Solar Panel Software

I need some software that will help me size strings of Solar Panels. Where would I find such a program?
I need a generic program, not one that is manufacturer specific.
Unforunately, I don't know where to get such a program, if it exists.
As you know, each inverter manufacturer generally has a sizing tool on their website. The calculations are dependent on the inverter, as you know, so the tool will size to keep the startup voltage, current, and operating voltage within limits for a particular inverter, over the expected temperature range, given the type of panel you intend to use.