Using a case study, this article explores the extent to which one area of law (privacy and data protection) can intersect with, and be challenged by, proposals by delivery of another goal greater energy efficiency. The article then explores the extent to which these fields are becoming more integrated; and also the risks of relying on technology (notably through Privacy by Design) to do this, particularly given the uncertainties embraced by lawyers and which can be problematic to technologies. Having identified challenges in meeting both energy efficiency and privacy/data protection goals at the same time, the article develops two responses. One looks more widely in law, to competition, to prevent particular activity and to confirm the relevance of greater legal interdisciplinarity. The other is a more multi-faceted collaborative governance approach, involving legal and technical expertise and consumer perspectives, with standards having a valuable role. Addressing climate change should be an appropriate motivation to bring about this second approach, which draws on wider environmental governance developments. With largely a UK and EU focus, but seeking to be of transnational relevance, the article makes key contributions as to the capacity and limits of how law can address societal challenges; explores the risks of assuming that social and legal problems can be readily addressed by technology; confirms the need for lawyers to look to other fields of law; and assists progress in an increasingly intersectional and dynamic field.