Solar Panel Query --- advice needed ...

Submitted: Saturday, Jul 04, 2009 at 00:39
ThreadID: 70379 Views:4372 Replies:8 FollowUps:25
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I have recently purchased, through eBay, a monocrystalline 80watt solar panel.
This panel has 36 cells.

When it arrived I found that it was sticker-marked 100 watts.

Subsequent inwestigations have revealed that there have been some other instances of 'incorrect labelling' by this mob,
not always to the customers benefit! I was initially happy that I had received "a better deal" - BUT ?

Thusly, my question/s is/are :

Is there any way that I can confirm if this is either 80w or 100w?
Or calculate it ???

Is there any way to measure the actual 'output ampage ?'

ie: do I connect it, via the regulator (non-digital) to my battery and measure with my trusty metery thingo?
AND:
should that battery be already discharged to a certain level ?

I have used the panel on a recent prospecting trip to maintain my second auxilliary battery, driving a 40l Engels,
which it did successfully.

I am happy with the panel overall - just wanting to make sure what I have.
Some " advisers" have implied that it may not even be an 80watt panel, ITHO it may be only 50 watts.

Any advice would be much appreciated .................

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Reply By: Boobook2 - Saturday, Jul 04, 2009 at 06:18

Saturday, Jul 04, 2009 at 06:18
It is pretty hard to tell exactly but try 3 things.

1)Get a pretty flat battery and connect it up as you describe. On a very sunny coldish morning with the sun unobstructed and with the panel pointing to the sun, measure the volts going IN to the regulator across black and red, it should be about 17 - 21V. Then the amps through the red cable ( should be about 4A - 5.5A). Multiply the two and add 5 - 10% for non optimal conditions and you will get close.

2)Measure the length and width of the unit and compare to other monos.

3)Ask the supplier why they shipped the different value and what the real story is.
AnswerID: 373015

Reply By: Mandrake - Saturday, Jul 04, 2009 at 08:09

Saturday, Jul 04, 2009 at 08:09
The only difference to the post above - when I test my panels - I wait for (hopefully) a sunny day and test at midday - Theoretically this will show the optimum capacity of the panel - 80 watts should produce consistently an output of 4.4 - 4.8 amps - 100 watts - 5.4 - 5.8 , 50 watts - 2.6 - 2.9 amps as a rough guide ..
Mine are rated at 18 volts ------- 80 watts / 18 volts = 4.44 Amps .
Open circuit voltage - straight from the panel will be close to 22 volts .

Hope that helps

Rgds

Steve
AnswerID: 373025

Reply By: MEMBER - Darian (SA) - Saturday, Jul 04, 2009 at 09:09

Saturday, Jul 04, 2009 at 09:09
If I read it right, my 'Rivers Book' states that manufacturers' wattage ratings for solar panels are only "perfect case scenario" anyway - they are rated after laboratory testing under perfect conditions - the point is, in the field, you never get those same conditions ! Closest you'll probably get is very chilly temperatures under brilliant sunlight overhead. So you are probably never going to get more than about 70% of the manufacturer's rated wattage in any panel. Rivers states that it is not a fraud in effect to use this system of rating, because the sound rationale for rating is all explained in the detail on the specifications sticker. In the end, your meter seems the only way you'll find out how many 'zaps' you are getting for your $ :-o).
AnswerID: 373032

Follow Up By: Maîneÿ . . .- Saturday, Jul 04, 2009 at 09:54

Saturday, Jul 04, 2009 at 09:54
The picture tells a slightly different story:
200 watts delivering 12 Amps to the Solar regulator
5 Amps charging 200ah of AGM's @ 14.3v

The solar system is mounted flat on the roof, so obviously it's not pointing in the correct position to gain anything like optimum performance, but it's not an elcrapo low performance solar system, maybe that is why it works reasonably well.

I assure you the pic was not taken on a chilly temp day, so if 12 Amp is about 70% of the best performance from a 200 watt Solar system I'm more than happy :-)

Image Could Not Be FoundMaîneÿ . . .
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Follow Up By: Nomadic Navara - Saturday, Jul 04, 2009 at 16:16

Saturday, Jul 04, 2009 at 16:16
Mainey

If you are getting 12 A into the controller and only 5 A into the battery I think there is something wrong. There are 3 possibilities I can think of:

1. Instrument error. One of the meters is way out.

2. There is a 7 A load on the system and this is not being taken into account.

3. The controller is wrongly installed. This is quite common with these controllers that were originally designed for positive earth installations (telecommunications systems.) The 3 negative terminals are all at different potentials where as the 3 positive terminals are connected together. If you read the technical articles in the Wanderer you will see many examples of where solar installers have stuffed up the installation in motorhomes.

