This paper provides a quantitative analysis of the in-service reliability of Active Power's flywheel-based CleanSourceŽ UPS (uninterruptible power supply) system versus a battery-based double-conversion UPS system using probabilistic risk assessment (PRA). The analysis shows that CleanSource UPS is approximately seven times less likely to fail versus a double-conversion UPS with batteries during a short utility outage. Study author MTechnology found "demand failures of the flywheel energy storage system are extremely unlikely. If the flywheel is operational at the moment an outage occurs, the flywheel will almost certainly function."
