Evaluation of the efficiency and resulting electrical and economic losses of photovoltaic home storage systems

The increase in electricity prices along with a decrease in the price of storage systems has led to a rapid expansion of the photovoltaic (PV) home storage system market, particularly in Germany. In order to be economically viable, PV home storage systems must fulfil certain performance criteria. The overall performance and achievable self-sufficiency ratio of a PV battery home storage system depends on (i) the efficiencies of the system components, (ii) the standby consumption, (iii) the reaction time of the home storage system as well as (iv) the intelligence of the overall system control software. So far, PV home storage system still show very big differences in their performance. However, poor system performance can result in the system being no longer economic viable. Up to now, there have been only a few studies that deal with the evaluation and systematic comparison of the performance of PV home storage systems. For this paper the performance of 12 commercially available PV-battery systems has been analysed with a focus on the overall system efficiency. The efficiency of the systems is mainly influenced by the battery efficiency, power conversion efficiency and standby consumption of the different system components. Therefore, a testing and evaluation method has been developed. In this work the method as well as the results of the systems are presented. A detailed study of the influence of the effects of the individual losses on both total energy and monetary losses was carried out. It is shown that power conversion has the greatest influence on energy and monetary losses. For the systems under evaluation the monetary losses per year due to battery efficiency losses range between 2 €/a and 40 €/a. Monetary losses due to conversion losses range between 33 €/a and 137 €/a and due to standby consumption between 1 €/a and 46 €/a. The individual losses can be summed up to give a total loss, which lies between 44 €/a and 174 €/a