Solar panel

Just bought a second hand solar panel that is supposed to be 250w.How do I know it is 250w panel? Also will a 250wpanel be enough to run two engels(40l and 32l) connected to a camper with 2 120 amp agm batteries.
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Reply By: Member - DW Lennox Head(NSW) - Thursday, Feb 13, 2020 at 04:44

Thursday, Feb 13, 2020 at 04:44
This might help a little to calculate your watts .

Watts=Amps x Volts

This explains the process to get the Amps and Volts. It should be on the back of the panel, if you are lucky.

https://www.selectsolar.co.uk/cat/171/testing-your-solar-panel-regulator

Cheers
Duncan

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Reply By: Member - Boobook - Thursday, Feb 13, 2020 at 08:13

Thursday, Feb 13, 2020 at 08:13
First up, the panel should be about 1m x 1.8m. If it's much smaller than that 250w is unlikley.

Also, it should show the voltage and current maximum power points ( MPP) on a sticker on the rear. Multiplied together they should be 250w. Typically it would be something like 21V and 12A. If it is more like 44V and 6A then you will definitely need an MPPT controller, which is highly advised anyway.

If the fridges are used above 0 degrees then it will be just enough on sunny cold days. If you use one as a freezer, or it is overcast, hot or partly cloudy then 400w plus is needed to keep the fridges going for more than a day or so.

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Follow Up By: The Rambler( W.A.) - Thursday, Feb 13, 2020 at 12:41

Thursday, Feb 13, 2020 at 12:41
Panel size is 1400 by 800
Open circuit voltage. 22.5
Max power voltage. 18v
Cell Tech. Mono-Si
Module application.. class A
Max System Voltage. 1000v

Certified by TUV Nord Germany.
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Follow Up By: RMD - Thursday, Feb 13, 2020 at 14:02

Thursday, Feb 13, 2020 at 14:02
Rambler
I see there is no current spec, so unless you know the short circuit current by testing and use a lesser figure of around 1 amp less and can hold by regulation to 18v max power voltage and multiply those two figures together, ie, amps and MPP voltage you won't have much idea of the output.
Many panels of Chinese origin DO NOT show current figures 'cos they don't want you to be able to work out what is going on. Most panels produce voltage easily, it is the associated current in the equation which matters to be able to work out suitability. On the panel size alone and 18% efficiency, working under ideal conditions indicates around 200w if you are lucky. To be realistic, cut 25% off that and you will be nearer the actual output. As Boobook mentioned, an MPPT solar regulator is the only way you will be able to take advantage of the current and voltage for a maximum harvest with any panel. because they operate to create the optimum operating voltage and current of the panel at any one time, and convert that to battery charge current. The solar input and the output to battery are completely isolated, unlike a PWM charge regulator which is less efficient. That panel seems to be quite a bit less than you will need to run two fridges, one of which, I presume will used as a freezer.
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Follow Up By: Member - Boobook - Thursday, Feb 13, 2020 at 17:10

Thursday, Feb 13, 2020 at 17:10
On first inspection, a Mono panel that Size is about 180 - 200W. What is the Imax or Impp?
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Follow Up By: Member - peter_mcc - Thursday, Feb 13, 2020 at 23:26

Thursday, Feb 13, 2020 at 23:26
Based on the size given above and the rule of thumb of 170W per m2, I would guess it is really a 190W panel at most.
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Follow Up By: RMD - Friday, Feb 14, 2020 at 17:16

Friday, Feb 14, 2020 at 17:16
Rambler
While certification is meaningful with quality panels with regard to output specs and efficiency etc, many Chinese panels which claim to be seemingly large output for a compact size cannot be true and they also use certification claims like, Certified by TUV Nord Germany., to further deceive the buyer. I suspect all certification for cheaper panels is simply a claim they have passed quality/performance control as nearly all fail what they claim to be. Also while some reputable manufacturers state they are a Tier One company, ie, process control to recognised international standards, all Chinese cheapies seem to claim they are Tier One too. Most likely bought the Tier One certification from dodgy Passport forgers or similar people. It is hard to determine output of panels from the specs, if supplied, because it just may not be true.

