Solar calculator to our website

The general idea is build a solar calculator which is gonna stimate the solar panels quantity that could be installed in a specific area and also cost-benefit relationship that this represent. This means that i need help in the following points for this site. 1) Select a specific area on the map and calculate the resulting area 2) Consultation of external databases for calculating irradiance according to the location selected on the map. 3) Also should be possible introduce the parameters mentioned above manually. The above will serve to estimate the amount of solar panels required, as well as the cost benefit ratio that the user would have. The cost benefit ratio will be calculated through a mathematical formulas that would be provided for me, I consider that point 1 and 2 are the most important.