For North Europe / UK - Solar panel to maintain house bank with fridge unit.

[Refueler]

Size of battery bank has quite an influence. When our domestic bank was 2 x 110Ah the morning voltage was 12.0 V or thereabouts. I increased the bank size to 3 x 110 Ah and now morning voltage is rarely less than 12.4 V. I assume the time to recharge will be about the same but far better for the batteries.

Charge rate of course varies with the overall voltage the controller detects - so I can well believe. Of course your addition increased capacity - so draw down is pro rata.
I could add batterys - but the present setup is in a custom designed enclosure under the stbd aft bunk. To add would mean balancing by creating similar under the aft port bunk..... then heavy cable through engine bay.

 

[Refueler]

It isn't. The fridge uses most of its power in the day when it's hot. This power will come direct from the solar while the battery is charging.

I don't think anyone is questioning whether LFP is better than LA, but it is a different subject than the thread

Thank you ... you catch my quest ...

I want to basically match the fridge demand so my battery bank has an easy life !! If I don't do that - then I'm into significant addition to battery bank ... which then brings in charging etc ..

 

[Refueler]

Go measure the real world & you`ll see that you're wrong, fridge will be the biggest draw at night. You can get the batteries back to 100% during the day using less solar with LiFePo4 than with lead acid. That's real world measurements, not some web forum opinion.

C'mon .. please put this LiFe cells option aside .. its not happening on my boat.

The simple matter as your LiFe cells - they accept high rate charge in for greater range of the cell than Lead Acid due to internal resistance. Second that LiFe can discharge deeper than Lead Acid.
These two factors constitute the 'advantage' of LiFe ... which is not the point on this thread.

 

[onesea]

I asked a similar question a whilst back.

@50N I have 2x 100watt solar panels vertically mounted they are my side screens) and a little 30watt horizonal. With 2 x 100amp LA.
Plus 15amp alternator when engine running, approx average 1 hour a day for berthing.

Running Fridge, charging phones, 2 tablets, plotter, auto pilot and other stuff torches etc. I estimate 2-amp constant drain.

I have been onboard since May no issues with power, I have had 3 days with cloudy weather and no significant sunlight.
Still no problems with batteries charging.
I have even sat next to a free (well included in berth) electric point and not bothered plugging in.
Lead acid are funny things to charge, the more run down they are the easier they take a charge. So on Grey day with batteries a bit low the solar works less to give more charge.

By my reading latitude makes little difference in summer as you get longer days. In winter is a different story.

 

[Refueler]

I have measured and have data for several years in the Victron portal with both AGM and LFP, thanks. I didn't say it wouldn't draw at night. I said that in the day when it's hot and therefore the fridges busiest time the power comes direct from solar, not from the battery. While this is happening the battery will also be charging and then at night the fridge uses that power. with 150W OP will hit 100%SOC on an AGM so making it more efficient is pointless for his use-case. I said above that it would be better, but that's not the discussion here.

OP asked how many watts of solar for a fridge and confirmed he's not interested in battery discussion in this thread.

Thank you again.

If I can install a reasonable Solar setup - then its done and dusted.

If anyone has followed my other thread on the Fridge vs Vevor unit ... I have considered wiring in a dedicated PSU - powered from the mains ... avoiding use of the battery bank. But I'm reluctant to start playing with the wiring as I have a rats nest already to sort. The Solar setup could be sufficient .. so the question was to other users in similar climate - what Wattage they had installed and success or not.

 

[Aja]

Size of battery bank has quite an influence. When our domestic bank was 2 x 110Ah the morning voltage was 12.0 V or thereabouts. I increased the bank size to 3 x 110 Ah and now morning voltage is rarely less than 12.4 V. I assume the time to recharge will be about the same but far better for the batteries.

Snap! Last season 2 x 130ah were being charged by 2 x 80w solar and engine when used.

This season added a further 130ah battery.

