Efficiency rate, self-consumption, rapid speed of regulation – the key figures to consider when purchasing an energy storage system.

The variety of energy storage systems currently available on the market is huge which is why even experts have difficulties to compare and evaluate them. And it’s even more complicated for end consumers. For this reason, various major German manufacturers, research institutes and associations tried to find key figures which make it possible to compare energy storage systems. VARTA storage is also part of this project. The result is an efficiency guideline for energy storage systems (currently only available in German). The guideline contains key data which allow a comparison of energy storage systems of different types. It also defines the measurement conditions for a consistent basis of comparison. The main goal was to create one key measurement which allows the comparison of different energy storage systems. For that they are currently working on the System Performance Index (SPI). The SPI measures the actual cost reduction from the energy storage systems compared to a theoretical saving potential of a loss-free system in an average household. However it’s difficult to find the right way to measure it which is why it’s still not finalized. There also other approaches to find the right key figure, so it’s currently unclear which key figures will become the norm. Nonetheless key data points like efficiency rate, self-consumption and rapid speed of regulation can give an indication. In combination with the consultation of an installer the decision for an energy storage system should be easier. That’s why we explain these key figures below. Efficiency rate The efficiency rate indicates the energy loss whilst charging or discharging the energy storage system. Simply said, an efficiency rate of 95 % means an energy loss of 5 %. The missing 5 % needs to be covered by energy from the public grid. Therefore, a high rate indicates an efficient way of using green energy. Because the efficiency rate is affected by different factors, it’s not possible to give one number. It’s rather a course which depends on the respective charge or discharge capacity. There is also an approach to use the weighted average, called EuroEta, as the crucial key figure for the efficiency comparison. But as mentioned before there are difficulties to use it for all kinds of energy storage systems. The following graph shows the efficiency rate course of the VARTA pulse 6. Overall the VARTA pulse 6 has a remarkable efficiency rate. Especially for a low base load, as is often the case in the evening or at night, the figures are excellent. Effieciency rate VARTA pulse 6 Self-consumption The self-consumption is also a significant figure for the efficiency of an energy storage system. The more energy the storage system needs for its operation, the less energy is available for the house consumers. The self-consumption is differentiated in the consumption during the operation and the standby consumption. As with other household devices, an energy storage system needs some energy to sustain the basic functions even if it’s switched off. The consumption during the operation and the standby consumption of the VARTA energy storage systems are outstanding. The VARTA pulse 6 needs only 15 W during operation and only 1.4 W in standby. With this low Standby consumption the VARTA pulse 6 is one of  the best on the market. Rapid speed of regulation The rapid speed of regulation is also an influencing factor for the efficiency. It describes the time period which is needed to switch from energy of the public grid to energy of the energy storage system. When switching on a household device, e.g. a kettle, first the energy of the public grid is used. Then it takes a few seconds until the energy storage system reacts and starts to provide energy. There is also a distinction between reaction time and transient time. The reaction time measures the times it takes for the energy storage system to react to the signal that energy is needed. The time it takes until the energy storage system can provide the actual needed capacity is called transient time. A rapid speed of regulation means less energy from the public grid and therefore less energy costs. The reaction time of the VARTA element 12 with 0.2 s and a transient time 2.3 s is extremely fast. It takes only 2.5 seconds from switching the device on to the moment the energy storage system starts to provide green energy. Compared to other energy storage systems, the VARTA energy storage systems have an outstanding performance. The following table summarizes the key figures of the VARTA pulse 6 and the VARTA element 12. Besides the mentioned key figures there are also other influencing factors like the dimensioning of the solar system and the energy storage system. It’s not efficient to combine a big energy storage system with a small solar system in a household with low annual energy consumption. Use our calculation tool to find a suitable energy storage system for your requirements. Because of the various aspects which have to be considered before buying an energy storage system, a consultation with an expert is essential. If you’re interested in buying an energy storage system, don’t hesitate to contact our service team. They will recommend to you a certified VARTA partner in your area. Here you can find an overview of our energy storage system. For current news, follow us on LinkedIn or Twitter.

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Emanuel Sican
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