Solar Panels What to Know
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Looking at buying Solar Panels?
Here is what you need to know:
Watts = Amps X Volts you need to know from the Spec's the following:
Voltage at Maximum Power Point Vmp (V): 18.6
Current at Maximum Power Point Imp (A): 10.8
200 Watts = 18.6 x 10.8
Open Circuit Voltage or Voc is how many volts the solar panel generates with no load on it. If you just measure with a voltmeter across the plus and minus leads, you will read Voc.
25°C is the standard temperature in Celsius at which the Solar Panels Spec's are be rated. It should look like this in the specifications:
Power Specification: STC:AM1.5,1000W/m2, 25°C
I found a supplier on Ebay which showed STC @ 2° which means their whole spec's are wrong to compare apples to apples
You have to also know your lowest Temperature your going to be Camping, Solar Panels work better at cooler temperatures to a point they generate the more Amps & Volt than the rating quoted at the STC of 25°C
These are the basic Spec's you'll need to compare Solar Panels, some will quote volts and amps with no reference to STC so it all means nothing.
This is what a good Seller will show for specifications:
Maximum Power Pmax:200W
Voltage at Maximum Power Point Vmp (V): 18.6
Current at Maximum Power Point Imp (A): 10.8
Open Circuit Voltage Voc (V):22.68
Short Circuit Current Isc (A):11.4
Power Specification: STC:AM1.5,1000W/m2, 25°C
Solar cell:Monocrystalline
Cell Grade: Grade A
Cells Efficiency (%): 17%
Application Class:Class A
Maximum System Voltage:1000VDC
Maximum Series Fuse Rating:15A
Fire Rating: Class C
Frame: Anodized Aluminium Alloy
Glass: 3.2mm Low Iron Tempered glass
IP Rating: IP65
Connectors: MC4
Operating Module Temperature: -45°C to +90°C
Module Dimension (mm):1030*680*30mm
Ideally anodising should be a minimum of 20um. 15um is ok. 10um is a bit poor. 25um would be really nice!
The 25C temperature specification is the panel temperature, not the ambient temperature. At 25C ambient, the panel might be at 50C or higher. Proper specifications will also include the degradation rate in performance at higher temperatures.
The "1,000W/m2" is the standard light intensity. In real life it will typically be less. A specification at 800 is useful, but rarely provided.
"Honestly" specified panels will typically produce between 150W (typical good quality) and 240W (top of the range and expensive panels from known top of the range manufacturers using the best cells available) per square metre at the standard conditions. If they claim greater than 200W it is probably false claim. Many are not true to label.
The example panel is 1030 x 680mm = 0.7M2. I would expect its real performance (at standard test conditions) to be between 100 and 140W. I doubt that there is a commercial panel anywhere in the world this size that will produce 200W.
There will be further losses in the cables and the controller.
The appropriate Vmp for any application will depend on the way the panels are wired and the type of controller used. Using panels with inappropriate Vmp will reduce actual yield.
Cheers,
Peter
-- Edited by Peter_n_Margaret on Friday 1st of May 2020 03:02:06 PM
Hi
Peter said "The appropriate Vmp for any application will depend on the way the panels are wired and the type of controller used. Using panels with inappropriate Vmp will reduce actual yield." VERY TRUE !
I would say that if you are using a PWM regulator(normal type) for 12V charging then you need to be careful you get the 36 cell panels. These should give Vmp around 18Volts or a bit more.If they are 30 cell they will be ~15V and may not work well at all, if 32cell at ~16V marginal except in good sun. Ignore the wattage shown, it is the current they produce that is important at a necessary voltage to charge a battery even when the sun is not so strong. You can just count the cells if you look carefully.
These lower count panels can be used in series pairs and using a MPPT regulator for very good results. Most second hand roof panels have lower cell counts because they are just made that way as they are used in series for much higher voltages. The cells are in rows so they make different configurations of 4x9 and 5x6 and 4x8 etc to make various shape panels.
Jaahn
-- Edited by Jaahn on Friday 1st of May 2020 03:36:20 PM
-- Edited by Jaahn on Friday 1st of May 2020 05:47:13 PM
I take it your referring to the Frame size: Anodized Aluminium Alloy?