PeterD
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Follow Up By: Maîneÿ . . .- Saturday, Jul 04, 2009 at 17:19

Saturday, Jul 04, 2009 at 17:19
Peter,
(1) No, there's nothing wrong with any of the instruments
(2) Yes, there could be a 7 Amp load on the 14.3v battery system (probably not)
(3) No installation problems either, I installed it :-)

The more obvious solution (to me) is:
maybe, just maybe, the 14.3v battery system is close to fully charged and the fridge is *not* running.
The Solar regular is obviously doing it's job of regulating the current going to the 14.3v battery system.

Just because the Solar system can collect 12 Amps, does not automatically mean they are *all* sent to the battery system all of the time, that would soon destroy any battery system.




This picture clearly shows the fridge is running
3.1 Amps from the 13.1v battery system
4.9 Amps direct from the Solar system
(~8 Amp draw) Image Could Not Be FoundMaîneÿ . . .
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Follow Up By: Boobook2 - Saturday, Jul 04, 2009 at 17:26

Saturday, Jul 04, 2009 at 17:26
The 70% efficiency comes from a standard regulator, not the Panels.

As per Mainey's example, he is getting 12A from 200W of solar panels. At say 17V that makes sense. But the output of the regulator, ie the usable power into the batteries the voltage is 13.1 on the voltmeter. 13.1 x 12A is 157watts.

157w divided by 200w = 78% efficient.

Mainey, the 12A doesn't just dissapear, 7.1A must be going to the load.
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Follow Up By: Lex M (Brisbane) - Sunday, Jul 05, 2009 at 00:16

Sunday, Jul 05, 2009 at 00:16
Steca PR1515 - PWM shunt regulator.

The extra 7.1A goes to heat in the regulator.

This explains how an analogue shunt regulator works.
http://www.waynecard.com/index.php?page=solar-shunt-charger

A PWM regulator works the same but has some more smarts controlling the shunt circuit.

So your getting 12A from the solar panel and 7.1A is doing nothing but heating up the shunt in the regulator. 100watts +. The regulator should be getting quite warm.

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Follow Up By: Boobook2 - Sunday, Jul 05, 2009 at 08:39

Sunday, Jul 05, 2009 at 08:39
Ahh yes. Forgot about that, thanks Lex.
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Follow Up By: Maîneÿ . . .- Sunday, Jul 05, 2009 at 10:13

Sunday, Jul 05, 2009 at 10:13
Lex,
Yes the Steca regulator is PWM controlled !!
Steca PWM technical specs the Steca regulator does not even get warm.

You can't seriously believe the Steca reg is simply wasting 7.1 Amps "heating up the shunt in the regulator" on any *permanent* basis, that just does not happen.
UNLESS-> your suggesting it's being "regulated" by the Steca regulator so it will not send the full 12 Amps to an already fully charged battery system, with-out actually using the word "regulate" ??


consider this:
will a Toyota 100 Amp Alternator, at ALL times, supply the full 100 Amps to the battery ?
or
will a Ctek 50 Amp battery charger, at ALL times, supply the full 50 Amps to the battery ?

-> of course not
reason being the 100 (or 50) Amps is "regulated" by the appropriate device
exactly the same as Steca Solar regulator "regulates" Solar power to the battery.



The picture posted above clearly shows what's happening:

Solar system delivering 12 Amps to the Solar regulator
Solar regulator sending just 5 Amps to *TRICKLE CHARGE* the 14.3 Volt battery system

Easy to see and understand, no tricks, no gimmicks and no problems


This picture (below) clearly show 10 'Plus' (cause it can't show 12) Amps is charging the battery system, however with the 7 Amps you claimed to be "wasted" heating up the shunt, takes the total to 17+ Amps minimum, from a 200 Watt solar system - I believe this pic shows your numbers & ideas don't add up to a credible explanation as I'm sure you will also agree, it's impossible to get 17+ Amps from a 12v, 200 watt Solar system.
Image Could Not Be FoundMaîneÿ . . .
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Follow Up By: Boobook2 - Sunday, Jul 05, 2009 at 10:42

Sunday, Jul 05, 2009 at 10:42
Mainey, I don't think Lex is implying that the Stecca will always use 7A internally. He is saying that as a shunt type charger, the "excess" available current is dumped to ain internal load to control the output. If the external load requires more current then less will be diverted, or shunted to the internal load. If your charge requires the full 12A then the charger simply won't divert the 7A ( which as you correctly point out isn't available).

