Note 6 – Inventory

Our inventory consisted of the following (in millions):

For solar energy systems, we commence transferring component parts from inventory to construction in progress, a component of solar energy systems, once a lease or PPA contract with a customer has been executed and installation has been initiated. Additional costs incurred on the leased solar energy systems, including labor and overhead, are recorded within solar energy systems under construction.

We write-down inventory for any excess or obsolete inventories or when we believe that the net realizable value of inventories is less than the carrying value. During the years ended December 31, 2020, 2019 and 2018, we recorded write-downs of $145 million, $138 million and $78 million, respectively, in cost of revenues.