In articles discussing heating energy usage, the term ‘kWhth’ may appear. The kWh indicates the amount of energy in kilowatt-hours and subsequent letters indicate type of energy. ‘th’ indicates thermal energy. To help clarify the term, sometimes the energy type is written in parenthesis – kWh(th) or as a subscript kWhth .
In addition you may encounter the term ‘kWhe’, kWh(e) or kWhe. In this case, the energy in question is electrical energy.
Such descriptions can help clarify the form of energy when discussing an energy producing or using system. For example, a (very small) nuclear power station may produce 3kWh(th) of heat energy from the reactor that is used to heat the water to create steam to drive the turbines. However the turbines only product 1kWh(e) electrical energy indicating that 2 kWh of energy is lost in the electrical generation process.
kilowatt-hours and joules
kilowatt-hours are often used in typical energy calculations used by domestic users. One kilowatt-hour is equal to the amount of energy used in one hour by appliances that are rated at one kilowatt. kilowatt-hours are used because they are familiar units that are convenient to use in a domestic setting.
There is no need to restrict the energy type suffix to kWh measurements and therefore joules or megajoules can be used just as well. For example megawatt hours (MWhth) and megajoules (MJth) or gigajoules ( GJth ) can be more convenient measurements. In the case of a real nuclear power station, these are much more convenient units to use given the significantly higher amounts of energy involved.