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ENERGY STORAGE SYSTEMS, NET
6 Months Ended
Jun. 30, 2021
Property, Plant and Equipment [Abstract]  
ENERGY STORAGE SYSTEMS, NET ENERGY STORAGE SYSTEMS, NET
Energy Storage Systems, Net
Energy storage systems, net, consists of the following (in thousands):
June 30, 2021
Energy storage systems placed into service$144,754 
Less: accumulated depreciation(39,848)
Energy storage systems not yet placed into service13,310 
Total energy storage systems, net$118,216 
Depreciation expense for energy storage systems was approximately $3.6 million and $3.4 million within cost of service revenue for the three months ended June 30, 2021 and 2020, respectively, and approximately $7.3 million and $5.7 million within cost of service revenue for the six months ended June 30, 2021 and 2020, respectively.