I don't think this is a comment on Steccas wasting 7 (or whatever at the time) amps, it is just the way that type of charger works.
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Follow Up By: Lex M (Brisbane) - Sunday, Jul 05, 2009 at 14:26

Sunday, Jul 05, 2009 at 14:26
At the time you took the picture you had 12A from the solar panel and 5A going into the battery. If you had no other load then where do you think the missing 7A is going? It has to go somewhere.

The solar regulator has to waste the excess current. That's how a shunt charger regulates.

How much it wastes at any time will be the difference between what the solar panel is putting out and what it needs to charge the battery appropriately at the time.

All regulators have to waste or limit power somehow when the solar panel is outputting more than needed. I believe solar panels don't like the load being switched when working, My panels have a warning about this. Therefore the common way of regulating is by switching the excess current to an alternative load internally, (a shunt). The solar panel doesn't see any difference from it's end so it's happy.
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Follow Up By: Maîneÿ . . .- Sunday, Jul 05, 2009 at 15:48

Sunday, Jul 05, 2009 at 15:48
With fridge disconnected from the 12v circuit, the battery shows 12.8v
with (about) zero Amps going to it from the 8.6 Amps available at the time
obviously because they were being "wasted" somewhere else

Where these "wasted Amps" go or hide, is not the point.

Just like the scenario above of the 100 Amp Toyota Alternator and Ctek 50 Amp battery charger, not all the Amps available from either of these devices are sent to the battery either, because they are also "regulated" efficiently, hence the terminology 'trickle charge' is applied, because only a small percentage (%) is sent to the battery as it reach's the point of being fully charged Image Could Not Be FoundMaîneÿ . . .
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Follow Up By: Boobook2 - Sunday, Jul 05, 2009 at 18:40

Sunday, Jul 05, 2009 at 18:40
Mainey an alternator or Ctek or similar charger are not similar examples. If you have a 100A alternator that is connected to a battery charging at 5A, and nothing else is connected, the Alternator only outputs 5A. Same for the charger.

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Follow Up By: Maîneÿ . . .- Monday, Jul 06, 2009 at 10:07

Monday, Jul 06, 2009 at 10:07
Can we agree to disagree, as I believe they are similar examples, reason being all three devices are very capable of putting out much higher current than is sent to the battery and in some instances more than the battery can handle consistently.
The current from all three devices must first travel via a *regulator* before it goes to the battery.
The total current produced by any device mentioned above does not go direct to the battery with-out first being regulated in some way.

You say: "If you have a 100A alternator that is connected to a battery charging at 5A, and nothing else is connected, the Alternator only outputs 5A. Same for the charger"

Are you sure?
if the Alternator is rated @ 100 Amps, isn't it's output "regulated" by the Alternator's *regulator* down to the 5 Amps you mention ?
Same with the 50 Amp battery charger, it's output is "regulated" - hence the terminology "trickle charge" and "boost charge" etc.

(where the 'missing' current goes to when regulated is not relevant, as it does NOT go to the battery)

Maîneÿ . . .
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Follow Up By: Lex M (Brisbane) - Monday, Jul 06, 2009 at 12:06

Monday, Jul 06, 2009 at 12:06
The difference is that a ctek or an alternator is "pre-regulated". That is they produce only the current needed as controlled by the INTERNAL regulator. They may be capable of producing more than needed but the regulator controls how much is produced.

A solar panel is usually "post-regulated".
It produces whatever it is capable of in the current solar conditions and the EXTERNAL regulator then disposes of that current as it sees fit.
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Follow Up By: Boobook2 - Monday, Jul 06, 2009 at 13:39

Monday, Jul 06, 2009 at 13:39
The other important issue is that Regulators don't regulate current. They regulate voltage. The current is a result of the (regulated) voltage and the load. You can have current limiters but that is totally seperate. A 100A alternator means that it can supply 'up to' 100A at the regulated voltage.
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Follow Up By: Lex M (Brisbane) - Monday, Jul 06, 2009 at 14:19

Monday, Jul 06, 2009 at 14:19
That depends on what you mean by "regulate".

