Solar Panels

Jun 20, 2005
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Time I fitted one to trickle charge the battery when in storage. Not worried about going off grid.
Any recommendations for wattage , type , ease of fixing installing. Are they wired direct to the battery? What stops the battery discharging into the panel at night for example?
Thanks DD
 

Parksy

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The easiest solar panel installation will be a free standing suitcase type with a built in regulator.
A good quality regulator will prevent overnight discharge, overloads and short circuits.
The biggest drawback with free standing solar arrays which connect directly to the leisure battery is the possibility of theft of the panel.
I'm not sure about the minimum wattage that you'll need, I have a roof mounted 80 watt panel which is for off grid use.
The only drawback to a roof mounted panelis the necessity of keeping the panelclean and dust free for it to work efficiently.
We could have an installation afternoon at the April Woosiefest if need be.
There will be a few of us there to keep your interior lights burning brightly because Confucius once said " Many hands make light work" 😁
 
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Parksy

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My advice would be to choose a monocrystaline solar panel kit from e-bay.
You get the panel, the mounts, cables and cable entry gland and the controller as a package. In addition you'd need a tube of Sikaflex, an inline automotive fuse and holder and the appropriate lendth of the correct gauge automotive cable according to the wattage that you decide on.
I wouldn't choose less that a 50 watt if you're using a roof mounted solar panel otherwise the roof mount won'tbe worthwhile, obviously the higher the wattage the higher the charging current that will be produced.
 

JTQ

May 7, 2005
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I would endorse the recommendation not to go sub 50 Watts, based on three points.
  • One the winter yield of a roof mounted unit can be very low, because of the sun angle, shadows, grime and dead leaves, etc, shorter hours of light and lower incidence of good days.
  • Second, panel prices now are relatively cheap making penny pinching pointless where the installation costs are about the same whatever panel you fit.
  • Third, solar panel controllers drain power to function, so too small a panel struggling in poor lighting might not make enough to feed the controllers demands and still meet the systems required duties.
The wiring size in this application is not really determined by the Wattage, that is almost certain to be adequate with any automotive cable, what is important generally in solar applications is to minimise the voltage drops. So choose something a bit heavier than needed.

As already said the controllers are parasitic taking some power from the battery all the time.
Unfortunately, I have found they are not all the same, I helped someone whose commercial panel was yielding near nothing overall, good in the daytime but not over a few days. I measured its various characteristics finding it took 24 x 7 hours, a massive drain current, about 20 times a better quality one I refitted for them.
 
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Hi DD,

Are you planning on installing the panel yourself, it's pretty simple to do.

As has been suggested I would go for minimum of 80w, more would be better and there is little difference in the panel cost.

You will get inefficiencies in voltage drop from incorrect wiring gauges being used.
Some panels come fitted with less than adequate wire gauges.

There is a diode on the panel to prevent battery discharge to the panel.

Controllers can be had at very low cost, in your case a PWM controller will suffice.

Use 10awg wire from the panels to the controller and 6mm wire from controller to battery, fit controller as close to battery as practicable, fit inline fuse between controller near to battery (10amp will do as a 100w panel will not output more than 5.5amps).

PM or call me if you wish Alan.
 
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Hi DD,

Are you planning on installing the panel yourself, it's pretty simple to do.

As has been suggested I would go for minimum of 80w, more would be better and there is little difference in the panel cost.

You will get inefficiencies in voltage drop from incorrect wiring gauges being used.
Some panels come fitted with less than adequate wire gauges.

There is a diode on the panel to prevent battery discharge to the panel.

Controllers can be had at very low cost, in your case a PWM controller will suffice.

Use 10awg wire from the panels to the controller and 6mm wire from controller to battery, fit controller as close to battery as practicable, fit inline fuse between controller near to battery (10amp will do as a 100w panel will not output more than 5.5amps).

PM or call me if you wish Alan.


What he said...
 
Mar 14, 2005
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Most of teh replies so far seem to have ignored DD's point about trickle charging the battery whilst in storage. I would dreadfully concerned if a battery lost 50Wh each day whilst in storage!

There are 12W panels that should be more than adequate even during winter to offset any self discharge of a battery. Such small panels rarely have charge controllers, but I couldn't say how much they may sap from a battery at night. Best to seek the manufacturers specifications and advice.
 
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JTQ

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There is a diode on the panel to prevent battery discharge to the panel.

