While online solar energy estimators like PVWatts can give you an idea of how a PV system will perform in your location, it’s important to pay attention to microclimates, which can have a marked effect on how much sun your array can collect. In our area, elevation changes and local weather patterns can greatly influence solar collection.
Thankfully, our property sits high enough to escape the fog that tends to settle on the valley floor in the winter. We also sit on an exposed knoll in one of the sunniest areas in the valley. From our house, if you travel about 13 miles in any direction (sometimes less), the sunshine can quickly give way to overcast skies. The local topography also impacts solar gain—mountains surrounding us decrease our overall solar window, since they block the early morning sun and make the evening sun disappear earlier than if our property sat at a higher elevation, though early or late-day sunlight does not count for much because of the angle of incidence.