How are Opex costs calculated and what are the units of Opex? For example, it looks like $/kWh with a default for batteries of $5/kWh. by Fabian Le Gay Brereton | Dec 24, 2021Opex are all annual costs that will be billed monthly in the cashflows. So, $5/kWh for storage would end up as an annual Opex of $500 if you had a 100kWh of storage. $42 a month in the cashflows ($500/12 months).