| By Akshat Rathi Guy Nicholson’s patience with antiquated grid systems has been wearing thin. When I spoke with him in late June, it was one of the hottest days of the UK summer, and he was standing outside in the sun. I asked him whether renewables make the grid more vulnerable to blackouts. “This weekend we had loads of solar and loads of wind. We had negative prices for electricity. So why is the UK still burning gas?” Nicholson, head of zero-carbon grid solutions at Statkraft, asked back. “It’s to maintain inertia.” Nicholson was giving me a tour of the facility that Statkraft built in Liverpool in north England to add inertia to the grid without burning gas. Yes, it’s that “inertia” we all learned about in school: Newton’s first law of motion states that an object remains in motion unless acted upon by an external force. But what does inertia have to do with keeping the lights on? Ever since the grid was built nearly 150 years ago, it’s been mostly powered by spinning objects: Turbines rotated by steam (generated by burning coal or controlled nuclear reactions), falling water (aka hydropower) and, more recently, directly burning natural gas. These physically spinning objects create inertia on the grid such that, if one power plant suddenly fails, there’s enough momentum in the system to absorb the change and keep power flowing to your home. Solar power needs no spin. Light falls on silicon and moves sub-atomic electrons to generate electricity. As the grids add increasing amounts of cheap solar to the mix, the system’s inertia declines and, without adequate measures, it makes the grid less able to deal with faults.  Photographer: Rebecca Noble/Bloomberg With politicians under pressure to lower the cost of electricity and meet climate goals, more renewables will need to be added to the grid. So the near-term solution to add inertia is using devices called synchronous compensators (or synchronous condensers). I didn’t just get to see one in action in Liverpool, but I also got to visit the Siemens Energy factory this month where they manufacture these grid-stabilizing devices. “It’s huge and complicated to build,” said Sharlena Brock, head of special electric machinery at Siemens Energy, during the tour of the factory in Mülheim, Germany. The factory has been flooded with demand for synchronous compensators. Without all the protective covering, the device looks like something out of a science-fiction movie. It’s made from thousands of individual parts that are precisely engineered and carefully assembled. That’s needed because the largest synchronous compensators that Siemens Energy builds can provide as much “reactive power” as a nuclear power plant.  The bars of a stator housing are installed in the winding shop, where further work steps also are carried out at Siemens Energy, Mülheim an der Ruhr, Germany on Aug. 8. Photographer: Fabien Ritter/Bloomberg Inside each synchronous compensator, a rotor — often weighing up to 100 tons (almost as heavy as a blue whale) — spins at 3,000 rotations per minute. The synchronous compensator's 100-ton rotor needs to match the frequency of alternating current, which swings between positive and negative voltage 50 times per second. This is the frequency at which most of the world consumes alternating current coming into homes and offices. If tires rotated 3,000 times per minute, that car would be going at 400 kmph — faster than any F1 car has gone. With a weight of hundred tons, you can get a sense of just how much energy is stored in these spinning devices. It’s why a synchronous compensator can have enough inertia to match that of a turbine in a large power plant that provides electricity to hundreds of thousands of homes. One day the grid could operate without any spinning devices. So-called grid-forming inverters attached to batteries can provide “synthetic” inertia, but grid operators haven’t seen them in operation long enough to fully switch to them. For more on grid-stabilizing technologies and what the Spanish blackout is teaching grid operators, read the full story on Bloomberg.com. | 
