At around 230 terawatt hours, industry is responsible for almost half of the total electrical energy demand in Germany. Measures to reduce energy consumption are therefore particularly worthwhile in industrial processes. In the manufacturing industry, for example, energy costs account for up to 10% of total production costs - in energy-intensive industries even up to 40%. Following key political decisions such as the Paris Climate Agreement, regulations and guidelines at national and international level are aimed at exploiting the potential for savings and reducing CO2 emissions. The requirements for companies therefore include the use of energy management systems in accordance with ISO 50001 as well as proof of their effectiveness in the form of efficiency improvements in accordance with ISO 50003 and the implementation of ecodesign requirements for electrical drive systems in the low-voltage range in accordance with the European standard EN 50598.

One way to significantly reduce the cost of electrical energy is to specifically cap peak loads. But that's not all: at around 70%, the majority of industrial electricity requirements are accounted for by electric drives and motors, which move industrial robots, servo presses, CNC systems, shelf operating devices, elevators and cranes, among other things. Most of these machines and systems are capable of recuperation and therefore allow kinetic energy to be converted into electrical energy when braking. As the motors in these applications are constantly alternating between braking and acceleration, the energy storage systems must have a high capacity in the short term. Braking energy can therefore only be used by extremely cycle-resistant and powerful energy storage systems.

Flywheel energy storage systems (FESS for short) have the right properties for these applications. The technology, also known as KERS from Formula 1, is based on electromechanical short-term storage systems that work according to the law of conservation of angular momentum and store energy in rotating masses. They consist of an integrated high-speed electric motor that is operated both as a motor and as a generator. The rotation stores energy kinetically, which is why flywheel mass storage systems are also known as kinetic batteries. Within milliseconds, full power is typically available for around 30 seconds. The higher and more frequent the load cycles, the more efficiently the system can be used.

Advantages of flywheel technology

With Gerotor HPS, energy recovery from Formula 1 can also be used for electric motors in industry.

© Gerotor

The Bavarian start-up Gerotor has optimized this principle for industrial applications with the Gerotor HPS high-performance storage system. As a mechanical component, the energy storage system is low-wear and low-maintenance, is not subject to any chemical ageing process and therefore allows an almost infinite number of charging and discharging cycles during its service life of typically 20 years, regardless of the depth of discharge. The efficiency is up to 95 %.

Rest losses caused by friction on the bearings and the flywheel masses are reduced by a vacuum chamber in which the flywheel mass runs. In addition, flywheel mass accumulators are largely insensitive to ambient conditions: In the case of the HPS, operation is possible at temperatures from -25 °C to +60 °C. Thanks to smart algorithms, the storage system is also able to optimize itself for maximum energy efficiency: As a self-learning storage system, it measures the behavior of the underlying application with high precision to ensure efficient operation. This behavioral data on machines and systems can then be recorded, pre-processed and made available via OPC UA for energy monitoring systems as part of IIoT, provided that all parties involved have given their approval.

The amount of energy stored in a flywheel depends on the mass of the rotor and its rotational speed. Low-speed flywheels rely on mass, whereby the energy doubles with the mass. The extremely high rotational speed of the Gerotor HPS of up to 60,000 revolutions per minute is particularly advantageous for the amount of energy (kJ) and power (kW) that can be stored. A faster flywheel mass system can therefore be relatively compact and still achieve very high performance. With a diameter of 220 mm, a height of around 250 mm and a mass of around 20 kg, such units can be connected directly to the DC link of the system or machine. Depending on the user's requirements, the storage capacity can be scaled as required by connecting several of the HPS units in parallel, each with a charging/discharging capacity of 50 kW nominal power and 60 kW peak power and an energy content of currently 135 to 300 kJ, or by combining them in power racks or power containers (AC) for groups of systems and entire plants.

Clean electricity without interruption

The Gerotor HPS energy storage system enables recuperation and thus reduces the energy drawn from the power grid. It can deliver high power to loads in a short space of time and thus also avoids peak loads in the energy supplier's power grid.

© Gerotor

With these properties, the described flywheel mass storage is suitable for various tasks. Basically, by compensating for harmonics, flicker and reactive power, it improves the power and grid quality both in internal DC grids and in the grid supply and prevents negative effects on sensitive components. It can also be used as a short-term uninterruptible power supply for up to 15 seconds in the event of power grid failures. As 97% of all power failures are in the range of up to 3 seconds, this bridging time is sufficient in most cases to transfer systems to a neutral operating mode. In unstable power grids, cost-intensive production downtimes can be avoided, which ultimately increases productivity.

Another application scenario is the use for peak load management in volatile industrial processes. Significant cost reductions in connected load and provision can be achieved here by smoothing load peaks and providing peak power. In addition to peak load capping, which focuses on reducing the cost of grid charges, the energy storage system reduces the energy drawn from the grid by recuperating braking energy. This reduces power consumption with the result that CO2 emissions are reduced in an electricity mix that is still heavily based on fossil fuels and climate targets can therefore be achieved more quickly.

In concrete terms, the cost savings from peak load management using a Gerotor HPS can add up to around 80 euros per kilowatt of connected load in medium-sized companies. Added to this are consumption reductions of 15 to 20 % on average thanks to recuperation. Depending on the application, significantly higher savings of up to 30% are also possible, for example for production machines in three-shift operation, as is common in series production in the automotive industry. The level of investment costs depends on the application and is typically in the mid to high four-digit euro range. The bottom line is that the purchase of such a storage system pays for itself within one to three years - often even faster due to the downsizing of other components and the reduction in base load consumption.

In summary, it can be said: Due to their power and energy density as well as their cycle stability, flywheel mass storage systems cover the requirements for active energy management in industry where battery storage systems are physically unsuitable.

Author
Marcel Werner is one of the founders of Gerotor.