They are getting better

And now they are claiming to be 160 watts!

Probably best to ask for a picture of the power output and characteristics of the panel to see what info is missing. Most of the cheapies don't have a complete inventory of specs so as to hide the obvious deficiencies. Claims of wattage are just that, claims. All the panels sold like this will have German certification and quality control stickers etc etc etc. All BS of course. The company gets these for a dirt cheap price because of the corners cut in production quality but sells at a seemingly bargain price. Same suburb different company this week. How much does a company register name cost. It must be cheap or they aren't even registered. All sold by CON merchant.

Yep there are no references to output or manufacturer at all on the 2 that I have.
The wiring was already starting to break strands inside the junction box from twisting when I got them so replaced it with 4mm twin sheath that has a flatter profile so the gland holds it well and use deutsch plugs to make configuring them easier.
Other than that they work well as 60 watt panels, have to see how they last when they spend some time in the sun.

I just purchased 2 x 200 watt Renogy panels. Tested both on the weekend with a Victron100/50 solar reg into a Renogy lithium portable setup. Both showed 10.5 amps going into battery. Total of 21Ah. Happy with that. About 11kg each. I made up some folding leags to make it easier to set angle towards the sun. Probably close to 25kg for the pair now.

Big fish,
Did you have them wired in series or parrallel, ive found series is where the victron makes a good difference especially if it is a long cable run from the panels to the reg.
Mine is a 75/15 and very impressed with it.

Parallel mate. Possibly could do the series but I,ve left them as Parallel as sometimes others in camp need extra solar and I therefore don't accidentally stuff some of their cheaparse PWM controllers...lol.

Bigfish
Although smaller output panels, I have a folding set which I added a toggle switch CLEARLY Labelled LOW and HIGH. Just one position or other gives, Amps x 2 and base panel voltage OR volts x 2 and single panel current. The latter, as QLD mentioned, is good for long runs and begins earlier and stops later with an MPPT.

Sounds interesting RMD. Any chance of a sketch showing how you did it?

About 70-80% for reputable panels rated at Standard Test Conditions., which is the usual rating.

Ozzie C
That is a piece of string question in a way. eg, I have two old 250w house panels in series running 68v and
12v system/batteries inverter and fridge at the end. Two days ago, around midday with batteries down a fair bit I noticed the Bluetooth monitor reading 477watts going into batteries, with clear direct sun access. So ok there. On the other hand I have other panels, one of so called 80w cheapie which side by side in same position, direct sun and both shorted to read max amps out, it could not do as well as a brand name 60 w panel beside it. With the cheap end, I work on no more than 55% of claim. If you get more, then that is a bonus and shows a bit better quality. All a gamble. Tattslotto anyone? Realistically our usage of panels rarely sees the panels in a perfect situation to try for the rated specs, and so not expecting too much and having sufficient panel albeit at lower outputs means what you end up with is often sufficient. IF it achieves more, then the reg will do it's job and charge sooner and shut off. My system at top does that in good sun but can be just enough when cloudy. That is what i calculate on.

Thanks but there is a rule of thumb that has been quoted on here before but I cannot find it - eg a good panel should be able to produce ?? watts per square m of panel in ideal conditions.

Does anyone know what this formula is?

Thanks

I use the formular that in perfect conditions there is 1100 watts of solar energy per square metre.
So work out the surface area of the panel, multiply it by 1100.

Then there is the variable of the cell efficiency which in cheap panels is anywhere fron 12 to 17 % .

So multiply the above figure by 0.17 will give you a closer to realistic figure. But that is in perfect conditions that basically never exist.

Ozzie.
You aren't asking for rule of thumb if wanting to know the watts per unit area. That is the actual, worked on by industry who make them, no thumbs involved. I didn't know the Watts /unit area had increased, it is all governed by the suns irradiation of earth surface which does vary. It used to be 1000w from previous calculations but the 12 to 17 % efficiency is realistic for cheap panel is a rule of thumb in gauging the harnessing of the energy. It is just some have bigger or smaller thumbs. So taking thumbs into account, QLD is right in stating the variation you may experience. Everyone gets the sun the same but the panel you hold , with your thumbs, might wildly vary according to quality.

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Ozzie, A quality panel in "ideal" conditions will produce about 150W per m2.
As conditions are never ideal, and neither are panels, you can expect to receive 100W per m2.
Anything more is a bonus. Less is a sorrow.

Thanks for those responses - I was just after the rule of thumb formula that I have seen used on this forum a number of times - looks like Allan's version is it - thanks.

