Walker, and 9 co-authors, of NREL reported in 2020 on a method for calculating costs associated with the operation and maintenance (O&M) of photovoltaic (PV) systems. The authors compiled details regarding the cost and frequency of multiple O&M services to estimate annual O&M costs ($/year) for each year of an analysis period, the net present value ($) of life cycle costs accumulated over the analysis period, and the reserve account amount ($) that might be required to fund unexpected repairs.
The reserve account includes parts inventory and is important for providing a source of funds to make repairs quickly and avoid lost production. This method allows a detailed selection of services to perform based on system size, market served (e.g., residential, commercial, or utility), type and configuration of system components (e.g., micro-, string, or central inverter), and site and environmental conditions (e.g., pollen, bird populations) which is an improvement over simple per unit valuations of O&M costs ($/kW/year). This model also distinguishes costs that vary from year to year and increase at different rates over time as modeled by heuristic failure distributions (e.g., Weibull or Lognormal distribution) based on actuarial data for many of
the services.
This cost model was created with input from the PV O&M Working Group of researchers and industry, sponsored by U.S. Department of Energy (DOE) Solar Energy Technologies Office (SETO). The PV O&M Cost model was developed initially as a Microsoft Excel spreadsheet and subsequently published as an on-line application by Sunspec Alliance at https://apsuite.sunspec.org (Contact the NREL authors for the spreadsheet version). AP Suite stands for Asset Performance Suite and includes both the PV O&M Cost Model and Open System Performance and Reliability Clearinghouse (oSPARC), which logs system performance.
The authors identified areas of high cost that should be the focus of efforts to reduce cost of renewables. The approach is general and can accommodate systems of different size, application (residential, commercial, utility), and under different environmental conditions. The authors have concentrated on developing the methods, calculations, and analytic framework, and the method has been programmed into an online implementation available at https://apsuite.sunspec.org.
The online implementation of the PV O&M cost model software is populated mainly with default values for labor and materials costs. While these default values reflect the considerable experience of the members of the PV O&M Working Group that provided and reviewed them, the intention is that default values would be replaced by actual cost experience of program users.
The authors recommended that future work include an encouragement for system and fleet operators to share their actuarial data on operations and maintenance in order to advance the accuracy and utility of cost estimating tools. Feedback from actual costs should be carefully curated to refine future PV O&M cost estimates. A covariance analysis is recommended rather than single variable regression in order to represent inter-dependencies between the O&M cost model line items (e.g., serial defects, cascading failures).
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