Solar panels

guydickinson

guydickinson

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Recurrent question. Assuming they are big enough , are solar panels worth the expense on a sailing boat for the leisure battery or should one just run the engine enough to keep both the engine and leisure batteries charged - do people think?!
 
I just fitted a 10 Watt panel. During a dull November afternoon it was managing to put 0.02A into the battery. When the sun came out it managed 0.25A, though when angled directly at the sun it managed 0.4A.
There is an LED in the charge regulator which I guess at this time of year with the long nights is using more power than what the panel is putting into the batteries. During summer I guess it will trickle charge the batts.
So in answer to your question, you will need to spend a lot of money on some big panels and get plenty of sun. I guess that a 40Watt panel during a summers day would help run some low power eqpt during a day sail and help prevent drain on your battery.
 
I would suggest because of the cost of solar panels, the difficulty of mounting and susceptability to damage that if you have an engine driven generator then you shouldn't bother with solar.

However if you don,t run the engine for a reasonable period fairly frequently like once per fortnight so (or you don't have access to a shore power charger) and you want the batteries to last well then a solar panel will keep the charge up.

Of course as with me if you don't have a motor and live on a swing mooring solar is great. olewill
 
I have recently bought a 20 watt panel and regulator.

Pleasantly surprised to find the battery fully charged (13.4 volts) after a week away.

I would guess that this size of panel will keep batteries up during weeks away, but doubt they have significant charging abilities if cruising.
 
I have 2 panels and never regretted fitting them. Forget the rating offhand but in bright sun I get about 5.5 - 6 amps. Even in winter when overcast I get about 2. That's a minimum of say 6 hrs x 2 amps x 7 days= 84 amp hours/week. I have a 3 battery set up with one battery dedicated to fridge. The panels not only balance out the fridge drain when cruising (which surprised me) but because they are permanently on, keep all batteries fully charged when not on boat. I expected that when cruising I would need a wind genny as well, but never fitted one as the intermittent use of engine +solar keeps everything charged. I am not economical with lights, heater, or anything really, but never have a discharged battery even when living aboard for weeks at a time. I do have "smart" charger on engine though. Absolute canine nut parts!
 
To answer the question properly, we really need to know your boat use, and what's the problem you're trying to solve.

Let's assume you're a weekend sailor with occasional fortnight cruises, that you've got a fridge on board which you only use when overnighting aboard, and you don't have access to shore power where you keep the boat, and you've got one domestic battery of about 100AH and a separate starter battery.

First question, do you monitor your battery charge state? With a voltmeter? and with an AH meter? If so, you know the extent of your problem.

Your task would then be ensuring that there was enough engine running time to replace the leisure battery drain while cruising, plus the slight daily loss from the battery while it's on its mooring.

Extra engine running time is a solution, but it's expensive, perhaps increasing your engine hours by 20% to 50% depending on your cruising habits. And engine fast idle time increases cylinder 'glazing', leading long term to loss of efficiency. This may not matter to you . . . if you only do about 100hr a year!

An alternative is to ensure your charging efficiency is high. Does your alternator regulator supply more than 14.0v to the battery terminal when the battery is well chargd? If so, smile. You're doing well. If 13.8v or below, a good course of action costing arond £200 is to fit a smart regulator which senses voltage at the battery, and demands whatever voltage is needed from the regulator to put 14.4v at the battery when it's low. Google 'adverc' for more info. This will reduce or remove the need to run your engine, and add to your battery life by reducing the amount of deep discharge.

A small solar panel (10 - 15w) will deal nicely in UK with the battery trickle discharge while at a mooring, but at 5ah a day will do nothing to re-charge stuff used by the fridge. Even 30ah in UK is only going to give you an average of about 7 to 10ah a day. OK, that helps - costs about £400. But you may then need a regulator to limit output whe you're on a mooring . Google 'barden uk' to learn more.

Bigger battery banks, no fridge, moorings with electricity, all these things change the story. Tell us more.

The benefits of good battery management are long battery life (10yr is possible, against 3yr for regular deep discharge) less main engine running time. Vital if you spend lots of time aboard. Not important if the boat is only occasionally used.
 
The short answer is that it depends what you expect the panel to provide.

Firstly, a panel of less than about 20 watts will do almost nothing for you during sailing but will recharge your batteries nicely between weekends.

A 40 watt panel is a useful addition but it won't run a refrigerator. If you locate it on deck it will suffer from shade for some of the time and it will not be 90 degrees to the sun, so don't expect its full rated power. I have one of these connected all year round, with a regulator, keeping batteries fully charged all winter.

