Solar panel troubles

jonathankent

jonathankent

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I'm having trouble with my solar panels... some help would be much appreciated (I have read the chapter in Nigel's Mech & Elec Manual, yet am still 'in the dark').

I have got 2 panels, 35cm x 45cm so not too small, one 75aH battery, and have just bought a regulator. The panels don't seem to be charging the battery - the voltage is actually decreasing!! I don't know the exact watts of the panels (the text on the reverse has faded) but can make out some values for quote "1000 w m-2" and "800 w m-2" and "13.7 watts", but this seems quite low to me. I am assuming 1000 w m-2 means 1000 watts per square meter (the 2 panels have a total of 0.32 sq m). The other morning, fairly sunny, I had approx 12 volts across the panels (open circuit not connected to anything), but shouldn't I be getting more - the book suggests 16-20v. My main concern is the amps being produced. I can make out on the reverse a 1.5a and a 0.92a, but this doesn't seem to relate to anything, well not that I can work out anyway. I have checked with a multimeter and was only getting 1.6 (which was using a 0-200mA scale) but surely 2 panels of this size with 12 volts would be producing far more than 1.6mA - the regulator uses 4mA!! - could explain why battery voltage is dropping, but not at the rate of 1volt in 3hrs.

Any suggestions would be much appreciated.

P.S. I have checked voltages at each stage through the wiring and all seems to "add up".
 
I'm sure you'll get the full story from someone but if the open circuit voltage, thats measured at the panels themselves, is less than 12 to 13V then they will put nothing into a 12V battery unless its really really flat.

Most batteries will not take current until the terminal voltage is 13V and more and as solar cell manufacturers understand this they add together sufficient solar cells to make circa 14V on a cloudy day and 18 to 20V on a sunny day (all measured open circuit). That isn't to say that on a cloudy day they will put loads into a battery but they will charge it. Your solar cells showing only 12V shows they are really a weak design, or one expecting Sahara sun or they are defective.

Simply, unless you see more than 13V you'll get no current.
 
Actually, a 35x45 panel is rather small, it should be in the range of 20 to 25 watts, i.e. 1.5 to 2 Amps - and that's maximum output in ideal conditions!

This seems to be confirmed by your measurement of 1.6 Amps.

What do you mean by battery voltage dropping by 1 Volt in one hour: is the battery feeding something, and you expect the panel to keep it charged (maybe optimistically, given the low output from panels) or is it only connected to the panels and not being charged (which would likely point to a fault somewhere)?

Also your statement about the 12V open-circuit voltage looks anomalous, it should be higher as suggested by the manual, but still, if the panel is able to send 1.6 Amps to the battery, there is an inconsistency.

From practical experience, 2 x 20/25w panels would normally not be enough (by far) to keep batteries charged while they feed the on-board equipment, while they would be quite adequate to top-up the batteries between week-ends.
I'm talking averages here, you need to quantify your consumption to make an accurate calculation.
Consider that your 2 panels would realistically produce in the range of 10 to 15 Amp-hours per day.
 
2 points....

I could only get 1.6mA - sound extremely strange to me, but being less than 12volts might not be doing anything.

The loss of 1 volt is just purely trying to charge the battery - nothing connected other than the panels.

Your last comment "2 panels would realistically produce in the range of 10 to 15 amp-hours per day" that is what I was hoping for. I only use the boat at weekends, so the panels should keep the battery topped-up during the week.
 
From your description it sounds as if you have taken all your readings with both panels connected together. It may be worth separating the two panels and taking the readings for each panel on its own. It may be that one is passed its best.

At the risk of stating the obvious....you have properly connected the panels together in parallel (+ to + and -ve to -ve)?

Wire OK? No poor connections?
 
To charge your battery the panels, under load, should be producing in excess of about 16volts. The regulator should be doing it's stuff and subsequently managing the voltage across the battery to something like 14 to 14.5 volts to effect a charge into the battery.

If you have only 12 volts across the panels and directly connected to the battery then the panels will act as a drain on the battery, the in-line regulator should prevent this from happening. (You say the regulator is new- so possibly faulty from new??)

You don't say that you have tried each panel individually - maybe one panel is dead and dragging the overall voltage down?

You also say "My main concern is the amps being produced",

Amps aren't "produced" (but volts are). Amps are a resultant of the voltage being applied to the resistance of the apparatus that the voltage is applied to. If your volts are low then the resultant current will be correspondingly low.
 
