It would operate at a cell voltage of 1.48 V. It would operate at a cell voltage of 1.24 V.įor a water electrolysis unit operating at a constant temperature of 25 ☌ without the input of any additional heat energy, electrical energy would have to be supplied at a rate equivalent of the enthalpy (heat) of reaction or 285.830 kJ (0.07940 kWh) per gram mol of water consumed. ![]() Īn ideal electrolysis unit operating at a temperature of 25 ☌ having liquid water as the input and gaseous hydrogen and gaseous oxygen as products would require a theoretical minimum input of electrical energy of 237.129 kJ (0.06587 kWh) per gram mol (18.0154 gram) of water consumed and would require 48.701 kJ (0.01353 kWh) per gram mol of water consumed of heat energy to be added to the unit to maintain that temperature. For example, an ideal fuel cell operating at a temperature of 25 ☌ having gaseous hydrogen and gaseous oxygen as inputs and liquid water as the output could produce a theoretical maximum amount of electrical energy of 237.129 kJ (0.06587 kWh) per gram mol (18.0154 gram) of water produced and would require 48.701 kJ (0.01353 kWh) per gram mol of water produced of heat energy to be removed from the cell to maintain that temperature. Ī fuel cell may be considered to be the reverse of electrolysis. The energy efficiency of a process involving chemical change may be expressed relative to these theoretical minima or maxima.The difference between the change of enthalpy and the change of Gibbs energy of a chemical transformation at a particular temperature indicates the heat input required or the heat removal (cooling) required to maintain that temperature. The change of Gibbs energy of a defined chemical transformation at a particular temperature is the minimum theoretical quantity of energy required to make that change occur (if the change in Gibbs energy between reactants and products is positive) or the maximum theoretical energy that might be obtained from that change (if the change in Gibbs energy between reactants and products is negative). Luminous efficiency, that portion of the emitted electromagnetic radiation is usable for human vision.'Total efficiency', e.g., for cogeneration, useful electric power and heat output per fuel energy consumed.Thermal efficiency or Fuel efficiency, useful heat and/or work output per input energy such as the fuel consumed.potential energy of water) is converted to mechanical energy ( work) Mechanical efficiency, where one form of mechanical energy (e.g.Electrical efficiency, useful power output per electrical power consumed.Failure to do so causes endless confusion. The two are separate but both must be stated. Net Heating value), and whether gross output (at the generator terminals) or net output (at the power station fence) are being considered. Gross Heating Value, etc.) or LCV (a.k.a. When talking about the efficiency of heat engines and power stations the convention should be stated, i.e., HHV ( a.k.a. However, other effectiveness measures that can exceed 1.0 are used for heat pumps and other devices that move heat rather than convert it. Efficiencies may not exceed 100%, e.g., for a perpetual motion machine. Generally, energy conversion efficiency is a dimensionless number between 0 and 1.0, or 0% to 100%. ![]() Goal or mission oriented terms include effectiveness and efficacy. Η = P o u t P i n Įven though the definition includes the notion of usefulness, efficiency is considered a technical or physical term. For example, a light bulb falls into the categories energy converter. Energy converter is an example of an energy transformation. ![]() All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle. Overview Įnergy conversion efficiency depends on the usefulness of the output. The resulting value, η (eta), ranges between 0 and 1. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radiation), or heat. Efficiency of power plants, world total, 2008Įnergy conversion efficiency ( η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms.
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