The hope that increasing use of renewable energies and the related geographic proximity between their sources and consumers would diminish the importance of power grids was short-lived. Today we know that this has not happened. Although photovoltaics, solar, wind and, above all, hydropower are by now contributing about one fourth to worldwide electricity production, they’re not leading to grid independence. Regional self-sufficiency remains a utopian idea even in the 21st century. The opposite is true: Only a connection with many other producers results in the requisite supply security delivered by the small-scale roof-top power plant or the wind turbine on a village field.

Proximity to the consumer is not always an advantage either: For instance, photovoltaic cells in tropical regions harvest more than twice as much energy from sunlight as comparable systems in more moderate climatic zones north of the 40th parallel, where the hunger for electricity in cities like New York, Berlin, Moscow and London is greater than elsewhere. In interaction with prices for modules and inverters, which have been in constant decline now for years, solar parks in sunny regions are becoming increasingly attractive. Such a solar park is currently developing in the desert state of Dubai, where the production costs for one kilowatt hour from solar energy are supposed to drop to a mere 1.5 cents, which is a fraction of what electricity from conventional power plants costs. Consequently, there’d be plenty of good reasons for creating global power transmission lines so that electric snowmobiles in the icy conditions of the Russian port city of Murmansk could be operated with CO₂-saving solar power from the desert city of Manamah in the future.

High-loss power transmission

If it weren’t for Q=I*L*R/Delta U, the formula that causes electric utilities and operators of transmission grids headaches worldwide. The formula expresses how electric current on its way through copper and aluminum suffers a voltage loss on every meter or yard it travels, while dissipating energy – usually in the form of heat – to the environment. To reduce these so-called transmission losses, the cross sections of the lines must be enlarged or the current stepped up.

Today, the so-called transport level of the synchronous grid of Continental Europe (formerly known as the UCTE grid) operates with 380 kV alternating current. Russia and Canada even transmit electric current at levels of up to 750 kV, with one to six percent of the transmitted energy being lost per one hundred kilometers (62 miles). The loss, for instance, increases when the line bundles heat up to 80 degrees centigrade (176° Fahrenheit) under load or emit their typical crackling noise via so-called corona discharges on hot summer days. The electrical energy lost by buried-cable transmission on the way to the consumer amounts to yet another fourth.

AC vs. DC

That’s why direct current has been seeing a revival for some time now by means of so-called high-voltage direct current (HVDC) transmission lines, for instance in the case of connections to offshore wind farms or point-to-point connections across long distances. That’s where 3-phase AC technology reaches technical limits, because its lines act like large electric capacitors. The line losses of direct current are up to ten times smaller, but the transformer and circuitry technology at the end points is clearly more complex. HVDC lines through the Skagerrak, for instance, have been reliably connecting the North-European synchronous NORDEL grid with the synchronous grid of Continental Europe since 1977.

In spite of such connections the European synchronous grids are far from being a highly efficient “supergrid” although respective initial concepts were developed even before the turn of the millennium. In such a supergrid, huge amounts of electricity could be hauled across longer distances – or imported, for instance from North African countries with plenty of wind and sunshine.

An agile and efficient distribution of large power packages from renewable energies across national borders or continents would also alleviate fears of capacity bottlenecks due to so-called “dark doldrums,” because there’s always a place in the world where the sun shines or the wind blows. That’s why supergrids would marginalize the requirement for huge storage capacities and conventional base-load power plants, according to energy expert Dr.-Ing. Gregor Czisch.

In view of so many positive aspects, the question arises why a supergrid isn’t crisscrossing our planet yet. “While regional supergrids could bring cleaner, more efficient, and more cost-effective electric power systems, their development is complicated by a number of factors,” explains Jessica Lewis, senior research analyst with Navigant Research. “These include limited political will, lack of harmonized standards, complex authorization and permitting procedures for cross-border transmission projects, and a conventional view of energy security as a national imperative, with individual countries reluctant to leave their supply security in the hands of others.”

Initial supergrid threads have been connected

Even so, the number of individual high-performance power transmission lines for renewable energy keeps growing. Offshore wind farms in the German North Sea deliver their electric power to the mainland via HVDC lines. The largest HVDC underground cable project in the world is to be implemented along the German SuedLink corridor. In the United States, such a connection exists for wind power across a more than 1,000-kilometer (620-mile) distance from Oklahoma to Tennessee. In Brazil, 600 kV flow through a 2,400-kilometer (1,500-mile) long HVDC line, and in the so-called Champa Project in India, it’s 800 kV across 1,365 kilometers (850 miles).

The construction of HVDC lines beyond the magic 1-megavolt limit is pioneered by China, which has been transmitting direct current with 1.1 megavolts from Changji to Guquan across 3,000 kilometers (1,860 miles) since 2019 – with a loss rate of less than five percent across the entire distance. For comparison: only 380 kilometers pass through the German 3-phase AC grid. Via the energy agency GEIDCO initiated by Beijing, the country is planning to drive the construction of a world-spanning energy grid by 2070, even across oceans. Estimated costs: a mammoth amount of 38 trillion U.S. dollars. The enormous costs are no doubt another reason why the global supergrid is currently very large-meshed.

The Chinese megaproject, as a supergrid level, is intended to interlink the continental transmission grids. The cumbersome shipping of energy across the oceans on board of gas and petroleum tankers could then become history and, instead, Saudi Arabian desert sun might heat the fishing lodges on the Aleutian Islands via electric power cables.

Innovative technology from Schaeffler for sustainable power

Mobility is intended to become more climate and environmentally friendly – for instance by means of electrically propelled vehicles. However, this only makes real sense if the electric power for them is produced in clean ways. Solar, hydropower and wind power systems are suitable for this purpose. Schaeffler supplies crucial components and system solutions for all of them.

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Wind power
Worldwide, near-ground-level wind power has the potential of delivering output of more than 400 terawatts – about 20 times the worldwide energy requirement. As one of the world’s leading roller bearing manufacturers and development partner of this sector, Schaeffler, with the requisite extensive expertise, has been producing large-scale bearings and other components for wind power systems for more than 30 years. State-of-the art calculation and simulation programs optimize their design. Schaeffler bearings are utilized in assemblies ranging from the rotor shaft to the transmission and generator to the wind tracking and blade adjustment systems. Schaeffler’s digital condition monitoring ensures high system availability and reduces maintenance requirements.

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Hydropower
Hydroelectric power stations around the world produce clearly more electricity than nuclear power plants and satisfy more than 16 percent of the global electrical energy requirement. Beyond the conventional utilization of hydropower, new technologies using the movement of waves and currents in the oceans to produce electricity are increasingly making headway. Be it for conventional or new approaches to harnessing hydropower – Schaeffler offers suitable bearing solutions and engineering resources.

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Solar power
Every day, the sun supplies enough energy to cover the worldwide requirement of a whole year. To achieve maximum capacity, solar power plants have to operate at particularly high levels of efficiency, precision and failure safety. As a development partner and supplier, Schaeffler is currently engaged in a range of projects such as parabolic trough, solar tower, Fresnel and Dish Stirling power plants. Schaeffler offers a diverse portfolio of rolling and plain bearings for the tracking systems of solar power stations.

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