Solmetric’s iPV iPhone app ($39.99) uses the iPhone’s camera, compass, and inclinometer as the user traces the outline of anything (mountains, trees, buildings, etc.) on the horizon panning from east to west. It generates a two-page report with monthly shading and performance estimates, the latter using a database of PV modules and inverters. One drawback is that it can’t save more than one location for future reference, so it can’t compare two locations. Another is that you have to choose from 200+ reference U.S. cities, which may or may not be close to your site. But for the price and convenience, it’s a good tool for homeowners. I’ve used it again for site assessments with friends who became interested in a system after seeing ours (scans below).