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When it comes to electricity grids, matching supply and demand is a tricky business. Utilities need to have spare capacity on standby to provide additional power whenever it is needed and that’s expensive.

What’s more, the problem is set to get worse given the growing reliance in many parts of the world on wind and solar energy, which is often unpredictable and cannot be switched on to match demand.

There are essentially two ways to tackle this. The first is to invest in more infrastructure, such as additional conventional power stations or energy storage devices such as batteries, and to switch these on when they are needed. 

The second is to use power more intelligently. One idea is to shift electrical consumption to times when demand is low. In other words controlling demand rather than supply. In this way, demand can be made to more closely match the supply.

Indeed, there are various examples of this in operation now. The British supermarket chain Sainsbury’s is currently fitting its network of refrigerators with so-called “demand control” technology that will aim to switch them on when electricity demand is low. The supermarket’s aim is to save around 100,000 tons of carbon dioxide-equivalent emissions in the next 10 years.

Today, Stefan Hild at the University of Glasgow in Scotland and a few pals demonstrate how simple it is to do the same kind of thing with laptop battery charging, a process that can often be done at night when demand is low anyway.

These guys point out that when the grid’s nominal operating frequency is 50 Hz, the frequency tends to drop when demand is high and rise when demand is low. So it’s straightforward to design a simple circuit that can detect these changes and switch a laptop charger on or off respectively.

In fact, more sophisticated control would be relatively straightforward. Operates could easily publish the state of the grid on the Internet or transmit information by modulating the grid frequency itself.  Laptop computers, of course, are in a good position to process this kind of data and act on it.

Hild and co have tested their idea by building smart charging circuit and declare that it works well on an ordinary laptop. They have also examined the historical record of frequency changes over the grid and say demand control technology should keep a laptop at least 40% charged with normal use.

Of course, the great benefit is not for the laptop owner but for the electricity grid and the country as a whole. Hild and co say that making this technology widely available will have a significant impact on the cost of operating electrical grids in future. 

“This will contribute significantly to the stability of the electricity grid, help to mitigate the power production fluctuations from renewable energy sources and avoid the high cost of building and maintaining conventional power plants as standby reserve,” say Hild and co.

Clearly worth looking at more detail.

Ref: arxiv.org/abs/1209.5931: Smart Charging Technologies for Portable Electronic Devices

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