Solar PV Module efficiency rating

westbranch
westbranch Solar Expert Posts: 5,183 ✭✭✭✭
I am looking at a 'family' of Mono panels that range:130W, 140W, 145W & 150W per panel.

The 130W has a module efficiency of 13.71%, 140W = 14.12%, 145W = 14.62% and the 150W efficiency of 15.13%.
External physical size is the same, and all panels have the same cell size so the panels rating is generated/produced by the lowest producing cell or cells, which probably can not be determined until the module is constructed and tested. Price per watt is the same, regardless of efficiency of the panel.
Tolerance is +- 3%,

Is there any margin going for the best producing panels vs the lowest or pick a midpoint?
 
KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar PV Module efficiency rating

    you know this is an old sore spot with me from way back because if you actually figured things out, there's too much overlap. when one has a pv that would output say 2% more at 140w that this is 140w x 1.02 = 142.8w. now the 145w pv at a -2%, which is well within tolerance would be 145w x .98 = 142.1w. so what are they going to charge you for when the pv is 2% over at 140w? you guessed it, they will charge you for a 145w pv with a -2% tolerance for more $. when they put increments of watts that close together it makes the +/-% tolerances they list into a joke. what they should've done was to have a +/-0% tolerance so there's no overlap where they can charge you more for a lesser pv. this makes it greater than or equal to the wattage they put to a pv.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Solar PV Module efficiency rating

    Thanks Niel, following that point, it is better to stick to the 10W increments, 130,140,150W rather than the 145 which is sort of splitting hairs....
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • jagec
    jagec Solar Expert Posts: 157 ✭✭
    Re: Solar PV Module efficiency rating
    niel wrote: »
    you know this is an old sore spot with me from way back because if you actually figured things out, there's too much overlap. when one has a pv that would output say 2% more at 140w that this is 140w x 1.02 = 142.8w. now the 145w pv at a -2%, which is well within tolerance would be 145w x .98 = 142.1w. so what are they going to charge you for when the pv is 2% over at 140w? you guessed it, they will charge you for a 145w pv with a -2% tolerance for more $. when they put increments of watts that close together it makes the +/-% tolerances they list into a joke. what they should've done was to have a +/-0% tolerance so there's no overlap where they can charge you more for a lesser pv. this makes it greater than or equal to the wattage they put to a pv.

    The math certainly works out, but I have my doubts that a large-volume manufacturer would actually save money if they were to individually test each panel to the accuracy level that it would take to ensure that you're always on the negative side of your tolerances. In other words, if you're manufacturing panels that have a +/- 2% variation in output, and you deliberately inflate your nameplate ratings by 2%, half of your panels won't perform as expected, and your 2% profit would go right out the window when your angriest customers start demanding refunds.

    If you try to get past this by individually measuring panels within tighter tolerances (0.5%, say) and binning them so as to ensure that they are within your "rated" tolerances (say, -1.5% of rating, +/- 0.5%), I would argue that the marketing advantage from selling them at actual output within tighter tolerances would be greater than the slight revenue boost from inflating your values.

    Just take a look at Canadian Solar's "plus only" 5% tolerances...clearly their tolerances are the same as everyone else's (+/- 2-3%), but they chose to deliberately undervalue their nameplate ratings so that customers can feel happy about "getting something for nothing".
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar PV Module efficiency rating

    what they do is pretest individual cells for an output range and then assemble them into pvs. the dimensions are almost always the same for all of the pvs no matter the wattage rating, but in putting cells that output in a certain area they can get higher or lower w capacity. with so many cells that can be off up or down this can create differences far greater than even what is already speced percentage wise. they pretty much guess the modules will be in a desired wattage area when assembling them and they do measure each for output and sell by that result. it is not that they were going for a 145w pv and wound up with a 148w pv or anything +/-% of a design wattage. if a pv winds up in the next higher bracket (tolerance range) they sell it as that next higher wattage.
  • SolaRevolution
    SolaRevolution Solar Expert Posts: 410 ✭✭
    Re: Solar PV Module efficiency rating
    westbranch wrote: »
    I am looking at a 'family' of Mono panels that range:130W, 140W, 145W & 150W per panel.

    The 130W has a module efficiency of 13.71%, 140W = 14.12%, 145W = 14.62% and the 150W efficiency of 15.13%.
    External physical size is the same, and all panels have the same cell size so the panels rating is generated/produced by the lowest producing cell or cells, which probably can not be determined until the module is constructed and tested. Price per watt is the same, regardless of efficiency of the panel.
    Tolerance is +- 3%,

    Is there any margin going for the best producing panels vs the lowest or pick a midpoint?

    As an example, if you are adding 12 modules to an existing off-grid system it may cost $ 250.00/ module for labor and mounting equipment.
    So, $ 3000 (12 x $250) plus the cost of the panels at $1/Watt would be:
    $ 4560 for (12) 130s, or $ 2.92/ watt. (12 x 130 = 1560 watts)
    $ 4800 for (12) 150s, or $ 2.67/watt. (12 x 150 = 1800 watts)
    To go with the higher rated panels you would pay about 9% more for 15% more Wattage. Your costs may vary greatly if you DIY, but in most cases you will get a better return for going with the more efficient modules.


    As far as the different ratings, I have come up with this explanation after conversations with many people in the industry over the last 12 years. This should be taken with all of the authority of an urban legend:

    Silicon cells are not identical even if they are of the of the same manufacturing batch or even if they are cut from the same ingot.
    Manufactures have used different meathods of insuring that each PV module of a particular model (part number) will have the same STC rating. Getting all of a particular line to have the "exact same" measured performance would require a degree of attention which is impractical. Therefore they have always had listed rating tolerance. Tolerance ratings have been stated as figures like " +/- 10%" or "<-5%/<+10%". Many are now listed as "= or <+5%".

