SOLAR PANELS ON SMALL BOATS

alisdair4

alisdair4

Well-Known Member
Joined
18 Jan 2004
Messages
690
Location
Isle of Bute
midnightdrifter.net
I'm about to exchange the pampered life in Medemblik for a swinging mooring in the Clyde. One of the few down-sides to this will be the loss of a trickle-charger operating on the mains when the boat is alongside.

Freya has an outboard with no charging system (at the moment). She has one house battery (60AH).She is too small (or I am too mean!) for a wind generator to make much sense.

Exam question, will a 60 Wh/d solar panel produce enough oomph to keep the battery charged up?

I would expect to use the boat for 3 days every 2-3 weeks.

Alisdair
 
I have a Solarex 30W semi flexible panel, which keeps my engine start battery(100Ah) topped up(during the summer -havent tried winter yet) while I'm away, sometimes 3-4 weeks, more usually 2 weeks and the battery shows 13+volts whenever I check it. So no problem.

The Solarex does not have an inline reverse current blocking diode, which was my choice, but others do to prevent night time reverse discharge from the battery but I have a small charge regulator (£70) in its place which does the same job plus it switches the panel surplus charge when the start battery is full, to the secondary services battery.

I am very pleased with this simple system but if you do not need a charge regulator, and opinions differ on this but I think with a 60W panel you should have one, then you can get panels with an inline blocking diode although these are of larger diameter than the supply cable and thus need a bigger hole to pass through the deck/coachroof unless you snip it off and reconnect it afterwards(if that is possible)
 
Unless you are leaving a fridge running, or similar, that will be more than enough. If your batteries are flooded - i.e. you can add water - you should be fine but if they are sealed you'd be best off with a charge controller to prevent overcharge/gassing.
 
I have a 6w solar panel - 28 quid from Ebay - it does the business when on my mooring. When I'm well charged up, I keep a light ply cover over it to prevent any over-charging and to protect it from any accidental damage.
 
If you've only got a 60Ah battery, 60W is more than enough to keep that charged up... obviously depending on the actual use it gets.

I have 2 panels totalling 25W, and these keep my 75Ah battery fully charged. I would recommend fitting a charge regulator, mine was <£20 from Compass and does the job fine - reduces input voltage from 18-20volts down to ~13.5v and charges fine. This also has an LED built-in to indicate the state of the batteries. I don't have any reverse blocking diodes on mine, and don't find any problems.... some books recommend not having them as the reduction in charging capacity does not equal the savings from reverse flow, if you get my drift.

The best I can get is 2A charging, but I would imagine yours would produce 4-5A, so a charge regulator would be recommended - Compass do 2 types, a 12v up to 4A one, and a 12/24v. Have a look here for more details on these.

When installing the panels though, try and make sure they are as perpendicular to the sun as possible and spend as much time as possible facing directly at the sun. Not easy on a swinger I know, but just something to bare in mind with fitting.

Have you actually bought these panels yet, or just asking? If not, personally I wouldn't buy such large ones, but IMHO of course.

Moving on to a swinging mooring and using solar panels for your use will not cause any problems.

EDIT: after reading VicS take on your post, what size panel are you actually talking about. I thought 60W panel, but Vic's take on it does make sense. Can you confirm for us?
 
I have a permanently mounted 5 watt solar panel which keeps a 48 Ah leisure battery topped up between weekend outings and the occasional whole week. Within reason the size of the battery is immaterial.

I do also have some charging from the outboard engine but unless it is run at a good speed for long periods its contribution is negligible. On a good weekend it only runs for a few minutes and at low speed.

With no engine starting requirements my electrical needs are small namely a couple of cabin lights, nav lights occasionally, a makeshift anchor light if the "hurricane" light blows out, an echo sounder (negligible), VHF (seldom used to transmit) and an Autohelm (aways in use).

With a small panel no regulator is required but you will find a rule of thumb for the max size that can be used without one vs battery capacity on the websites of solar panel suppliers.


I am not sure how that equates to your quoted 60 Wh/day but I suppose if mine is supplying 5 watts for 12 hours every day that's 60 Wh /day. If you feel that may not be enough, and only you can calculate your requirements, then go for a larger one, say 10watts, if you have the space for it or two 5 watt ones.

IMHO a wind generator is not an attractive option on a small boat on grounds of cost, space, and maybe noise if running at night. I would consider one of the small vertical axis ones (Forgen) but they are stupidly expensive for their small output. I'll stick with the solar panel. I reckon that along with the Autohelm the solar panel is one of the most useful extras I have bought and would replace it with the same again if it failed.
 
Hi Vic, how you doing?

[ QUOTE ]
I am not sure how that equates to your quoted 60 Wh/day but I suppose if mine is supplying 5 watts for 12 hours every day that's 60 Wh /day.

[/ QUOTE ]

Ooopps... hadn't read it that way, thought a 60W panel. Your explanation does make more sense though, and would tend to agree with you.
 
