4. PREPAID EXPENSES AND OTHER CURRRENT ASSETS

As of December 31, 2019, prepaid expenses and other current assets primarily consisted of alternative fuel credits of $476,992. As of December 31, 2018 alternative fuel credits was $331,120.

During the year ended December 31, 2018, the Company entered into purchase commitments to acquire second generation charging stations with an aggregate value of $3,156,629. As of December 31, 2019, the Company had a remaining purchase commitment of $1,563,600 which will become payable upon the supplier’s delivery of the charging stations. The purchase commitments were made primarily for future sales of these charging stations.