Table of Contents warranty liability are thoroughly reviewed by management on a quarterly basis. The key estimates used by us to estimate our warranty liability are: (1) the number of units expected to fail and returned for replacement over time (i.e., return rate); and (2) the per unit cost of replacement units, including outbound shipping and limited labor costs, expected to be incurred to replace failed units over time (i.e., replacement cost). Estimated Return Rates — Our Quality and Reliability department has primary responsibility to determine the estimated return rates for each generation of product. To establish initial return rate estimates for each generation of product, our quality engineers use a combination of industry standard Mean Time Between Failure estimates for individual components contained in that generation of product, third-party data collected on similar equipment deployed in outdoor environments similar to those in which our product are installed, and rigorous long term reliability and accelerated life cycle testing which simulates the service life of the product in a short period of time. As units are deployed into operating environments, we continue to monitor product performance through our Enlighten monitoring platform. It typically takes three to nine months between the date of sale and date of end-user installation. Consequently, our ability to monitor actual failures of units sold similarly lags by three to nine months. When a product fails and is returned, we perform diagnostic root cause failure analysis to understand and isolate the underlying mechanism(s) causing the failure. We then use the results of this analysis (combined with the actual, cumulative performance data collected on those units prior to failure through Enlighten) to draw conclusions with respect to how or if the identified failure mechanism(s) will impact the remaining units deployed in the installed base. As the vast majority of our microinverters have been sold to end users for residential applications, we believe that warranty return rates will be affected by changes over time in residential home ownership because we expect that subsequent homeowners are less likely to file a return than the homeowners who originally purchased the microinverters. Estimated Replacement Costs — Three factors are considered in our analysis of estimated replacement cost: (1) the estimated cost of replacement products; (2) the estimated cost to ship replacement products to end users; and (3) the estimated labor reimbursement expected to be paid to third-party installers, or estimated labor cost expected to be incurred for field service technicians, performing replacement services for the end user. Because our warranty provides for the replacement of defective products over long periods of time (typically between 5 to 25 years, depending on the product and the generation of that product purchased), the estimated per unit cost of current and future product generations is considered in the estimated replacement cost. Estimated costs to ship replacement units are based on observable, market-based shipping costs paid by us to third-party freight carriers. We have a separate program that allows third-party installers to claim fixed-dollar reimbursements for labor costs they incur to replace failed units for a limited time from the date of original installation. Included in our estimated replacement cost is an analysis of the number of fixed-dollar labor reimbursements expected to be claimed by third-party installers over the limited offering period. In addition to the key estimates noted above, we also compare actual warranty results to expected results and evaluate any significant differences. We may make additional adjustments to the warranty provision based on performance trends or other qualitative factors. If actual return rates, or replacement costs differ from our estimates in future periods, changes to these estimates may be required, resulting in increases or decreases in our warranty obligations. Such increases or decreases could be material. Fair Value Option for Microinverters and Other Products Sold Since January 1, 2014 Our warranty obligations related to products sold since January 1, 2014 provide us the right, but not the requirement, to assign our warranty obligations to a third party. Under Accounting Standards Codification 825, “Financial Instruments” (also referred to as the “fair value option”), an entity may choose to elect the fair value option for such warranties at the time it first recognizes the eligible item. We made an irrevocable election to account for all eligible warranty obligations associated with products sold since January 1, 2014 at fair value. This election was made to reflect the underlying economics of the time value of money for an obligation that will be settled over an extended period of up to 25 years. Enphase Energy, Inc. | 2023 Form 10-K | 60