what size solar panel

[Rainbow21]

Hi,

Bit of a Newbie to solar panels so please excuse my questions.

I have just purchased a boat and found that the solar panel is not charging the 12vt car battery. Solar panel has no details on it and former owner doesn't seem to know either. The boat has a simrad Chart plotter, depth and speed as well as a auto pilot, not sure how much power they consume.

My question is what size wattage would I require to install to keep the battery fully charged. I have been considering a 100 watt flexible panel complete with 30A controller system and have also seen others of 300 and 600 watt, would a100 watt panel be enough to charge the battery.

 

[dukeofted]

A 50 watt panel would be enough if that is all your electrical demands. I have a 60 watt panel under the boom so not ideal, and that keeps both of my batteries fully charged. I am running a gps tracker to keep an eye on the boat and this is a small but constant 30mA drain.

but solar is cheap so fit the biggest panel you can fit, silly not to. A good MPPT charge controller is just as important as the panel, it gives much better charge if you get shading and non ideal conditions. I bought a Victron Smart Solar 10A controller for £70 off of Amazon and it is brilliant. Solar panel was from Craigsolar as it was the size and shape that fitted my boat best.

 

[William_H]

First thing for OP is to confirm the original solar pV panel is dud. Disconnect it from all loads and connect a volt meter across terminals in the sun. Should get around 18 to 20v then change volt meter to amps and measure short circuit current. If 50 w then should give around 2 amps. (yes it is ok to short the pv panel)
Assuming pale does not produce and wiring to it looks ok then explore connections to panel. Sometimes you can see where a bad panel has corroded with strange coloration pattern of some cells under glass. (in which case throw it away) If panel is good then look at wiring and controller.
Probably easiest to replace with a physically similar sized panel. But essentailly fit as big a panel as you can reasonably mount. ol'will

 

[MontyMariner]

what size wattage would I require to install to keep the battery fully charged.

That's not really the full question!
A low wattage panel will keep the battery fully charged in the fullness of time if there is no load on the battery and it is left for long enough. ie when the boat is left unattended for a prolonged period of time.
What you need to assess is the draw on the battery and the number of daylight hours you hope to take to get the battery up to full charge. These parameters will differ with the size of the battery (bank).
The answer is the more solar you can provide the better. The limit is the space you have available to deploy the solar and the size of the battery bank.

 

[Neeves]

If it has not been said:

Welcome to the forum.

Words of advice - start any threads you like (that's what the forum is for). Most of us are very free with our comments (though sometimes the comments are not useful. . But full detail and photos (the photos are not necessary in this case) make it easier for us to respond. For example - do you only have on battery?

Your auto pilot can eat amps as if they are going out of fashion and it will eat more amps than necessary if the sails are not trimmed. Over a long enough period, of sailing under AP, you could drain the battery to such a point it will not turn over the engine (especially if its an old battery).

It sounds, from your opening post, that you have one battery - that one battery is a critical item.

If I'm correct (and I'm often wrong) you will enjoy further more useful comment from others.

Jonathan

 

[Refueler]

OK ... lets be basic.

What size Battery ?

Is there only one battery ?

OK .... on to old panel and checking ....

It is unwise to disconnect battery while panel still connected to controller ... according to instruction leaflets with controllers I've seen. The controller needs connection to battery before panel etc.

So to check system ... disconnect panel from controller. With panel disconnected - you could meter the voltage out .... which should be 18v or higher. Then disconnect battery from controller. Make sure battery is switched off from all items on boat. Meter the idle voltage of battery.
Now reconnect battery to controller ... reconnect panel .... Make sure that all items on boat are still off. Meter battery again ... the voltage should be higher as panel should (of course you do this in daytime with sun !) be charging the battery ...

If voltage does not change - then somethings not working ....

If panel is putting out 18v or more - then its most likely connections / cable or controller. Is there a fuse in the system ? Sometimes its just a simple matter of cleaning up connections / replacing fuse ...