The aluminium frame, usually 6060 alloy, the thicker the anodising the better. A lot of the cheap stuff would barely have 5um. It looks thin, doesn't have a depth to it so to speak.
Yes I know Yall,
The 25° Celsius is referring STC is an industry-wide standard to indicate the performance of PV modules and specifies a cell temperature of 25°C and an irradiance of 1000 W/m2 with an air mass 1.5 (AM1.5) spectrum. These correspond to the irradiance and spectrum of sunlight incident on a clear day upon a sun-facing 37°-tilted surface with the sun at an angle of 41.81° above the horizon.
However I am trying not confuse everyone looking at Solar Panel purchasing or updating with technical jargon just trying to help them, with details which will assist them to make an informed decision.
I could write a thesis on all the variables and merits Poly vs Mono solar panels, of MTTP vs PWM Solar Controllers there overall performance based upon the solar panels positioning and adding in Wire sizing AWG (American Wire Gauge) sizing based upon the distance from the Solar Panel to the Solar Controller. The merits of Parallel vs Series connection of Panels and amperage differences and wire required depending upon the Volts.
But I didn't I just put forward a simple way in which a novice looking at Solar Panel might be able to compare Apples to Apples, I didn't want to go into Solar Controllers or sizing them based upon where your permanently fitting them to a roof of your RV or ground based which you change the angle hourly to face the Sun and the above paragraph. The ambient temperature of the coldest place which they will visit and the effects that this will have on their solar power production.
Just a simple means of comparison Brand A vs Brand B
Hi Yall,
The PV generator exhibits a nonlinear v-i characteristic, and its maximum power (MP) point varies with the solar insolation and temperature. At a particular solar insolation, there is a unique operating point of the PV generator at which its power output is maximum. (Vmp)
So using panels with inappropriate Vmp will reduce actual yield
This gives a module area of 1.030 x 0.68 m2 = 0.7 m2 ( the area of actual cells is probably less)
If the solar irradiance is as specified 1000W/m2 then the panel receives 1000 x 0.7 = 700 W
If the panel efficiency is 17% as specified then the max panel output would be 0.17x 700= 119W.
However the panel is rated as 200W max implying an efficiency of 200/700 = 28%.
Whats wrong ??
Ken
My 20 watt panels.
If one packs all the actual solar cells together (Photoshop) they take up 72.7% of the panel. So 155 watts/m2. The larger the panel, the border will be a smaller percentage of the panel area.
But you do need a frame & space between cells.
Ken,
Why thank you for your detailed analysis of the Solar Panel Specifications, what's wrong!
I put up a KIS solution for people who maybe be looking to purchase Solar Panels, but for some weird reason people have it in themselves to tear it down and confuse people with jargon.
Really if someone asked how can I compare Solar Panels, you'd leap into telling them Modulel sizing and cell irradiance. But what if they had 5 busbars, 4 busbars or 3 busbar, what if the technology allowed for overlapping the cells a new technology! your unaware off.
Incidentally the spec's are a Chinese Manufacturer of thin film technology developed through their German Subsidiary, so here's a quick blurt on thin film Technology not from their site.
Thin-film cells are laminated to make the later module more robust and resistant against weather or other environmental impacts. They can be produced either in single-junction or multi-junction configurations.
While the single-junction configurations involve only one cell and only cover one part of the solar spectrum, the multi-junction configurations refer to combined sets of single thin-film cells.
These use different parts of the spectrum from their respective angle to jointly convert the respective portions into electricity, thus using a much larger range of the input of sunrays.
Seriously instead of picking on things to pull down, why not come up with a better way in which a novice could compare Solar Panels and what to look out for.
I'm reminded of the following thread . . .
https://thegreynomads.activeboard.com/t66202769/stay-away-from-outbax-camping-solar-panels/
. . . where almost every spec sheet I looked at was flawed in some way. I notice that you pledged to "post what Spec's you need to know to make a balanced judgement on buying Solar Panels in another post". However, it appears that you yourself have found yet another flawed spec sheet.
Nevertheless, thank you for the info in this thread. I appreciate your attempt to clarify the mess, but it seems that the industry just can't get it right.
