As photovoltaic systems are increasingly combined with battery energy storage systems (BESS), understanding their long-term performance and reliability is becoming essential. A new report published by IEA PVPS Task 13 examines how the operational performance of PV + BESS can be assessed and monitored to support more reliable, efficient and cost-effective energy systems.
This report provides an overview of common battery technologies, typical PV + BESS applications and practical methods for evaluating system performance in operation. It also presents field experience from residential installations, demonstrating how operating conditions, system design and use case influence battery ageing and overall system performance.
“PV + BESS performance in the field is driven by far more than battery chemistry alone. This report shows that system topology, inverter behaviour, control logic, operating profile, temperature and firmware all materially shape efficiency, degradation, end-of-life estimation and dispatch reliability.” – Ulrike Jahn, IEA PVPS Task 13 Manager
Key takeaways
- The performance, reliability and lifetime of PV + BESS depend on technology, use-case and environment. Battery chemistry and design, system topology, control strategy and duty jointly shape degradation behaviour and end-of-life outcomes.
- A robust assessment of PV+BESS should be based on six core performance indicators. Capacity, power tolerance, internal resistance, round-trip efficiency, response time and standby losses provide a practical basis for state-of-health assessment, fault detection and ageing-aware operation.
- Field evidence shows substantial gaps between nominal and real-world performance of PV + BESS. Results from residential inspections and case studies reveal wide variation in efficiency, inverter losses, state-of-charge estimation, cell balancing quality and temperature or firmware effects. This underscores the need for harmonised monitoring, high-quality open data and validated ageing models to enable reliable, cost-optimal deployment of PV + BESS.
