Specifically, I am referring to section 690.7(A)(3). I am curious as to how this would actually be implemented.
From my understanding, this section allows a licensed engineer to perform system modelling via the Sandia method (PVsyst, etc.) to calculate a more accurate/realistic maximum system voltage. The idea being cold temperatures do not occur at the same time as high irradiation, so the simple temp. correction is conservative. If developers are able to add an extra module to each string, they could realize substantial BOS savings.
My question comes down to the actual implementation of this method. PVsyst (amongst other modelling software) can produce 8760 files including a value for array voltage. I would imagine the Sandia method inherent to the software adjusts the array voltage for the specific atmospheric conditions, as well as module orientation, inverter MPPT operation etc. In doing so, one could sort the 8760 voltages and identify the highest value, ensuring it is below 1500V. I have actually done a variation of this in the past (with AHJ approval).
I guess my question comes down to if there is any resource or guidance out there that can back-up my understanding. I would like to have more confidence in my methodology, and if there is a better way of doing things, but nothing has surfaced in my web searching. Everything done here comes down to the inputs into the model. For example, if I were to select the TMY3 weather data, could I be reasonably confident that the results represent a worst-case year? And we are trusting the manufacturer provided files as well (e.g. pan).
Any thoughts are much appreciated.
From my understanding, this section allows a licensed engineer to perform system modelling via the Sandia method (PVsyst, etc.) to calculate a more accurate/realistic maximum system voltage. The idea being cold temperatures do not occur at the same time as high irradiation, so the simple temp. correction is conservative. If developers are able to add an extra module to each string, they could realize substantial BOS savings.
My question comes down to the actual implementation of this method. PVsyst (amongst other modelling software) can produce 8760 files including a value for array voltage. I would imagine the Sandia method inherent to the software adjusts the array voltage for the specific atmospheric conditions, as well as module orientation, inverter MPPT operation etc. In doing so, one could sort the 8760 voltages and identify the highest value, ensuring it is below 1500V. I have actually done a variation of this in the past (with AHJ approval).
I guess my question comes down to if there is any resource or guidance out there that can back-up my understanding. I would like to have more confidence in my methodology, and if there is a better way of doing things, but nothing has surfaced in my web searching. Everything done here comes down to the inputs into the model. For example, if I were to select the TMY3 weather data, could I be reasonably confident that the results represent a worst-case year? And we are trusting the manufacturer provided files as well (e.g. pan).
Any thoughts are much appreciated.
