Submitted: Sunday, Apr 11, 2021 at 15:35
ThreadID: 141381 Views:8002 Replies:7 FollowUps:7
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Maybe this information is on the forum somewhere, but I’ve seen all the blurb about cheaper panels not being up to their claimed output.
I’ve got a couple of cheap ones I’m using via a victron mmpt and the best I’ve seen via the App is 50% of the claimed wattage in pretty good sun. Are any panels going to be up to say 75 to 80% . If not I’ll just stay with th cheap ones.
So , other than trial and error , how do you determine which panels actually produce more for less area.
I have a fair bit of space to put panels , but the more power per square metre the better unless the more efficient panels are way to expensive, that’d be my decision.
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Reply By: Member - Siringo - Sunday, Apr 11, 2021 at 15:51

Sunday, Apr 11, 2021 at 15:51
Amorphous panels are said to be the most efficient, but they're also the most expensive. If you have plenty of space I'd bang on a few more panels.
AnswerID: 635946

Reply By: Member - Jim S1 - Sunday, Apr 11, 2021 at 16:29

Sunday, Apr 11, 2021 at 16:29
G'day Shane

Hard Korr offer some decent gear, usually at a reasonable price.

They give the figures that they expect and most seem pretty happy with them. I have the 150W fold up blanket which works very well.

"Sometimes I sits and thinks, and sometimes I just sits." A fisherman.

"No road is long with good company." Traditional

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AnswerID: 635948

Reply By: RMD - Sunday, Apr 11, 2021 at 17:20

Sunday, Apr 11, 2021 at 17:20
The Victron works well but you may not see the max of panel ability, as current on an app, unless the batteries are down a fair bit and the voltage difference of reg and battery are very different, it is definitely operating on MPPT mode, AND you are looking at that particular time. I have a few cheap panels and all seem to be able to develop much more than 50% current of stated ability in a short circuit test. My fixed system with a Renogy 40 amp and BT app has recorded 477watts from 500w of house solar panels, two in series there. It must have been a short term event though as most is around 340w with normal use and normal recorded maximums. On the ute I have 3 cheap panels, which in theory are quite a bit more than the 25a DCDC unit can handle as input wattage, I took a chance and have three panels in parallel. It seems their total never gets to the 25A input max. Couldn't do series connected as input voltage is limited to 27V. Always go on the actual size of the cell area and not the frame dimensions of the panel when calculating solar. As I see it, If I get more than 60% of stated in a short circuit test then ok with the cost of the cheap panels.
AnswerID: 635950

Reply By: Frank P (NSW) - Sunday, Apr 11, 2021 at 17:36

Sunday, Apr 11, 2021 at 17:36
Collyn Rivers, in one of his well-regarded articles on Solar for RVs, said a good rule of thumb is expect about 70% of the claimed wattage for most solar panels.

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AnswerID: 635951

Follow Up By: Peter_n_Margaret - Sunday, Apr 11, 2021 at 18:02

Sunday, Apr 11, 2021 at 18:02
Problem is that the "claimed wattage" are totally fictitious in many cases.
I recently had a dispute with Kogan in regard to some panels I purchased. Their claimed performance was significantly more than was technically possible by the best commercial panels in the world.
I eventually received a sizable refund.

A good starting point is 150 to 170W/m2 under standard test conditions.
OKA196 motorhome
FollowupID: 913772

Follow Up By: RMD - Sunday, Apr 11, 2021 at 18:22

Sunday, Apr 11, 2021 at 18:22
The problem is, with good sun, unless the solar is fitted to a tracker of the sun then the claimed or achievable output is not happening nearly all the time. To charge batteries it is the average of what you can achieve, not some ficticious maximum.
FollowupID: 913773

Reply By: Member - shane r1 - Sunday, Apr 11, 2021 at 18:53

Sunday, Apr 11, 2021 at 18:53
Thanks guys,
It sounds like what I’ve got probably aren’t doing too bad. And I do have plenty of space , so I’ll just fill it up I think.
I’d be pissed off if I spent a heap more on presumed “better “ panels and didn’t get much better performance.
As RMD said if they’re not tracking the sun , they won’t get optimum much or any of the day.
AnswerID: 635952

