The Calpine (2020) and Ormat (2020a) O&M costs are derived from their annual reports, i.e. SEC form 10-k. In 2019, Calpine reports "Operating and Maintenance Expense" of 1001 M$ and "Property, plant and equipment" asset value, without depreciation, of 18810 M$. Thus, the O&M fraction is the ratio of these, or 5.3%. Similarly, Ormat (2020a) reports a total cost of electricity revenue of 313 M$ and 6240 GW e -h generated, resulting in an electricity cost of 50 $/MW e -h. Unfortunately, the O&M cost itself can't be discerned from the form 10-k as Ormat (2020a) includes both debt service cost and O&M costs in their electricity cost value. Instead, we use an O&M value of 25 $/MW e -h reported by Ormat (2020b). Thus, we assume 50% of the total cost of electricity revenue is due to O&M (i.e. 313/2 = 156 M$). Ormat (2020a) reports total undepreciated generation assets of 2883 M$. Thus, we find the Ormat O&M fraction is the ratio of total cost of electricity revenue due to O&M to the total undepreciated generation assets, or 5.4%.