Solar panel - trickle and quick charging?

[Tim Good]

I know there is a million posts about solar but I wanted to ask anyway.

I have two batteries which can be switches to either or both. I want a panel I can just leave in the cockpit when its on its swinging mooring to keep the batteries topped but ideally also one I can whip out when at anchor or on a long passage that will actually do some reasonable charging in just the few hours its out.

I've been offered a marine grade 30w panel with regulator. Would this do it or would it be neither here nor there? I.e. too much as a trickle and not enough to charge any reasonable amount on weekend trips while using the batteries?

 

[Richard10002]

I understand that my 100W panel can supply 5A at best, so, in full sunshine, at the right angle, 30W could supply about 1.5A, so a reasonable trickle at best.

It would hardly contribute to your useage while you are on board using the batteries.

 

[William_H]

There is an inevitable nexus between panel size and current supplied. As said you 30w panel will give max 1.5 amps.
No way could you ever call that a fast charge for a battery. Indeed for a really fast charge say 20 amps you would cover a small boat in panels so forget that idea. Yes the 30 w panel will keep the batteries topped up. If you are on a swing mooring then it will only be looking at the sun a portion of the time or if it is horizontal then efficiency will be limited. (not being angled to the sun).
So you might anticipate average 4 or 5 amp hours per day in summer.
You will need to leave the batteries on both to get both charged. Or get a regulator with outputs for 2 batteries or do without a regulator a fit 2 diodes in +ve line so both batteries are charged but still isolated.
I would go for no regulator. Remember a regulator can only reduce the charge current (unless it is a MPPT type) and you are not starting with much power. good luck olewill

 

[cmedsailor]

I have my 45W solar panel connected through a regulator to the services batteries (200amp in total). When at anchor, I consume around 35amp in 24 hours and the solar gives back, in total, around 15amp (2.1amp/hr maximum in the middle of the day). It's enough for my needs and no need to start the engine the first 3 days. However, I live in the Med.
So, it depends how sunny is where you live and how many amp you consume. For trickle (to engine or services battery? not sure if you can connect to both) is more than enough.

 

[prv]

For what it's worth, when we put Kindred Spirit up on bricks to sell her, I bought a 5w panel off eBay to keep the batteries topped up. That was before Christmas. I've just been to check on her again last night, and the Smartgauge meter was reading 93% capacity (which is higher than when we put her ashore) with a voltage of 12.85. I was pleasantly surprised, as it's not exactly been prime sun-harvesting conditions, and I really only expected it to slow the rate of self-discharge.

Pete

 

[winsbury]

Fairly dissapointed with our solar set up so far - brand new 40W panel semi flexible via ebay ( not one of the expensive NASA versions but not particularly cheap either ) mounted on the sliding hatch , generates about 24v in sunshine but only 150mA short circuit, I don't know if that's normal but certainly isn't anywhere near 40W - more like 400mW.

 

[William_H]

Fairly dissapointed with our solar set up so far - brand new 40W panel semi flexible via ebay ( not one of the expensive NASA versions but not particularly cheap either ) mounted on the sliding hatch , generates about 24v in sunshine but only 150mA short circuit, I don't know if that's normal but certainly isn't anywhere near 40W - more like 400mW.

You need to remove the solar panel and aim it directly at the sun both azimuth and elevation around mid day. It should give you 2 amps short circuit or nearly that directly into a battery. If it is getting full sun with no shadows and not getting 4 amps you have got a fault . good luck olewill

 

[fireball]

We have a 30w panel on the coach roof permanently fixed. With the older knackered house batteries it kept them from discharging at best ... With the newer 2 x 140Ah + 1 x 80Ah engine battery and the twin output regulator the batteries are always at top charge when we get onboard.

I have no illusions that the solar panel is providing enough to keep us going whilst we're onboard as we run a fridge, two chartplotters etc etc ... but it's there and providing a charge when it can with no human intervention.

 

[MASH]

A 5W panel should be fine for keeping a battery topped up. imo 30W would be far too much.