 

[fredrussell]

The only thing I have to add is beware of claims made by eBay sellers of panels re their output. For new panels, if it works out at less than, say, 60 pence per watt they’re probably lying about output, or of such low quality you really don’t want it anywhere near a boat. There are plenty of trustworthy sellers but a couple to begin with are Renogy and Photonic Universe. That’s assuming OP is in UK.

 

[Refueler]

The only thing I have to add is beware of claims made by eBay sellers of panels re their output. For new panels, if it works out at less than, say, 60 pence per watt they’re probably lying about output, or of such low quality you really don’t want it anywhere near a boat. There are plenty of trustworthy sellers but a couple to begin with are Renogy and Photonic Universe. That’s assuming OP is in UK.

But if panel works and is cheap - what's problem ? Of course - I don't think anyone daft enough to believe claims of output ... I have so-called 20W panels that I don't believe do more than 10W if lucky - but price is cheap .. came with controller ... batterys are charged..... all of eBay ..

 

[Stemar]

Another vote for as much solar as you can conveniently fit. On my Snapdragon, it was 40W, on our current boat it's 160w. If you do only have one battery, it'd be well worth getting a second dedicated engine starter battery so, if you do run the other one down, you can still start the engine. A simple system with a 1-2-both switch and a voltage sensitive relay will get you going without breaking the bank, I can help with a circuit if you're interested.

With two batteries, you'll want a solar controller to split the charge. On my Snapdragon, I had a cheap as chips PWM controller that was set to charge the starter battery, which never took much, but that way I was sure to start the engine, then turned its attention to the domestic. It wasn't the most efficient, but it did the job. On Jazzcat, with bigger panels, I have an MPPT controller that splits the charge in some clever way, but essentially does the same job.

One final thought: the easiest place for solar panels may be on the hatch garage under the boom. That means they'll be partially shaded much of the time. If that's your case, get a pair of smaller panels, as a bit of shade will reduce the output of the whole panel significantly. Two panels means that, if one is shaded, at least the other is working at full strength.

 

[Refueler]

On Superanne ... my PWM controller splits charge to two batterys independently .... it has Solar in ... Bat 1 out .. Batt 2 out ...

The only function I lost was that it has no USB out ... as with most single battery PWM controllers.

 

[PaulRainbow]

Hi,

Bit of a Newbie to solar panels so please excuse my questions.

I have just purchased a boat and found that the solar panel is not charging the 12vt car battery. Solar panel has no details on it and former owner doesn't seem to know either. The boat has a simrad Chart plotter, depth and speed as well as a auto pilot, not sure how much power they consume.

My question is what size wattage would I require to install to keep the battery fully charged. I have been considering a 100 watt flexible panel complete with 30A controller system and have also seen others of 300 and 600 watt, would a100 watt panel be enough to charge the battery.

Fit the biggest you have room for, no question, you can't have too much power.

I would avoid cheap and nasty Ebay panels, Photonic Universe would be a good choice.

 

[fredrussell]

But if panel works and is cheap - what's problem ?

Because I’m of the old fashioned belief that sellers should give accurate specs on their products. It’s not much use offering advice along the lines of “well, just buy any old panel off eBay, that’s what I did and mine worked”. Better surely to help OP work out the size and output he needs and then suggest reputable suppliers of panels so they actually end up with what they’re after.

 

[Stemar]

Would I be right in thinking that a solar panel will give, more or less X watts per sq metre? If it's rated at around that, it's probably OK. but if they're promising 2X, they're telling porkies

 

[Alan S]

Correct, about 200W unless they are very expensive.

 

[doug748]

Hi,

Bit of a Newbie to solar panels so please excuse my questions.

I have just purchased a boat and found that the solar panel is not charging the 12vt car battery. Solar panel has no details on it and former owner doesn't seem to know either. The boat has a simrad Chart plotter, depth and speed as well as a auto pilot, not sure how much power they consume.

My question is what size wattage would I require to install to keep the battery fully charged. I have been considering a 100 watt flexible panel complete with 30A controller system and have also seen others of 300 and 600 watt, would a100 watt panel be enough to charge the battery.