At 80 watts in the Mediterranean we can anchor without running the engine for three nights at the height of summer, two nights in September. Battery voltage drops to about 12.0 V overnight and mostly recovers during the day. In Uk panels that size will not run the fridge very successfully.

We are now in the process of putting new panels, 100 or 120 watts, on a stern goalpost, when we hope to become completely self-sufficient.

The cost of this is going to be close to £1000. Talking to an owner of a boat berthed next to us this year, he said he had a high output alternator that he ran for 15 minutes per day. From a cost point of view this is very attractive. It just depends on your preference but for UK this seems to me to be the preferred option, maybe with a small panel for mid-week charging.
 
Not my experience of a 10w panel charging 2 100AHr Batts. Over winter, with no other charging, it keeps batteries full and I can recharge a phone or PDA directly off it - a lot more current than an LED would use.
 
In May 2007 I left a 10 W panel in my camper van to keep the domestic battery in good condition over the summer . It's a single 100 Ah battery, fully charged when I left it. When I returned in October the battery was completely flat. The only service left on was the main switch, which lights a couple of LEDs.
 
[ QUOTE ]
When I returned in October the battery was completely flat

[/ QUOTE ] You do not say what type of battery it was but a decent low maintenance battery still in good condition should retain a good proportion of its charge for 6 months if there is no drain.

My experience on the boat has been that a 5 watt panel is more than enough to keep a small (45 Ah ) leisure battery fully charged for the entire summer.
 
A 10w solar panel will ensure you arrive on your boat after a week or two away with the battery still topped up. Don't expect it to replace heavy useage, you still have the engine to do that. The benefit is that you shouldn't have your weekend ruined by arriving to a flat battery. I have had one for about 12 years now and it has been an excellent investment.

yoda
 
A 10Watt panel is only going to produce 0.8 Amps when woking at its max ie pointing straight at an unobstructed sun, then there is a drop due to wire length resistance, reverse flow diodes are going to block at least another 0.6v. Then there is the angle of the sun at this time of year, and only 9 or 10 hours of daylight, cloud cover etc. So even at 0.2 amps for a few hours a day its not going to do much for 70 A/H battery especially with an LED drawing a small amount of current from it 24hrs a day. Hopefully through the summer months though it should keep the battery topped up.
 
Re: Supplementary question

Have just bought a 60 watt Solar Panel from Sunshinesolar .co.uk for £275 on a recent special to add to the two 50 watt Siemans which have been sufficient crossing the Atlantic,Autopilot lights etc no engine or generator required. Now with extra electronics we will need more amp hs.
 
Thanks v much, Jim. Well the basic set up is - a 34 ft Van de Stadt Legend (1973) with a 1973 Sabb diesel (2H). Sail most weekends in the summer and occasional other day and evening. Trips if time off - week here or there but hope more when retire in a couple of years. On a swinging mooring (Weymouth) and in yard in winter . No fridge (at present anyway). 2 batteries both 110. One for engine, one "leisure" - ie lights, instruments, occasional self steer, radio, v occasional tiny TV etc etc. Considered a cabin top Barden panel (?23 or 34 watt).
 
Vyv you need to get a multimeter set on amps (milliamps to check actual current consumption with the power switch on. Things like radio memory back up remote lock sensor burgular alarm are some things that do draw current. Significant when you are talking 24/7 for months.
A ten watt panel should give about .6 amps for several hours per day.
That equates to a break even continual load of less than 100milliamps (.1 amp) or less, not allowing for natural battery discharge. But then of course the battery may have been Cream Crackered bfore during or after the long period of inattention.

To GuyDickinson I would suggest you can do very well without solar. It would be a nice to have luxury or toy so if you need a new sail that would be a much better priority. olewill
 
For that sort of use a small solar panel (20w) should be fine. Search for panels for caravans/camper vans - for some reason these seem to be cheaper than buying through chandleries!

You'll need to consider whether you need to keep both batteries up. Probably won't matter in season (as long as one is there to start the engine!) but for winter you'll either need to swap the panel from one battery to the other once a month, or arrange a double diode system to spread the charge. Paralleling the batteries would work, but if one should get a bad cell, that would bring both down, so it's not advisable.

Long term, once you're at sea for longer periods aboard, think of an ammete/ah meter to monitor what's going on, and if you've got low voltage charging (13.8v max), add an adverc or similar to get the best out of your alternator.
 
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