NREL released a new version of PVWatts® in September 2014 which changes the results significantly to more accurately reflect PV performance outputs from current systems. Note that the results will typically increase 7 to 10 percent. This version updates the default derate/loss values, uses a modern inverter curve and adds several options. You can read more about this update here. The old versions PVWatts V1 and PVWatts V2 have been retired.
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