Mono Perc vs Mono in high temperature areas

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drraptor
drraptor Solar Expert Posts: 218 ✭✭
in Solar Beginners Corner #1
I have been out of touch with solar industry for last 5 years. During this time New Half cell perc Mono panels have been introduced in the market. I want to know what advantages these Half cell perc mono panels have and are there any benefits in high temperature areas like mine. I live in Lahore, Pakistan?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    A couple of articles (probably written based on Marketing Literature):


    I understand the smaller cells being more rugged than a single large cell... Mono crystalline have always been a bit more efficient vs poly crystalline. And running a higher voltage panel means lower current, so smaller wires/less P=I^2*R heating/voltage drop losses.

    In terms of efficiency... You are looking at 10%+/- better efficiency with Mono/PERC panels. Not a bad thing--But if you have enough roof/rack mounting space--You would not need to pay extra for a "smaller array" vs adding a couple more panels..

    One of the "gotchas" in solar panels has always been matching the Vmp-array (and Voc-array-cold max voltage) to your charge controllers...

    GT Inverters are typically "high" voltage designs--Vmp~400 Volts or higher is pretty standard.

    However, with solar--You have the limits of PWM controllers (matching Vmp-array to battery voltage--Such as Vmp~18 volts for the array to a 12 volt battery bank; Vmp~36 volts for 24 volt, and Vmp~72 volts for a 48 volt batteyr bank).

    And with typically MPPT solar charge controllers, they tend to run in the Voc-array max input voltage of 100-150 VDC.

     Which means getting Vmp-60 or Vmp~72 volts starts limiting your choices... For example, Vmp-array for a 48 volt battery bank should be (at a minimum of 1.3 x Vbatt or) Vbatt~60 volts charging * 1.3 = ~78+ volts... But for cold climates, the Voc~140 VDC max controller input voltage makes Vmp-std (standard temperature range) to be roughly 100-110 volts or so...

    That means that Vpm~60-70 VDC "high voltage" panels may not work for you on a typical MPPT controller... 60-70 Volts is "too low" for charging a 48 volt battery bank... 2x those panels in series can exceed Voc-cold maximum voltage or ~140-150 Volts on cold days.

    There are higher input voltage MPPT controllers these days--And more are being designed/sold lately... But watch the prices, they are usually not "cheap" controllers.

    So--Look at Vmp and Voc of the panels, look at your minimum temperature for your area, and check that the minimum temperature does not cause Voc-cold array to exceed the controller's input.

    Some controller manufacturers do have a website (or downloaded program) to help you plan the array configuration vs controller limits. Midnite is one:


    As always, do your paper design(s) first--And make sure that everything plays together well.... Loads=>Battery bank voltage and AH size; Battery Bank+Loads => Solar array size. And your charge controller (PWM or MPPT) defines the limits on your array configuration.

    Solar panels are relatively cheap these days... And manufacturers (and solar retailers) are going into and out of solar business all the time... The Warranties may not be something you can collect on 10 years in the future. And the "typical" panels of today may be quite different in Vmp/Voc/Imp/Isc in the future too (have a 175 Watt Vmp~30 panel fail today, may be very difficult (and expensive) to find a near match that will replace the failed panel in an existing array (as an example).

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #3
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    Compare the panel you can get with the best from Panasonic, LG and SunPower. They will have temperature data. They often have the most watts per square foot also.

     SunPower has always been the best at working really well in high temperatures and getting the most watts per square foot for my clients, and me ;)

    Some searching and you will find out why. The other 2 I listed have caught up and they all have 25 year product and power warranties.
    Not too many panels offer that kind or product warranty. You need the exact model and the same companies can have models that are not that level of quality. They often are called Tier 1. They are much more plentiful now and below is a list. This listing does not mean they will perform as well as a panel that has a good temp curve for high temperature conditions. It just means that they are built to take the conditions, stay in warranty, and an investor would require this for commercial projects.

    https://regenpower.com/articles/list-of-tier-1-solar-panels-q2-2020/


    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,044 ✭✭✭✭✭
    #4
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    My understanding is that the72 cell equivalent cell (144 cell panels), for example. consist of 2 banks of cells. This configuration, in portrait orientation, become more shade tolerant by acting more like two separate panels when a portion becomes shaded.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • drraptor
    drraptor Solar Expert Posts: 218 ✭✭
    #5
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    I am planning on installing a Grid tied set up with 7KW +/- 500 panels with Net metering.  the following link has all the information by my local grid company.  regarding the net-metering. which inverter I should use and which panels are  recommended for such a setup http://www.lesco.gov.pk/Registration/NetMetering.asp
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    edited December 2020 #6
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    Primary new items in PV tech is reducing reflection from cell surface allowing more energy absorption and use of N doped subtrates which have a little better efficiency.

    There are two reasons for making panels with half cells.  A full standard sized 156x156 mm cell produces 8 to 9 amps of full sun illumination current.  Each cell has max power point of about 0.5v so each standard sized full cell produces about 4-4.5 watts.  With 4.5 watts per cell and minimum number of series cells to make a given panel voltage the power level for a panel is dictated.  This may be too high for lower wattage panels so cells are cut in half to reduce the panel power for a given panel voltage. 

    Other reason to cut cells in half is to improve manufacturing yields. Defects usually occur at spot points so a manufacturer can cut off half the cell to eliminate the side with more defects and get better matching on cells for a given panel.  Dominant defect is leakage spots which can be graded for quality groupings.  Well matched cells with lower net leakage current loss gives better low light performance.  If a panel has half cells in parallel then it is clear the halfing is for manufacturing yield improvement.

    You have to be careful on how some manufacturer specs their panels as they can count their half cell count for their stated cell count.  There are '144 cell' panels that have 72 series x 2 parallel half cells so their Vmp is about 37 vdc.  The downside of halfing cells is it doubles up on interconnects which gives more opportunity for interconnect failures during panel temp excursion cycles.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #7
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    And the downside of all the connections is where the higher cost panels make up. Sunpower always had 3 connections to each cell. The OP wants good specs at high temperature and should not confuse that with efficiency that I may have been writing about.

     Even better if you can get both if mounting space is an issue!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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