Navitron Renewable Energy and Sustainability Forum

SOLAR PHOTOVOLTAIC => Solar Photovoltaic Systems => Topic started by: Ricc on March 04, 2019, 12:52:18 PM



Title: What would you go for for ?????
Post by: Ricc on March 04, 2019, 12:52:18 PM
  Hi All,
       If you had the choice to choose between 6kw of panels of 275w or the latest 310w Bifacial panels what would it be.
          Looking at low light performance ie winter to spring.
          Mounting would be on a garage roof with a frame. Roof is metal so can be painted white to reflect sun light.
          Price difference would probably be 1000...
          Standard 16A 3.6kw installation.

              cheers

                    R   


         


 


Title: Re: What would you go for for ?????
Post by: RIT on March 04, 2019, 02:15:28 PM
How much light would get reflected back from the roof? After all, you have an array of panels putting the roof in near constant shade.



Title: Re: What would you go for for ?????
Post by: knighty on March 04, 2019, 02:22:51 PM
I'm guessing you're limited by space?

I think you're better spending the extra 1000 on more standard panels... maybe have some in a different orientation ?


Title: Re: What would you go for for ?????
Post by: dan_b on March 04, 2019, 02:32:58 PM
Too many known unknowns to make a proper decision, such as:

Are you limited to 6kW by space or budget?
Which is the more expensive set-up for that 6kW?
What is the modelled generation output difference between the two installs over their lifetime?
Are you getting any FiT or Export payments for the install?
How much do you think you can self-consume?
Do you have a home battery, hot water diverter or an Electric Car which you could charge at home to soak up any excess?


Title: Re: What would you go for for ?????
Post by: stannn on March 04, 2019, 03:11:58 PM
Bifacials are for solar farms. They are sometimes used in the vertical plane on balconies.
Stan


Title: Re: What would you go for for ?????
Post by: dan_b on March 04, 2019, 03:27:52 PM
What does "they're for solar farms" mean in this context?  Everyone who puts up a solar panel is creating a solar farm of some description? 
Do they create more power per square meter of panel? Yes?  Are they a more cost-effective solution to a lower cost, lower power rated, non bi-facial panel? That's the difficult question to answer.


Title: Re: What would you go for for ?????
Post by: Ricc on March 04, 2019, 03:30:18 PM
     Hi,
      6kw by reasonable budget.  But if it makes more sense to go more Kw with cheaper panels.   As the 300w panels are newer technology is lower light performance more important.
       Space is not really an issue.
       Orientation is almost due South...
       Non fits as house is a Stone farmhouse, have made strides with insulation, way to go but is way better than it was.  
       Previous owner did many interesting things !!!!!   Rear garden way over flour level ...  Central heating system 2 pumps opposing each other etc. boiler controller half connected !!!
       Self consumption will be high.      Hot water, background level,  servers, etc.  No batteries.    In the future there appears to be a hidden stream for GSHP.....
        PVGiS says  4320  6kw    and  5760 8kw
        
      
        So the question I suppose is lots of cheap panels versus  fewer more expensive panels (newer technology does it really work) to get the winter power.

         I know its a bit of how long is a piece of string question but everyone here has more insight and practical experience than me so ....


                 cheers


                    R








8Kw
Fixed system: inclination=70, orientation=-20
Month   Ed   Em   Hd   Hm
Jan   6.78   210   1.01   31.4
Feb   12.00   336   1.83   51.4
Mar   17.80   553   2.78   86.2
Apr   22.50   674   3.60   108
May   24.70   766   4.04   125
Jun   20.70   621   3.49   105
Jul   20.40   633   3.44   107
Aug   18.80   582   3.09   95.8
Sep   17.80   535   2.89   86.6
Oct   12.20   378   1.91   59.2
Nov   9.11   273   1.39   41.6
Dec   6.55   203   0.97   30.0
Yearly average   15.8   480   2.54   77.2
Total for year   5760   927



Nominal power of the PV system: 6.0 kW (crystalline silicon)
Estimated losses due to temperature and low irradiance: 6.5% (using local ambient temperature)
Estimated loss due to angular reflectance effects: 3.1%
Other losses (cables, inverter etc.): 14.0%
Combined PV system losses: 22.1%

Fixed system: inclination=70, orientation=-20
Month   Ed   Em   Hd   Hm
Jan   5.08   158   1.01   31.4
Feb   8.99   252   1.83   51.4
Mar   13.40   415   2.78   86.2
Apr   16.90   506   3.60   108
May   18.50   574   4.04   125
Jun   15.50   466   3.49   105
Jul   15.30   475   3.44   107
Aug   14.10   436   3.09   95.8
Sep   13.40   401   2.89   86.6
Oct   9.14   283   1.91   59.2
Nov   6.83   205   1.39   41.6
Dec   4.91   152   0.97   30.0
Yearly average   11.8   360   2.54   77.2
Total for year   4320   927



Title: Re: What would you go for for ?????
Post by: Ricc on March 04, 2019, 03:47:45 PM

   Hi Dan,
        That is the question, the lower light performance is key... do the newer bi-facial work better ???