Don't overlook it is not as simple as that, as I mentioned there will be the controllers "self consumption" current drain, even through the night time hours. Taking a decent controller the Morningstar SS range , this is 8mA, so over a winter's night, equating to a tenth of an Ah, but I have measured far higher on cheap, auction site, units.

Most of teh replies so far seem to have ignored DD's point about trickle charging the battery whilst in storage. I would dreadfully concerned if a battery lost 50Wh each day whilst in storage!

You would not be alone in that, but then there is zero chance in winter of a 50 Watt system yielding 50Wh in winter on a dull day. The sun angle drops to 15 degrees and shadows become a big issue as the sun tracks round. If one obtained a tenth of the rating over the light hours it would be doing exceptionally well. That as the day last 24 hours means it would be receiving a twentieth of its rating.
Then the controllers cope easily with countering overcharging, it is a primary feature of their design. The Morningstars I use have a regulated float charge of 13.7 V, with tripping to 0 amps taken from the panel, ideal setup for trickle charge duties.



There are 12W panels that should be more than adequate even during winter to offset any self discharge of a battery. Such small panels rarely have charge controllers, but I couldn't say how much they may sap from a battery at night. Best to seek the manufacturers specifications and advice.

The point has already been made panels are just part of the expense of an installation. The cost savings of minimising the panel size to something with very likely with grime, shadows, rain, and dead leaves, would yield so little power, to be pointless.
Even a 12 Watt panel come summer could way over charge a battery, during a series of bright days, if no controller is fitted. IMO it would be a very unwise option to go controller free.
If it is worth doing then it is better to do something that will not let you down; you only need to flatten a battery and leave it flat once, to write it off.
 
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Mar 14, 2005
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Hello JTQ

I can't help feeling that most of the suggestions are using sledge hammer to crack a walnut. DD is only asking to trickle charge his battery whilst in storage.

I'm assuming DD is anticipating no appliances drawing any power whilst in storage, so all that he is looking for is enough charge capability to offset the batteries normal internal leakage.

How much that is does largely depend on the batteries age and condition. so its not possible to be too specific, but for a battery in serviceable condition it should only be a few mA at most.

I accept that even a 12W panel could over charge a battery given enough light and time, so for a permanent connection a charge controller might be a good idea. If that is the case then provided the panel can still provide enough charge to recover the power used by the controller and still bring the batter back up to its optimum storage condition then that's all that's needed.

I haven't done the sums on this one, for the available light, but I strongly suspect a 50W panel is over kill, and will cost considerably more than the optimum solution.

He doesn't need a sledge hammer to crack this nut.
 
Jan 31, 2018
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As Prof says we had a very small solar panel, not sure how big but less than 10w. Connected directly to the battery and left in the heki roof light, held in by the blinds as it was light and small-had a built in diode to prevent discharge and we never had a flat battery, even in the middle of winter and with high motor mover use! no charge controller needed.
 
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JTQ

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I haven't done the sums on this one, for the available light, but I strongly suspect a 50W panel is over kill, and will cost considerably more than the optimum solution.

He doesn't need a sledge hammer to crack this nut.

With respect Prof John, neither you nor I have any chance of doing any meaningful calcs.

We critically don't know about the grime, shadows, bird dumps, snow or dead leaves , some of which will come into play during the winter. Plus we don't know how the weather will be set, but can assume it will not be wall to wall sunshine month on month, more likely overcast for appreciable periods. Clearly we know the sun angle and predicted lighting, but don't know how much of that will actually get through to the semiconductors.

All the above can have massive degrading effects on available yield, a 50 Watt figure in direct standard reference sunlight, bears no relationship to the probable yield in this case.

Achieving an adequate yield becomes very important, because if adding this system, if it fails to yield, it will do more damage than if it was not fitted.
If a battery is just dealing with a healthy level of self drain, it becomes counter productive to put in even a minimised system. If healthy and without parasitic losses, it needs nothing for two to three months

If we are going to do anything, then it could well turn out we need a sledge hammer to crack a nut. Knowing its performance could be very low, over designing is prudent.

Few purchasers are going to be enamoured after investing, to write off the battery because a wet leaf got stuck on it or there was a fortnight of dull weather. IMO, do it well to mitigate losing the battery or not bother.

Apart from paying a few tens of pounds to buy a larger panel there is no real downside to going over the top, after all that overspend is a fraction of the replacement battery cost it could save.

The technical side is well capable of dealing with excesses, a decent controller simply shuts down the solar panel's current output, as and when required.
 