No seperate diodes. If there are any they must be built-in. Reading the manual though it is often deemed best not to have the diodes as the loss in performance during the day does not equal the saving overnight.
 
Time for a systematic investigation!
1) take a deep breath
2) relax
3) DISCONNECT EVERYTHING
4) check each panel individually: expect an open-circuit voltage around 16/17 Volts, if not probably dead.
5) check battery voltage BEFORE connecting the panels to it and with no charge connected (lower than 12.5 Volts is suspicious)
6) try to connect ONE panel (exposed to sunlight) at a time directly to the battery (don't worry, the regulator is not needed for a short while)
7) check voltage at battery terminals with panel connected: if lower than at point 5 above, the panel is drawing power from the battery, so probably dead.
8) repeat with the other panel
9) if Voltage was equal-or-higher than at point 5, then panels are OK(ish), go on checking the regulator
10) insert regulator and check again input AND output voltage on the regulator: if either voltage anomalously low, regulator is probably faulty (or wrongly connected).

Consider that with small panels a regulator is advisable, but not really mandatory; you can certainly make a test leaving one panel connected to the battery for a couple of days with no harm (AFTER having passed the test at point 7/8!!).

As a side note: a 1 Volt drop at the battery in one hour suggests a fairly large output from the battery, like if the regulator is faulty and drawing current (is it getting hot?).
 
i bought a solara panel from compass supposedly 56 watts, about half a metre by 1 metre, in average sun it puts out about 18v plus with open circuit. it puts in enough voltage to a twin 85 amp battery bank during the week to allow a wife and two kid weekend, frig, tv (12v) and lights on like families do. am well happy with ti
stu
 
The regulator isn't getting hot - the instructions said it might, so I expected it, but nothing.

Now for the obvious... just got to check everything from first base...
I am using the DC voltage on the multimeter.
I've connected the +ve of the multimeter to the +ve on the panel, -ve to -ve, and get a positive voltage, so +ve is +ve.
I've connected the same +ve to the regulator, then another wire out to the +ve battery terminal, and likewise for the -ve.

What voltage is deemed to be a fully charged battery?

I will be stripping everything and checking each individual stage as been suggested by 2 or 3 posts. Hopefully I will know more then.

I will post the update tomorrow.
 
[ QUOTE ]
What voltage is deemed to be a fully charged battery?

[/ QUOTE ]

It's not a straightforward answer, and depends also on the charger's ability to actually reach full charge: say anywhere between 13.5 and 14 Volts, just to quote a magic number.
 
I see a fundamental problem with all the regulators I've looked at, that might have a bearing on your problem. This applies both to solar panels and wind turbines.

Firstly, they don’t start charging the batteries until the input voltage rises to something like 0.7 volts above the terminal voltage of the battery. So any energy produced by the panel below this threshold is completely wasted. Secondly, they dissipate as heat, excess energy produced by the panel when the voltage rises above the maximum charging voltage of the battery (14.7V I think)

Also, solar panels generally become less efficient as they age, and so produce a lower output voltage in a given environment. This might be the root of your problem.

The way to solve this would be to engineer a more ‘intelligent’ charge controller that could multiply the input voltage to suite the conditions, and to reduce the voltage and increase the current in strong light conditions. A regulator that could do this could be engineered, but I couldn’t say how inefficient it would be.
 
Just to reiterate. Disconnect and put the regulator to one side. Look at each panel individually. If you can't measure about 18 vollts in the sun with no connections then there is a problem. You may have a little junction box at the back of the panel which the wires go into. You may have a dud diode (in the box) or a broken wire. Try putting the multimeter on amps straight across the out put of the panel. You should get more tha say half an amp in the sun. Sun as in having distinct shadows. Not just daylight. it does not hurt to short out small solar panels. Ultimately solar panels are not the long life foolproof device we might hope for and don't last forever. Failure is often due to corrosion from moisture entry.
Beware my neighbour connected up solar panels on his mobo and couldn't get any sense of voltage readings only to find the battery was dud.
your solar panels should do what you want if they are working properly.
regards olewill
 
Had a fiddle this morning before work....

Seperated the panels, got 13.1v and 14.1v each, this was just after 8am and fairly cloudy, so am hoping for more later on.

When connecting both together, the voltage dropped. What could be the cause of this?
 
It looks like you might need to use schottky diodes, else you need an 'intelligent' charging system.

The output of the panel with the highest voltage is being fed into the other panel, lowering the total voltage.
 
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