solar panel size?

[Niander]

Hi what size solar panel would be recommended to just keep the leisure batteries topped up with just occasional use of the auto bilge pump needed

ether 1 battery 85 ah
or two 85 ah connected in parallel

would a 10 w or 15 w panel be ok?

 

[orizaba]

i would think its a bit small,due to the "occasional use of the bilge pump" it depends on how big the pump is and how often it runs.I rang solarex when i got mine and found them very helpful,and were able to give me very good advice.
there are 2 types of solar panel ,one more usefull in the uk due to less sun gives slightly less output but for longer
the other higher output in bright sun,
on there advice i have one of each, admittedley the uk type one was used mainly on the nb but it works well out here as well.

 

[Niander]

If the there was no pump would it keep them topped up?

 

[orizaba]

if you are leaving the boat for sometime i would leave the pump there,better to be safe than sorry, i assume you don't think the pump will be working often, but do you have a problem with the batteries going flat and if so over what sort of time scale

 

[VicS]

[ QUOTE ]
If the there was no pump would it keep them topped up?

[/ QUOTE ] A 5 watt panel is more than enough to recharge my battery after a weekend out keep it topped up. It used to be a 45 Ah one but is now bigger but I forget what (60Ah I think). I am in a sunnier location maybe but even the little 1 and 1.8 watt panels will keep a charged battery topped up provided they get enough light and there is no load.

To determine what you need with an auto bilge pump in use , as already indicated, you need to know the power consumption of the pump and the amount of time it operates and then compare the product with the power output from the panel and the average length of time it will be effectively producing power.

Are you in a windy location such that a wind turbine is an attractive option?

 

[aknight]

Do you know how many Amps your automatic bilge pump draws? If you have a smaller pump, rated at 500gph say, then a draw of approximately 2A is a reasonable guesstimate (for example, an Attwood Safari S500 draws 1.5A at open flow, and a Rule 500 draws 2.5A).

Similarly, how long do you think the bilge pump is switched on for each day? If you leave the pump on while you’re on the boat and moored up sometime, you should be able to have a guess. I’d reckon no more than one hour, absolutely worse case, unless there’s a serious problem. So on the guesstimate above, you’re talking about 2 Amp-hours per day.

The solar panel needs to meet at least that need. However, you also want it to keep your your 85A leisure battery topped up, possibly both batteries in parallel.

At first sight a 15W solar panel looks generous, but the reality is somewhat different. The nominal 15W rating has to be divided by the panel’s rated voltage (which can be as much as 16.5V, not 12V) which gives a result in 0.9 Amps produced in every hour. Moreover, many reputable solar panel suppliers recommend that you assume that on a “typical” British summer’s day, whatever that means these days, the panel may generate (from dawn until dusk) only 4 hours equivalent of charge after allowing for the changing angle of the sun and other factors such as shading. They then suggest you discount that figure by 20% to allow for battery resistance and loss in the cabling.

This suggests a daily output of 2.9 Amps from a 15W solar panel – enough to cover the guesstimated draw from the bilge pump, plus a bit less than 1 Amp to spare to put into the battery, which is not a very generous charge.

People (including myself) do quite often say that they often get better results from their panels than the above calculation suggests. That does however depend on the weather, and in any case, as the days shorten with the onset of autumn, the panel’s output will fall.

In your situation I’d be tempted to go bigger. My boat is 22’ loa and it was no difficulty to fit a 34W panel onto the coachroof – beyond that, the size was getting a bit out of hand (the 34W panel is 590mm by 460mm), as was the cost. As a possible compromise, the same suppliers (Barden UK ) also offer a 23W panel, which would give you about 4.5A charge per (summer) day.

 

[William_H]

If you live in the Outer Hebrides (I think high latitudes) then you will not have so much solar power. This would be made worse if the boat is on a swing mooring. If the boat is fixed in one orientation and you can angle the panel to suit midday sun then you will do a lot better.

I think ultimately the size depends on what size you are willing to mount on the boat and your budget. Certainly 10 watts will do some good but bigger might be necessary for long term battery maintenance and occasional bilge pump work.

My tiny 14AH wet NiCad charges and runs occasional lights and battery on a 5watt panel on a swing mooring. I clamp it to the boom cover over the main with bungee cord and remove for sailing. (but then at 32degrees south we get lots of sun). Certainly 10 watts here would be finefor your requirements. good luck olewill

 

[pyrojames]

[ QUOTE ]

Similarly, how long do you think the bilge pump is switched on for each day? If you leave the pump on while you’re on the boat and moored up sometime, you should be able to have a guess. I’d reckon no more than one hour, absolutely worse case, unless there’s a serious problem.

[/ QUOTE ]

Blimey. I had a wooden boat that I figured was OK if it leaked a gallon or two a week, or 10-20 seconds on the pump. An hour a day seem like a very serious leak to me!

 

[Niander]

It will have the pump in...the pump shouldn't have to work very often
and i recon 2 times 85 ah batteries would last a long time anyways
that's quite a lot of stored power...a panel would help...

 

[davierobb]

I use a 12W panel to keep 2 X 110 ah batteries topped up and it seems to cope ok.

 

[aknight]

[ QUOTE ]
Blimey. I had a wooden boat that I figured was OK if it leaked a gallon or two a week, or 10-20 seconds on the pump. An hour a day seem like a very serious leak to me!

[/ QUOTE ]

/forums/images/graemlins/grin.gif It would seem like that to me too! But to be fair, I don't think that's how automatic bilge pumps work. They activate whenever the float is pushed up by water in the bilge, and are not pumping out anything like their peak flow rate when they do so. The result is a lot of short bursts of activity that I suspect add up to more 10-20 seconds a week.

However, I agree that one hour a day is excessive - I was trying to indicate a worst case figure that would help the OP make some calculations about consumption, not to suggest that one hour a day was normal. You could say half an hour (about 1Ah per day) or 15 minutes (about 0.5Ah per day) which would obviously reduce the draw on the battery and hence increase the retained charge.

 

[MarkJohnson12345]

I recently bought a 10 watt panel to see how it did.

My Electronics guru said it would produce the 10 watts if pointed directly at the sun, in bright sunshine light.

Other times when either the sun is at an angle or cloudy it would only produce from 0.2 amps to 0.5 amps.

Tried it in the Scillies, it really only produced up to 0.5 amps max or so in our so called summer.

If you are really serious and want to keep batts charged up after hard use, then you will need a bigger panel.

Don't forget the batteries will only accept 1/2 of the nominal charge anyway, ie if they need 30 amps you will probably have to put in 60 watts anyway.

Unless you have substantial wattage in this latitude, solar panels are a bit of a hope rather than a certainty.

Wind power might be a better bet, or certainly an value added extra.

They are so expensive anyway, and tend to get in the way when sailing briskly in a force 5, unless you can rig then to produce extra sail area....

Now there's an idea..................

Mj

 

[Bajansailor]

"They are so expensive anyway, and tend to get in the way when sailing briskly in a force 5, unless you can rig then to produce extra sail area....

Now there's an idea.................."

This has been tried down under - have a look at http://www.solarsailor.com/
I hate to think what the cost of all the panels on their Solar Wind would be though....

 

[Niander]

Solarsailor !
Lolz no way am i sticking them things on my boat!