I am just wanting to moderate the exaggerated claims made by ebay sellers as to what their panels produce so I do not pay too much eg $300 for a 300w panel that is really only 180w in ideal conditions.

I certainly appreciate that perfect conditions are very rare and I can measure it with the Watt meters I have but I would like to know what a panel of a given size should be able to produce rather than what the seller says.

.
Ozzie, I had a Jaycar 120W rated panel on the Troopy that measured just under 1m2. At best it was inputting 7.5 Amps via an MPPT regulator, so roughly 100W.

I am currently installing four 120W Enerdrive panels on the new rig so we'll see what that provides. They each are about 0.84 m2 which equates to the "150W per m2 rule" so I may get a total of 336W on a good day. 28 Amps. Hopefully it will keep the beer cold.
These are quality panels at $250 each so it will be interesting to see their performance.

Will be interesting Allan, hopfully they are quality cells, that is a high price so theoretically they should be good quality panels but cold beer is cold beer so worry about it if it gets warm.

Way the weather has been here since I got back from perth solar is pretty poor.

.
Well Qldcamper, Enerdrive has a good reputation, both as a company and products, which is why I selected them. So I have high expectations.
It will be a couple of months yet before the rig is ready to go so I'll make a fanfare if it lives up to my expectations. If not then you will maybe hear nothing from me! lol

Evening Everyone

One thing to remember, solar panel ratings are calculated on there output ( pre regulated voltage).

So to use Al's figures.. 120w panel gets about 100w @ 7 amps

120w panel ..output voltage 17- 18v @ 7 amps = 119 to 126 w

Regulated back to 13-14.4 v @ 7 amps = 91 to 100w

Figures will vary from panel to panel

These are some of the reasons, together with system loses why you will never get what the solar panel states.

Regards

TrevorDavid

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Sorry TrevorDavid, perhaps I should have been more explicit. The 7.5A I referred to was the output from the regulator inputting to the battery. So nominally 7.5A X 13.5v = 100W and I was happy with that result. But it would be unwise to see that performance as anything more than indicative.
My instrumentation measured only the current to-and-from the battery and the battery terminal voltage...... this was the only data that mattered to me.

Because the solar radiation falling upon a panel will vary due to latitude, the sun's inclination elevation of the sun, atmospheric clarity, temperature and panel orientation, the solar industry adopted an international standard of relating the outcome of a "standard" radiation upon a panel and its resulting electrical output. It is not mumbo-jumbo but an established industry standard which permits evaluation of comparative solar panels. It should not be expected that this nominal rating will be achieved in consumer use.
However, some manufacturers and retailers may express wattage ratings that would not be sustained by evaluation in accordance to the "standard". Buyer beware.

Solar panel performance is constantly improving but at the moment you can expect to achieve no more than 150W per m2 in ideal conditions and somewhat less for some panels. If total array output is important it may be prudent to invest in reputable panels at possibly higher prices.

It appears to me that TrevorDavid figures are ok with a PWM regulator which locks/holds the panel to not much above battery voltage and therefore missing out on MPP of the panel to provide near to full Panel ability. With an MPPT regulator of decent worth, the panel voltage should be held much higher than near 13v or so and then the additional voltage X amps ability of panel, WILL provide more amps into the battery for exactly the same panel. ie harvesting near max of what is available. That is what happens with my Three MPPT chargers everyday.

Hi Allan & RMD,

Yes Allan your post was explicit enough, as was yours RMD, I'm not disputing anything.

All I was saying is that the solar panels ( in this case a 120w ) is called/ rated at 120w at its output voltage not the regulated voltage.

As soon as we put a reg on that panel we have de-rated its output, Its still putting out what is says it can, 120w, but we regulated it back, and in Allan's example back to 100w. Remove that reg and once again there is 120w.

This is part of the reason why we don't get / use what the panels rated output is.

Regards

TrevorDavid

Those selling cheap panels will juggle the figures however they can to make them sound good. Those selling good quality panels dont need to do this.

But back to my original observation,
How efficient would the cells need to be to claim 160 watts from 660 by 770 panel? I think you would need some pretty big thumbs to prove that one, and more that 2 thumbs at that.

QLD
Around 31% efficiency. These cheap chinese have nailed it, don't you think?

QC

All panels are supposedly subject to Standard test conditions for the rated output.

Mmmmm are they??

Regards


TrevorDavid

Dam clever those chinese RMD.
Must be very expensive getting into their universities that teach that sort of technology, explains why so many of them slum it and attend Australian Uni's.

