energy storage

Why Do Wind Turbines Need Virtual Inertia?

Skeleton is working with leading wind turbine manufacturers and wind park developers to ensure the power quality of the grid. 

Peter Rudling from Energy Education blog summarized:

Several media reported on a delicate situation in the German power supply. On the evening of August 14 2021, the production of renewable energy collapsed. Power generation could no longer keep up with power consumption. As was reported, the demand for electricity in Germany in the early evening of 14 August was around 50 gigawatts. However, the production of solar power, which was still over 30 gigawatts in the afternoon, collapsed to just 3 gigawatts.

The need for renewable energy has never been so urgent, both from the perspective of sustainability as well as energy dependence from foreign sources. However, substituting traditional power sources with renewable alternatives comes with technological challenges. One of them is grid instability due to the lack of system inertia.


Traditional generator-dominated power systems using coal, gas, hydro, and nuclear energy contribute to maintaining grid stability and balancing energy production and consumption. However, in inverter-dominated power systems using energy storage, PV, and wind systems, the low inertia caused by the lack of rotating masses, becomes a problem. As a result,...

Skeleton wind warm supercapacitor grid energy storage

Grid or system-level solution 

Naturally, there are many ways of solving grid instability issues and the best alternative depends on the specific problem at hand. However, one key component of different solutions is energy storage for frequency regulation and peak energy deferral. Some countries in Europe are addressing the challenge on the grid level. For example, German transmission system operators (Tennet, Transnet BW) are incorporating both static synchronous compensators but more interestingly virtual inertia devices (e-STATCOMS, with multi-digit megawatt level of power). 

However, integrating grid level solutions is slower and more expensive than deferring the problem to the energy generator. For example, getting necessary permits is time-consuming and the achieved result lacks flexibility. That is why manufacturers of wind turbines and wind farms are interested in delivering the solution themselves at the system level. Skeleton is working closely with the leading wind power original equipment manufacturers (OEM) to support the incorporation of virtual inertia with supercapacitors.

Our supercapacitor energy storage can provide extra power to emulate the inertial response of spinning masses, reducing drastically frequency issues in the grid. One of the key advantages of supercapacitors is their capability to respond to demand almost instantly. They provide a great level of active power for a short duration at a much lower footprint than all other main energy storage technologies. As a result, supercapacitors are ideally suited to stabilizing the grid frequency in virtual inertia applications. 

Skeleton is a vertically integrated company starting from producing the raw material of supercapacitor cells to providing the OEMs a standard or customized cabinet level solution with our rack-mounted modules that can be easily integrated to the overall system and controlled with grid forming algorithms to ensure better power quality.

Why choose supercapacitors? 

System level energy storage can be based on either batteries or supercapacitors with both having their pros and cons depending on the circumstances. In the case of providing virtual wind inertia, supercapacitor-based solutions, such as the modular SkelGrid supercapacitor system, are better equipped to deal with the high cyclic requirements and many charges and discharges needed daily. In addition, wind turbines equipped with virtual inertia systems can also provide low voltage ride through (LVRT) capability. In case of faults in the transmission system, it is essential that a wind park stays online in order to prevent major blackouts by feeding the fault with extra load for a certain amount of time. Supercapacitors can supply this overload, leaving the upstream turbine un-affected and giving the grid enough time to clear the fault while keeping its functionality.

To achieve the same power with battery-based system, a footprint of 5-10 times the size would be needed, depending on the system requirements. Additionally, supercapacitors require a much less sophisticated safety system compared to the chemical reaction-based battery solution. Supercapacitors are inherently safer since they store energy in an electric field and do not go into thermal runaway, causing catastrophic failures. Furthermore, in the highly unlikely case of supercapacitors catching fire, the flames can be extinguished with a dry chemical or water extinguisher by removing the oxygen supply to the fire. Lithium-ion batteries, on the other hand, need to be let burned out, as the reactants of the combustion are already present inside the cell and thus can’t be physically separated.

Benefits of supercapacitors: 

  • High power density & low resistance. 
  • Over 1 million cycles & longer calendar life: 15 to 20 years.
  • -40°C to +65°C operating temperature range. 
  • Considerably lighter than batteries for high power applications. 
  • Systems easily fully discharged for safe maintenance operations. 
  • Simpler monitoring and system health checks for systems and modules. 
  • Supercapacitors do not leak or contain acid or lead. 
  • No use of rare earth materials, cobalt, or other unsustainable elements which put stress on the global supply chain, and at the same time complicate drastically the recycling process. 

Get in touch with us to hear more about the advantages of supercapacitor energy storage in renewables.

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