Hi Ram Man
I could say welcome to the forum but perhaps you do not feel welcome and seemed to be a bit peeved.
It is a public forum and people can post their thoughts within the rules. I guess I was surprised that for a first post you came on and chose to post about something technical that I thought might have missed some of the important things to look out for. So I added what I personally have found out and commented on what Peter had said which I also though should be said. Some of the other posts may have been peripheral IMHO.
I regularly post on this forum and have always attempted to help people and comment when I see it is appropriate and share my experience on solar. Indeed several members have chosen to PM me for a discussion on their ideas or problems and thanked me for my help. I usually tell people to look on this part of the forum and do some reading and make an assesment of the worth of the postings. I will still continue to do that including your post.
I have also recommended that people buy a good book by Colyn Rivers on Solar out of the several he has written. But most people seem to think that investing ~$40 is a waste of money even though they may spend a thousand (or more if using lithium) on things recommended on a forum and posted by people they do not know, or even by some commercially inclined business who they do not know either ?? Strange ! IMHO
Jaahn
-- Edited by Jaahn on Saturday 2nd of May 2020 07:12:28 PM
Hi Dorian,
Well maybe you could write up something on how to compare Solar Panels
, you recommend a book the only question is the book relevant when was it write. As we all know technology moves at quick pace these days.
I found that when looking at Solar Panels and I looked at over 40 various different specs and 4 different experts and I settled on 2 for their knowledge.
The frustration for people is with little knowledge is how to attain a greater understanding of a subject, people talking about the module sizes and such where technology has moved past what some may have know to be true is now outdated.
Yes, I find it annoying that people like to critic but fail in offering a alternative or positive view and even you say I have found a flawed spec yet offer no alternative
of what Specifications someone should look for in Solar Panels.
If someone actual wrote a as I did a simple means of what one should look for in Solar Panels and how to compare them, well then that would be a positive reply.
Hi Ram Man,
I am sorry if I upset you by pointing out an inconsistency in the panel specifications you posted, which should be questioned.
Perhaps a better example would be the one shown below from a local supplier : Lowenergydevelopments.
As you can see the surface area of the module is 1.27 m2 (1.58 x 0.808m). The actual cell area would be somewhat less.
Using the Standard Test Conditions Solar Irradiance of 1000w/m2 as specified then the incident solar power on the surface area of the panel is 1270 W
Then using the minimum specified cell efficiency of 16.8%, the panel output would be 213W. but actually somewhat less because cell area is less than panel surface area.
In this case the calculated power of 213W is consistent with the published specifications.
This was not the case with the specifications you originally posted, which calculated to aprox 120W (not 200W) at the specified and realistic efficiency of 17%.
Certainly cell efficiencies are improving, but irrelevant in this case as the efficiency was quoted as 17%
I have no disagreement with the general thrust and motive for your original post
The key to making good decisions is an understanding of specifications, and how to interpret them - not blind faith.
Two mottos should be :
Question Everything together with Dont believe everything you are told and especially what you tell yourself
ModelPANEL200W-12V
Ken
-- Edited by kgarnett on Saturday 2nd of May 2020 11:16:25 PM
Hi
Just for the record I do not believe that solar panel technology suitable for a van rooftop has changed much over the 20 odd years i have been interested. It is fashionable to go to new sites on the net and read a lot of sales BS and think you know everything, but actually the tried technology will work well if correctly selected, is robust and long lasting and is available for a good price if you shop carefully. Indeed if you want bargains then second hand panels that are being replaced by "better" panels are available everywhere. But I guess they are not good enough !! Please tell me what new technology is available that actually works better on a van roof in Australia.
The same applies to controllers. The basics have not changed in 20 years(or longer). PWM units have got much cheaper but not all do as they promise. MPPT has not changed in operation, certainly plenty more cheap fakes. Better brands just work the same. There is just the availability of Bluetooth/WiFi for the yuppies to show others what the solar is doing on their iphones. Who needs to know, if you have a system that works well, then it just works every day the sun comes up. I would not pay more for that technology, it might help for setup but you should only need to do that once ! However I guess if you need to look at it every hour or every day then go for it. Tell me what new technology is available for controllers that has improved charging.