Early on, I bought some folding panels from ALDI, and while they do work OK, they do not produce near what they claim, and now they live outside to power my house fridge everyday, the substrate in the panel shows many hairline cracks across the silicon wafer surfaces.
If using more than one panel. they can be linked in series which halves the current from the two but doubles the voltage and IF using an MPPT reg which can handle the full open circuit voltage of two panels in series, you will find it starts charging earlier in the day, and shuts down later than in parallel. The double voltage and half the current = same energy level available but the MPPT reg can make better use of it for the battery system recharge time.
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Follow Up By: Allan B (Sunshine Coast) - Friday, Feb 14, 2020 at 19:26

Friday, Feb 14, 2020 at 19:26
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RMD,

I Wouldn't trust any specifications coming out of China.
My son worked for a year in China as an instrument/electrical inspector for the construction of plant for the Ichthys LNG plant. You should hear what he has to relate.
Normally not prone to excess, he calls China the "most dishonest society on the face of the planet".
Cheers
Allan

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Follow Up By: Member - J&A&KK - Friday, Feb 14, 2020 at 21:14

Friday, Feb 14, 2020 at 21:14
Allan

Interesting comment by your son. And an aside to the topic of the OP.

I started working in PRC on oil exploration projects in the early 1990’s. In one case, after 6 weeks of BS negotiations, my translator told me ( in the middle of a meeting) that we needed to tell some lies. My response was that was not how we Aussies worked usually. He responded that we should because everybody else was lying.

Subsequently I went on to manage a couple of PRC companies that were wholly foreign owned (WOFE’s). It took me a very long time to convince the local managers that the truth would not hurt them but a lie would. Losing face is a serious issue in many parts of Asia. That I know from direct experience. So telling the truth and losing face become mutually exclusive. As for exaggerated claims - that’s common everywhere you go.

Cheers John
John
"There are naive questions, tedious questions...There is no such thing as a dumb question" Carl Sagan

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Follow Up By: The Rambler( W.A.) - Friday, Feb 14, 2020 at 22:47

Friday, Feb 14, 2020 at 22:47
Thanks for the helpful replies,but at no time did I mention that the panel was of Chinese origin.As far as I am aware it could be a panel of the very best Quality ever built and the proof is how it performs when professionally connected to my two agm120amp batteries.
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Follow Up By: Allan B (Sunshine Coast) - Friday, Feb 14, 2020 at 23:03

Friday, Feb 14, 2020 at 23:03
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Rambler, Nobody alleged your panels are of Chinese origin.
I was responding to RMD on his comments of... "many Chinese panels which claim to be seemingly large output for a compact size cannot be true".

So I'll ask you the question now.... are your panels of Chinese origin?
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Follow Up By: The Rambler( W.A.) - Saturday, Feb 15, 2020 at 00:54

Saturday, Feb 15, 2020 at 00:54
There is no evidence shown on the panel indicating it is Made in China.
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Follow Up By: RMD - Saturday, Feb 15, 2020 at 17:51

Saturday, Feb 15, 2020 at 17:51
Rambler
If it DOESN'T have full specs and show open circuit voltage, maximum short circuit current, maximum current at peak operating voltage, then I would suggest it IS definitely a Chinese made panel. That is what they do. Not that it is necessarily a bad thing but most of the cheaper offerings from China that I have seen are the ones which have vital info missing on the info panel. That way they are not actually stating what it is, and only by testing it's output by various means will you have a definite idea of what it's performance really is. THEN you can decide what additional solar panel requirements you may need to run your fridges successfully.
If 170 W is achieved by a 1 sq metre panel, best performance happening there, your panel of 1.12 M2 is at absolute maximum on a perfect day with everything in your favour, 190W a stated by others. Not enough to run fridges in hot or adverse conditions.
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Reply By: RMD - Thursday, Feb 13, 2020 at 08:33

Thursday, Feb 13, 2020 at 08:33
Rambler
Perhaps you should say what size/area the panel is and it's "claimed" specs on the rear info notice so we have some idea for replies. Many sold are far too small to be able to deliver anywhere near the claims so a realistic assessment must be done. The short circuit current measurement in full sun midday is an indicator and the a couple of volts less than open circuit voltage is near to the mark. That will supposedly give the Volts x amp = watts calc. If it isn't a top class panel it possibly will not be over 16- watts I suspect. That is in full sun so the actual harvest of it may not be enough.
I have a 160 cheap panel and an 80 watt better panel/ side by side the 160 cheap only delivers 1.3 amp more than the better 80 watt panel does. That is some indication of the lesser performance of many cheapies. Judge your requirements on slightly over half of what is claimed if used like boobook mentioned.
AnswerID: 630026

