First Solar has evolved its approach to modeling and predicting operation and maintenance (O&M) costs for solar power plants. Originally, O&M costs were estimated using an Excel model with limited failure rate data and assumptions. First Solar now uses reliability block diagram modeling along with field failure data to predict component-level and system-level availability and costs more accurately. This allows optimization of system designs to maximize energy production and minimize total cost of ownership, which is increasingly important as the levelized cost of energy is the primary metric used to evaluate solar projects. First Solar aims to further improve cost predictions by working to standardize reliability data reporting across suppliers.