The First Law
While in daily life it is frequently useful to consider energy consumption, this concept is not scientifically well-defined. The process that is generally termed energy consumption is, in fact, energy transfer and transformation.
The first law of thermodynamics mathematically states that the total energy of an isolated system remains constant. For our purposes, an isolated system can be defined as a system whose borders do not allow for the transfer of energy or mass. In practical terms, this formulation stipulates that energy cannot be created or destroyed; it can only be converted from one form to another. When paying for electricity from the grid then, one is actually paying for the right to transform a quantity of electrical energy into whatever form of energy is selected to accomplish a particular task. Despite being pedantically inaccurate, the amount of energy transferred into a particular device is typically referred to as its energy consumption.
To better illustrate the concepts of energy conservation, we can consider the energy flow in an internal combustion engine found in an automobile. During operation, it consumes a fuel, such as gasoline, as well as oxygen, while producing carbon dioxide (CO2), water and other byproducts. In combustion, chemical energy stored in the fuel is converted to heat in a highly exothermic (energy releasing) reaction with oxygen. Using a clever mechanical design, a portion of that heat energy is converted into mechanical energy which is used to propel the car. Typical gasoline internal combustion engines achieve thermal efficiencies of around 25%. This means that for a given amount of heat energy derived from combustion, about one quarter of that energy is converted into usable mechanical energy by the engine. A car’s radiator dissipates this waste heat to its surroundings. During winter, this thermal energy is also used to warm the vehicle’s cabin.
A similar line of reasoning can be applied to other facets of our everyday relationship with energy. Household appliances convert electrical energy into whatever form is desired by the consumer, less the device’s inefficiencies. For instance, a light bulb converts some percentage of its electrical input into light output with the remaining balance being converted into waste heat. According to the Environmental Protection Agency, a conventional incandescent light bulb offers an efficiency of approximately 10%. That is, 90% of the electrical energy sent into the lamp is converted into heat energy, while the remaining 10% is converted into visible light.
With other electrical devices, it is often less evident how to define efficiency or analyze the energy flow into or out of the appliance. While the purpose of a clothes washer is to clean clothes, it is not obvious how to define this objective in terms of energy flow. Such a complex appliance is made up of many different individual mechanisms whose operating principles and functions differ. Conservation of energy could still be applied to the system or each individual component that comprises it. Each input and output could be considered in detail in order to paint a complete picture of energy balance involved in washing clothes. However, since the desired output of the appliance is not a different form of energy, but instead the abstract concept of cleanliness, such an analysis would be necessarily nebulous in terms of overall appliance efficiency.
Whether driving your car, or gazing upon festive lights, always remember to conserve energy, not that you have a choice! From all of us at the Solar Initiative, we wish you a happy, energy conserving (pun intended) holiday season!