SPI 2021 - Results at a glance

Inverters from KOSTAL

The storage experts

The PLENTICORE and PIKO MP plus series from KOSTAL once again excelled in the 2021 Energy Storage Inspection carried out by HTW Berlin.

The 2021 Electricity Storage Inspection

KOSTAL inverters, 2021 SPI

Suitable for every solar system and the most diverse requirements: hybrid and battery inverters from KOSTAL are always the right choice and this was again confirmed by HTW's 2021 Electricity Storage Inspection.

The 2021 Energy Storage Inspection carried out by the Berlin University of Applied Sciences (HTW) investigates standard practice for solar storage systems in the 5 and 10 kWp range using two reference cases.

In reference case 1, the storage inspection considers solar systems used to operate a 5 kWp system with an annual electricity consumption of 5010 kWh. In reference case 2, a heat pump (2664 kWh/a) and operation of an electric vehicle (1690 kWh/a) are added alongside operating a 10 kWp PV system with the same annual electricity consumption.

In the energy storage inspection, direct current (DC) and alternating current (AC) battery systems were considered separately. Depending on the type of installation, both types of coupling fulfil specific purposes and have individual cost-benefit advantages. DC-coupled systems are often used for newly installed solar systems with a battery storage connection. AC-coupled applications are mostly used when retrofitting existing solar systems.

The inverters of the PLENTICORE series as hybrid inverters (PLENTICORE plus) and battery inverters (PLENTICORE BI) can be flexibly used both for a DC-coupled battery system and for the AC-coupling system preferred in repowering. 

PLENTICORE plus: the top performer


The PLENTICORE plus hybrid inverter has already been awarded the highest rating several times between 2018 and 2020 and has occupied top spots in terms of storage system efficiency.

The PLENTICORE plus was able to confirm this exceptional position in 2021, again ranking in the best efficiency range and obtaining the "very good” rating.

Together with the BYD Battery-Box HVS 7.7, the PLENTICORE plus 5.5 achieves a System Performance Index (SPI) of 91.2 per cent. The system is ideally suited to solar installations in small output classes and overall delivers considerable cost savings in operation. In reference case 1, the KOSTAL inverter showed that it can control the supply of powerful consumers very well in combination with a storage system.

The DC-coupled storage system of KOSTAL PLENTICORE and BYD is also impressive in reference case 2 and with higher energy requirements. In combination with the battery box of the Premium version HVS 12.8, the 10 kW version achieves an SPI of 93.7%, which earns the combined system a top place in the overall rankings.

The PLENTICORE plus is considered particularly innovative due to its flexible range of use, because the battery function is only activated by activation code when in use.

PLENTICORE BI: the universal performer

With an SPI of 92.7%, the PLENTICORE BI 10/26 battery inverter with the BYD HVS 12.8 battery proved to be an extremely efficient combination in the 10 kWp reference case.
The KOSTAL battery inverter is therefore the ideal choice for a simple storage connection, especially when integrating into an existing solar system.

The PLENTICORE BI can be used universally and is suitable for any system. It's not necessary to replace or substitute existing components. In addition, a high charging and discharging capacity of 10 kilowatts can be achieved by connecting large storage capacities – no other system could rival it in this respect in the test.  

The PLENTICORE BI can be combined with battery storage units with capacities ranging from 5.1 to 66 kWh, making it just as suitable for use in commercial applications as private households.

PIKO MP plus: the economical performer


For single-phase systems, the PIKO MP plus inverter from the KOSTAL product portfolio is the ideal choice.

The PIKO MP excels both as an AC-coupled system and in the DC connection in conjunction with a storage unit.

This is thanks to its high battery efficiency coupled with fast settling time and low standby consumption with high inverter efficiency.

The single-phase inverter of the PIKO MP plus series is particularly economical as a conversion and control instrument for solar systems. In combination with the KOSTAL Smart Energy Meter, the PIKO MP plus serves as a solar, hybrid or battery inverter in the 1.5 - 5 kW power range.

Summary: smart investment, smart advice

The inverters from KOSTAL in combination with the Premium HVS Battery-Box from BYD achieved the best rankings with their efficiency values in both reference cases of the 2021 Energy Storage Inspection.

The System Performance Index - What does the SPI tell us?

The System Performance Index was launched by HTW Berlin to allow the interaction between components available on the market (inverter, battery and PV modules) to be compared in one overall system and thus to create more transparency for customers.

In the study carried out by HTW Berlin, the System Performance Index (SPI for short) is determined for each storage system using reference situations relevant to real life. The SPI shows all energy loss mechanisms of the PV battery systems as an indicator of efficiency.