But why do your batteries need topping up? Surely its more important to find where they're losing their charge because it shouldn't be going anywhere.

Batteries in reasonable condition should keep their charge for many months - 6 at least. If they don't there's something draining them. Leaving one of the leads detatched is a sure way of achieving isolation and takes seconds to refit on arrival, surely far less trouble than messing about with solar panels.

I've just gone back to my tractor that's not run since September and it fired up like it was last run yesterday. That's what you'd expect from a good battery.

 

[Tim Good]

But why do your batteries need topping up? Surely its more important to find where they're losing their charge because it shouldn't be going anywhere.

Its not that the batteries are loosing charge but because I'm on a mooring without power then If i use the boat for a weekend I end up putting her to bed with half full batteries. After 2-3 trips they're dead and the engine doesn't get used enough to charge them. I tend to sail 90% of the time. So I think from this thread I need a 5-10w instead and save some space. The comment about being on a swinger is a good one though. I used to be on a trot with huge amounts of sun but as you say, being on a swinger might be an issue.

Do you think a 5w facing directly up at the bottom of the cockpit will be enough if it can't orientate itself? I leave the boat for 2 weeks on average between each trip.

Tim

 

[noelex]

Do you think a 5w facing directly up at the bottom of the cockpit will be enough if it can't orientate itself? I leave the boat for 2 weeks on average between each trip.

Tim

5w will only keep up with the self discharge.

To work out what sized solar panel you need you need to work out how much power you are using. Pick the worst month you still go sailing a select a solar panel size that will put out this much power/14 + a bit for self discharge and battery inefficiency.
It is very hard to guess without any indication of how much power you are using.

The other technique is to get the biggest panel you can fit. Solar is cheap and overkill won't do any harm.

 

[VicS]

Fairly dissapointed with our solar set up so far - brand new 40W panel semi flexible via ebay ( not one of the expensive NASA versions but not particularly cheap either ) mounted on the sliding hatch , generates about 24v in sunshine but only 150mA short circuit, I don't know if that's normal but certainly isn't anywhere near 40W - more like 400mW.

You need to remove the solar panel and aim it directly at the sun both azimuth and elevation around mid day. It should give you 2 amps short circuit or nearly that directly into a battery. If it is getting full sun with no shadows and not getting 4 amps you have got a fault . good luck olewill

I agree with William. In fact angled directly at full summer sun you should be able to get a bit more than 2 amps.

40 watts is the maximum power but will correspond to a terminal voltage of something in the region of 16 or 17 volts. ( and therefore 2.3 to 2.5 amps) The technical specs should tell you this voltage together with the current at maximum power and the short circuit current.. which will be slightly higher.

If you cannot get close to the spec figures send it back.

 

[Rigger Mortice]

Do you think a 5w facing directly up at the bottom of the cockpit will be enough if it can't orientate itself? I leave the boat for 2 weeks on average between each trip.

Not for two batteries that are fairly heavily used over the weekend. A panel left at the bottom of the cockpit will be in shade during much of the day and, if it is also in the shadow of the boom, then it isn't going to produce much power.
For what you are describing the 30w panel, or an even bigger one, with a regulator would be a better choice.

It's difficult to be more precise without knowing the size of your batteries, the true consumption which you have over a weekend and how much charge you get from your engine.

 

[BAtoo]

I've got a 20W panel with an on-off regulator that keeps my 140AH full between the too infrequent visits.
Its mounted horizontally in front of the sprayhood & thus under the boom. Works for me but I would never expect any "fast charge" from a panel/s - the boats just not big enough!
In winter I take the sprayhood off and drop the boom end down to the deck and this improves exposure for the reduced sunlight.

 

[AllanG]

... With the newer 2 x 140Ah + 1 x 80Ah engine battery and the twin output regulator the batteries are always at top charge when we get onboard.

Hi Fireball,

What make and model of twin output regulator are you using?

Many thanks, Allan