Intelligent power grid organizes itself

Central control against fluctuating mains frequency is not required

The expansion of renewable energies such as wind power also places new demands on the electricity grid. © freeimages
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Self-organization in the electricity grid: Intelligent electricity meters could independently adapt the electricity grid of the future to the fluctuating supply of renewable energies. A central control point is unnecessary, as a computer model of German scientists shows. Instead, a decentralized, intelligent power grid would be much safer and much cheaper, say the physicists.

The expansion of solar energy and wind power is progressing in Germany: since the beginning of 2014, renewable energies have reached a record level of 28 percent of German electricity consumption. However, this also creates a problem: the power grid has to deal with larger fluctuations. Because a cloud front pushes over southern Germany, the photovoltaic systems suddenly deliver less electricity. And when a storm comes up, electricity production in the wind farms suddenly increases and fluctuates even more than it already does.

An intelligent power grid or "smart grid" should be able to buffer such increased fluctuations. So-called "smart meters", intelligent electricity meters, are to regulate the consumption depending on the offer and turn on and off appliances in the house accordingly. If wind and sun supply a lot of energy, for example, cooling units in data centers and warehouses, refrigerators at home or chargers for electric cars are to be started up. If there is a lull, they should temporarily go to sleep.

Security risks with central control

Previous concepts of an intelligent power grid assume that the data of all consumers and producers go centrally to the energy supplier. If necessary, this counteracts the measured fluctuations. But that carries risks: "Such centralized control is a potential target for hackers, " warns Benjamin Schäfer of the Max Planck Institute for Dynamics and Self-Organization.

If somebody breaks into the control center via the Internet, in the worst case scenario he could paralyze the supply network. "So far, it is also unclear how the data protection is to be ensured if customer consumption data is constantly transmitted to a central location, " says the physicist. display

Central network (top left) and decentralized grid of the future fed by many smaller generators. MMCD according to MPI for Dynamics and Self-Organization

Sch fer and his colleagues have therefore investigated whether a central control of the smart grid must be at all. Could not smart local electricity meters directly match supply and consumption without having to go through the central energy provider via a central office? The advantage of such a decentralized control would be enormous: Beyond the security aspects would also be the creation of a communication infrastructure, which otherwise would have to connect millions of smart meters with the energy providers in the future.

Intelligent network keeps itself stable

The physicists developed a mathematical model simulating power generators and consumers. The decisive factor in this is the so-called grid frequency with which alternating current in the supply network oscillates. It is 50 hertz and may deviate from this value at most by 0.2 hertz due to fluctuations in the network. If the supply decreases or the demand increases, the frequency also drops.

If, for example, the sun supplies more electricity again, or if large electrical consumers such as industrial plants are temporarily disconnecting from the grid, the grid frequency increases again. These fluctuations are what the network operator must actively compensate for. A decentralized network lacks this active control - so can such a network organize itself and keep it stable? According to the physicists, this is possible if the smart meters react directly.

The current control units are therefore in a position to use frequency changes as a measure and to control the power consumption of the connected electrical appliances themselves. "So far, there has hardly been a study that has analyzed in detail whether a smart grid can function without central control at all, " summarizes study director Marc Timme. "Our analysis has now shown for the first time that this is possible in principle."

Fast reactions are not necessary

A particular challenge arises with short-term frequency changes, which sometimes occur within milliseconds. Many appliances can not react so quickly: A refrigerator, for example, reacts in a decelerated manner when the compressor first has to be switched on or off. The router, which is supposed to control the electrical devices in the house in a future network, needs computing time before it reacts.

Fortunately, the smart meters do not have to respond immediately to such rapid fluctuations: they often balance themselves within a few seconds. For larger fluctuations, however, such a delay makes sense. So it is ideal if the smart meter averages the frequency values ​​for a few seconds and then regulate and adjust the consumption accordingly.

(Max Planck Society for the Advancement of Science eV, 28.01.2015 - AKR)