For example a battery charger controls the current dependant on the voltage measured at the battery. The voltage at the battery terminals is dependant on a number of things, eg state of charge - current input - internal impedance to name a few.
The charger controls the current into the battery while monitoring the battery voltage for what the charger deems appropriate for it's charging program.
Does it regulate the voltage? Maybe, but they do it by controlling current and thereby indirectly controlling voltage

An simple alternator regulator controls battery voltage by controlling field strength which controls the current supplied by the alternator and reduces field strength to keep the voltage down to a safe level.
Does it regulate the voltage? Once again it controls the current.

Am I being pedantic?
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Follow Up By: Lex M (Brisbane) - Monday, Jul 06, 2009 at 14:27

Monday, Jul 06, 2009 at 14:27
A 100A alternator means that it can supply 'up to' 100A at the regulated "voltage."

Missed that point. A 100A regulator means that it can supply a max of 100A.
This is dependant on the physical characteristics of the alternator, field strength - impedance of windings etc.

The voltage at that time is dependant on the external connections, EG short circuit a 100A alternator and it will supply 100A at zero volts (but probably not for long).

I'm being pedantic again. :-)
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Follow Up By: Boobook2 - Monday, Jul 06, 2009 at 17:10

Monday, Jul 06, 2009 at 17:10
I guess so Rex,

I would have thought that a 100A alternator was designed with the physical characteristics of the alternator, field strength - impedance of windings etc to cope with a 100A load at it's rated output. That's why it is a 100A alternator yeah?

And sure, a short circuitwould mean zero volts, output. A short circuit across a nuclear power station would mean zero volts by definition too, also for a very short time. Maybe we are at crossed purposes REx, my point was that a 100A alternator will output 0 to 100A ( under rated loads).

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Reply By: RV Powerstream P/L - Saturday, Jul 04, 2009 at 09:26

Saturday, Jul 04, 2009 at 09:26
Monocrystaline is the easiest panel to determine what it is as they are made from solid crystaline billets and you have a distinct size like 150MM Square and the panels will normally be smaller than other types on solar panel.

Small mono panels can be made of segments of the main billet which are offcuts.

Take the overall dimensions of the panel and check it against any other mono panel for identification.

The only other problem you may have is the quality of the billet used may vary the performance slightly.

The higher the stated working voltage shown the more efficent the panel is in real terms but do not expect to get that voltage from the panel as the 80W is based on the maximum working voltage shown and your battery cannot accept that voltage and if the battery accepts 14.4V then the difference between 14.4V and what the panel produces (say 18V like stated in the post above) you lose from the panel in heat.

That loss could be up to 30% so effectively that panel would perform at peak at 56W.

This loss can be offset by MPPT (Multi Point Power tracking ) an expensive regulator which converts the excess voltage back to useable voltage.

So measure the panel size and compare that size with other 80W mono panels to get a better idea.

Ian
AnswerID: 373035

Reply By: Mandrake - Saturday, Jul 04, 2009 at 10:16

Saturday, Jul 04, 2009 at 10:16
It would appear that in-practice and theory are slightly different .. as per Mainey above - my similar case -
80 watt panel angled to the sun produces 4.5 - 5 amps of charging power as measured by my little ammeters at the regulator .. I have not seen any loss of claimed output on my panel -
Pictues a bit small below but the little box on the side of the camper has input and output ammeters so I can monitor fairly closely what goes in and out of the battery ...
Cheers
Steve
AnswerID: 373042

Reply By: oldtrack123 - Saturday, Jul 04, 2009 at 11:04

Saturday, Jul 04, 2009 at 11:04
Hi
Panel open circuit voltage for good charging is usually about 21v So 1st check if you get this voltage.
When connected to a battery this output voltage will be about 17v[ you will not be able to test this but it is the point @ which the panel watts are max & the power @ which they are rated.
An 80w panel @ 17v gives about 4.7 amps depending on sunlight entensity.
A 100w should give about 5.8amps
Another means to check is the short circuit test , these panels do not encrease the current much under short circuit so the 80w would give about over 5amps & 100w about 6.25amps.
All these test are sunlight intensity dependant.
As mentioned in an earlier post physical size can be a very good way to determine as long as you are comparing apples with apples
AnswerID: 373044

Follow Up By: V8 Troopie - Sunday, Jul 05, 2009 at 01:11

Sunday, Jul 05, 2009 at 01:11
Of all the interesting replies above, you are the only one to suggest the quickest and simplest way, measure the short circuit current.

