The Company had purchase commitments of $22.4 million at December 31, 2015. The purchase commitments outstanding at December 31, 2015 are expected to be paid as follows: $14.7 million in the year ending December 31, 2016, $6.6 million in the year ending December 31, 2017 and $1.1 million in the year ending December 31, 2018.

GRE must obtain a certain percentage or amount of its power supply from renewable energy sources in order to meet the requirements of renewable portfolio standards in the states in which it operates. This requirement may be met by obtaining renewable energy credits that provide evidence that electricity has been generated by a qualifying renewable facility or resource. At December 31, 2015, GRE had commitments to purchase renewable energy credits of $41.8 million.

At December 31, 2015, Afek’s estimated liability for environmental remediation in the Golan Heights in Northern Israel was $0.2 million, which is included in “Exploration expense” in 2015 in the accompanying consolidated statement of operations. The estimated liability is expected to increase as Afek continues its up to ten-well exploratory program.

The Company is subject to audits in various jurisdictions for various taxes. Amounts asserted by taxing authorities or the amount ultimately assessed against the Company could be greater than the accrued amount. Accordingly, provisions may be recorded in the future as estimates are revised or underlying matters are settled or resolved. Imposition of assessments as a result of tax audits could have an adverse effect on the Company’s results of operations, cash flows and financial condition.

At December 31, 2015, the Company had letters of credit outstanding totaling $7.7 million primarily for the benefit of regional transmission organizations that coordinate the movement of wholesale electricity and for certain utility companies. The letters of credit outstanding at December 31, 2015 expire as follows: $4.2 million in the year ending December 31, 2016 and $3.5 million in the year ending December 31, 2017.

GRE has performance bonds issued through a third party for the benefit of various states in order to comply with the states’ financial requirements for retail energy providers. At December 31, 2015, GRE had aggregate performance bonds of $11.9 million outstanding.

The future minimum payments for operating leases at December 31, 2015 are as follows:

(in thousands)
Year ending December 31:
2016	$	306
2017		165
2018		14
2019		—
2020		—
Thereafter		—
Total payments	$	485

Rental expense under operating leases was $1.2 million, $0.8 million and $0.6 million in the years ended December 31, 2015, 2014 and 2013, respectively.

As of November 19, 2015, IDT Energy and certain of its affiliates entered into an Amended and Restated Preferred Supplier Agreement with BP Energy Company (“BP”). The agreement’s termination date is November 30, 2019, except either party may terminate the agreement on November 30, 2018 by giving the other party notice by May 31, 2018. Under the agreement, IDT Energy purchases electricity and natural gas at market rate plus a fee. IDT Energy’s obligations to BP are secured by a first security interest in deposits or receivables from utilities in connection with their purchase of IDT Energy’s customer’s receivables, and in any cash deposits or letters of credit posted in connection with any collateral accounts with BP. IDT Energy’s ability to purchase electricity and natural gas under this agreement is subject to satisfaction of certain conditions including the maintenance of certain covenants. At December 31, 2015, the Company was in compliance with such covenants. At December 31, 2015, restricted cash—short-term of $0.8 million and trade accounts receivable of $27.0 million were pledged to BP as collateral for the payment of IDT Energy’s trade accounts payable to BP of $8.3 million at December 31, 2015.