Of all the factors to consider when designing a solar array, one that is the most important is the record low temperature for the area where the array is being installed at. Interestingly enough, a solar module's operating characteristics is directly affected by the outside air temperature. The colder it is outside, the more voltage is produced and conversely, the hotter it is outside, the more voltage output begins to degrade. As a matter of fundamental design criteria, the record low temperature is determined first to ensure that the inverter is capable of handling the increased voltages at low temperatures. Applying a solar array voltage in excess of the inverter rating will damage the inverter which is why I base the sizing of the array in conjunction with the inverter on the record low temperature.
Fortunately, Oregon is considered an ideal climate for electric solar arrays due to the moderate to cool climate we enjoy. Also, adequately spacing the solar modules off the roof provides air flow between the array and the roof which aides in cooling the array as well. These are just a few of the design factors I incorporate into all my array installations.
