In a recent article Mabee et al. [2012, Energy Policy 40(1), 480-489] describe the German legislation to promote renewable electricity generation (Erneuerbare-Energien-Gesetz). The erroneous assumption that an annual degression of feed-in tariffs for any given power generating facility are stipulated in the law leads to a wrong calculation of net present values of the revenue stream. Reduction of feed-in tariff rates only holds for new additions. There is however one exception in offshore wind energy where the operator can opt for a degression. The implications of the newly introduced option are discussed in this comment. (C) 2012 Elsevier Ltd. All rights reserved.