charging especially sun panels over winter. The 18 months that I left the yacht, with a reduced output settings on my 2 x 85 panels to Victron mmpt, I had an insurance survey and the surveyor - one W Walsh found the batteries very very hot, so disconnected the whole set up. That was with 5 100 amp/h batteries - about 4 years old. Most likely cause - just a single failed cell in one of the batteries - no where for the energy to go. So heat - and fire could be the end result. Also on unmonitored shore power could have the same effect.

I dont know what the answer is apart from disconnect the whole lot - or just pay the yard to charge 1 day per month or every other month - the latter is probably best.

 

[Mistroma]

One word of warning to anyone using un monitored charging especially sun panels over winter. The 18 months that I left the yacht, with a reduced output settings on my 2 x 85 panels to Victron mmpt, I had an insurance survey and the surveyor - one W Walsh found the batteries very very hot, so disconnected the whole set up. That was with 5 100 amp/h batteries - about 4 years old. Most likely cause - just a single failed cell in one of the batteries - no where for the energy to go. So heat - and fire could be the end result. Also on unmonitored shore power could have the same effect.

I dont know what the answer is apart from disconnect the whole lot - or just pay the yard to charge 1 day per month or every other month - the latter is probably best.

I have to agree an did say "Nothing is risk free with batteries these days." in #13. I think I gave some examples but have probably run into people with every combination of problems over my years away from UK.

e.g.
Pay yard to monitor batteries:
A friend had one battery blow up in winter. The yard claimed they had checked the batteries regularly. The yard discovered that Hallberg-Rassy had actually fitted one pretty old flooded 6V battery and that was probably the fault (it wasn't).

Same friend had dead batteries a couple of years later, very expensive AGM. The yard were paid to look after them but had just been connecting shorepower every so often. The yard weren't at fault as he had a faulty charger (real reason for earlier 6V problem).

Just leave mains power connected:
I heard that the yard next door had a lot of customers with dud batteries. They blamed high levels of condensation inside distribution boxes causing power cuts. Nobody was paid to check and many discharged over winter.

Just disconnect batteries completely
Normally a reasonable option with AGM and then Covid comes along. I imagine a few AGMs might have suffered after 2+ years with no charge.

Leave solar connected:
I've heard of failures with good quality chargers and battery failures. I've also seen YouTube trials with small unregulated panels and batteries being over-charged.

I was lucky with my batteries during a 2 year absence. Sod's law meant my remote monitoring system had failed and I had to revert to my plan B for some minimal feedback.