Via getsolar.com, 20-10-2011

Few people live far enough north or south that they can have sunlight all day long, so most people understand their rooftop solar installations cannot always provide them power. What people might not understand is the concept of intermittency and how great a challenge it poses to the renewable energy industry as a whole.

While solar installations are given a maximum peak capacity, usually listed in either kilowatts or megawatts, the actual output can vary substantially based on the angle of the sun, which changes throughout the year, and the amount material blocking sunlight from the panels, from clouds to fog to dust.

This might seem primarily to be an issue of production, with larger solar installations and more power providing a simple solution, but the larger problems for intermittency actually have more to do with transmission. Most people never consider issues of electrical load on power lines because at least for most residents there is little noticeable change other than functional and non-functional.

However, different power lines are designed to carry different amounts of power, which accounts for the difference between major interstate transmission towers and the wires strung along street lights throughout the country’s suburbs. When a power line has too little electricity, voltages can drop and devices can fail to function. But if a power line has too much electricity, voltage levels can rise to much the same effect, and substantial surges can trigger breakers that will shut off power completely.

Particularly in residential areas that were initially designed for lower power levels, large clusters of solar installations can cause consistent problems as utilities struggle to account for the fluctuations in power generation. If solar systems are all close enough to vary roughly in line with each other it can magnify the size of any spike of power flow, making it even more difficult for power companies to adapt. Solar Novus Today notes that grid operators already make use of complex systems in order to predict fluctuations in demand without even accounting for intermittent power sources. Added to the inflexibility of some types of power plants, the problem can prove substantial.

The Australian reports that the problem has already emerged in some areas of that country. Queensland has even rejected applications for residential solar installations because of the issue and Western Australia imposed restrictions on the density of such systems of an area.

Solar power is not the only source of energy that suffers from intermittency, with Bloomberg reporting that German utilities were forced to give away electricity below cost because of a massive surge in wind power. However, with these two prominent sources of renewable energy suffering from the problem, a growing number of researchers and businesses are looking into methods to accommodate intermittent power sources.

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