Follow Up By: RMD - Sunday, Apr 11, 2021 at 21:57

Sunday, Apr 11, 2021 at 21:57
If your panels, maybe cheaper variety, can be connected in series and the combined OC voltage isn't beyond the Victron reg input voltage, when sun solar is a bit less, a panels voltage is usually still high, but current is less. With MPPT which you have, it can take advantage of lower current from panels and the higher additive voltage and be more productive in amps to battery. It is all a combination of amps and voltage, but my shed system which runs two at a max of around 70V sees, on average, 4.6 times the panel current as MPPT current to battery, sometimes a factor of 5. It works very well. My reg is 100v max input though. Better than panels in parallel through same reg.
FollowupID: 913779

Follow Up By: Member - shane r1 - Monday, Apr 12, 2021 at 08:07

Monday, Apr 12, 2021 at 08:07
G’day RMD
I’ll try them in series. the victron is a 100/50 .
Thanks again for the advice.
FollowupID: 913782

Reply By: StormCamper - Monday, Apr 12, 2021 at 03:18

Monday, Apr 12, 2021 at 03:18
A good rule of thumb with any solar in real world is to de rate the genuine max wattage to just 60% to take into account all the losses like heat (panels get very warm in summer) winter (suns Ray's dont strike direct earth but much more of an angle), imperfect leg positioning angle, faint clouds, mppt losses, etc etc.

Most cheap panels are usually false advertised like so many things were there are no rules. Trying to determine the actual wattage based on area is only a rough guess due to the fact you need the conversion efficiency (usually 17%) and the sellers of cheap stuff just like.

Long story short put up with the cheapest or buy quality brands from reputable sellers.
Mono vs poly glass it dont make that big of a diff with top brands, but usually the best mono is 19-21% efficient, any higher is lies.
And finally forget those semi flex panels they are notorious for dropping output over time. Glass and alloy all the way!

AnswerID: 635957

Follow Up By: RMD - Monday, Apr 12, 2021 at 09:02

Monday, Apr 12, 2021 at 09:02
I love those curved flexy panels, they claim they work well wrapped around something, NOW, where can I find a curved sun so the rays hit all the panel evenly at one time. Having them is a bit like custom made partial shading.
FollowupID: 913783

Reply By: qldcamper - Monday, Apr 12, 2021 at 07:13

Monday, Apr 12, 2021 at 07:13
A good start to knowing if you are getting a reasonable panel is to look at the ratings on the back of the panel.
Most of the cheapies these days have nothing related to power output, just voltages.
They are ordered this way so the sellers can say whatever they want.
Also neither the packaging or panel show any reference to the manufacturer.
This is because the manufacturer wants no responsibility for the claims made by the sellers.
AnswerID: 635959

Follow Up By: RMD - Monday, Apr 12, 2021 at 11:59

Monday, Apr 12, 2021 at 11:59
The problem with reading the panel is that you don't own it to see it before purchase. Sometimes the website claims/panel info, is different to that info on the panel. All found after purchase and delivery. If you are buying at half the price of a Hard Korr panel or wildly expensive panel, and it doesn't give the same result then it is probably ok value in reality. ie, half the price but delivers more than half the output. How long they last is another issue. Most panels develop close to or full voltage even with some light available but the current developed is the issue over the whole range of illumination. The characteristics of the electrons moving within the panel silicon wafer is the decider. That spec decides how it performs/converts but the info isn't available. We just take a chance.
FollowupID: 913788

Follow Up By: qldcamper - Monday, Apr 12, 2021 at 12:49

Monday, Apr 12, 2021 at 12:49
Ask the seller for a pic of the specs, the most likley answer is we cant because we are not at the warehouse.truth is they dont own the panel or warehouse for that matter, just advertising them then having them shipped straight to you after they pay for them, they never have them in their posession to do any testing.
If there isnt a pic of the specs on the panel included in the advertising then good chance the spec sheet either contradicts what the seller is saying or there is no reference to output capacity.
Either way steer clear of it.
FollowupID: 913791

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