Jaahn
-- Edited by Jaahn on Sunday 3rd of May 2020 12:25:59 AM
You have me confused with someone else.
I often profess my ignorance of this subject and I have many more questions than answers. I certainly don't have any relevant experience other than my residential, rooftop, grid connected solar system. Currently I'm just a spectator, not a participant. I enjoy the threads for their technical information (especially the teardowns), even if they may become a little too "passionate" at times.
BTW, just in case it wasn't clear, I am not blaming you for picking a flawed spec sheet. That was just bad luck. I confess that I didn't see the inconsistency until it was pointed out by others.
-- Edited by dorian on Sunday 3rd of May 2020 05:52:16 AM
Hi Ken,
Thanks for that extra information, I am certain it will help people find the correct Specifications when looking for Solar Panels.
A positive comment and helpful to everyone is just what I was hoping for, thank you again Ken.
12V mono solar panels with a cell efficiency of around 17- 20% should be roughly 0.0064m2 per watt. If there is a substantial variance from that, you are being misled. With that in mind, heres roughly the sizes you should be looking at:
80W panel = 0.51m2
100W panel = 0.64m2
120W panel = 0.77m2
150W panel = 0.96m2
160W panel = 1.02m2
200W panel = 1.28m2
250W panel = 1.59m2
If you want to know that the panel you are looking at is actually the wattage advertised, do the maths above, or jump on a reputable sellers website (like Redarc, Projecta, Bosch or Australian Direct) and compare sizes.
Just image you are novice how would you better explain it, to someone. If they asked you for advice on a say 200W Panel.
What would you tell them to look for?
No point having a 200 watt panel on the roof & it has a small shadow until 10am. It will be brought to its knees.
Better with a smaller panel with absolutely no shadows.
I would measure up the roof & calculate clearance for shadows. Only then work out what multiple of panels will fit on the roof.
Cheers,
Peter
Jahhn. One of the reasons theres a lot of second hand solar panels (house type) is that solar installers refuse to use the older panels for an upgrade in size, even if they are still quite good. Its allso very hard to even find an installer that will fit a second hand setup. Generaly it all comes down to money. Prices for good second hand panels is $50 each or mutch less or even free.
-- Edited by DeBe on Tuesday 30th of June 2020 07:19:56 PM
Hi DeBe
Bargains ar'nt they. I have quite a few in the yard.
The installers give lots of reasons why they cannot use them, mostly BS. Money yes ! But it is true that the old ones are not on the approved list for grid connect. But no problem for battery connect !!
If you use a proper MPPT controller you can use the smaller panels two in series and then parallel strings or the higher voltage larger ones just in parallel strings and both ways give great results for minimal cost. And you can get significant charge in low sun or overcast situations. The quality Aussie made old panels put out almost their sticker current too under test.
There are crap cheap chinese panels on roofs that are failing so be careful and inspect and test them. I looked at a set for a friend that only one out of 10 was working properly?? But you could see the corrosion, bad connections, faulty cells and defects by eye.
Just as a note the original supplier of those was out of business by then so the 10 year warranty was useless.
Jaahn
-- Edited by Jaahn on Tuesday 30th of June 2020 09:21:19 PM
Even though my setup is tiny, 6 x 20 watt panels. The panels were a small percentage of the overall cost. I just can't see the point fluffing around to save a few dollars & end up with a third rate system.
Do it right, the cost is amortised over many years & it will more than likely be cheaper in the long run.
Hi
You are entitled to your opinion but I am happy with mine. I do not consider the systems I use(d) are third rate or second rate but first rate and work as good as they should.
I guess it is just a matter of having confidence in my ability to get quality gear at a good price. 
If you cannot do that then buy new and from expensive quality places. I choose to spend my money other ways. Horses for courses.
I fail to see the logic of this statement "it will more than likely be cheaper in the long run" but please do not justify it. Similar to the "you get what you pay for" statement i see used on here occasionally. My problem is I guess I was born poor and tried to stay that way.
Jaahn
I'll put it another way. I bought a pair of 36db earmuffs. Cost a fortune but it's cheaper in the long run saving my hearing.