Doing a bit of guessing here but..
Sounds like you may have a smaller boat with no, or little, engine charging, maybe you day sail. A 100W panel is big, I would not lumber myself with that unless the boat is over 30ft and even then it is huge overkill for many.
Unless there are special circumstances not mentioned, I would get a 20W job and if it does not suit buy a second one. If you don't like the sound of that, 50W would probably be fine.

.

 

[Refueler]

Because I’m of the old fashioned belief that sellers should give accurate specs on their products. It’s not much use offering advice along the lines of “well, just buy any old panel off eBay, that’s what I did and mine worked”. Better surely to help OP work out the size and output he needs and then suggest reputable suppliers of panels so they actually end up with what they’re after.

Hi Fred .,.. if you read my post - it does talk about power out - its not just saying buy cheap and then no info at all ...

I too wish for responsible specs on any product page ... but sadly in todays market - that seems a generally forlorn hope. Of course now the 'troupe' will jump on me and say 'reputable' manufacturers do state accurate specs ... Oh Yeh !!
The number of owners I have asked about their panels .... the general reply is far short of quoted specs ... and that includes expensive - reputable panels. Most have said clearly - that their prime requirement is to do the job ... even if it means the panels are only delivering part of their supposed output.
My small ~10W keeps my mobo bilge pump battery good .... the ~20W on Superanne tops up the two Lead Acids on board ....

As to the ~40 - 50W job on Anisette .... controller shows it working - but there is no display being old. That will be changed to a unit with display info.

I also agree get the best and biggest panel that can be sensibly mounted .... I was just illustrating the other side of the coin.

 

[Neeves]

Simply put it would help, the OP, enormously if the OP came back and commented on his thread - and provided the information missing of his circumstances so that a sensible answer could be provided.

If he uses his yacht once a fortnight - a small panel would suffice. Buying a big panel would simply get in the way - on a small yacht.

Jonathan

 

[Wansworth]

Is there a little book like solar power for dummies

 

[ashtead]

Curious as to how you propose to fit600w of panels? Maybe you are a cat or have a stern gantry though? Are you looking at having frames on the rails which tilt maybe? I ask as output is likely to be dependent on size of panel however I guess with one battery the boat isn’t that large? How old is existing panel? My impression is panels degrade over time - another thought is to buy a small portable suitcase panel for say photogenic and see how it goes and not splash cash on new panel but maybe more detail would help forumites design a suitable instalation

 

[Rainbow21]

Doing a bit of guessing here but..
Sounds like you may have a smaller boat with no, or little, engine charging, maybe you day sail. A 100W panel is big, I would not lumber myself with that unless the boat is over 30ft and even then it is huge overkill for many.
Unless there are special circumstances not mentioned, I would get a 20W job and if it does not suit buy a second one. If you don't like the sound of that, 50W would probably be fine.

.

I have 21ft sailboat with an 6HP outboard, the electric system runs led nav lights, saloon led lights. Raymarine autohelm speed and depth, Raymarine autopilot plus a Simrad chart plotter. I normally day sail most days but looking to go further as my experience grows.

The outboard has a charging system attached but is not connected to the battery yet, still have to learn how to do this. I also have shore power connection. the solar panel is old and the connections seem to be poor as the battery doesn't seem to charge, cabling all seem connected correctly. The controller/ volt display meter showed 9vts of charge so have had the battery checked and have replaced the battery.

Hi,

Bit of a Newbie to solar panels so please excuse my questions.

I have just purchased a boat and found that the solar panel is not charging the 12vt car battery. Solar panel has no details on it and former owner doesn't seem to know either. The boat has a simrad Chart plotter, depth and speed as well as a auto pilot, not sure how much power they consume.

My question is what size wattage would I require to install to keep the battery fully charged. I have been considering a 100 watt flexible panel complete with 30A controller system and have also seen others of 300 and 600 watt, would a100 watt panel be enough to charge the battery.

A big thanks you to all those who have responded to my question. From some of the answers I have seen a 20 to 30 watt with a decent controller would be my best way forward.

Cheers guys, please forgive the newbie question I still have lots to learn