Victron has gone from 12.2v discharge overnight to the least I've seen this year as 12.43v.

I think battery capacity is important. There's no point in installing 200w of solar if your controller is just going to dump the excess.

 

[lustyd]

just going to dump the excess

It doesn't necessarily get dumped, it will be consumed for house loads first and foremost. If it's not being consumed then the panels just don't produce the power, so dumped wouldn't be the right word either.
It's always nice to have a bit of leeway for cloudy days or late season. I do agree that 200W isn't necessary here, although as ever with solar it'll probably come down to what fits since I imagine budget isn't a constraint with the small difference in price between the panels

 

[Refueler]

Price is not a constraint - but I am a 'bargain hunter' .. Wife calls me Scrooge !

Dumps ? As Lustyd says - the controller doesn't dump it .. where would it go to ? It would either have to be via resistive load (heat generation) or to Regenerative capacity. Which Solar Controllers do not possess.
The output just reduces as batterys charge level increases until the controller is just passing a float minimal amount ... OR powering the Fridge !!

What is good though with increased battery capacity - is the reduced cycling of controller for charging ... or at least greater time steady and greater time off

 

[noelex]

The location for your solar panels is likely to be reasonably prone to shadows and unfortunately this will have a significant impact on the output.

I would estimate you will need around 200 W of solar to run the fridge.

The battery bank allows you to average good and poor solar days, but the amount of "energy in" has to be greater than the "energy out” irrespective of the battery bank size or chemistry.

 

[Refueler]

The location for your solar panels is likely to be reasonably prone to shadows and unfortunately this will have a significant impact on the output.

I would estimate you will need around 200 W of solar to run the fridge.

The battery bank allows you to average good and poor solar days, but the amount of "energy in" produced has to be greater than the "energy out” irrespective of the battery bank size or chemistry.

The shadows ... I don't have sprayhood so hatch garage is only subject to boom / sail. I think overall the two positions are best possible considering that I will not add structures to the boat - she is for racing primarily.

Of course my intention is greater potential charge than demand ...

 

[noelex]

she is for racing primarily.

Especially for racing boats I agree windage and weight are vital.

However, your project needs a realistic approach to achieve its goals. I think you will be surprised how much impact the shadow of the boom and sails will have on the overall output for a solar panel on the companionway hatch. Even the tiny shadows from the two sheets shown in post # 12 will have a noticeable effect. This is especially true in the areas you plan to sail. These locations have long solar days resulting in a reasonable total solar output, but the sun angle is relatively low. This exaggerates the size of shadows. Hopefully, you can push these shadow sources out of the way at anchor, but when sailing the effect will be significant.

Any solar output is helpful even if the panels do not deliver their full potential output. Solar panels are cheap these days. There is nothing wrong with a panel over the companionway, but you need to take the effects of this location into account when estimating the energy it will deliver. Given your racing application I would not advocate you install an arch or solar panels on the rails, but perhaps a supplemental portable solar panel array may be a good solution for making up the difference?

Good luck with your project. There is something magical about using the free and silent energy from the sun to produce electricity.

 

[B27]

I have a 50W panel, mounted horizontally on a post at the stern.
My fridge draws on average 1 A , with the first day being virtually free, because we usually start off with a bag of cold food from home including a frozen chilli or curry or something, that means the fridge starts off cold with no power input.
This year's sailing has been quite overcast, we've done a few 3 day trips, not had battery problems or milk gone off yet.
We tend to motor in and out of a harbour every day, a lot depends on how much your alternator stuffs into the battery in that time..

Our other electrical needs are small, we only use the autopilot much if we're motoring, our plotter is an ipad etc etc.

More is generally better, until you fall in the water trying to get off the boat with the guardrails cluttered with panels or something?
I'd like more solar, to extend things into Autumn, less sun, using heater etc.

It's a very ill-defined requirement, because a food-safety nazi would want the fridge never to get above 2 degC, while we're a bit flexible only keeping stuff a day or three, fridges vary, alternators vary, wiring varies, and people use their boats differently.

