nergy payback, and state which form of renewable energy has the lowest payback period and the lowest cost at present. which two types of energy are collected under the title of marine energy? what is meant by geothermal energy? list some examples of how and where it is tapped. why are all geothermal resources not used to generate electricity? what are some environmental issues associated with geothermal energy? describe the difference between the two methods of absorbing energy from sunlight. what is the difference between active and passive systems? what is meant by solar thermal electricity, and how is it generated? describe the operation of a solar power tower that uses molten salts. what is meant by the term cogeneration? write the general chemical reactions involving metal oxides by which a fuel can be produced by using concentrated solar energy. state the second law of thermodynamics. according to this law, what formula gives the maximum fraction of heat that can be transformed into electricity? define the terms photovoltaic effect and band gap. why is amorphous rather than crystalline silicon used in some solar cells? describe the process of chemical vapor deposition. describe the workings of