Investment by energy firms in innovation can have substantial economic and environmental impacts and benefits. Firms engage in innovation for different reasons. The main objective of this paper is to analyse the role that the different innovation objectives have on firms' decisions to invest in each of three types of innovation activity: namely, internal R&D, external R&D, and the acquisition of advanced machinery, equipment, or software. We consider four objectives: process innovation, product innovation, reducing environmental impact, and meeting regulatory requirements. With this approach, we examine how energy firms innovate to reduce their environmental impact in comparison with other innovation objectives. In carrying out the empirical analysis, we draw on data for private energy firms included in the Spanish Technological Innovation Panel for the period 2004-2016. In the empirical analysis, we take the potential persistence of innovation activities into account and we use multivariate probit models to control for possible complementarities between the different R&D and innovation investments. Our results show that internal and external R&D are undertaken to address environmental objectives and to meet regulatory requirements while the acquisition of advanced machinery has the purpose of developing process innovations.