Solar Energy and the Circular Economy
MRS Energy & Sustainability
MRS Energy & Sustainability links materials research with technological forecast, policy, and social change. Inspired by a large European initiative on carbon dioxide (CO2) reduction and synthetic fuel production powered by solar energy (SUNRISE ), we invited papers for a special issue on circular economy. By circular economy we simply understand the return of used material back into production, also known as "re-cycling". The hierarchy of waste and waste management (compare ) has led to the 3R (Reduce, Reuse, and Recycle) and eventually 4R principle (Recover), which includes resource management.
In the worst case, spent material ends up in the pure environment as illegally deposited waste. Legal ways of waste disposal includes adding to landfills or burning in incinerators, the latter of which will bring about heat, which can be used for district heating, and ash, which may contain valuable materials including noble metals. More sophisticated ways of waste disposal encompass recycling methods, which, depending on the material and industry, can represent an industry of its own.
The ancient Greeks and Romans collected metal and glass, and remelted them, showing that recycling is nothing new. Likewise, circular economy is not new, as Sikdar points out . The SUNRISE initiative aims to expand the technology of thecircular economy towards CO2 assimilation. This is the type of circular economy which has been demonstrated in the natural world for billions of years. This is known as carbon cycle  and includes one of the most fundamental processes of primary production by photosynthesis. Practically, this is the conversion of atmospheric CO2 (and CO2 from industrial point sources) along with water to hydrocarbon fuels (which Melvin Calvin projected as petroleum plantations ) and base chemicals. It also includes the production of nitrogen compounds such as ammonia [6, 7], which has its own biogeochemical cycle. The necessary energy for powering these cycles shall come from renewable sources, primarily from solar energy. Worldwide research activity on renewable energy can easily be interpreted as circular economy research efforts.
The contributions to this special issue serve as a snapshot of technical efforts and policy worldwide towards use of renewable energy, some of it well-established and some quite novel. We hope that readers will find inspiration to further their own work or encourage the work of others to further these goals toward a circular economy fueled by solar energy.
Guest Editors: Artur Braun, Rita Toth, Selma Erat