.
TrevorDavid,

My "120W rated" panel was not "putting out 120W" as you said. It was rated by the manufacturer to be able to produce 120W in ideal controlled conditions but does not reach that level in practice for the reasons I have enumerated.
My 120W panel was actually producing 100W and that was not reduced by the regulator because that was an MPPT type which modifies the voltage and current to suit the battery but maintains the wattage, (minus a small inefficiency amount).
If my regulator were a PWM (Pulse Width Modulated) type then there would have been significant losses between the panel's prospective output and what was actually delivered to the battery. It may have been more like 85 or 90W rather than the 100W actually delivered. A PWM regulator simply clips any voltage in excess of what the battery can accept and therefore does not deliver the full available wattage.

If my metering had been before the regulator it would have shown higher voltage and proportionally lower current but that still would equate to the same 100 Watts.

.
Careful QC, or you'll get yet another embargo slapped on us! lol

Allan,

You are 100% correct as per normal.

The panel is rated to the standard test conditions (STC) , this were the 120w comes from. That is all I'm saying, Will you get the 120w , no never, unless you can replicate the STC, not likely in the real world.

So back to my original post, the 120w rated output is from the STC which will be 17-18 volts depending on the panel. Rated is the key word, will you get it ...no.

Reg's have nothing to do with rated outputs.( as you know).

So once again the rated / stated output of the panel will be not what you get & even worse for second rate panels & less again through a reg. ( as you know once again)

Not every one will know that they will not get what the panel states, what I have been trying to explain is on of the main reasons.

Regards

TrevorDavid

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............"Not every one will know that they will not get what the panel states.......

Yes TD, I see your point. If you buy a domestic electrical appliance which is declared to be of a given kW rating then you expect, and are entitled, to be able to achieve that performance.
Many people would expect that if they purchased a solar panel rated at a specific value that they should receive that performance. They probably would appreciate that they would not get that output on a cloudy day, but that they would achieve it on a sunny day with the panel pointed at the sun.

Alas, of course they will not see that "rated" performance.

However I am unable to suggest an alternative representation of panel "size" that would be fair to the consumer. Anyone have a suggestion?

Here is an example of why I asked the question.

I have a set of folding panels that have an actual solar panel area of .72m. I bought them 10 years ago and they were advertised a 120w panels - using the 150w per sqm formula they come up as 112w - good enough for me.

This current ebay listing HERE are very similar to the ones I have and are the same size - these are advertised a 160w but using the formula they come up as the same as mine at 112w - so an example of advertisers embellishing the output of their panels.

I need to buy two large panels to fix to the roof of my camper and vehicle and I want to make sure I get the right size for my need rather than what the seller says they are.

Thanks for the discussion - was very worth while.

Maybe a good way to measure a panel's actual output power would be to put a watt meter like this one between the panel and a good quality MPPT regulator which is connected to batteries known to need a bulk charge - ie discharged to 50% or lower.

The regulator would be trying to get the max out of the panel and the watt meter would give a direct reading of the output of the panel in watts.

You'd have to wait for a good solar day, though. (Probably not worth the effort in NSW right now. It's been raining for a week with another week to come)

I did such a test a few years ago on a particularly good cold, clear day, but didn't record the results and now cannot recall the numbers, other than I was satisfied with my oldish glass panels and then new thin panels fixed directly to the roof of my van.

I was with a mate who's an engineer. We tried dousing the panels with water to cool them. There was a significant improvement - enough to prompt engineer mate to set up water cooling on his home rooftop solar.

Spotted what seemed to be nice 350w panel on ebay - applied the 150w per sqm rule and it comes out at only 130w - was a good price for a 130w panel but if it was actually 350w panel it would be an exceptional price.

.
Interesting stuff Frank which gives one an idea of the installed panels instantaneous performance but I am unclear of what practical purpose it provides. Because solar radiance varies so considerably any comparison with the retailer's declaration is futile. The only way to determine "a panel's actual output power" is by the Standard Test Conditions.

The big questions on most peoples' mind is "What panel do I buy" and "What do I get for my $".
The short answer is: Buy quality and you will get 100W per m2 on a good day..
The long answer follows................

Panels are usually marketed with a declaration of output expectancy in "Wattage". This is supposed to convey the panel performance based on "Standard Test Conditions" which are a cell temperature of 25C, sunlight irradiance of 1000W/m2, and an air mass index of 1.5. So, if a manufactured panel were to be subjected to those conditions it would produce a particular electrical wattage and that should be the labelling of the product. Whether that procedure is reliably carried out is moot and the wide variation in retail offerings of solar panel wattages compared to their area would suggest that it is not. It is possible that some retail specifications are more based on "What wattage do you reckon we can put on this?" And of course, the output achieved under those testing conditions is not what will be obtained in real-life.

