Smart grid thinking

The European electricity grid is past its sell-by-date and creaking at the seams as it attempts to cope with a distributed generation scenario that it was not originally designed for. E&T takes a look at the moves to create a European Super Grid.

Today, Europe's energy supply is characterised by structural weaknesses and geopolitical, social and environmental shortcomings, particularly as regards security of supply and climate change.

While energy remains a major component of economic growth, such deficiencies can have a direct impact on EU growth, stability and the well-being of Europe's citizens.

These three elements provide the main drivers for energy research, within the context of sustainable development, a high-level EU objective that links economic development, protection of the environment and social justice.

It is vital that Europe's electricity networks are able to integrate all low-carbon generation technologies as well as to encourage the demand side to play an active part in supply. This must be done by upgrading and evolving the networks efficiently and economically.

It will involve network development at all voltage levels. For example, substantial offshore and improved onshore transmission infrastructure will be required in the near-term to facilitate the development of wind power across Europe.

Distribution networks will need to embrace active network management technologies to efficiently integrate distributed generation (DG), including residential microgeneration, on a large scale. There are many other examples but all will require the connectivity that networks provide to achieve the targets for energy security and environmental sustainability.

There are complex interactions between the demands of the network users, which require a more secure and sustainable electricity supply. Also, market and regulatory challenges need to be addressed.

"The network is fairly strained at the moment, particularly because more and more people are wanting more and more power, not just in the traditional, developed countries, but in countries where the power usage per head has historically been lower, such as China and India," says Richard Charnah, technology director at AREVA T&D. "Then there are environmental concerns. We have to generate 'clean' energy and find ways to integrate those clean energies. You then have to make it available to people in a way that keeps the whole system functioning."

"The UK's traditional power grid is based on large, centralised power stations that supply end-users via long-established transmission and distribution systems," Peter Jones, head of technology for ABB Power, says. "Over the years it has performed well, but times are changing. The UK government's challenging renewable targets will require the existing grid to operate in ways for which it was not originally designed.

"There has been a great deal of discussion in the media about smart grids; it is a term that can mean many different things to different people. In my view, a smart grid is an infrastructure that puts the emphasis on active rather than passive control."

A good analogy is the control of traffic on a busy motorway. During off-peak periods, cars can drive freely with no speed restrictions other than the maximum speed limit. But in the rush-hour the warning signs are used to impose speed limits on specific lanes. So, by restricting the speed of movement of individual streams, congestion is avoided, optimising the flow of traffic. More intelligent control of power flows in the transmission and distribution systems will allow higher use even during high demand.

With the balls all up in the air still as governments juggle their requirements for energy security with the needs to reduce CO2 emissions, any new grid will need to be generation neutral. That is, it must have the ability to cope with new centralised generation from coal-fired or nuclear plants as well as being able to incorporate a whole new raft of renewables and more local generation. "Wherever the power is generated, we have to make sure it gets to where it is needed," Charnah says. "There has to be flexibility and the system will need to be self-healing and reconfigurable.

"At the moment the grid is remarkably reliable considering it's analogous to a mechanical telephone switchboard, the type with wires and plugs helping you to get your trunk calls. Running tomorrow's grid, a smart grid, through that type of system just wouldn't work. It has to be a system where the grid can configure itself and allow power flow in different directions.

 "At the moment, power flows in one direction, from large central generation plant to the consumers, and at every split in the line there is power coming in from upstream and going downstream," Charnah explains. "In future, that might not be the case. In fact, it's highly likely that it won't.

"Individuals will want to be able to install power generation locally and send it back upstream, in the direction where power normally comes from. Also, there will be slightly bigger units, and embedded generation and industrial units with 'spare' power in the distribution network, who will want to send power back upstream."

This brings us on to another important and often misunderstood area. There are political aspirations for the individual grids across Europe to be totally interconnected. This is more likely to appear as a series of major AC connections plus some large high-voltage direct-current (HVDC) links, both back-to-back and point-to-point. We shall also see growth in the number of micro grids. "You may not get everything connected to everything, but you are going to get more interconnection and you are going to get micro grids," Charnah predicts. "There is going to be more complexity. On the other hand, with the complexity and equipment that is self-monitoring or self-healing, there should be higher reliability and more resistance to problems. There is an analogy with the Internet, which was devised arguably as a way of resisting security problems."

Technologies

Using power electronics will be very important for a smart grid with technologies such as HVDC transmission and flexible alternating current transmission systems (FACTS) devices. These are things that will allow wind farms to connect to the grid more flexibly and to use the power more flexibly.

Big power electronics will also help bulk power get from where it can easily be generated, areas where there are raw materials or water cooling, to the main centres of consumption. In the UK for instance, there is a lot of wind power out at sea and a lot of hydropower in Scotland, but the main areas for consumption are further south.

Another important technology will be energy storage, and again it is going to be required at different levels - small local storage and high volume centralised storage.

There is an enormous amount of energy storage, mainly hydro, in Switzerland and Norway - this is just one form of energy storage available in quite large amounts but at a few minutes notice.

You can have local storage using flywheels such as those used in the metro systems around the world. These store the dynamic power from the braking of the train as it comes into the station and as that surge of power, the regeneration of power, goes back into the system it is stored in a flywheel. It is then released when the train wants to pull away again.

For any modern network, energy storage implies some kind of power conditioning as well as you have to condition the power to DC to store it and then you have to get it out of the DC and into the grid, which is AC, to get it back. Therefore, power conversion by power electronics is also necessary for energy storage.

Then there are a lot of information and communication technologies that are making possible the control and management of very complex systems. A smart grid, as we have already established, is certainly a complex system.

Much has been made about the intermittent nature of much of the renewable energy sources. And although many exponents would argue against the word intermittent, claiming that through advanced modelling techniques wind, Sun and tides are highly predictable, there can be no contesting the fact that the generation is not continuous.

"One way is to generate and use the wind power whenever it is available so that you are always using all of the wind power available to you," Charnah suggests.

"The down side of that is that when you transmit power over long distances, say it happens to be windy in Norway and the power is needed in Sicily, there are losses in the transportation. One way round this is to incorporate more HVDC transmission, where the losses are much lower than in an equivalent, conventional AC system. An alternative solution would be to incorporate [local] energy storage, which shifts the consumption in time."

Evolution

All this is well and good, but is it realistic? Nobody is going to build a brand new grid, so any developments will certainly be add-ons or upgrades.

The scenario will be evolution rather than a revolution. "There will be parts of the network that are upgraded or renewed, or have new lines installed, and there will be new protection schemes and so on. This means that there will be evolution," Charnah concludes. "It may be that in 2020, 2025, or even 2030, the grid looks quite different, but it's going to be an evolution."

Jones agrees with the evolutionary nature of grid change. "We expect to see a gradual transformation of the systems that have served us for many years into a more intelligent, more effective and environmentally sensitive network to provide for the UK's future needs.

"Rather than a smart grid, which will remain the ultimate aim, what we are really moving to is a smarter grid; one that will incrementally add the technologies and innovations over a period of years, or more likely decades."

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