Also, I'm a casual sailor, so if I abuse my batteries a bit ten weekends a year, they will last 6 years instead of 7.
If you are a crusty liveaboard, you need to cosset your batteries or they won't last 2 years.

 

[chris-s]

We added an isotherm ge80 this year and so far the existing 80w fixed and 80w part time wandering panel with a pair of old 100ah agm batteries has kept it running 24/7 along with instruments and a bit of led lighting.

 

[William_H]

I can appreciate Nigel's question of just how much is enough. But I think the solar decisions need to start from the other direction. Just how much (large) solar panels can I fit or am I prepared to fit on the boat? The actual size you can reasonably fit will be limited. You may be willing to go stern gantry with lots of panel area. But with added wind resistance and probably sailing performance limiting. Cost I would not think a significant factor. If you decide to limit panels to flat cabin top area then that is it. What you get from solar is what you get. Of course depending on so many factors like orientation to the sun shading and weather. What you don't get from sun you either do with out (turn off fridge) or run the engine to charge. (bigger batteries can help here with more charge current accepted). I am sure you know all this already Nigel but jut to reiterate for other readers. ol'will

 

[Sandy]

Have you considered mounting the solar panels on the 'guard wires'?

 

[Refueler]

Have you considered mounting the solar panels on the 'guard wires'?

In the early posts here - I think I mentioned portable ...

Yes of course ... I watched a boat week or so ago in the yacht Hbr do exactly that ...

I have been looking at Dugo Folding panels .. not cheap but they fold up into protective carry bags ...

If I add a panel on Hatch garage - I can easily have a parallel connection for guard line hung panels ..

 

[plumbob]

If I may add my interest in this thread although I'm not a rag and stick boater. I am literally about to install a 125 watt panel, with a split controller, to 1 x 105ah starter battery and a3x 105 ah house system all lead acid. The controller can be adjusted to anything between 50/50 and 90/10 to both banks but when 1 is charged it switches all the input to the other bank. My hope is to be able to run the larger of the 2 fridges on solar alone while we are moored up and use the other fridge for drink while the engine runs. I don't think there's any point in altering the charge split from 50/50 initially as hopefully the single start battery will charge quickly under engine and then the generated power will charge the rest. The kit comes with a meter that indicates what's happening so will keep an eye on things. Not that it's relevant but I measured the voltage of the batteries after they had stood uncharged for a week at 12.6 and 12.7 respectively so hopefully they're in reasonable condition. Thanks

 

[lustyd]

use the other fridge for drink while the engine runs

I knew it! You motor boaters are all on the gin while driving

 

[B27]

Portable panels are all very well, but to top up a battery after a sail, you need panels fitted when you've gone home.
Also, we do catch some power while sailing in overcast, even drizzle conditions.
Our fixed panel was working while beating into 20knots true yesterday.
Also you need to consider where the wiring will run.
The other thing is, we don't really have great storage space for temporary panels.
We don't want something to fff with on sunny days, we want a permanently fitted solution that's working as best it can by default.

 

[Refueler]

I have intention when not racing .. to have my Vevor portable fridge on board ...

This brings in another variant ..
This is just a discussion project - not what I plan ... so its open for solutions.

The built in Fridge - can stay as is .. with increased solar to approach its demand watts.

The Vevor can be solar powered but will need a battery to be the 'control' between solar controller and the Vevor unit. That battery can be small as long as its 12v as a minimum .. a small lawn tractor battery as example of about 20 - 30A/hr. The solar would need to be able to deliver 4A on a grey day ..
We can ignore night as the Vevor maintains good temp during off periods.
This then would provide low temp fridge while the built in can be set to a lesser demand setting ..
The solar could be portable and independent of the fixed ..

??
Go on guys comments / thoughts on that ... as I would like to cover all bases with a dual setup.