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The inverter technology by STABL Energy
Inverters from STABL Energy are more than just a component of a battery storage system. Thanks to the innovative modular approach, they simplify the design of electricity storage systems and enable affordable, sustainable energy supplies for trade and industry. Compared to conventional products, energy losses are reduced by up to 70 % and operating costs are lowered by 40 % - all with almost the same investment costs. Find out more about the technology and what's behind the award-winning inverters here.
Conventional power storage systems consist of a high-voltage battery pack and a central inverter. Several permanently interconnected modules form the battery pack, which can have lethal voltages of up to 800 V. The central inverter converts this DC voltage into AC voltage suitable for the grid and thus connects the storage unit to the power grid. This results in energy losses that cost the operator money and also increase CO2 emissions.
With the technology by STABL Energy, the construction of electricity storage systems is considerably simplified. Instead of statically interconnecting the modules, our STABL modules interconnect them dynamically. The power storage is a conglomerate of absolutely safe battery modules with touch-safe voltages of less than 60 V. This approach makes the central inverter unnecessary. Compared to conventional systems, losses are reduced by up to 70 % and both operating costs and CO2 emissions are reduced by up to 40 % per year.
The advantages of the STABL technology
Normal battery inverters switch the high voltage of the energy storage system on and off for different lengths of time. This process is called pulse width modulation. The resulting voltage must be smoothed by a so-called line filter so that it complies with the standards and requirements of the power grid. That costs efficiency and causes losses.
In science, the STABL Energy approach is referred to as a “modular multilevel inverter” and is widespread in high-voltage direct current transmission. STABL Energy was the first company to optimize it for battery storage systems. Here the sinus voltage is simulated by connecting the individual battery modules one after the other in series. The step voltage generated in this way is much more similar to the desired grid voltage than that of conventional inverters. This means that the line filter can be smaller and losses are minimized.
In conventional electricity storage systems, the weakest cell determines the storage system's performance. With increasing use, the maximum capacities of the battery cells drift apart and so the cell with the lowest capacity determines the capacity with which the remaining cells can be charged. The capacities can be redistributed through so-called balancing - but this costs energy and causes further losses.
With the modular approach from STABL Energy, the weakest cells no longer have an effect on the entire storage system, but only on the module level. Furthermore, the modules are charged and discharged depending on their individual state of charge, so that the states of charge of the modules automatically align with one another. This allows you to get more energy out of your storage and use it longer than conventional storage.
Proof of function
In a master's thesis at the Technical University of Munich, the efficiency of our modular design was tested and compared to that of a conventional inverter.
The results show a very high efficiency of our approach with up to 99.4%. Compared to a conventional central inverter, higher efficiencies were found over the entire power range, which is mainly due to the significantly lower switching voltages and frequencies. Instead of switching the entire voltage of a high-voltage pack, with STABL technology, the alternating voltage is generated by dynamically connecting and disconnecting battery modules with low switching voltages. Another advantage of the STABL technology is the significantly lower total harmonic distortion (THD) before filtering. The values achieved make it possible to install smaller, cheaper and more efficient filters.
The high conversion efficiency affects the efficiency of the entire storage system, thus reducing the cost of electricity (LCOE) and enabling an earlier and higher return on investment.
Further advantages, possible uses & outlook
Deep battery analytics
The STABL modules can measure the battery modules during operation and automatically save the data in the STABL Cloud. STABL Energy generates the most precise data on health status, temperature, current and voltage in real time and thus helps battery manufacturers to monitor the performance of their cells. For example, battery manufacturers can discover defects in certain batches or find out which external circumstances have which effects on the cells. Insurers also benefit from this data, as the data enable reliable risk assessment and insurance and reinsurance companies can use it to design attractive insurance policies.
Returns from used vehicle batteries will pose a major economic and environmental challenge. In fact, batteries from electric cars are deemed unsuitable as soon as they contain 80 % of their original capacity. But these batteries are still well suited for stationary systems and it is estimated that they can be operated for up to ten years. With the modularity of STABL Energy inverters, second-life storage systems can be operated more efficiently and cheaply than with conventional inverters.
Diverse fields of application
Our inverter can output any imaginable output voltage, including DC voltage. Thanks to its software-defined function, we enable storage integrators to simplify their product portfolio and open up different markets with one and the same hardware. In an electric car, it is even possible to charge the battery and operate the engine with the same power electronics.
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