Reversible chemical reactions operating in a thermochemical energy transfer system have been proposed for solar electricity generation in order to solve not only the problem of energy transport from the solar collection field to a central power plant, but also potentially the long term lossless energy storage problem through underground storage of the reaction products. A number of reactions have been proposed for solar thermochemical power generation and in this paper the thermodynamic and chemical engineering criteria for comparing the reactions are examined and are applied to the four prominent systems based on water-methane, sulphur trioxide, ammonia and methanol, each of which is associated with a broad industrial base. The overall efficiency for conversion from the solar thermal input to electricity is evaluated for each system and the component processes of heat transfer and work production are examined in order to highlight the areas that must be given special attention in calculating the system efficiency when alternative reaction schemes are considered. The sulphur trioxide system has the highest efficiency of 23 % but is associated with several areas of concern regarding the practicalities of implementation and their effect on capital cost. In the absence of detailed comparative cost optimization data, it is considered that the system based on ammonia dissociation/synthesis has the best blend of overall efficiency (19 %) and moderate level of chemical engineering difficulty to be a good choice for first generation solar thermochemical power generation.