The STABL technology
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Inverter for battery storage from STABL Energy
Inverters from STABL Energy are more than just a component of a battery storage system. Thanks to the novel modular approach, they simplify the design of electricity storage systems and enable a low-cost sustainable energy supply for commerce and industry. Compared to conventional products, energy losses are reduced by up to 70 % and operating costs are cut by up to 40 % - all at almost the same investment cost. Learn more about the technology and what's behind the award-winning inverters here.
Conventional storage consists of hard-wired battery modules.
All battery modules must be of the same series and have the same states, internal resistances and State of Health.
If a battery module fails, the entire storage system fails.
The central inverter requires high input voltages. This is the only reason why battery storage systems are built the way they are.
Konventionelle Wechselrichter für Batteriespeicher sind zu ineffizient und benötigen zu viel Platz.
We decouple the battery modules from each other and each battery module is connected to a STABL module.
The STABL modules are dynamically interconnected. The STABL master receives the commands from the energy management system and orchestrates the interconnection.
The battery modules are independent of each other due to the new design. This means that modules of different states can also be installed in one storage unit.
The STABL modules can be easily integrated into your existing rack concept. No additional space is required due to an inverter the size of a refrigerator.
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
The dangerous high-voltage battery pack is switched on and off.
no matter which nominal voltage is currently required.
The grid wants a perfect sine wave voltage.
Conventional inverters periodically switch the full battery voltage on and off. This is inefficient and dangerous. In addition, the resulting pulse pattern must first be filtered so that the output voltage of the inverter is grid-compliant.
Depending on the voltage value currently required, the STABL technology first switches one, then two, then three, and so on battery modules in series. This creates a staircase voltage that resembles the sine wave much more than the pulse pattern on the left.
The result: more efficiency for you and your customers.
Instead of using the dangerous static HV battery pack, safe battery modules are dynamically interconnected to generate the output voltage.
By the way, the frequency and form of the voltage is completely flexible. The STABL inverter can also output DC voltage, 60 Hz sine or a step voltage.
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, STABL Energy's approach is called a "modular multilevel inverter" and is widely used in high-voltage DC transmission. STABL Energy was the first company to optimise it for battery storage systems. Here, the sinusoidal voltage is simulated by connecting the individual battery modules in series one after the other. The step voltage generated in this way resembles the desired mains voltage much more than that of ordinary inverters for battery storage. This means that the grid filter can be smaller and losses are minimised.
In conventional battery storage, the weakest cell determines the performance of the storage. With increasing use, the maximum capacities of the battery cells drift apart and thus 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 of a battery storage system, higher efficiencies were shown across the entire power range, mainly due to the much lower switching voltages and frequencies. Instead of switching the entire voltage of a high-voltage pack, STABL technology generates the AC voltage by dynamically switching battery modules on and off at low voltages. Another advantage of 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 of used vehicle batteries will pose a major challenge to the economy and the environment. In fact, batteries from electric cars are deemed unfit for use as soon as they still contain 80% of their original capacity. But for stationary systems, these batteries are still good to go and it is estimated that they can still be used for up to ten years. With the modularity of STABL Energy's inverter technology, second-life storage can be operated more efficiently and cheaply than with conventional inverters for battery storage.
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.