Note 3.  Accounts Receivable, Net

Accounts receivable as of April 30, 2018 and October 31, 2017 consisted of the following:

We bill customers for power plant and power plant component sales based on certain contractual milestones being reached.  We bill service agreements based on the contract price and billing terms of the contracts. Generally, our Advanced Technologies contracts are billed based on actual recoverable costs incurred, typically in the month subsequent to incurring costs.  Some Advanced Technologies contracts are billed based on contractual milestones or costs incurred.  Unbilled recoverable costs relate to revenue recognized on customer contracts that have not been billed.  Accounts receivable are presented net of an allowance for doubtful accounts of $0.1 million as of April 30, 2018 and October 31, 2017.  Uncollectible accounts receivable are charged against the allowance for doubtful accounts when all collection efforts have failed and it is deemed unlikely that the amount will be recovered.

Accounts receivable from commercial customers (including unbilled recoverable costs) included amounts due from POSCO Energy of $12.2 million and $6.2 million as of April 30, 2018 and October 31, 2017, respectively, and amounts due from NRG and NRG Yield of $0.02 million and $0.1 million as of April 30, 2018 and October 31, 2017, respectively.