Creating the Site model.
The important difference with solar studies is you need a larger area of site model. Normally when you get a site survey, you only get the site you are working on. For a solar study you need the surrounding area as well because you want to place adjoining houses and see their shadows on the ground. You can often get the additional information from the local authority (city council, district council and so on).
The information does not have to be as detailed as the information you get for your site.