[ QUOTE ]
60W is more than enough

[/ QUOTE ] He said 60Wh/day. That's not the same as 60W. As I have said in my post 60Wh/day is equal to only 5W for 12 hours every day.
 
I have a similar arrangement to yourself.

Outboard pull start with some charging.
Occasional Nav Lights.
Echo Sounder.
VHF Radio
Hand held GPS picking up power off boat battery.
Battery 85AH wet leisure.

10 W Solar panel.

Boat on swinging mooring on Windermere.
Use every other weekend and for a couple of weeks in the summer.

Our ten watt panel fused between panel and battery with an external blocking diode keeps our battery topped up OK. It may struggle in winter. IMHO 5 watt may not be enough as the panel is likely to have shadows on it or be turned away from the sun for a lot of the time on a swinging mooring.
 
[ QUOTE ]
IMHO 5 watt may not be enough

[/ QUOTE ] It depends on how much power is used. It is essential that anyone cotemplating any form of solar or wind charging should calculate their requirements. It has been my experience that 5 watts is enough for my needs. As I could not easily fit a larger panel that is convenient.

The 5watt panel is a bit more than a foot square and on my boat is fitted to the sloping cabin front which is amply large enough for a panel that size but would not accomodate a 10 watt panel. It is not at bad angle either, a bit steep for the mid day summer sun perhaps but pretty good at the ends of the season or early morning and late afternoon during the summer.
 
Does having two smaller panels work out better than one? I guess you can angle them differently to get the sun in different places, whats the best way to mount them, Fixed, or moveable? Are 2 panels at 25w cheaper than one 50w, which is more electrically efficient? Are they wired in parallel or series?
 
Yes JMKENT, it was a 60 Wh/day panel which I was quoting - and I haven't yet bought it. It sounds as if it may be enough. The good news is that there shouldn't be too much shade where I plan to moor the boat, so I'll get the maximum sunshine available. I thought of buying panels which you can walk on such as the Solara panels here:http://www.energyenv.co.uk/SolaraCompleteSolutions.asp.

However, they look pretty expensive compared to the Compass ones.
 
[ QUOTE ]
Yes JMKENT, it was a 60 Wh/day panel which I was quoting

[/ QUOTE ] So thats 15 watts peak output then (Or 18watts according to Compass) I must admit I thought you would get more than 60Wh/day from a 15watt panel but I suppose thats an average figure over the whole year so it will be much greater during the summer but lower during the winter.

£315 for the kit sounds expensive to me compared with an internet price of £189 for exactly the same panel ,+ £18 for the regulator, from Compass. The cable and glue cannt possibly be worth the difference. You realise that panel is 630 mm x 250 mm, OK if you have a suitable area of deck that big but I'm afraid I am not familiar with the Foxterrier.

In my experience it will be far larger than you will need unless you have a whole stack of electrical gear to run. It'll give you 5Ah per day at 12volts so in 14 days it will produce 70 Ah. In theory more than enough to completely recharge your battery. Do you normally run your battery right flat in a weekend? That would be bad for the battery anyway and if you come anywhere close to that you should be fitting additional battery capacity as well as the solar panel. Maybe you are in need of a wind generator rather than a solar panel.

You should work out your electricity consumption to determine what size of panel or wind generator you require and then shop around for best prices.
 
[ QUOTE ]
Does having two smaller panels work out better than one? I guess you can angle them differently to get the sun in different places, whats the best way to mount them, Fixed, or moveable? Are 2 panels at 25w cheaper than one 50w, which is more electrically efficient? Are they wired in parallel or series?

[/ QUOTE ]
Well, don't have all the answers, but will have a stab at it....

Two smaller better than one - don't know. I've only ever had the two I've got now, and have to admit that is because they came with the boat. I would have probably gone down the solar panel route, but how many and what size I would choose I don't know.

I have mine completely moveable. I have them wired into a deck plug and then ~8ft of cable after that. Each panel has a small hole in each corner, with which I put a small shackle through and attach them to the guard rail. I rest the bottom of the panel on the cabin top and forms about a 30-40 degree angle. Its probably not the best setup, but is cheap and I can put them wherever may be the best for the location. I do remove them when out on the boat though.

Two panels cheaper than one - again don't know. IMO, I wouldn't expect so though.

Efficiency of one compared to two - again don't know.

Series or parallel - mine are in parallel.

Thats not all the answers, but hopefully someone will be able to fill in the gaps.
 
Alisdair,

I have similar setup / usage to VicS and DavidPBO on a swinging mooring. I have found a "10W" panel is fine for us (65AH sealed leisure battery). I got it from a stall at the boatjumble - a trader who sells these, not a one-off. I keep it in a locker when sailing, and just leave it in the cockpit between times. I'm sure it's not the most efficient panel in the world (thin film, I think) about a foot square, and cost £20. It's got a blocking diode, but no regulator.

