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The renewable share of the world’s total energy mix is increasing steadily. Germany alone today generates 25 percent of its total requirement from renewables. But renewable power generation is at the mercy of the weather and daylight conditions. It fluctuates wildly, with the result that conventional power grids that receive any appreciable percentage of their in-feeds from renewables are at the very limits of their ability to maintain stability. The solution to this problem is smart grids – decentralized power networks that use intelligent energy management systems to ensure that electricity is consumed when and where it’s produced.

moma – the world’s first smart grid

The world’s first smart grid, spanning 1,000 households in the German cities of Mannheim and Dresden, was implemented and tested over a four-year period from 2008 to 2012. The results show that smart grids are not only very efficient at utilizing renewably generated energy, they also deliver significant cost savings to consumers. Not surprisingly, the project – known as the "Model City of Mannheim," or "moma" for short – has received a lot of international media coverage, including reports by major global news organizations like CNN .

How does the moma smart grid work?

One of the key features of moma is the "Energy Butler" – an intelligent control unit about the size of a DSL router that’s installed in each household. Together with a smart meter, it measures the power consumption of each household electrical device while monitoring how much electricity is available in the network. It also knows how much that electricity costs at any given hour, thanks to tariff schedules that the electricity supplier sends to it directly via the grid’s integrated broadband powerline data network every night. Thus, when prices on the energy exchange are low owing to good wind levels off the North Sea coast, the Butler knows it’s OK to give free reign to the household’s most energy-intensive appliances. It might pre-cool the freezer, for example. Later on, when the wind has dropped and power prices are higher, the Butler runs the freezer only intermittently, keeping it ticking over just enough to maintain the set temperature. "Once it has collected enough data, the Energy Butler is able to create dispatch schedules for the household’s electric appliances," said moma project manager Andreas Kiessling.

Smart grids achieve savings through "load shifting." This is a kind of juggling act in which certain power-consuming appliances – generally those that can be powered off without causing disruption or inconvenience – are disconnected from the grid until there is plenty of renewable electricity available and prices are low. These shiftable "loads" are among the key aspects of the moma project. They provide the demand-side flexibility needed in order to tailor network load to fluctuating supply from renewables. Kiessling estimates that shiftable loads make up between six and eight percent of overall load in private households.

"There are already commercial chillers and large cool stores out there that are suitable for intelligent load management. They have load-shifting potentials ranging from several hours to entire days."

The smart grid model centers around accurate and rapid data interchange between all local-grid components. In the case of moma, this is achieved via what is known as "broadband powerline" technology – an Internet technology that transmits data via the actual electricity network.

Cellular system architecture incorporates “prosumers”

Not that tomorrow’s households will be pure electricity consumers; they will be "prosumers," meaning that they will also produce electricity in systems like rooftop solar arrays and feed it into the grid. This will eventually make electricity flows in local power grids so complex that they will exceed the management capabilities of central control systems and possibly lead to blackouts. Which is why the moma network is structured into decentralized cells – corresponding roughly with city precincts – that are connected to one another via multiple transformer substations. Each cell can function independently of the rest, partly because it has its own embedded generation plants, such as solar cells, wind turbines and CHP units. Each transformer substation has a software component that monitor’s its client cell’s consumption and generation – much as the Energy Butler does at the household level – and "imports" energy from the other cells in the grid to make up any shortfalls.

"You have to think in terms of cells. Each grid segment must be able to 'talk' to the other segments in order to create an integrated system."

All of the cells are interconnected via a higher-level "system cell" that manages the smart grid as a whole and ensures reliable operation.

Stability and reliability of supply

The moma smart grid offers two other key benefits: grid stability and security of supply. Kiessling: "During severe winters, fuel supplies for large coal-fired power stations could be too slow in coming and transmission lines might break under the weight of heavy snow. In the current centrally controlled transmission system, either eventuality has the potential to trigger grid outages on a nationwide or even Europe-wide scale. But in a decentralized system in which the cells control themselves with a high degree of autonomy, individual grid segments can fail without compromising other segments. So having cellular architectures, rather than central ones, is in itself a contribution to security of supply."

At HANNOVER MESSE you will have multiple opportunities to discuss new directions in energy supply with industry experts. One such opportunity is the Smart Grids Forum .