As wind and solar farms replace polluting forms of energy generation, we increasingly hear the question: how do we keep the electricity grid stable?
A thesis out from Chalmers University of Technology in Sweden explores this issue and makes a compelling case for a forgotten piece of grid technology: the synchronous condenser. It might not sound glamorous, but in a future powered by renewables, this low-key machine could become one of the grid’s most vital players.
The Problem: The Grid Is Losing Its Anchor
Traditional power grids were built around large spinning machines (powered by coal, gas, hydro and nuclear plants) that generate inertia along with electricity. Inertia acts like a buffer: when something fluctuates in the grid (say, a sudden drop in demand or supply), these heavy machines slow down the rate of change. They absorb the shock.
But wind turbines and solar panels, connected via power electronics, don’t spin in the same way. They offer little to no inertia, and that means modern grids are becoming faster—sometimes too fast for their own good. A sudden fault or frequency dip could cascade into widespread blackouts.
That’s where synchronous condensers come in.
What They Are—and Why They Matter Now
A synchronous condenser is essentially a spinning generator that’s not connected to any load. It just sits there, turning. But in doing so, it provides three critical services:
- Inertia, stabilising frequency;
- Reactive power, which helps control voltage;
- Short-circuit strength, which helps the system detect faults.
These services used to come “for free” from fossil fuel power stations. In a renewable-powered world, we have to rebuild that stability with other tools. This thesis shows that synchronous condensers are one of the most proven, cost-effective ways to do it—especially during the transition phase, before fully digital grid solutions (like grid-forming inverters) are rolled out at scale.
What’s New in This Study?
The author of the thesis didn’t just review the benefits of synchronous condensers; they simulated their impact on a model of the Swedish grid under high-renewables scenarios. Using MATLAB/Simulink, they analysed how these machines behave during short-circuit events and frequency instability.
Key findings include:
- Adding synchronous condensers significantly improves voltage and frequency stability, even when renewable penetration is above 70%;
- Their performance is consistent and predictable—unlike battery-based or inverter-driven alternatives, which can vary by technology and control design;
- In grids where nuclear plants are phased out (as in parts of Sweden and Germany), synchronous condensers can replace many of the stabilising functions those plants used to provide.
A Bridge to the Future Grid
While many engineers are excited about next-generation grid-forming inverters (and rightly so), those systems are still maturing. This thesis positions synchronous condensers as a bridging technology: not a competitor to digital solutions, but a way to keep the lights on while we modernise.
They require minimal new infrastructure, can be retrofitted from decommissioned generators, and have operating lifetimes of 30+ years.
Across the Nordics and Beyond
Though this study was based in Sweden, its conclusions apply far beyond. Countries like Canada, Finland, and Norway are phasing out fossil fuels while increasing wind and hydro power. These grids need inertia and voltage control—but without the legacy machinery that used to provide it.
Synchronous condensers offer a clear, technically mature option—one that energy planners, policymakers and grid operators would do well to revisit.
The Key Takeaway
While leading-edge tech points to better cleaner energy possibilities, sometimes, the solution is already sitting in a warehouse, half-retired. This study makes a powerful case that these quiet, steady and reliable synchronous condensers deserve a central role in the clean energy transition. Because if we’re going to electrify everything, the grid itself needs something to hold onto.
Source
Evaluation of Synchronous Condensers in Modern Power Grids for Enhancing Grid Stability, Master’s Thesis, Chalmers University of Technology, 2025
Boˆreal 