foreign welcome to the segment on string sizing in the last video We examined inverter specification sheets in this section we'll combine photo take a module and array data to find the appropriate inverter for the system let's begin by looking at an example where we need a 7400 watt or 7.4 kilowatt system and then choose a module and an inverter that matches this requirement we're going to use this example of an inverter that has a nominal output of 7200 watts and a maximum usable input of 8640 Watts so we're going to start with the assumption that 7400 watts are required and we're using 300 watt photo take modules by dividing 7400 Watts by 300 watts per module we get 24.7 modules because we can't have fractional module we'll need to round down to 24 modules so now we know our system will have 24 full take modules and these modules are listed as having an open circuit voltage of 38.2 volts and a maximum power voltage of 36 volts the short circuit current is rated as 8.6 amps and the maximum power current is rated at 8.3 amps now that we have the values for the input of the inverter and the output of the foldable attack panels we can determine if the system will work together first we'll look at what happens when we wire 24 modules in series we want to look at the absolute highest voltage the system could produce which would be at open circuit conditions the VOC at STC is 38.2 volts and multiplied by 24 modules gives us a total system voltage of 917 volts by looking at the spec sheets on the inverter we see that the maximum input voltage is 600 volts that means that this system in a series string will not work with this inverter and it's also an excessively high voltage to solve this problem we'll Instead try a parallel string to provide two series strings if we have two series strings then there are only 12 modules per string and 12 modules times the 38.2 VOC is 458.4 volts this is acceptable because it's below the 600 volt maximum 12 modules times the 36 volt maximum power voltage is 432 volts which is within the operating range of the inverter as well the next step is to look at the maximum current that could be produced by the foldable tank modules which is the short circuit condition we're now working under the assumption that we'll have two serious strings and each string has a short circuit current of 8.6 amps well 8.6 amps multiplied by the two strings that we determined previously is 17.2 amps looking at the specification sheet for the inverter we see the maximum input current for that inverter is 18 amps so we're below the maximum input current allowed for the inverter in this case it appears that the final design would include two strings of 12 300 watt modules the total system power is still calculated to be 7200 Watts under standard test conditions this is a little bit lower than the maximum usable input power of the inverter of 8640 Watts when the PV array output is too far below the maximum usable input power of the inverter we would want to consider an inverter that has a slightly lower input requirement in order to maximize the overall system efficiency still it would work in our case here so we settled on two strings of 12. but is that the only option well let's look at other possibilities we know that there are 24 modules that are being considered and that one string of 24 provides a voltage that is too high 24 modules could be wired in several ways however such as one string of 24 two strings of 12 three strings of eight four strings of six and so on so let's see what happens when we try three strings of eight in this case each string would have an open circuit voltage of 305.6 volts and 208 volts at maximum power this fits within the specifications of the inverter which requires less than 600 volts at VOC and that the operating range be less than 480 volts because we're going to have three strings in parallel however we need to add the current for each string in this case it would be 8.6 amperes which is the short circuit current for each string multiplied by three this gives us an operating short circuit current of 25.8 amps which exceeds the maximum input this means that we cannot have three strings of eight and our only option in this case is two strings of 12 for this inverter and module pair now there are situations where modules can be wired in several different ways to meet the input requirements for both current and voltage of the inverter in general High voltages pervert over High current so there's less loss due to resistance which is also why we wouldn't want to use say 12 strings of two or where where low voltages with large numbers of parallel strings so in summary the process of choosing an inverter begins with first defining the size or the power of the full voltaic array you must then choose a module and an inverter and balance the output of the photovoltaic string with the inverter's input requirements you'll likely need to go through a few iterations to match and maximize the system efficiency so this concludes the lesson for this module and course you should now be able to calculate solar gain based on location use online resources to determine solar gain and calculate losses due to shading tilt and Azimuth explain circuitry Basics and electrical output for a module and an array as well as calculate changes based on temperature apply PV specifications to determine power and energy output and finally size full voltaic system strings using module and inverter spec sheets