09/14/ 2023
Source: Energy & Management Powernews
Researchers are finding large differences in efficiency among popular electricity storage systems. Two 10-kW systems are among the latest test objects they have subjected to an investigation.
In the evaluation of home storage systems, the energy management of the systems is currently not considered, as the researchers at the Berlin University of Applied Sciences (HTW Berlin) note. Since energy management has a direct influence on battery aging and thus the economic efficiency of the system, they have developed a standardized test for solar power storage systems in the "Perform" research project together with the Karlsruhe Institute of Technology (KIT).
From the range of lithium-ion systems commonly available on the market, the researchers acquired "two frequently installed" solar power storage systems. These, the researchers explain, were two independently acquired DC-coupled storage systems consisting of a hybrid inverter and a lithium-ion battery storage system. They subjected these systems to tests using a specially created efficiency guide for PV storage systems. This is intended, as HTW Berlin explains, to provide uniform, verifiable criteria with which the performance of home storage systems can be assessed.
Power Storage Inspector is intended to enable comparisons
The two 10 kW systems recently investigated can now be found in the so-called "Power Storage Inspector" of HTW Berlin. This builds continuously on the results of conducted investigations and was developed to support private individuals in their search for an efficient home storage system. All characteristic values listed in the on-line callable Tool would be, so it assures the university, determined by independent test institutes and examined for plausibility. The university also offers interested storage manufacturers the opportunity to provide "more transparency in the storage market" through the independent testing of their products. They can still participate in the next edition of the electricity storage inspection - the "Electricity Storage Inspection 2024" - until November 15, 2023. Contact person for this is the research group solar storage systems of the HTW Berlin.
The two most recently examined solar power storage systems classify the scientists according to their investigation results on the places 16 and 20 - of altogether 20 current storage products already evaluated in this year.
With view of the determined, low energy efficiency classes Nico Orth, scientific coworker at the HTW Berlin, notes: "The conversion efficiency of a photovoltaic storage system should be above 92 percent even with low power consumption at night of a few hundred watts." However, the results would show: If one of the two battery storage systems is discharged with, say, 525 watts, the electrical consumers in the household would only be able to use 443 watts of that due to the high conversion losses in the hybrid inverter. "This corresponds to an inverter efficiency of only 84 percent, the lowest value of the hybrid inverters analyzed this year," Orth said. In comparison, the most efficient systems available on the market could show ten percentage points higher efficiencies at the same load.
"The second system is far behind with a standby consumption of 64 watts," said Robert Schreier, who tested the two systems at KIT. The settling time is also above average at nearly 11 seconds, he said. The settling time indicates how long the power storage unit needs to ramp up to the currently required power. By comparison, the most efficient devices in the 2023 power storage inspection scored with a settling time of less than 200 milliseconds and 2 watts in standby mode.
Further results of the two recently studied home storage units can be found on the KIT website. The Electricity Storage Inspector as a free web application is also available there. The study already carried out "Stromspeicher-Inspektion 2023" is there - with naming of the manufacturers - also as a PDF downloadable.
Author: Davina Spohn
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