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  • Solar System Loss Percentage

    When designing a commercial solar system with the size of 1 MW, what is the system's acceptable loss percentage ?? I have noticed that some people use 16% and some use 18% while some other use 22%. The difference is wide and can make a big difference in the system output. What is the recommended loss percentage ?

  • #2
    It would be hard to answer that for all systems. My guess is what ever the customer says is acceptable for loss based on their need for power consumption.

    Another difference would be the location of the solar array. Anything far from the equator will see more losses then closer.

    Also the amount of cloud cover throughout the year makes a difference in how much a solar array will produce. Too many clouds may require more panels to cover the loss.

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    • #3
      The customer in this case has no experience and the final say if for the service provider / contractor. Factors to consider for the loss are : soiling, shading, snow, mismatch, wiring, connection Degradation, light-induced, nameplate rating, age, and availability. Not to mention the inverter's loss (from DC to AC). However, deciding the percentage for each category is what makes it tricky somehow. A system with total loss of 18% would yield much energy than the system with 22% or more. The question: based on what criteria should the % of loss for each category (soiling, shading, mismatch .... etc) be decided ???

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      • #4
        Originally posted by Dodee214 View Post
        The customer in this case has no experience and the final say if for the service provider / contractor. Factors to consider for the loss are : soiling, shading, snow, mismatch, wiring, connection Degradation, light-induced, nameplate rating, age, and availability. Not to mention the inverter's loss (from DC to AC). However, deciding the percentage for each category is what makes it tricky somehow. A system with total loss of 18% would yield much energy than the system with 22% or more. The question: based on what criteria should the % of loss for each category (soiling, shading, mismatch .... etc) be decided ???
        shading is hardly 'loss', it's part of design. Some soiling research was very informally done around here by member JPM and IIRC it's < 8% in San Diego area on his roof. YMMV. Snow is the beast and I think you'll be forced to clean it if any production from the array is expected.

        On top of that with clear skies and none of the factors above any system yearly output varies by 50%. The panels themselves also degrade with time and this number is part of their specs. These are not 'losses' but still affect production greatly and need to be accounted for.

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        • #5
          Originally posted by Dodee214 View Post
          The customer in this case has no experience and the final say if for the service provider / contractor. Factors to consider for the loss are : soiling, shading, snow, mismatch, wiring, connection Degradation, light-induced, nameplate rating, age, and availability. Not to mention the inverter's loss (from DC to AC). However, deciding the percentage for each category is what makes it tricky somehow. A system with total loss of 18% would yield much energy than the system with 22% or more. The question: based on what criteria should the % of loss for each category (soiling, shading, mismatch .... etc) be decided ???
          If there was a penalty associated with the systems performance goal and if I was making the decision I would be conservative and make sure I do not tell the customer the system will produce more than it can so I would use a higher % loss value.

          If there is no penalty then designing a system with a marginal span of X% to Y% loss would be my criteria.

          Unfortunately there is no perfect answer to your question.

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          • #6
            Originally posted by Dodee214 View Post
            When designing a commercial solar system with the size of 1 MW, what is the system's acceptable loss percentage ?? I have noticed that some people use 16% and some use 18% while some other use 22%. The difference is wide and can make a big difference in the system output. What is the recommended loss percentage ?
            Do you have a load that the system is supposed to meet ? What background do you have in system design ? In Solar system design ? Engineering background/experience ?

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            • #7
              The idea is to have a solar system to replace diesel generators during the daytime. So increasing the loss% would require more panels, thus more cost. The load of the system around 1.1 MW.

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              • #8
                We're not blowing you off. There are just not many of us that have experience with commercial systems, and your question is very broad and unspecific. My instinct would be to mentally consider a 20kW system, then try to multiply/aggregate that to 55 such systems. Lots of factors that small designers don't have to deal with, some I probably haven't even considered. Seems the same for you, some things you listed might be considered losses to some, to others they might be design constraints.

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                • #9
                  Originally posted by Dodee214 View Post
                  The idea is to have a solar system to replace diesel generators during the daytime. So increasing the loss% would require more panels, thus more cost. The load of the system around 1.1 MW.
                  shadows are not losses. It is layout and modeling of production you are talking about.

                  This part though "...solar system to replace diesel generators during the daytime..." is a bit more concerning. What exactly are you trying to do here?
                  are you thinking of making a 1.1MW bimodal off grid system?
                  OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                  • #10
                    Originally posted by ButchDeal View Post

                    shadows are not losses. It is layout and modeling of production you are talking about.

                    This part though "...solar system to replace diesel generators during the daytime..." is a bit more concerning. What exactly are you trying to do here?
                    are you thinking of making a 1.1MW bimodal off grid system?
                    Maybe it is time to ask the OP approximately where this 1MW system is being installed.

                    It sounds like the existing power generation are diesel generators that are both noisy and expensive to run.

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