Follow Up By: The Rambler( W.A.) - Thursday, Feb 13, 2020 at 12:48

Thursday, Feb 13, 2020 at 12:48
I put some more details on the follow up to reply by boobook.
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Reply By: swampy - Friday, Feb 14, 2020 at 09:05

Friday, Feb 14, 2020 at 09:05
HI
RE camper trailr .org and other publications
40ltrs around 40ah consumption in 24hrs in hot demanding situations
Fridge consumption is temp dependant
Fridges used as a freezer use a lot of power also
200 watt panels in100% sun and using PWM controller produces around 48ah in 24hr period

In demanding situation 200watts wont be enough . The system will rely on the batteries gradually flattening them . Add another 160 w min,, ideally 200watt min .

Batteries will thankyou ,system will recover quicker and cloudy days will be tolerated far better
AnswerID: 630042

Reply By: Batt's - Saturday, Feb 15, 2020 at 01:56

Saturday, Feb 15, 2020 at 01:56
My 170w panel is 1460 x 660 I reckon yours is not much bigger like others have been saying. You could re-sell it and buy a good quality one or by another panel to add to it if 2 panels fit your camper. It seems to be quite common of late that panel sizes haven't increased but claims of out put have buyer beware do your research to help avoid becoming a victim.
AnswerID: 630060

Reply By: qldcamper - Sunday, Feb 16, 2020 at 08:49

Sunday, Feb 16, 2020 at 08:49
You have already bought it so have the electrical install done, which will be the same for whatever panel you finally install, just choose a regulator that will handle twice what that panel claims to be.
Hook it up and and see how it performs, thats the only way you will ever know what it can or cant do.
AnswerID: 630075

Reply By: HKB Electronics - Sunday, Feb 16, 2020 at 10:49

Sunday, Feb 16, 2020 at 10:49
Think someone already mentioned, put it in bright sunshine on a clear day, measure the open circuit volts
then the short circuit current and work the watts.
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Follow Up By: Allan B (Sunshine Coast) - Sunday, Feb 16, 2020 at 11:03

Sunday, Feb 16, 2020 at 11:03
.
That can't possibly be right Leigh. It sounds too simple. LOL
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Follow Up By: RMD - Sunday, Feb 16, 2020 at 12:53

Sunday, Feb 16, 2020 at 12:53
For a maximum output calculation with no testing, for other than recognised brand panels, Read the watts "claim" and cut 40% off that, I reckon it would be about right and max output for all unbranded/unknown panels.
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Reply By: OzzieCruiser - Sunday, Feb 16, 2020 at 17:49

Sunday, Feb 16, 2020 at 17:49
As an aside, I am looking for a single panel of about 300w to permanently mount on top of my truck.

Using the 170w per sq meter rule of thumb, I checked the first 20 300w panels listed on ebay caravans and household panels.

The worst of the 300w panels came in at 160w and the best came in at 230w. Price did not seem to factor, though a 230w (300w) panel came in the most expensive but then one also came in somewhere in the middle at $160.

So how reliable is the 170w/sq m rule of thumb - it certainly helps in working out what you are actually getting.
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Follow Up By: RMD - Sunday, Feb 16, 2020 at 23:06

Sunday, Feb 16, 2020 at 23:06
Ozziecruiser.
While a single panel is OK, if it suddenly retires it's services then you have NO panel. If using two smaller panels then you still have some capacity if one fails. I have 3 cheapies of 160w in parallel by Y connectors to a dc dc unit. In theory the 3 panels are more than the dc dc unit can handle but the good point is none of the three put out anywhere near the 160 W. So with working out the area and 170/m2 the panels have to be that efficiency to ever get to/near the stated output. Most cheapies are far less efficient than the makers claim and so the area is useless, only the loaded voltage at maximum load current is the info to use. However practically no cheap panels will state that. Only testing one will approximate what they will deliver. Always make sure the reg is higher input voltage than the panels can get to. If used in series with a DCDC or reg, the voltage of the panels in series and the DCDC or MPPT reg input becomes quite important.
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