John Cantor studied mechanical engineering and gained much of his early experience working in research and development. He became interested in Alternative Technology in the late 1970s, joining the Centre for Alternative Technology in Machynlleth. He found himself to be the only one in that field with an in-depth understanding of heat pumps, so his niche was found, and he manufactured his own systems in the early days. He has a wide and varied portfolio of experience, and is conversant with the technical quirks of most heat pump models. He was a heat pump installation inspector for the first UK heat pump grant scheme under BRE, and now mostly operating as an advisor and consultant.Gavin D. J. Harper is the author-co-author of a number of books including Domestic Solar Energy (Crowood, 2009) and Small-Scale Wind Power Generation (Crowood, 2010). He writes extensively on sustainability issues and is currently researching the subject of green business models for sustainability for a PhD at Cardiff University Business School. Gavin is a member of the Institute of Engineering and Technology, and holds two honours degrees from the Open University and three masters degrees.