A lot of people seem to be not aware of that it is quite OK to short circuit the panel with an Amp meter, no regulator or battery need to be involved. Actually, do NOT connect anything other than the Amp meter when doing this test. And DO set the Amp meter to the expected DC amp range if its a multimeter.

My only difference in opinion with the answer above is the comment:
"When connected to a battery this output voltage will be about 17v"
When one connects a solar panel directly to a battery one measures the battery terminal voltage at that time, no more or less. 17V would certainly ring alarm bells if I measured that.

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Follow Up By: oldtrack123 - Sunday, Jul 05, 2009 at 10:21

Sunday, Jul 05, 2009 at 10:21
V8 Troopie posted:
my difference in opinion with the answer above is the comment:
"When connected to a battery this output voltage will be about 17v"
When one connects a solar panel directly to a battery one measures the battery terminal voltage at that time, no more or less. 17V would certainly ring alarm bells if I measured that."

Hi V8

Probably did not make it clear,when I said that " you will not be able to read that".
Because as you say you will be reading the bat voltage which will be a bit higher than the state of charge, but certainly should never be higher than 14.5<15v, depending on battery type.
The point I was trying to make was that the panel max output[watts] is usually based @ about 17v for 36cell panels.
Many panel do have a graph on the back showing the output volts versus current.
They are constant current devises which means they will give virtually the same current outpt under load from short circuit [0v]TO loads with an equivalent impedance of about 3.8ohms @ which the output volts will be approx 17v[max watts]
This of coarse based on sufficient & constant sun intensity.l
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Follow Up By: Maîneÿ . . .- Sunday, Jul 05, 2009 at 10:35

Sunday, Jul 05, 2009 at 10:35
yes, and "This of coarse based on sufficient & constant sun intensity" differs greatly from hour to hour, hence the reason we get sooo many different Amperage reading at different times of the day

Maîneÿ . . .
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Follow Up By: oldtrack123 - Sunday, Jul 05, 2009 at 14:06

Sunday, Jul 05, 2009 at 14:06
Hi

Of course if the bat voltage is 14.5v@ 4.5 amps input, " watts " INPUT from the solar panel is 65.25w, about 81.5% of its rated capacity[watts] for an 80w panel.
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Follow Up By: oldtrack123 - Sunday, Jul 05, 2009 at 14:13

Sunday, Jul 05, 2009 at 14:13
Maîneÿ . . . posted:
yes, and "This of coarse based on sufficient & constant sun intensity" differs greatly from hour to hour, hence the reason we get sooo many different Amperage reading at different times of the day
Maîneÿ . . .

Hi Mainy

Very very true.

High intensity light say reflected from clouds can actually give a significant increase in current < about 10%
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Reply By: Maîneÿ . . .- Saturday, Jul 04, 2009 at 11:32

Saturday, Jul 04, 2009 at 11:32
Pedro,
depending on the brand you purchased, the 'usual' average size of an 80 watt Solar panel is about 1200 x 540, or said another way about two thirds (2/3) of a square Mtr in area.

The 100 watt panel is about 20% larger in area and a 50 Watt panel will be smaller in area.
(most tape measures are reasonably accurate and easy to use)

Maîneÿ . . .
AnswerID: 373047

Reply By: bks - Saturday, Jul 04, 2009 at 22:44

Saturday, Jul 04, 2009 at 22:44
Out of curiosity I had a look on ebay at the solar panels. The prices are way below normal retail.

I'm not an ebay user so wonder if the panels are OK
AnswerID: 373121

Follow Up By: Maîneÿ . . .- Sunday, Jul 05, 2009 at 10:25

Sunday, Jul 05, 2009 at 10:25
I wonder that too, but I'm not going to denigrate a product with unknown specifications.
The numbers quoted are not totally relevant to real life performance in the bush.

Would like to see an 80 Watt compared to a BP 80 Watt, as a direct comparison, however from the East coast over here to the Best coast is a long way to run extension cables.


Maîneÿ . . .
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Follow Up By: oldtrack123 - Sunday, Jul 05, 2009 at 10:32

Sunday, Jul 05, 2009 at 10:32
Hi
I believe that some are not rated @ load conditions as above but @ open circuit volts.
You need to ensure you are getting applesfor apples specs wise.
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Follow Up By: wazzaaaa - Sunday, Jul 05, 2009 at 14:42

Sunday, Jul 05, 2009 at 14:42
Have a look at my last ebay purchase to add to the other six I already bought from this guy a couple of years back.

Wazzaaaa

link
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