Bridging the Transition to a Renewable Energy Mix

It is now possible to stabilize frequency drops in power networks within milliseconds thanks to a new combination of reactive power compensation and supercapacitors from Siemens. Up to 200 megawatts of power can be called up in an extremely short time. This technology closes a widening gap in power networks that are facing reduced input from conventional power stations while making use of ever more renewable energy and power from distributed generators in their energy mix.

 

by Sandra Zistl

It’s morning in Germany. Millions of people are starting their day, production facilities are powering up, and the need for energy is on the rise. More power is generated when it’s needed, and power stations ramp up their output accordingly… that was how things were in Germany and in many other parts of the world for a long time. The transition to a new energy mix, however, has made the situation more complex in many ways. Demands on grids are changing. Conventional power stations, which are responsible for maintaining network stability, are being closed down. But renewable power is available only when the sun shines or enough wind blows; input comes from small, distributed generators; hundreds of kilometers may separate generation facilities – some are on the open sea, for example – and energy consumers. Given these circumstances, a major consumer, such as a steel production plant, can have a noticeable effect on grid frequency, which will literally begin to fluctuate as such a facility ramps up or down.

Preventing Blackouts

“If no new solutions are implemented to stabilize grids, blackouts will become normal in just a few years,” says Alexander Rentschler, head of the Product Lifecycle Management (PLM) unit at Siemens Energy Management. The very first seconds following a frequency drop in a power network are crucial in terms of whether or not a blackout will occur. In view of this, Siemens is now introducing a technology that can make power available during these critical moments and thus balance fluctuations. Combining its SVC Plus (static synchronous compensator) with supercapacitors – known as SVC Plus FS – closes the gap caused by shutting down conventional power plants.

“If no new solutions are implemented to stabilize grids, blackouts will become normal in just a few years.”

To understand the innovative nature of what SVC Plus FS achieves, you need to comprehend the current situation in the power network. Although power networks always have to be capable of compensating for fluctuations, the transition to a new energy mix has heightened this need. It also means that the tools now available to accomplish this are of limited value. “When the number of gas or coal-fired conventional power stations is reduced,” explains Rentschler, “opportunities for natural cushioning are lost. Normally, the energy that is stored from generator flywheels or from steam generators, for example, is directly available.” Balance is restored within the grid within seconds. Experts call the energy thus stored in the rotating masses of generators “grid inertia.”

Huge Potential Costs

All of this changes when more environmentally friendly energy sources enter the picture. “Renewable energy is fed in via converters,” explains Rentschler. “In other words, there is no direct access to the stored energy in a wind turbine. Or take the energy storage stations in the grid, such as pumped-storage power plants – these can respond to a frequency drop only after an interval, once a mechanical slide valve in a pressure line has been opened, for example.”

But a stable grid is so vital for both industry and infrastructure that any lost seconds can have serious repercussions. “For example, major consumers can be deliberately switched off if the frequency drops from the standard 50 Hz to below 49 Hz, and power plants are taken off the grid at 47.5 Hz,” says Rentschler. Such outages can result in huge costs. To avoid this threat, power stations are operated on stand-by, which is very inefficient. “In addition, this situation acts as a brake on the energy transition.”

 

Robust, Agile Power Networks

 

According to Rentschler, SVC Plus FS makes the grid more robust and increases its inertia. It creates a bridge for the energy transition. Siemens is the first provider to offer a reactive power compensator in combination with supercapacitors, making it possible to access up to 200 megawatts of power in an extremely short time. “The benefit of supercapacitors lies in their structure. Whereas a chemical process takes place when a battery charges, the process with supercapacitors is electrostatic: charging and discharging are much faster if electrons rather than molecules are set in motion,” Rentschler explains.

Siemens is the first provider to offer a reactive power compensator in combination with supercapacitors.

In addition, the capacitor panels in which Siemens bundles the units built by partner entity Maxwell take up less space. Managing the combination of reactive power compensation and supercapacitor, the connection to the grid, and system integration is assured by Siemens. “We adapt the system to suit the customer’s specific requirements,” notes Rentschler. “If they need more power, they can simply install more panels.” That gives them a competitive advantage. They can make power available directly to stabilize the grid if frequency drops occur. SVC Plus FS also means operators do not have to rely on other buffer solutions, which may be inefficient, such as bypass operation at power stations. Transmission system operators worldwide – for whom this situation poses a problem and who have been considering the option of batteries or flywheel storage – have expressed interest in this solution.

2018-08-21

Sandra Zistl

Picture credits: from top: 1. picture alliance / dpa

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