Note 6 - Inventory

As of December 31, 2016 and 2015, our inventory consisted of the following (in thousands):

	December 31,		December 31,
	2016		2015
Raw materials	$	680,339	$	528,935
Work in process		233,746		163,830
Finished goods		1,016,731		476,512
Service parts		136,638		108,561
Total	$	2,067,454	$	1,277,838

Finished goods inventory includes vehicles in transit to fulfill customer orders, new vehicles available for immediate sale at our retail and service center locations, pre-owned Tesla vehicles, and energy storage products.

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

We write down inventory as a result of excess and 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, 2016, 2015 and 2014, we recorded write-downs of $52.8 million, $44.9 million and $15.6 million in cost of revenues.