As of December 31, 2015, NRG's derivative assets and liabilities consisted primarily of the following:
Forward and financial contracts for the purchase/sale of electricity and related products economically hedging NRG's generation assets' forecasted output or NRG's retail load obligations through 2021;
Forward and financial contracts for the purchase of fuel commodities relating to the forecasted usage of NRG's generation assets through 2018; and
Other energy derivatives instruments extending through 2024.
Also, as of December 31, 2015, NRG had other energy-related contracts that did not meet the definition of a derivative instrument or qualified for the NPNS exception and were therefore exempt from fair value accounting treatment as follows:
Load-following forward electric sale contracts extending through 2026;
Power tolling contracts through 2039;
Coal purchase contract through 2018;
Power transmission contracts through 2025;
Natural gas transportation contracts and storage agreements through 2030; and
Coal transportation contracts through 2029.
Interest Rate Swaps
NRG is exposed to changes in interest rates through the Company's issuance of variable rate debt. In order to manage the Company's interest rate risk, NRG enters into interest rate swap agreements. As of December 31, 2015, NRG had interest rate derivative instruments on non-recourse debt extending through 2032, the majority of which are designated as cash flow hedges.
Volumetric Underlying Derivative Transactions
The following table summarizes the net notional volume buy/(sell) of NRG's open derivative transactions broken out by commodity, excluding those derivatives that qualified for the NPNS exception as of December 31, 2015, and 2014. Option contracts are reflected using delta volume. Delta volume equals the notional volume of an option adjusted for the probability that the option will be in-the-money at its expiration date.
December 31, 2015
December 31, 2014
The increase in the natural gas position was primarily the result of additional retail hedges, as well as the settlement of generation hedge positions. The decrease in the interest rate position was primarily the result of settling the Alta X and Alta XI interest rate swaps in connection with the repayment of project-level debt, as described in Note 12, Debt and Capital Leases.