of ITCs or other adjustments as required by the U.S. Internal Revenue Code, we defer the recognition of the respective adjustments and recognizes the adjustments in non-controlling interest on the consolidated statements of operations on a straight-line basis over the expected life of the underlying assets giving rise to the respective difference. Similarly, where we have acquired a controlling interest in a partnership and there is a resulting difference between the initial fair value of non-controlling interest and the value of non-controlling interest as measured using HLBV, we initially record non-controlling interest at fair value and amortize the resulting difference over the remaining life of the underlying assets.
Impairment of Renewable Energy Facilities and Intangibles
Long-lived assets that are held and used are reviewed for impairment whenever events or changes in circumstances indicate carrying values may not be recoverable. An impairment loss is recognized if the total future estimated undiscounted cash flows expected from an asset are less than its carrying value. An impairment charge is measured as the difference between an asset's carrying amount and its fair value. Fair values are determined by a variety of valuation methods, including appraisals, sales prices of similar assets and present value techniques. During the year ended December 31, 2018, we recognized a $15.2 million impairment charge related to an operating project within its Enfinity portfolio due to the bankruptcy of a significant customer. During the year ended December 31, 2017, we recognized a $1.4 million impairment charge, related to its portfolio of residential rooftop solar assets. Impairment charges are reflected within impairment of renewable energy facilities in the consolidated statements of operations (see Note 5. Renewable Energy Facilities for further discussion). There were no impairments of renewable energy facilities or intangible assets recognized during the year ended December 31, 2016.
Impairment of Goodwill
Goodwill is tested annually for impairment at the reporting unit level during the fourth quarter or earlier upon the occurrence of certain events or substantive changes in circumstances. A reporting unit is either the operating segment level or one level below, which is referred to as a component. The level at which the impairment test is performed requires judgment as to whether the operations below the operating segment constitute a self-sustaining business or whether the operations are similar such that they should be aggregated for purposes of the impairment test.
In assessing goodwill for impairment, we may elect to use a qualitative assessment to determine whether the existence of events or circumstances leads to a determination that it is more-likely-than-not that the fair value of our reporting units are less than their carrying amounts. If we determine that it is not more-likely-than-not that the fair value of our reporting units are less than their carrying amounts, we are not required to perform any additional tests in assessing goodwill for impairment. However, if we conclude otherwise or elect not to perform the qualitative assessment, then we are required to perform the quantitative impairment test. In January 2017, guidance was issued which simplifies the test for goodwill impairment by eliminating Step 2, the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge. We early adopted this guidance, which is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019 on December 1, 2018.
As part of our risk management strategy, we enter into derivative instruments for the purpose of reducing exposure to fluctuations in interest rates, foreign currency and commodity prices. We enter into interest rate swap agreements in order to hedge the variability of expected future cash interest payments. Foreign currency contracts are used to reduce risks arising from the change in fair value of certain foreign currency denominated assets and liabilities. The objective of these practices is to minimize the impact of foreign currency fluctuations on operating results. We also enter into commodity contracts to hedge price variability inherent in energy sales arrangements. The objectives of the commodity contracts are to minimize the impact of variability in spot energy prices and stabilize estimated revenue streams.
We recognize our derivative instruments at fair value in the consolidated balance sheets, unless the derivative instruments qualify for the normal purchase normal sale scope exception to derivative accounting.
Derivatives that qualify and are designated for hedge accounting are classified as either hedges of the variability of
expected future cash flows to be received or paid related to a recognized asset or liability (cash flow hedge) or hedges of the
exposure to foreign currency of a net investment in a foreign operation (net investment hedges). We may also use derivative contracts outside the hedging program to manage foreign currency risk associated with intercompany loans. In all cases. we view derivative financial instruments as a risk management tool and, accordingly, do not use derivative instruments for trading or speculative purposes.