Solar- how much to run 12V Fridge?

[RuK]

Hi, I'm seeking views on how much solar I need to run my 12v fridge. It's not a modern one, it's an oldish Lec. I plan to switch it on in daytime only, and it'll be used prob April - September only.

 

I know there are many factors involved but I am looking for views on how many W of solar will do to run a fridge, personal experiences would be great, finger in the air job is fine but please try and put a figure on it. Many thanks

[Phil Ambrose]

Hmm, I have a under counter 12v Shoreline fridge likewise freezer, (rebadged LEC) with 300 watts of PV array at this time of year they will happily run my cold kit with bank voltage remaining at 14.4v

I have never turned off either the fridge or freezer. Hope this helps.

Phil

[Paul C]

We have a modern 12V fridge/freezer (under counter model, to give an idea of size) and I also fitted 200W of solar. The solar panel capacity was sized after a bunch of calculations to see what's most cost effective. One thing to bear in mind - there is no 100% correct answer, its more a case of "if I run this fridge (and other items) and this much solar power, what months of the year will the solar be same or more energy in, than the loads are energy out?" I designed ours for April-Sept too, but in fact this year tried it out in March and it works fine, so can do March-October with no additional engine running. Months with more sunlight (eg now onwards) means that the solar will support other stuff too, without needing to run engine. In the summer, we can run pretty much anything/everything the boat has, electrically, and not need to run the motor.

 

Its worth also having a proper battery monitor so you KNOW its okay, or whether you need additional charging, and a way to read current (amps) which is invaluable for knowing when your batteries are charged, and getting a bit of accuracy when you measure everything to do a power audit.

[RuK]

Great answers thanks. I have a pretty good voltmeter which of course measures amps, if I simply put this across my wires while a load is on will I get an accurate reading of the current ? And do you have an idea what the startup current is to your fridge?

[Paul C]

You'd need to put the multimeter's ammeter in series, which can be awkward for some things - you'd need to make up connectors and undo the load's connection. By using a clamp ammeter or having a shunt installed (properly), its easier to make the readings. But it could be done with the multimeter if needed.

[bottle]

A volt meter measures volts and that is when you 'put it across the terminals.

 

To read amps you need an ammeter there are two types, those that go in series in one of the cables and a clamp type that goes round one of the cables.

 

They both need to measure DC amps not all of them do.

Edited April 24, 2015 by bottle

[Lady Muck]

Dunno if this helps you, but we've got three (knackered, cheap brand and seven year old) leisure batteries, 550w of solar, an outback mppt controller, a shoreline 12v fridge and we charge up phones, tablets and run two laptops. We've been away for three weeks now, mostly moored up, only cruising twice a week and have run the engine when moored up, just twice, for an hour each time. I expect when we replace the batteries, which I will do soon, we won't need to run the engine at all. I don't switch off the fridge at night, no need. If we weren't onboard all day using tech, then I'd imagine 300w would be enough.

Edited April 24, 2015 by Lady Muck

[Paul C]

Dunno if this helps you, but we've got three (knackered, cheap brand and seven year old) leisure batteries, 550w of solar, an outback mppt controller, a shoreline fridge and we charge up phones, tablets and run two laptops. We've been away for three weeks now, mostly moored up, only cruising twice a week and have run the engine when moored up, just twice, for an hour each time. I expect when we replace the batteries, which I will do soon, we won't need to run the engine at all. I don't switch off the fridge at night, no need. If we weren't onboard all day using tech, then I'd imagine 300w would be enough.

 

Out of interest (and partly related to all things power...) how much do the laptops draw, in power?

[Dinz]

Just remember.

You do your power audit.

You do your cable sizing.

You do your batteries.

You work it all out to the last watt.

THEN...............You moor under a tree!

Whatever you work out, add 50%[ish]

[Lady Muck]

Out of interest (and partly related to all things power...) how much do the laptops draw, in power?

3 to 6 amps each depending on how they are being used at the time? But I've just upgraded mine to solid state. It runs for 7 or 8 hours off its battery, but takes about 90mins to charge. I charge it up when the leisure batteries have gone onto float and run it off battery at night.

We will swap lights for LEDs eventually but havent got round to it yet. I think its important to attack power use from both sides. Tablets are great, they run for hours and take very little energy to charge up. We watch TV on a tablet when cruising.

Just remember.

You do your power audit.

You do your cable sizing.

You do your batteries.

You work it all out to the last watt.

THEN...............You moor under a tree!

Whatever you work out, add 50%[ish]

Lol so true!

[FadeToScarlet]

We had a 136 watt flat stick on panel with an MPPT regulator on the previous boat, which kept up with a fridge easily from about April- September. The 200 watt flat stick on panels we have now are easily enough.

[Ssscrudddy]

Everything I've read about fridges seems to suggest fridges use about 4 amps. But no one said what fridge they had.
Everything I've read about solar seems to suggest 200-300 Watts of solar would be enough for a fridge.

Well I reckon my fridge uses about 6 or 7 amps. It's a 12V Shoreline fridge/freezer, the fridge part is 26 inches in height (finishes 4 1/2 inches under the counter), & the freezer part is another 17 inches in height.

I installed 660 Watts of solar in November. What I found, in December, on the few sunny days we had (no clouds all day), was that they would produce enough to run the fridge for 8 hours. Of course the real problem was that most of the time it was cloudy & so the solar produced virtually nothing.

Roll on this Easter (5th April) I went for a cruise & was happy to find my solar was already producing enough power to meet all my needs (not just fridge).

Last night I noticed that I hadnt turned my charger back on since using the pumpout last Sunday, which means all my electric has come from my solar this last week, which has been nice & sunny & no rain. This was as the sun went down, light enough to see by but nothing meaningful coming from my solar & the batteries were reading 13.8V. The lowest I saw my batteries was 12.4V Friday morning around 5.30 am, & that was after using my desktop PC with 2 monitors all night until around 2 am

Edited April 26, 2015 by Ssscrudddy

[FidoDido]

Got an old Engle fridge. It uses 4.5A when cooling. It uses about 40 Ah/day left on 24 hrs. I have one 170W panel and MPPT controller and a 420Ah bank. It happily copes with the fridge on 24/7 from March though to end October.

 

Hope that helps

 

A "three-way" fridge, however, would draw significantly more (a Dometic one I looked up the specs for used 2.5KW/24hr!! thats about 250Ah / day !!! ).. be sure your fridge isn't one of those.