Glasgow, Scotland has the dubious distinction of being the cloudiest city in Europe. You’d never think solar could pay off there, would you? But gloomy Glasgow recently outfitted eight of its schools with solar photovoltaic panels — and the solar installations are expected to save the city £780,000 in electricity costs over the next 20 years.

Many people think it’s impossible to get a return from solar panels on cloudy days, or in cloudy climates. A quick peek at cloudy cities all over the globe, however, reveals increasing numbers of solar rooftops quietly cranking out power — and proving this “common knowledge” to be nothing more than myth.

For example, overcast Germany generates a higher percentage of its electricity from solar than nearly any other country. Singapore, a city known for its cloudy climate, is aiming to raise its percentage of electricity generated from solar to 20 percent by 2050. And the U.K. recently enjoyed an unbroken six-month period where it generated more electricity from solar than from coal.

The Silicon Lining For Cloudy Cities

North America, too, has its share of cloudy cities — and solar skeptics. But a quick look at solar insolation statistics from various locations reveals that virtually every city in the United States has more than enough solar potential to make an investment in panels worthwhile.

Solar insolation is a measure of how much sun power is available in a particular location — the higher the number, the more solar gain. For example, sunny Las Vegas has an annual average insolation level of 5.3. Honolulu tops the charts at nearly 6. In comparison, Bonn, Germany checks in at 2.8, and Glasgow rates a lowly 2.65 — numbers that even rainy Seattle can handily beat.

In fact, these annual average insolation levels for American cities located outside the Sun Belt drive home just how viable solar is, even in the Northeast:

Annapolis, MD — 3.98

Boston, MA — 3.58

Chicago, IL — 3.72

Detroit, MI — 3.58

Hartford, CT — 3.59

Montpelier, VT — 3.43

New York City — 3.53

Seattle, WA — 3.53

Trenton, NJ — 3.58

Washington, D.C. — 3.9

How Do Solar Panels Work on Cloudy Days?

All sunlight is the same above the clouds, but conditions in the lower atmosphere and objects near the surface of the earth can change its quality.

There are three types of sunlight that can hit your solar panels:

  1. Direct sunlight, which travels in a straight line from the sun
  2. Diffuse sunlight, which has been scattered and diffused by water vapor and particulate in the air
  3. Reflected sunlight, which has bounced off an object such as a roof or even the ground

The type of sunlight hitting your panels affects solar panel efficiency. Cloudy day conditions deliver more diffuse light than direct light. While solar panels work best in direct sunlight, panels can also utilize diffuse and reflected light. So even on a cloudy day, a solar panel can still crank out power at about a 20-percent efficiency. This may not seem like much, but it adds up over the course of the year. And, of course, even cloudy locations get direct sun, too — at least some of the time.

The price of solar has dropped so low in recent years that solar is now a smart investment, even in cloudier parts of the country such as the Mid-Atlantic. In fact, ROI from solar panels in many areas (including Washington, D.C.) beats the S&P 500!

If you have always believed solar wouldn’t work in your climate, perhaps it’s time for a change in forecast. Why not call us for a free solar estimate? You may be surprised how sunny your outlook for solar can be.