You may gain something by using two panels on a swinging mooring if you put them on opposite sides of your boat - maybe one will always have a direct view of the sun. Otherwise no difference. Connect ~12v panels in parallel.

Works well for us - no need to bring the battery home to recharge for 2 years. Tried to put the charger on the battery when the boat was out last winter, but the charger told me the battery was fully charged.


Andy
 
Like Jonathan Kent I don't know the answers to all those questions.

If you have two small panels then you may be able to position them so that when one is not working the other is but on the other hand with one panel double their size you would get double the potential output when it is working. Swings and roundabout situation.

Mine is fixed (bolted down to the deck) that way it cannot be stolen. I would have thought that moveable means removeable.

Generally two small panels are more expensive than one twice the size but that is not always the case. You can study the price lists as well as I can!

I'm not sure that efficiency is quite the right term. If two panels are equally illuminated then they will have the same ouput as one panel double their size similarly illuminated.

Two panels should be connected in parallel not series (although two 12volt panels could be connected in series to provide 24 volts) Just like batteries.

Not mentioned on this thread so far: You must not neglect to incorporate a fuse in the wiring, as close as possible to the battery. It should obviously be rated to pass the maximum output current but should be lower than the current rating of the wiring in order to protect that in the event of a short circuit.
 
The suggestions that you need to work out your current consumption are not quite appropriate for you. I think you have said that the battery when fully charged suits your overnighting needs. So the solar panle size will dictate how quickly it can recover the battery charge after one of your wild weekends.
If we assume you have half discharged your 60AH battery tyhen you need something over 30AH replaced. A 10 watt panel will give you about 1 amp for about 8 hours per day. ie roughly 4 days to recover from your weekend.
Now that is hardly even ballpark figure as it depends on what direction the boat hence the panel faces and what the weather is like. So you shouolld have no probs getting recharge in 3 weeks. You could eveen manage with a 5 watt panel but I would suggest 10W.
My little boat has something less than 5 watt panel which has not dissapointed my in my usage style. But that is Oz summer only and very little current usage.
I would from experience sugggest you mount the panel in a tempory manner ie remove for sailing. I went through 4 panels over about 18 years having them fixed on the front hatch lid and finding them damaged in various ways. Now Ilash it on to the boom sail cover with 2 bungee cords and plug the wiring in just inside the entrance. I think it best to angle it straight up due to the swinging of the boat you can't point it toward the sun (south for you)
A 10 watt panel should not present overcharge problems with 60AH battery without a regulator.............. Olewill
 
Vic,

I take your point about the cost disparity. I actually have the deck space, as the Fox Terrier has a large(for a 22 foot boat!) flat deck (locker top) -at the aft end of the cockpit. In terms of power input from a solar panel I had assumed that more surface area was better, as I wouldn't expect to gain the rated output all of the time, due to the prevailing weather conditions. However, I will take the (very useful) advice given here and do an electric audit before parting with too much of my hard-earned dosh!
 
If you have the space to fit the larger panel, and the dosh to buy it, then fit it. Perhaps the aft end of the cockpit will be more likely to have shadows over it than a point forward of the mast and a horizontally mounted panel will never develop its maximum output, that would be achieved with one inclined towards the sun, but at least it will never be facing totally the wrong way which mine does, at times, of course. My concern is than it is going to get trampled on where you propose fitting it so make sure you buy one which will withstand that sort of treatment. Also make sure the wiring will not be damaged by flexing when the locker is opened!

I'm not sure if a 15w panel will need a regulator when connected to a 60Ah battery or not. I can't find the guidance on that which I refered to earlier. I think I would feel inclined to fit it even if not absolutely necessary.

Your assumption about power and area is correct. The output will be direcctly proportional to the total surface area of the cells in the panel.

I can't agree with William Hines that calculating the energy consumption is not appropriate. IMHO that is the very basic information you need although you know it is not more than 60Ah in a normal sailing session and of course the actual output will you get from your panel depends on so many variables that are difficult, if not impossible, to estimate in advance. Also you will have to size your panel larger than theoretical because it is never going to produce its peak output lying flat.

I don't know what theft from boats is like in your area but there are places in the south where I reckon you could lose more than the 4 panels in 18 years that Will has had damaged. Maybe my mind has been forever poisoned as a result of having everything of value from the torch to the outboard engine stolen in the first 6 months that I had the boat.
 
I have 2 X 20W panels (£79.99 from Maplins) connected directly to my batteries - that's one to each - for winter maintenance. They sit on the cockpit seats so will get direct sun for just a few hours in the winter, and get plenty of leaves and crap on them during the course of the winter.

Come the spring the batteries are 13.5V or more.

I also use them in exactly the same way in the summer, with no ill effects due to overcharging. When on the boat and using a cool box at the height of summer I have them paralleled up to just the domestic battery which helps, but doesn't quite keep pace with demand.
 
You must log in or register to reply here.

Share this page

Top