Generally speaking, nontracking PV arrays in the northern hemisphere will experience the most solar exposure by facing true south at a tilt angle equal to within 5° of the latitude. However, region-specific factors can alter when your array receives the most sunlight. For example, in areas with extremely cloudy winters (like Seattle, WA), a tilt angle of latitude minus 15° can yield the highest annual production for a grid-tied system—summer energy gains at the more shallow tilt far exceed the winter gains at the steeper tilt. Another situation that favors a different array orientation is if your site regularly gets early morning fog. In this case, you will want to shift your array orientation toward the west. See “Optimizing a PV Array” in HP130.