The solar installation Tool can be run locally by going to the index.html from any browser depending on where one may choose to store the file. I am accessing it by typing /home/samuel/Developer/solarPowerMapper/index.html for example. It will work as long as there is an internet connection in order to get the proper libraries.
I used the leaflet.js framework for this as it provided everything I needed to create the maps,style it with the tiles I wanted, search bars, drawing tools, and it's free.
The only assumption I made was when calculating the nominal power I used 5.5 as a factor for kWh/m^2/day taken from this map. This factor is constant across the whole map. https://www.solar-electric.com/learning-center/solar-insolation-maps.html/#Map1