Capturing solar energy in unlikely weather

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Over the coming years energy needs are predicted to rise sharply. Yet, the need to reduce emissions of harmful gases into the atmosphere grows more urgent by the day. The good news is that we are surrounded by more sustainable energy resources than we could ever need. In just one hour the sun provides more energy than the world consumes in a year.

Our sun has unlimited energy potential and it can help us solve many of the problems we face. As the demand for solar energy continues to grow, the costs of the technology will decrease dramatically, because of economies of scale. According to Ajay Gambhir of Imperial College London, by 2030 the cost of solar should be comparable to that of even the dirtiest (ie. cheapest) forms of coal and natural gas.

The great thing about the sun is that it shines everywhere; so solar PV is possible in any area of the world. You don’t need to live in a desert or in an area known for its many hours of sunshine: a solar panel will also produce electricity under a cloudy sky. So, in spite of its cloudy weather, the sun radiates enormous amounts of energy on the British Isles. The solar potential of the UK is far larger than most people imagine, as much as 60% of that of the equator.

Sun and clouds

How come cloudy weather is not a barrier in solar energy production?

The truth is that solar panels aren’t as efficient under overcast skies as during sunny weather. In these conditions, productivity is reduced by around 50%. Nonetheless, solar photovoltaic panels still produce a significant amount of energy on cloudy days.

This is because of the “photovoltaic effect” of solar cells. The photovoltaic effect happens when many solar cells are wired together to form a single panel and the excited electrons from the sun pass directly from one cell to the other multiplying many times over the small charges created by a single cell. The result is the production of a significant amount of wattage from a whole panel. Even if the energy production capacity of a solar panel is reduced by 50%, if we multiply that by however many panels are in an array the resulting energy output can still be significant.

Also important to mention is that ultraviolet light still reaches the earth’s surface even during cloudy and foggy days, which is why dermatologists insist that you wear sunscreen when spending a lot of time outdoors, even when it isn’t apparently sunny. A lot of advances are being made in this area. For example, the U.S. Army recently patented a super thin cell that combines layers of silver and gold between semiconductor layers but is only a few hundred nanometers thick (that is 1,000 times thinner than conventional solar cells). The silver and gold enable the cell to absorb and convert more light from the ultraviolet and infrared spectrums. More info about this new technology here.

The “edge of cloud” effect

Additionally to all the above, an odd phenomenon exists that makes cloudy skies very interesting when it comes to solar energy production: the “edge of cloud” effect.

The “edge of cloud” effect happens when the sun passes through the external edge of a cloud, magnifying the sunlight. It literally behaves like a magnifying glass. The concentrated light causes a solar array to increase its power output temporarily, which can help balance losses from full cloud cover.

These sudden surges, if very extreme, can even cause equipment damage or malfunctioning. Most modern solar energy systems use a component called a charge controller to help protect against these sudden changes and take full advantage of the “edge of cloud” effect.

And what about cold weather?

Cold weather does not hinder the functioning of solar panels. On the contrary, the colder it gets, the more efficiently the solar panels operate, since the electricity can flow more freely through the cells thanks to a reduced resistance in its conductors.

The biggest constraint of setting up solar energy installations in a very cold place is snow. If snow builds up on a solar panel it can obstruct energy production due to the simple fact that the layer of snow doesn’t let the sunlight reach the panel’s surface. To avoid the build up of snow or other unwanted elements, and to better track the sun, most panels sit at an angle and thus allow snow to slough off on its own. Moreover, progress is being made to help keep the panelling clean and unobstructed, such as small self-propelled robots that move freely between the panels and clean them up. These types of robots are also being used to deal with sandstorms in desertic locations.

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