The verttec app is a webapp I made for my thesis in school.
It's a tool to calculate the cost, yield and profits for an array of solar panels.
There's several settings you can tweak which update the values dynamically.
After you've filled in all the necessary settings the app shows you charts with the results and an option to create a PDF estimate.
The app is based on the 3-tier architecture and uses a one page interface and a membership system.