An inexperienced person may consider that the marked wattage will be obtained on a "sunny day" but then be dismayed to find that is not the case. He would do better to evaluate his purchase with my nominated 100W/m2 and he will only get that with a quality panel on a clear day from October to February and between about 10am and 2pm, decreasing progressively outside those times.

So, how to select the brand and size of panels? Well, if a gambler, go for the cheapie with the highest wattage per size and cross the fingers. If you want some surety then do some sums to assess your electrical consumption using an aid such as member John's Electricity for Camping and purchase the required area of panels from a reputable supplier. This will of course cost more but will deliver the power you need and provide value for the investment. If you wish to be cautious in your outlay, select size conservatively and be prepared to add further if it is inadequate but purchase quality.

Performing accurate technical assessment of solar panel performance is beyond the ordinary punter but there are many websites that provide information. One that I consider worthwhile and understandable is "PV Education". The section 2.5 "Measurement of Solar Radiation" deals with the subject of how solar panels are evaluated for output performance.

TravorDavid said" a reg has nothing to do with rated panel output" Well no, but YES it does. No One uses a panel without a regulator and so it is the Regs ability with whatever is available in energy to create/convert the charge into battery. I like Frank's idea of using a wattmeter in line, But I have tried that and they have electronics in them to do fancy stuff, and found when I had mine in line the spurious signals in the wire confused the MPPT and it stopped MPPT'ing. Out of line all worked again. May not happen with other regs though but did with two regs of same make.

In China where many many panels are made, they have so much smog there is no way they could ever test via suns output and so must use an estimation of Smog Factor Effect of what the panel is producing and then claim proportionately higher figures in the tech specs. Yeah, that is it! What ever OC voltage you get and SC amps means?

Allan,

"Interesting stuff Frank which gives one an idea of the installed panels instantaneous performance but I am unclear of what practical purpose it provides. "

None!!

But it kept a couple of techies amused for a while. LOL

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Frank, are you also bored? lol

G'day RMD

A reg has zero to do with the rated output, but it does with the actual output.

But wait it gets better.

Standard test conditions evaluate solar panels in a solar simulator called a flash tester , they are exposed to artificial sunlight, with the figures supplied by Allan a couple of post's back.

China's smog doesn't come into it.

Yes STC are misleading in the real world.

Regards

TrevorDavid

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OzzieCruiser,

From an offered 350W to a probable 130W is a significant difference at any price.
If the supplier is telling porkies about the specifications then what else is unreliable?
Are they poor performing cells with inferior temperature coefficient?
Is the glass of poor quality and liable to crack?
What else might be inadequate?

With commercial products, high price does not guarantee high quality, but you can be sure that low price is a sure indication of low quality.

.
TrevorDavid,

RMD is introducing a red herring alluding to China's smog.
Manufacturer's will be applying laboratory Standard Test Conditions, or at least they should be.
CSIRO have a NATA certified facility that employs both indoor "flash testing" and outdoor solar radiated assessment. See here.

Consumers find it difficult to comprehend the application of Standard Test Conditions to the product they are considering but that does not mean that it is misleading. But then, how do they evaluate how many horsepower (kW) do they need in their 4WD vehicle engine etc? STC is the only way to provide a performance expression that is universally applicable for evaluating solar panels. What IS misleading is the untruthful expressions made by manufacturers and retailers about panel outputs. But their untruthful behaviour is sustained by purchasers looking for a bargain.

Yes Allan yes

You really are bored. LOL

You did hit the nail on the head though, purchase your panel from a reputable dealer & you should get something like your actually after. STC correctly included , quality cells etc etc .

Regards

TrevorDavid

Light heartedly, I thought the smog has to be the reason, Ha ha, for low output and higher claims, is there any other possibility? Perfect marketing, easy purchase, free delivery, what more could you want. It works! I simply want some of that artificial sun to keep the panels churning during the night time, not sure the chooks will be happy though.

Allan,

"Frank, are you also bored? lol"

You betcha. It's pi55ing down here, raindrops like golf balls, street flooded, front yard flooded, back yard flooded, but house dry thank heavens (the appropriate authority, LOL). Cannot go outside unless to wash the clothes you're wearing, little to do but acknowledge Happy Hour is here and respond accordingly!!

Cheers

.
I've been watching the news about your weather Frank. Not nice. Raining here on the Sunshine Coast but gently.
Alright for you with Happy Hour. You're one hour ahead of us!

I do hope this is the end of this Thread. But it has been entertaining and filled in time.