Recent assessments show that such a transformation is achievable in technological and  economic terms, but it will present formidable supply- and demand-side challenges as well as problems of  governance, transparency and reliability across scales.  
 This policy brief presents a long-term vision for the energy system and describes the elements required for the  transition towards this vision. 
 To succeed, this transformation must integrate several key components, including  a focus on high levels of energy efficiency and the scale up of investments in technology deployment as well as  research, development and demonstration (RD&D).