Does solar energy work in the Pacific Northwest?

This is one of the questions that we hear the most because intuitively it would seem that solar panels wouldn’t function in cloudy rainy weather. Depending on the density of the cloud cover, the panels continue to produce at about 10-25% of their rated capacity. One interesting fact is that you will see your panels produce the most when the sun peeks across the edge of a cloud. This is known as the “edge of cloud” effect and it can result in your panels producing in excess of their rated capacity.

Solar production can be very accurately calculated based on decades worth of weather data for a given location. Solar radiation tables are available that show the amount of average sun hours for each month of the year and the average yearly sun hour total. A sun hour is defined as the number of hours of pure solar radiation per day. For example, in Portland, OR a South facing array pitched at 30 degrees will receive 1.7 hours of sun per day in January and 6.3 average sun hours in July.

Let’s take a look at the yearly average sun hours for some cities; locally, nationally, and globally.

Portland, OR: 4.0

Pendleton, OR: 4.7

New York City: 4.6

Phoenix, AR: 6.5

Tokyo, Japan: 3.26

Berlin, Germany: 3.06

It is interesting to take note that Portland receives more sunshine than both Tokyo and Berlin. Germany and Japan have installed the most solar capacity in the last ten years and clearly the lack of sunshine has not been a major influence. Probably, the two most important factors that drive a local solar market are available incentives and the cost of electricity.