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What size solar panel to just run 12v fridge?


Québec

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Being summer, we'd like to keep our 12v fridge running when we're away from the boat - often for a few day - with everything else off - except the bulge pump. We have a spare 12v leisure battery, and so are wondering whether we could run it off that and connect it to a solar panel. In which case, if feasible, what's the minimum size solar panel we'd need?

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What type of fridge ?

A 'modern' 12v (such as a Waeco) will use something in the order of 43-45Ah per day, an old Electrolux could use 120Ah per day.

Outside temperature, the inside temperature, how much is in the fridge, and how often you open the door all affects the electricity usage

The fridge should 'normally' run approximately 33% of the time (hence the 45Ah)

 

Take for example 50Ah per 24 hours,

so in a day (say) 10 hours of daylight you need to produce 50Ah

 

In the Northern latitudes (such as the UK) I work on panels producing 50% of their theoretical output,

So, you need a panel that in theory will give you 100Ah per day (10 hours)

 

A 100w panel (in theory) should give about 8 amps so about 80Ah per day - but - don't forget the 50% 'rule.

A 100w panel will probably give you around 40Ah per day,

 

So, it looks as if a 150Watt panel would do your job and allow a small leeway for the odd cloudy day.

Suggest you use 2x 110Ah batteries to allow for the odd cloudy / rainy day

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Why use a spare battery? Connect the solar to the battery bank and assuming you have at least two decent batteries then you will store some power for the cloudy days. Having more than two batteries is even better.

Sounds as though you live aboard so you should have at least 440a bank. Connect a couple of panels total around 300w and you will spend a lot less on diesel when on the boat moored.

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Thanks both. Very useful. The fridge is a Shoreline c. 6 yrs old.

 

The reason for asking is as follows. We're not live aboards, more 'every weekenders', and are usually on a 240v shoreline when moored in our marina. However, we've just had a hull survey which shows we need complete overplating due to serious pitting (it's a 30 year old boat) which can't be done for a while. The advice was that we could go back in the water, not go anyway until the work is done, and not use the 240v shoreline when we're not on board. We have 3 leisure batteries, but also the spare leisure one. I just thought it might be easier just to run the fridge from the spare. Yes, we could just turn everything off and empty the fridge everytime leave...but would rather not.

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As said, if going to the expense of buying and wiring in solar then wire it in to your domestic battery bank than just the fridge battery. Otherwise if you use the boats domestic batterys then they are not being fed by solar so you would need to run the engine to recharge them as you don't want to use 240 volt landline. Also install a Galvanic isolator to prevent galvanic corrosion.

 

Have a look at bimble solar for solar panel kits.

 

Jamescheers.gif

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I don't live aboard, but like to use like you. earlier this year, I fitted a 100watt panel, and whilst moored with nothing on, the panel keeps 330 ah bank up to full charge. Last week, we stocked up the fridge and left on for three days, still with full charge.

Whilst out, watching TV, showering, lights, found 2 -2 1/2 hours cruising bought everything up to scratch. Chose the 100watt as its physical size was most convenient. Hopefully during summer cruise, we'll be able to hole up for a day or two without engine running.

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