                     R





What does "they're for solar farms" mean in this context?  Everyone who puts up a solar panel is creating a solar farm of some description? 
Do they create more power per square meter of panel? Yes?  Are they a more cost-effective solution to a lower cost, lower power rated, non bi-facial panel? That's the difficult question to answer.


Title: Re: What would you go for for ?????
Post by: dan_b on March 04, 2019, 05:29:29 PM
I guess the only way to answer that is by looking at, and trusting ,the datasheets for their power outputs across different light conditions.  Bearing in mind that all panels do badly in low light and/or shade, you may still find that the 300W bi-facial panel generates more power in lower light even if it is on paper less "efficient".   Do you have the data sheets?

The other aspect you could consider instead is whether you can have your panels on different aspects, or perhaps on a steeper pitch?  If you're not going to be able to fully consume say 5kW at 1pm on a June day (rare you'll see the full 6kW peak even in spring time), but what you do want to do is maximise generation on a November evening, then you might well be better off with some West-facing panels and/or some S facing ones at a steeper pitch which would be better optimised for the lower angle of the sun during autumn/winter...

If none of that is possible as it's all going on one roof, then I'd personally just go for the most powerful panels and the biggest array you can afford and work out ways to soak up as much juice as possible.   If you don't want to go for  bi-facial, SunPower's most efficient residential solar panel is rated at 370W so you may well find you can get more electrons from your set-up than you thought...


Title: Re: What would you go for for ?????
Post by: biff on March 04, 2019, 06:13:15 PM
The Bi-facial panels do work better,
                       That is a fact. Bi-facial panels also shed snow quicker which is an advantage in the winter months.
  However, the best result that I can glean from the specs is a tilt of 20 degrees gives you a 14 per cent advantage over the mono.
 There are contradictory statements concerning the junctions boxs and picking up light from the rear. The benefit is not clear cut and average gains seem to be nearer 10% than 14%.
 They also perform better with snow on the ground in places like Canada.
   If it were me, I would go for ordinary PV and increase the area. Possibly going for an added Ground mount. (if possible) ground mounts are easy accessed and repaired and you can shift the snow easy with a long handled rubber bladed snow scraper. I would buy as standard a panels as possible so in future if you want to expand you can do so knowing that the panels are still in production.
    Have fun,
                Biff


Title: Re: What would you go for for ?????
Post by: pdf27 on March 04, 2019, 06:59:47 PM
Normally I'd model both options in Sunny Design (https://www.sunnydesignweb.com/sdweb/#/) - it isn't perfect (limited to SMA inverters, etc.) but should give you pretty good answers when comparing two panel options to one another.
Provided there aren't any regulatory restrictions then for a conventional pitched roof mount I'd personally go for the biggest array the budget will allow - the silicon isn't transparent, so you're relying on light being reflected from the roof onto the back side of it. For a solar farm where there is a lot of space between rows of panels, there is quite a bit of light reaching the back surface, and the additional cost of an extra coating step is quite modest when you've got the wafer in the process already. With a roof the story is very different: the panels are mounted closely together and close to the surface of the roof, so the amount of light reaching the panels is going to be very small compared to in a solar farm case.
The only case where it is less clear (and I'm not at all clear if this applies to you or not) would be on a flat roof - there you're basically in the solar farm case, and you're probably going to have to rely on the modelling (Sunny Design or similar).


Title: Re: What would you go for for ?????
Post by: Ricc on March 04, 2019, 09:26:02 PM

     Hi Biff,
          You make very good pionts about going for bog stadard panels as they will be in plentifull supply if you need more.
          Plus they should have got making them down to a tee ie very reliable...

    dan_b  I can make the pitch what ever I want as the garage roof is almost flat.  Plus I plan to biuld an open composting shed (Charles dowding no dig gardening) its not really a ground mount.....

    pdf27   I have put the details into the sunny designer....   Its an almost flat roof so painting it white for reflections is possible.

     Thanks all for your comments I think I am tending towards normal panels...


                   cheers

                        R