Solar panels

[Jetblack57]

Hello all, looking for advise on solar panel suitability,……….

I have 4 x12v x 105 amp hour batteries all newly installed, 2 are set as leisure batteries & 2 are set as starting batteries., all are wired in paradel, here’s the bit I need to know, …….what Solar set up do I need to keep all 4 batteries charged & what charge rate & amperage should my anticipated solar set up put out to keep the batteries both charges & topped up .

I will add the batteries are charged from the 12v alternator when the engine is running, via split charging. I wold like the batteries charges topped up to capacity, when on the mooring & when the boat is not in use for any given period.

Thanks for the advise & comments in advance.

 

[john_morris_uk]

My first question is, ‘Why two engine start batteries?’

 

[Jetblack57]

Emergency power.

 

[RJJ]

It depends. Sorry.

To charge and top up on the mooring with no load requires a very small solar setup. 20 or 30W. Really easy.

To run battery output off grid depends, well, how much output you need. A couple of 12v outlets to charge your phone or laptop? Tiny. Fridge? Medium, 100-200 W should do it. Air con, watermaker, lights, fans, induction cooker, nespresso....then you need a few hundred Watts, bigger batteries and a really big inverter.

For given wattage output, say 240W, divide by 12 (volts) for the amps going in (20). On really a good UK day maybe you get 5 hours at full output, plus a couple more at partial output so call it 6. So 100 Ah. Deduct 10-20pc efficiency losses. Result: 80Ah a day. On a good day. Less in winter.

That's the maths. Then go ahead and budget for both stock and flow for how you intend to live on board. If you want to sustain yourself at anchor indefinitely then you need your solar output to meet your daily demand; also you need your daily demand to fit well within the acceptable discharge of your batteries so you cope with nightfall and also overcast days.

If you want to do it underway on an ocean passage then you have to allow more as the sails get in the way and you need to run the instruments.

 

[adamlang]

Emergency power.

You might find it better to have three house batteries and then have a emergency parallel switch between the two banks should you ever need it.

Having a two battery starter bank might hide a fault in one of the batteries and cause problems, also a three battery leisure bank should last longer, both in terms of cycle length and number of cycles.

 

[Jetblack57]

It depends. Sorry.

To charge and top up on the mooring with no load requires a very small solar setup. 20 or 30W. Really easy.

To run battery output off grid depends, well, how much output you need. A couple of 12v outlets to charge your phone or laptop? Tiny. Fridge? Medium, 100-200 W should do it. Air con, watermaker, lights, fans, induction cooker, nespresso....then you need a few hundred Watts, bigger batteries and a really big inverter.

For given wattage output, say 240W, divide by 12 (volts) for the amps going in (20). On really a good UK day maybe you get 5 hours at full output, plus a couple more at partial output so call it 6. So 100 Ah. Deduct 10-20pc efficiency losses. Result: 80Ah a day. On a good day. Less in winter.

That's the maths. Then go ahead and budget for both stock and flow for how you intend to live on board. If you want to sustain yourself at anchor indefinitely then you need your solar output to meet your daily demand; also you need your daily demand to fit well within the acceptable discharge of your batteries so you cope with nightfall and also overcast days.

If you want to do it underway on an ocean passage then you have to allow more as the sails get in the way and you need to run the instruments.

 

[Jetblack57]

RJJ & Adam, ..Thanks for the responses. I’ve only 12 v outlets & I’ve 230v for marina hook up which also tops up the batteris or it’s engine run with 12v alternator charging to top up when out, I’ve a motor boat , which has all 12v usb, tv, radio & lighting, also has a small 12v fridge, generally the fridge is on when along side when mains is there to get it cold , then set on low just to chill when out, or if a day trip its off. Power used is generally phone top up, & radio, in the evening a bit of light & tv for say 3 or four hours. No inverter is fitted.