    Originally manufacturers offered fewer models and they had wider tolerance ratings. As performance reviews were published, the brands who's modules performed better as compared to their STC (or PTC) ratings got the best reviews. (Rightly so.) Manufactures started sorting their modules more carefully and ended up with different grades within a particular batch. They could offer many ratings of modules which were visually identical and also some which didn't make the grade labled "B" (blemished).

    A listed tolerance of +/- 3% would allow them to list a range of modules in increments of 5 watts. (ie. 130W, 135w,140W, 145W & 150W) The modules you listed did not include 135s. It could be that all of the 135s were batched with ones as low as 130s. They may be the best $/watt statistically.:roll:

    The coveted module efficiency ratings are based on insolation of 1000w/sq meter. So a 150 which was one sq meter would have an efficiency rating of 15% while a 130 in the same size frame would be 13% efficient.

    I have seen many people fall into the trap of going for the cheapest cost per watt only to end up with a more expensive per/watt installation. A couple of years ago some particular thin film 60 watt modules were liquidated for $ .50/watt. People were clamboring for them. They had a very good tempurature coefficient and were very efficient if you looked at STC vs PTC ratings but their area efficiency was around 1/3rd of crystaline modules. I did a case study and found that if you had to pay for labor it could be about the same cost if you spent $2/watt on more efficient panels and the array would require about 1/3rd of the area. I had several friends and clients who were extatic about the great bargain until I threw the wet blanket of reality on them. There were actually a few installations where the more surface area was desireable to provide more cover for a roof in a hot climate or to have a larger array for PR value for a commercial project or for water pumping where there were only a few panels anyway.

    Alex Aragon
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Solar PV Module efficiency rating

    Hi wb,

    You must have reasons for looking at modules in this power range ... perhaps it is because you aready have some, perhaps it could be snow load, etc. However, as you know, larger PVs are considerably lower cost, unelss things have changed in the past month or so. And, as alluded to previously, the installation costs will be considerably higher of modules with these ratings vs those in the 230-250 watt STC ratings.

    Am certain that the manufacturer does 100% flash test at the end of final assembly, and DO bin them based on output. The individual cells have been tested as well, but each module with its collection of cells, plus the individual variations in assembly, and things like variations in the transmissivity of glass etc will affect the output. A production line flash test takes almost no additional time or labor, and should be well worth the effort (IMHO). Good luck with your project, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Solar PV Module efficiency rating

    On my batch of Evergreens, they came with a rating sheet for each individual panel tied to its serial number. These were plus 5% minus 0 percent rating guarantees. so most of the panels were plus 2.5%. Of course in the real world, I expect there are so many other variables, it would be hard to catch. I am not sure on Evergreens but my older Sharps polycrystaline panels came with a notice that they would initially exceed the rated output and the output would degrade via a log curve (rapid at first then tapering down to minimal impact over the life of the panels.

    I got some B specs mixed in the Evergreen lot and expect they many of the cells in each panel are higher than normal output dragged down by some of the blem cells.
  • SolaRevolution
    SolaRevolution Solar Expert Posts: 410 ✭✭
    Re: Solar PV Module efficiency rating
    Vic wrote: »
    Hi wb,

    You must have reasons for looking at modules in this power range ... perhaps it is because you aready have some, perhaps it could be snow load, etc. However, as you know, larger PVs are considerably lower cost, unelss things have changed in the past month or so. And, as alluded to previously, the installation costs will be considerably higher of modules with these ratings vs those in the 230-250 watt STC ratings.

    There are some other considerations for economy of scale. Take for example the XW MPPT80-600 CC. Max input rating of +/- 4000 watts.

    If you are trying to get the maximum allowable PV array voltage to allow for the smallest size wire run, you may only be able to use one string of (14) 37ocv, 230 watt modules (3220 watts).

    In order to fully load your expensive high voltage MPPT CC, you may need to use two strings of 12, 44ocv, (24) 165 watt modules (3960 watts)

    Or better yet, one string of (14) 37ocv, 285 watt modules (if you can get them.) 3990 watts.

    Alex
  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    Re: Solar PV Module efficiency rating
    These were plus 5% minus 0 percent rating guarantees. so most of the panels were plus 2.5%. Of course in the real world, I expect there are so many other variables, it would be hard to catch.

    According to my charge controller (which logs the daily power production), my 2 month old array of Evergreen ES-E-200s has so far been putting out about 4% more than its combined STC rating nearly every morning when there's full sun. This is with ambient temperatures in the 60s or 70s (so around 20 C). This output lasts only a few minutes before they warm up, but it's consistent with that range.
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Solar PV Module efficiency rating

    thanks for the feedback Guys. A few clarifying statements on my part may help here
    - the final setup is planned for 2 - 12 panel arrays, 6 x 4 to 2 MN Classic 150 CC's
    - I am looking to match some existing panels
    - Snow load is an issue as it can dump 24 " of wet heavy snow in 24 hrs
    - I am in a HIGH GUSTY wind site so am looking to keep sail area as small as possible
    - I will , due to shadows etc, need multiple array locations around the house
    - I can manage install the smaller panels single handedly
    - with the smaller Wattage panels I can go as high as 5/array with a Classic 150 If I needed to
    - right now the 130's get me to a ~ -50 Whrs out of 6000 Whrs use per day in December, so in Summer I will be overloaded and then the overcharging issue comes up.
    - nothing new bought, so if needed I WILL go for the 150's, since , As SR pointed out, they are the best bang/$

    ADD: I would like to keep the MN Cl 150 down in the 80 - 90% max range if possible, less heat to worry about, stc

    HTH
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada