The new millennium has marked an increasing interest in citizens as energy end-users. While much hope has been placed on more active energy users, it has remained less clear what citizens can and are willing to do. We charted user inventions in heat pump and wood pellet burning systems in Finland in years 2005-2012. In total we found 192 inventions or modifications that improved either the efficiency, suitability, usability, maintenance or price of the heat pump or pellet systems, as evaluated by domain experts. Our analysis clarifies that users are able to successfully modify, improve and redesign next to all subsystems in these technologies. It appears that supplier models do not cater sufficiently for the variation in users' homes, which leaves unexplored design space for users to focus on. The inventive users can speed up the development and proliferation of distributed renewable energy technologies both through their alternative designs as well as through the advanced peer support they provide in popular user run Internet forums related to the purchase, use and maintenance of these technologies. There are several implications for how such users can be of benefit to energy and climate policy as well as how to support them. (C) 2012 Elsevier Ltd. All rights reserved.