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Mar 14, 2005
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Hello JTQ

I agree we cannot know the amount of detritus that will collect on the panel, but that would apply to what ever size of panel was fitted, And we cant know the direction or the angle of the panel, But these are all features that I would hope a responsible owner would consider to maximise the effectiveness of their panel.

I also agree that if a larger panel than necessary were fitted, it might benefit the user during holiday stays also.

But DD laid out a quite specific set of circumstances, and his wishes would be met with a considerably smaller panel.

Only DD will be able to decide if the extra expense of a bigger panel would have value to him
 

Parksy

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Most of teh replies so far seem to have ignored DD's point about trickle charging the battery whilst in storage. I would dreadfully concerned if a battery lost 50Wh each day whilst in storage!

There are 12W panels that should be more than adequate even during winter to offset any self discharge of a battery. Such small panels rarely have charge controllers, but I couldn't say how much they may sap from a battery at night. Best to seek the manufacturers specifications and advice.
DD indicated that he'd prefer a roof mounted solar panel Prof.
If you had read the previous replies, I did in fact mention in my earlier reply that free standing suitcase type solar panels are available, complete with connecting cables, regulators and diodes to prevent night discharge and indeed Jezzer B has explained how his panel works from his rooflight.
In view of the preference expressed by DD it wouldn't be worthwhile roof mounting a lower wattage panel.
The installation procedure for any caravan roof mounted solar panel is the same, so my advice would be to fit the best one for the budget of the prospective buyer.
 
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JTQ

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We were told the panel was to go on the roof, I had assumed its angle to the horizontal would therefore be zero or close to, and so its orientation to the sun irrelevant. Horizontal in winter the strike angle will seriously derate the panel, relying a lot on reflected light off the clouds.
Many storage slots are fixed, so if tree shadows are thrown on that patch these are unavoidable, and with winter sun angles tree shadows are very long. My case had assumed the storage probably was not in a tree less large field.
 
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As Prof says we had a very small solar panel, not sure how big but less than 10w. Connected directly to the battery and left in the heki roof light, held in by the blinds as it was light and small-had a built in diode to prevent discharge and we never had a flat battery, even in the middle of winter and with high motor mover use! no charge controller needed.
Exactly what we have, the alarm being the only drain it keeps the battery topped up fine, simple to connect when we leave the van and costs less than £20.
 
Mar 14, 2005
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Hello Parksy
I had not ignored DD's point about roof mounting, and I do agree the cost of fitting a small panel will not be significantly different to a larger on (except for the cost of the panel itself), and on that basis it would make some sense to go for the largest panel that will fit and you can afford. But for the stated purpose - it would be over kill.

I'm also not ignoring JTQ's points about available light and angle, such point are of greater significance if you are trying to replenish a battery that is being used to power some appliance, but again for the stated purpose of keeping a battery in good condition whilst in storage, the actual power requirement is small - probably less than a couple of Watts. and as such there is no need even allowing de- rating due to angle, and debris, it would not require a 50W panel.

I'm sure anyone who was taking the conscious decision to have a system like this fitted would only contemplate it provided their storage location did have good access to day light other wise it would be a somewhat pointless exercise and expense.

However it has just occurred to me, that it might be worth considering a bigger system such as an 80 to 100W might be justified. Consider when trying to sell on the caravan, if it were fitted with a system that was big enough to allow the caravan to be used for extended periods off grid, that could enhance the value of the caravan, where as if it had a small system fitted that did not really cover off grid working, that might be seen as a negative and reduce its value in the eyes of prospective purchasers.

That's a consideration for DD to ponder.
 
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Thanks Steve

I’m thinking of a permanent roof mounted one.
I put one on the roof of my Bailey 510/4 after our woodburner cowl came off and put a wacking great hole in the roof:) It also helps with keeping my expensive Leisure battery in good condition...I used to replace my battery nearly every season before installing one.The only problem I've yet to sort out is putting the caravan cover on in winter ...I thought about cutting around the s.panel and sowing in some elastic to not block the sunlight out ...I'm surprised they have not designed a cover to somehow cope with solar roof panels,then again not everybody puts them in the same place to design one:)
 
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I would endorse Parksys suggestion to buy a full kit from eBay, which is what I did. I recommend ensuring that it comes with long edge side supports as well as the corners, as the surface area of the corners alone for bonding to the roof is not that great.
I installed a voltage datalogger to measure what was going on during winter/overnight, and found that the voltage did fall a little overnight as expected, but you wouldn't really expect much fall, if any, when in storage. For me its a non-issue.
 
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