The fire was the result of thermal runaway of Vistra’s batteries. Thermal runaway is a self-sustaining chemical reaction within a battery that occurs when the heat generated exceeds the heat dissipated. This leads to a rapid increase in temperature and pressure, potentially resulting in fires or explosions. Once initiated, thermal runaway is difficult to stop and may lead to explosion and fires as occurred at Vistra’s Moss Landing Phase One.
Key Causes of Thermal Runaway
Internal Short Circuits
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- Physical Damage: Vistra may have allowed the batteries to be handled in such a way as to allow them to become damaged. Damage can result from punctures or crushing that can result in internal short circuits. This leads to direct contact between the anode and cathode, resulting in a rapid increase in temperature. In 2021 a thermal event occurred at Phase One when the fire suppression system leaked.
- Manufacturing Defects: The batteries Vistra used may have had flaws from the manufacturing process, such as impurities or defects in the separator, which can also cause internal short circuits. LG Chem supplied the battery cells and modules to Vistra. Their products have been subject to many recalls. At this point, it’s unclear whether Vistra returned the batteries in response to the recalls.
Overcharging and Overdischarging
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- Overcharging: Vistra may have overcharged a battery beyond its recommended voltage. That can cause excessive heat generation, which stresses the battery components and increases the risk of thermal runaway.
- Overdischarging: Similarly, if Vistra allowed a battery to discharge below its safe voltage limit, that could have lead to internal damage and heat generation, contributing to thermal runaway
Heat Sources
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- High Ambient Temperatures: Vistra may have allowed its batteries to be exposed to high temperatures. High temperatures can push a battery beyond its thermal limits, triggering thermal runaway .
- Proximity to Heat-Generating Devices: If Vistra placed a battery too close to a heat source, or near each other or in poorly ventilated areas are more susceptible to overheating, that can cause thermal runaway. We know that batteries in the Vistra plant were packed in a dense configuration.
Electrolyte Breakdown
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- If Vistra allowed the batteries temperatures to rise to high, the electrolyte within the battery may have decomposed, generating gases and additional heat. This exacerbates the thermal runaway process
Poor Battery Management Systems (BMS)
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- Inadequate Monitoring: if Vistra’s BMS failed to accurately monitor and control the battery’s temperature, voltage, and current, it could have led to unsafe operating conditions.
- Faulty Safety Mechanisms: if the safety mechanisms within Vistra’s BMS were ineffective, they may have failed to prevent conditions that lead to thermal runaway
Age and Wear
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- Degradation Over Time: As batteries age, their internal components degrade, making them more prone to failures that can trigger thermal runaway. It is important for operators such as Vistra to replace batteries as they age