Heat Stress Tests Photovoltaic Systems and Battery Storage

## Heat Stress Tests Photovoltaic Systems and Battery Storage Heat waves in Europe have become the norm, and their impact on photovoltaic systems and battery storage is a growing concern. While strong sunlight is not the primary issue, temperature plays a critical role in determining the performance and lifespan of these systems. Solar modules are designed to operate under standard test conditions, with a cell temperature of 25 degrees Celsius. However, in the field, cell temperatures can reach significantly higher levels, especially on hot days. ## Photovoltaic Systems and Temperature Crystalline solar cells typically experience a power output decrease with increasing temperature. If the cell temperature is not 25 degrees Celsius but 65 degrees Celsius, this corresponds to a power loss of approximately 16 percent compared to standard conditions. This distinction is crucial for operators, as it highlights the importance of considering temperature when evaluating the performance of photovoltaic systems. ## Battery Storage and Heat Stress Battery storage systems are particularly vulnerable to heat stress, which can accelerate aging and reduce their lifespan. Lithium-ion batteries, commonly used in energy storage devices, are sensitive to temperature, state of charge, depth of discharge, C-rate, idle times, and operating strategy. High temperatures, high states of charge, and deep cycles can accelerate aging, making it essential to monitor and control these factors. ## Designing Systems for Heat Stress When designing photovoltaic-plus-storage systems, operators must consider the impact of heat stress on their systems. This includes evaluating the design of the system, taking into account how it behaves on hot days, and identifying potential heat build-up areas. Components such as storage systems, inverters, and electrical infrastructure must be ventilated or shaded to prevent overheating. ## Testing Regulatory Capacity Under Stress Conditions Operators must test the regulatory capacity of their photovoltaic-plus-storage systems under stress conditions. This involves evaluating the control concept, validating it in operation, and ensuring that the system remains controllable when multiple demands are at play simultaneously. This includes checking whether setpoints are reliably adopted, the system reacts correctly to specifications at the grid connection point, and active and reactive power control function even under high load. ## Data Quality and Performance Evaluation Data quality is the basis of every evaluation, and operators must ensure that irradiance, ambient temperature, module temperature, wind, inverter data, string data, battery temperatures, state of charge, and operating conditions are plausible. Faulty sensors can lead to incorrect diagnoses, which can result in unnecessary call-outs or overlooked problems. ## Prioritizing Local Risks Operators must consistently prioritize local risks, such as hotspots, shading, and pollution, especially under high solar irradiance. Vegetation control, cleaning strategies, thermography, and visual inspection should be considered as part of a comprehensive risk management strategy. Electrical infrastructure also deserves attention, as connectors, cables, junction boxes, distribution boxes, switch cabinets, and transformers are subject to stress during periods of heat. ## Thermal Transparency and Aging Battery storage systems require thermal transparency, with cell, module, rack, and container temperatures being measured and evaluated in context. Not only is the absolute maximum temperature relevant, but also the temperature distribution. Large temperature variations within a system can indicate cooling problems, airflow issues, sensor malfunctions, or uneven load distribution. ## Consciously Controlling Charge Level and Aging Operators must consciously control the charge level and aging of their battery storage systems. State-of-charge (SOC) windows should be carefully selected, and the system doesn't need to be constantly maintained near 100 percent SOC just because a lot of photovoltaic energy is available. Especially at high ambient temperatures, it can be beneficial to design operating strategies that minimize the impact of heat stress on the system.