ABSTRACT
Heat is the lowest common denominator of energy, the dregs, the least useful form. The heat of a gas measures the average energy of those moving molecules. In practice, the heat created by burning a fuel drives the expansion of gases: gaseous combustion products, in the case of an internal combustion engine; steam, in the case of a conventional boiler; or another so-called working fluid. The trick in efficient utilization of energy is to avoid turning it into heat at any step in the process. Although tidal energy is of course not derived from the Sun—the energy comes from the rotation of the Earth—the same sorts of issues arise as for surf power and low-head hydropower. The conventional geothermal energy, even more than hydropower dams, often involves a tradeoff with aesthetic values, because many of those areas with anomalously high heat flow are also places of great scenic beauty.
