Property, Plant and Equipment

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment

Property, Plant and Equipment

8.  Property, Plant and Equipment

Property, plant and equipment at December 31, 2021 and 2020 consists of the following (in thousands):

	December 31, 2021		December 31, 2020
Land	$	1,165	$	1,165
Construction in progress		169,415		15,590
Leasehold improvements		2,099		1,121
Software, machinery and equipment		112,068		78,859
Property, plant, and equipment	$	284,747	$	96,735
Less: accumulated depreciation		(29,124)		(22,186)
Property, plant, and equipment, net	$	255,623	$	74,549

Construction in progress is primarily comprised of construction of hydrogen production plants and the Gigafactory in Rochester.  Completed assets are transferred to their respective asset classes, and depreciation begins when an asset is ready for its intended use. Interest on outstanding debt is capitalized during periods of capital asset construction and amortized over the useful lives of the related assets. For the years ended December 31, 2021 and 2020, we capitalized $5.5 million and $0 of interest.

Depreciation expense related to property, plant and equipment was $6.9 million, $4.8 million, and $3.6 million for the years ended December 31, 2021, 2020, and 2019, respectively.