If you have a new account but are having problems posting or verifying your account, please email us on for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact

Mono-Facial versus Bi-Facial Panels for a Ground Mount System

  • 08-05-2023 11:27am
    Registered Users Posts: 150 ✭✭

    Hi all,

    I'm hoping to get some guidance on which system is more efficient for a ground-mounted system:

    System 1: 22 x 415W mono-facial panels

    System 2: 18 x 520W bi-facial panels

    Is is as simple as 22 x 415 = 9.13kW and 18 x 520W = 9.36kW therefore System 2 is the one to go for? Or am I missing something?

    Any input is greatly appreciated!!



  • Registered Users Posts: 2,251 ✭✭✭SD_DRACULA

    Is that 520w from both sides? Because that might be best case scenario and you might never get anywhere near those values.

    Really depends on your set up/location

    This is a good video of some guy testing the bifacials:

    Also depends on cost, if the bifacials are a lot more then defo go for the monos.

  • Registered Users Posts: 150 ✭✭Dev1234

    Thanks for the quick response and the link SD!!

    It looks like for an apples to apples comparison in terms of panel size (W) the bi-facial provides more power.

    My concern is that I am reducing the number of panels from 22 to 18 if I go with the bi-facial system.

    On a clear summers day I expect that the 18 x 520W bi-facial panels will produce more power over the course of the day compared to 22 x 415W mono-facial panels. I believe the power rating for a bi-facial panel refers to the front face only but I will double check this with my installer.

    But what about for the rest of the year and overcast days. Is the output of a 300W, 400W and 500W panel the same on a really overcast day? Lets say the 300W panel has a peak production of 250W at 12pm. Would a 400W and 500W panel have the same peak of 250W? Or do they have the capability to produce more power for the same ambient sunlight?

    If production is the same irrespective of panel power rating when the power output is below the lowest power panel am I sacrificing system capacity when I reduce the panels from 22 to 18 - essentially reducing the capacity by almost 20% on days here the max output of a panel would be less than the 415W panel on System 1? (22 x 250W = 5.5kW versus 18 x 250W = 4.5kW in the example above) I understand the bi-facial have increased efficiency but I would need that to be over 20% to off-set the loss of 4 panels on system 2

    I've read more panels is better but want to make sure I am making the right decision!!

    The cost to install either system is the same so that's not a consideration at the minute.

    Thanks again!!

  • Registered Users Posts: 2,251 ✭✭✭SD_DRACULA

    Also what direction are they facing, if 100% south then you probably won't have any decent amount of light hitting the back to make it worth your while.

    Ideally if you can put something very reflective/white behind them it might help a bit too but it's mostly speculative.

    If the 520w relates to front only and then it might boost past this if the back gets some light, then that's what to go for.

    200w is not going to make any sort of different to a system this size anyway so price is key here, if the monos are cheaper I'd say go with them.

    And yes on the bad days (which there are a lot of) the more panels will generate more probably.

  • Registered Users Posts: 150 ✭✭Dev1234

    Thanks again SD,

    It will be south facing and I can paint the concrete they are mounted on white to aid with reflection. Not sure of this will offset the 4 panel reduction on cloudy days though.

    I'll see what the installer comes back with.


  • Registered Users Posts: 2,251 ✭✭✭SD_DRACULA

    If I had the space for ground mount I would do that and add a solar tracker for the whole thing, think about it if it's something you can DIY of course.

    Though I'm not sure you can fit 22 panels on one 😂

  • Advertisement
  • Registered Users Posts: 1,419 ✭✭✭DC999

    Few people here have added manual tilt so can change the angle, but not the orientation. As in they move up and down, but not side to side. Someone did one for winter (higher angle), summer (flatter) and one in between afaik. Then split the panels into a few supports so you move 1/3 of the overall at a time. It’s a manual job to move but only 2-3 times a year.

  • Moderators, Sports Moderators Posts: 18,800 Mod ✭✭✭✭slave1

    better off spending the cash on a tilting array that you can move more vertical in Winter and more flat (to the sky) in Summer

    My stuff for sale on Adverts inc. outdoor furniture, roof box and EDDI

    My Active Ads (

  • Moderators, Home & Garden Moderators Posts: 5,902 Mod ✭✭✭✭graememk

    The difference in the 550 and 400w ones are all down to size. The 550 are just physically bigger.

    Bifacial usually only rate the main side,

    Whatever is the cheapest per watt.

    If similar price, I'd prob go for the bifacial, esp on a ground mount.

  • Registered Users Posts: 150 ✭✭Dev1234

    Thanks for all the replies folks!!

    I don't think I'll go down the rabbit hole of a tilting array at this stage but may come back to it once I see the scale of the system and my output over a year or so.

    Given the replies above and what I've read up on bi-facial panels I'm going to go with them for this install.

    Thanks again

  • Registered Users Posts: 6,819 ✭✭✭10-10-20

    If you have the option of using self-binding sand (path sand) under and around the panels, this might provide some solar reflective gain rather than a non-reflective grass cover. It would also help with weed management.

  • Advertisement
  • Registered Users Posts: 150 ✭✭Dev1234

    Thanks for the suggestion 10-10-20, I'll look in to it!!