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

[Refueler]

This is for those in N. Europe / UK and have Solar Panels to maintain batterys on board and running a typical built in fridge .. lets say about 40ltr Danfoss (ie Ice Box size conversion). The fridge I have appears to need about 6A cooling down and then 3 - 4A once cooled intermitently ..

What size / wattage panels are you using and total A/Hr capacity of the bank ? Also what ampage does your fridge use ?

Why am I asking ? I want to change or add to the panel I have at present - looks like a 40W and obviously that's not enough ...

I'm thinking that given usual summer where I am has useable solar from about 0600 to 1900 (longer but lets keep to reasonable sun angle) ... solar panel total of about 150W would be needed ?

 

[GHA]

My BD35 averages about 3.5A @ 13.3v, draw isn't constant. Ambient temperature makes huge difference to duty cycle.

What batteries do you have? LiFePo4 will accept a fair bit more energy than lead acid over a day & don't care if they aren't charged back to 100% so worth considering even just a small drop in to run the fridge.

 

[Refueler]

Honest answer - I am not at this time considering changing batterys ... over here - its easy to swap Lead Acid - but Life is not. I have enough hassle getting LiPo's and LiFe for model use ..

Really my question is what Solar Panel wattage ... which really is not battery dependent - but fridge / demand dictated. If I can just exceed demand with panels .. then batterys should remain good regardless of form. Its only the shortish dark hours to consider then ..

 

[vyv_cox]

No idea for the Baltic but my 125 watts of solar runs my Danfoss BD35 fridge totally for about two midsummer months in Greece. Outside June/July I need to run the engine occasionally.

 

[fredrussell]

The general answer for this is fit as much solar as will fit sensibly on boat. No one ever complained about having an excess of energy. For your needs, which are similar to mine, I would want a minimum of 160watts. Panels are smaller than they used to be for same output- the 200w one on my camper van roof would fit on your boat where the 40 watt one is perhaps. From memory it’s about 120cm x 60, but you can look up actual size : it’s a Renogy 200w semi flexible.

 

[Aja]

56°N and 2 x 80W is not quite enough to run my Danfoss BD35 fridge and chartplotter/instruments on a 'normal' day. Nowhere near enough when overcast and wet.

 

[Refueler]

No idea for the Baltic but my 125 watts of solar runs my Danfoss BD35 fridge totally for about two midsummer months in Greece. Outside June/July I need to run the engine occasionally.

Baltic summers are average 25C + ..... and of course we have long daylight hours.

125 ..... mmmm .... that may be not enough for me then ... FredR has 160W reccomendation ..

I'm quite willing to stay with the 40 on deck - save wrecking the area as its screwed down and obviously been there significant time. To add panels I can hang on rails to bump up the total watts to 200 or more ...

So here's a question ....

The controller is mounted in the WC ... basically in line with where the deck panel aft edge is. If I was to add panels - then it would mean having to install wiring from another area where panels can plug in .. wiring to go back to that controller and be parallel connected ...

Think I need go back to boat and measure deck again.

 

[Refueler]

56°N and 2 x 80W is not quite enough to run my Danfoss BD35 fridge and chartplotter/instruments on a 'normal' day. Nowhere near enough when overcast and wet.

I'm 57+ ... so that's good info.

I do not expect to have every day enough .. and when sailing of course - with gear on such as Autopilot etc - there is no way it can keep up unless I cover entire deck !!

My thoughts are gravitating toward 200w ...

 

[NormanS]

I have a similar fridge/general use installation. I have 180w fixed, and another 2x50w panels that I can sling over the mizzen boom if required (not when sailing, obviously).
We're on the W coast of Scotland, and just back from a six week cruise in mainly very dull weather. No problem with battery voltage - never below 90% capacity. Theoretical battery capacity 3x170 ah. (Some use of engine as well).

 

[dunedin]

I would just be pragmatic and fit what you can comfortably fit in. An old 40w panel is way too little but 200w perhaps on the generous side. We have 150w in three semi flexible panels, as that is what we can comfortably fit - with one of the 50w panels a roving one that can be moved to maximise its benefit.
Seems plenty for the fridge between 56N and 60N in summer, but difficult to be precise as when sailing we have a lot of other nav / autopilot demand, and we always have hot showers each evening so if on anchor tend to have to run engine for 20 minutes on day 2 for hot water.

 

[lustyd]

We have 200W and that easily keeps up with the fridge and other loads from spring to autumn in the UK so I'd say 150W would probably be adequate. If you have the space 2x100W would obviously be better, but if your other loads are light then 150 should suffice.

This setup worked for us with lead just fine with 2x110Ah AGMs so although LFP would be nicer and charge faster, it's not necessary

 

[Refueler]

OK ...

Existing panel is 67cm wide and 56cm long in a space that can take 80cm x 75cm without moving cable through deck.

Another area that could take a fixed flexi panel is the hatch garage ... at 80cm x 50cm.

Now to find what panels can be in those sizes .. and what Watt's !!

The hatch garage is good as I never allow anyone to step there and also I have easy access to wire in..... already have cables via deckhead to / from mast.
My concern with that fwd deck area - I don't like stepping on panel ... and increasing the size makes it harder to avoid.

 

[seumask]

We have a 120W Hard panel that I occasionaly see 80W on the Victron controller from. We Sail the channel for a few weeks every year in July and August. This keeps up pretty well for up to 3 days on the hook and a standard compressor fridge with 200AH ( 2*100AH) of LA in sunny weather . Longer and we need to run the engine which we usually do as we move to different anchorages or a marina and plug in. I can only remember running the engine just to charge up a couple of times in the last few years. When we are not on the boat it is massive over kill but the batteries are always full when we get on board at the weekends.

 

[GHA]

Really my question is what Solar Panel wattage ... which really is not battery dependent -

Except it is. You'll get more energy out of solar using LiFePo4 than lead acid with identical usage, istr geem has some data on it from when he swapped, something like 30% increase istr. WIth LiFePo4 you can get away with less solar due to the awful acceptance of lead acid once it gets to a higher soc, plus with the higher voltage the current is lower.

Every day a school day

 

[vyv_cox]

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.

 

[lustyd]

Except it is.

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

 

[GHA]

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

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.

 

[lustyd]

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.

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.

 

[LittleSister]

. . .

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

The OP is typical of thread starters, thoughtlessly asking a different question to the ones that subsequent posters want to answer!

 

[Refueler]

Except it is. You'll get more energy out of solar using LiFePo4 than lead acid with identical usage, istr geem has some data on it from when he swapped, something like 30% increase istr. WIth LiFePo4 you can get away with less solar due to the awful acceptance of lead acid once it gets to a higher soc, plus with the higher voltage the current is lower.

Every day a school day

I've been using Lithium batterys since literally they appeared retail years ago .. LiCd .. LiPo .. LiIon ... LiFe ..

With respect - I did say earlier that there is no intention to swap LA for Life ..

My comment was just a general comment that means that as long as the battery bank is well charged and the solar output = or exceeds the load demand - then what batterys are used is not an issue.