Publisher Summary Man is capable of performing additional energy conversion processes by means of various devices invented. Such devices may be classified according to the type of construction used, according to the underlying physical or chemical principle, or according to the forms of energy appearing before and after the action of the device. This chapter surveys methods that may be suitable for the conversion of renewable energy flows or stored energy. A discussion of general conversion principles outlines engineering design details for specific energy conversion devices, ordered according to the energy form being converted and the energy form obtained. If the high-quality energy form desired is electricity, and the initial energy is in the form of heat, there is a possibility of utilizing direct conversion processes, rather than first using a thermodynamic engine to create mechanical work followed by a second conversion step using an electricity generator. The conversion of heat to shaft power or electricity is generally achieved by one of the thermodynamic cycles. Photo-electrochemistry is an area of confluence between solar cell technologies. This chapter describes a number of general principles that are of use in designing actual conversion devices primarily those aimed at utilizing the renewable flows of energy.