Heat Energy

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Heat is one of seven different forms of energy on Earth: heat, chemical, mechanical, electrical, atomic, light, and sound. The amount of motion (usually referred to as activity) of atoms and molecules determines the amount of energy stored as heat, or thermal energy. Fuels used by power plants or vehicles contain a set amount of potential heat energy, which scientists can measure using a device called a calorimeter. A calorimeter burns a specific amount of fuel, and the heat given off by the burning then transfers to water flowing through the calorimeter. The difference in water temperature from when it enters the device and when it exits expresses the potential heat energy of the fuel.

fuel energy per volume = exit water temperature - entry water temperature

Industrial processes rely on various fuels for producing the heat they need; the heat energy is often captured and used in the form of steam. Common industrial fuels are coal, natural gas, oil, coal gasification, and solar. It takes energy to make energy, meaning that fuels consume a certain amount of energy in order to make them usable for industry. Coal requires the energy of large machinery to dig it out of the ground, and solar cells require energy to gather components and assemble the devices. At each step in these processes, a bit of heat energy is lost according to the second law of thermodynamics. For that reason industrial fuels are evaluated by a ratio called the net energy ratio, shown here:

usable energy ÷ energy used to produce the fuel = net energy ratio

A ratio greater than 1.0 indicates that a fuel provides energy rather than consumes energy. The higher the ratio number, the higher amount of net energy a fuel produces.

Industries that need heat energy have tended to rely on surface- and underground-mined coals because these coals have net energy ratios of more than 25. By contrast, natural gas and oil have ratios of about 5, and coal gasification and solar devices have ratios of only 1.5 and about 1, respectively. When industrialists speak of the need for solar energy to “come down” before being profitable for business, they are talking about the net energy produced by solar devices compared with coal.

Even manufacturing plants that wish to rely on coal’s heat energy can do some things to reduce wasted heat and thereby increase efficiency. The Energy Research Center of the Netherlands has described three technologies that may soon make traditional manufacturing more energy sustainable:

1. reheating waste heat so that it returns to a high temperature useful for the production process
2. storing waste heat for other uses, such as heating offices
3. transporting waste heat to use in other facilities or homes

 Unless these or other technologies to manage heat energy become available at a reasonable price, traditional industries may have little incentive to dismantle their coal-fired power plants for cleaner energy-generating methods.