Derat Factor for big commericals!

BatikikikBatikikik Solar Expert Posts: 141 ✭✭✭✭✭
Usually ideal derate factor is 0.803 (central inverters with 96% eff)
Can you apply that derate factor on big commercial projects if your inverter has same 96% eff.?
There are dc wiring factor and soiling factor which is i think has to be adjusted for big commercial projects.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Derat Factor for big commericals!

    You don't really know the "proper" deratings over time until you get a chance to ACCURATELY measure a big installation...

    Just in PV watts, they have a whole bunch of derating factors that add up to their 77% derating.
    [B]Derate Factors for AC Power Rating at STC
    [/B]Component Derate Factors         PVWatts Default         Range
    
    PV module nameplate DC rating         0.95         0.80–1.05                 
    Inverter and transformer         0.92         0.88–0.98                             
    Mismatch         0.98         0.97–0.995              
    Diodes and connections         0.995         0.99–0.997             
    DC wiring         0.98         0.97–0.99              
    AC wiring         0.99         0.98–0.993              
    Soiling         0.95         0.30–0.995              
    System availability         0.98         0.00–0.995             
    Shading         1.00         0.00–1.00              
    Sun-tracking         1.00         0.95–1.00              
    Age         1.00         0.70–1.00              
    Overall DC-to-AC derate factor         0.77         0.09999–0.96001
    
    With a large customer--Do you have to have a performance guarantee? And how would somebody "prove" one way or another that you are meeting the specifications or not?

    You can have a 10-20% year over year change in yearly average solar irradiation.

    A 5-10% error in production output could be the difference between profit and loss...

    The little I have seen here--A site may not even choose to instrument each solar array string--But instead base power production measurements on a 100-500+kW solar block... There could be a dozen dead panels in a block before generic measurements could catch a 2% variance.

    But instrumenting each string (an option supported by some/many/all? GT systems vendors) is expensive and, apparently, not always chosen.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BatikikikBatikikik Solar Expert Posts: 141 ✭✭✭✭✭
    Re: Derat Factor for big commericals!

    Performance guarantee you have to provide for every project. And before giving any guarantees you have to know exactly every detail. Yearly output depends mostly from derate factor, which is for small systems <10kw it is easy to determine. For big projects I think derate factor will be smaller then 0.803 or 0.799 even if you use 97% efficiency inverter. I think this factors has to be changed

    DC Wiring
    Soiling

    What is your opinion ?
  • BB.BB. Super Moderators, Administrators Posts: 32,007 admin
    Re: Derat Factor for big commericals!

    My opinion is probably pretty much next to worthless...:cool::roll:

    Not many people on our forum here have experience with large commercial systems.

    Finding a consulting engineer / firm with a good CV (lots of successful installations) for your first project or two may be worth the money. You learn and your customers have systems that perform to specifications.

    I would also assume that many of the GT Inverter companies offer courses and design support/modeling to their distributors/installers. Pick a vendor and work closely with them on first few installs.

    Try to interview/take a tour at a couple of local large PV sites and and get some understanding of what made them happy/unhappy.

    I am sorry I do not have any better answers... But I am not sure there are any "simple" answers either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Derat Factor for big commericals!

    A homeowner will probably buy whatever good story is told to them.

    A commercial installation owner should have someone that knows the business to advise them - especially during any performance testing. That person should be difficult to blow smoke at.
  • BatikikikBatikikik Solar Expert Posts: 141 ✭✭✭✭✭
    Re: Derat Factor for big commericals!

    Ok, I am sorry I did not know that in this forum nobody know about commercial projectsl
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