During the summer of 2016 articles from our growing archive will be republished. This one was first published in September 2012.
In the environmental debate, green sources of energy and energy conservation measures are oft-discussed topics. But between those endpoints, there are environmental benefits to be reaped as well. The future electrical grid will offer more flexibility, reduce transmission losses, and enable bidirectional energy flows and distributed generation.
The evolution of the grid
The first transmission grids were constructed at the end of the nineteenth century, based on direct current technology. Since wire losses were huge, coal-fired power plants had to be located centrally, near the consumers. Eventually, a shift was made into three-phase alternating current, which allowed for long-distance transmission and more remote power plants – such as hydroelectric stations, placed in rivers far from the centres of population.
The structure of the grid that then emerged has only seen minor adjustments until the present day. During the last decades, aerial cables have started to be replaced by underground cables – but for the most part, the Swedish electrical grid still has a network topology similar to the original one. Local grids merge into regional, interconnected through a public utility backbone of 15000 km high tension lines and fed by a relatively small number of large-scale power plants. As the electricity makes it way toward the end users, it is branched by distribution substations while converters gradually lower the voltage.
A new paradigm of power production
The process outlined above comes at a price, however. More than a quarter of the energy produced globally – corresponding to a billion tonnes of carbon dioxide emissions annually – is lost in transmission. Additional emissions are incurred by the way electricity production is matched to a fluctuating demand; in many parts of the world, regulating power and peak load power is provided by the burning of fossil fuels.
So, there is room for improvement. Transmission losses could be reduced by new technology in combination with a decentralized, distributed model of power production, where a larger part of the energy comes from renewable sources and local producers. But in order to make that happen, new infrastructure is needed. We need to build the smart grid.
What does it take then, for a grid to be called smart? The key word is flexibility, and perhaps the most important feature is adding real-time communication between consumers and producers, coupled with bidirectionality of the energy flow – so that, for instance, a house with solar panels can switch from being a consumer to feeding the grid whenever a surplus of electricity is generated.
The automatic information exchange between nodes in the grid would ease the balancing between production and demand. Demand could even be controlled in part, for instance by adjusting the price as production varies; producers and consumers connected to the smart grid would all take part in an on-going discussion, to find the most cost-effective and energy saving distribution of resources at any given moment.
While the traditional grid could be thought of as centralized producers surrounded by passive users, the smart grid would rather be a network of participants with no such predefined roles – akin to the difference between television and the Internet.
The components of the grid would be upgraded switches, transformers, and lines – but also a parallel system of computers, control systems and information technology. Compared to many other countries, Sweden has come a long way in replacing old electricity meters with new ones, capable of remote monitoring and control. This is a prerequisite for the more advanced features of the smart grid, thus making Sweden a leading country.
There are also other Swedish initiatives in the field. Smart Grid Gotland is a development project launched in 2012, a collaboration between the Swedish Energy Agency, the Swedish National Grid and a number of corporations. Until 2015, a large-scale pilot experiment will try out new technology in the existing grid, while also incorporating a substantial amount of wind power. The aim is to provide valuable experience for a future country-wide smart grid. A coordination council for smart grid was also appointed in 2012, bringing representatives from authorities, organizations, the business community and research settings together. A road map with recommendations will be presented on December 1st, 2014.
Grid energy storage
One of the main challenges for the future grid will be how to handle distribution and load-balancing, as renewables become a larger part of the power production. Most visions of the future energy mix predict solar, wind and other renewable sources to play a much more important role. These sources share a common disadvantage, however: production dependent on weather is intermittent in nature. For them to be able to grow beyond a certain point, a well-established smart grid capable of smoothing out the fluctuations might be a prerequisite.
One such smoothing feature could be provided through grid energy storage – which, for instance, might be implemented through a larger fleet of electric vehicles. When electricity is cheap and abundant, the vehicle fleet would be automatically charged. At other times, when electricity is scarce, their batteries would serve as a giant power buffer. In addition to this, the grid could strive to flatten load peaks by communicating with consumers, and working out a schedule for their energy usage – perhaps by asking boilers to suspend heating temporarily, or by restraining certain industrial processes.
High-Voltage Direct Current
Balancing a weather-dependent power production would of course be an easier task if grids were interconnected over a wide area, to include a multitude of weather conditions. Such transcontinental super grids would, however, require a backbone of very effective high tension lines.
A suggested future “super grid” linking renewable sources in Europe and in the MENA region together. (DESERTEC)
When the first DC lines were replaced by three-phase AC, the reason was to minimize loss. If the voltage is very high, however, DC actually suffers less loss than AC. But simply increasing the distribution voltage would have lead to another stumbling block, in the costly conversion to a lower voltage suitable for users. Back then, power conversion was more readily accomplished with AC – but since then, developments have been made. With new switches, converters and the advent of semiconductor electronics, HVDC, or high-voltage direct current, is once again state of the art technology. HVDC might be the enabling technology needed for wide area transmission across great distances, with negligible losses.
Sweden excels in HVDC research and development, with ABB, building on a heritage from three-phase pioneer Asea, being one important player. The company recently reported a breakthrough in switch technology, which might put the super grid within reach; HVDC switching used to entail a trade-off between fast but lossy semiconductors and slow but effective mechanical switches, but ABB claims spectacular results from combining the two together.
ABB is also developing a variant of HVDC called Light, designed to transmit power over long distances underground and under water. In the super grid puzzle, HVDC Light could be used for connecting offshore wind farms, and to act as a link between asynchronous AC grids.
There is reason to believe that we move towards a more efficient energy economy. Transmission of electricity will always be associated with energy loss, but by making the grid more flexible, conditions are put in place for more electricity to be locally produced and stored. At the same time, HVDC technology is beginning to make wide area transmission feasible. The puzzle is not yet entrirely put together – but more and more of the necessary pieces seem to be at hand.
The article was published in October 2014