The absorber is coated with a selective surface to absorb energy from the high energy content of the ultraviolet spectrum, thus reducing energy losses. A summary analysis of renewable energy options using simple spreadsheets will be conducted first, based on procedures laid out by the Office of the Deputy Prime Minister (ODPM). The process has been repeated for the other renewable energy systems, and the results summarised in. This chapter explains what to specify in order to carry out analysis of renewable energy systems and how to interpret results. Combined heat and power (CHP) is effectively an internal combustion engine, just like a lorry engine. If, instead of running a lorry, people attach this engine to run an electricity generator, the work of this engine will be converted into electricity energy. A system consisting of a CHP and an absorption refrigeration plant is called a tri-generation system. It provides heating, cooling and electricity.