Energy, The Grid and Battery Storage: What do KWh, MWh, W, kW and MWh mean?
Part 1 of 4
By Randall Pearce
Energy is used for a myriad of purposes in our community including in heating, in manufacturing goods, and to move people and goods around the country.
Energy can be present in many forms, such as thermal energy (heat), kinetic energy (motion), potential energy (height), chemical energy (enthalpy), atomic energy (energy within atoms), sound energy (noise), visible energy (light) and electrical energy (charge). The measurement of each form of energy is typically made relative to some base condition, such as ambient temperature; no motion relative to the earth; a given ground level, and so on.
Many forms of energy can be converted between one form and another, with varying degrees of efficiency and with the loss of some of it in other forms, such as heat, noise or light. Electrical energy is one of several forms and is typically expressed in kilowatt hours (kWh) or megawatt hours (MWh).
Electrical power is the flow rate of electrical energy and is typically expressed in watts (W), kilowatts (kW), or megawatts (MW). One kilowatt (kW) = 1,000 watts; 1 megawatt (MW) = 1,000 kW; 1 gigawatt (GW) = 1,000 MW.
Household electricity meters are being progressively replaced with Smart Meters, which communicate directly with the electricity distributors (Distributed Network Service Providers (DNSPs). These smart meters display the accumulated readings of energy
imported or exported (in the case of solar PV generation) in kilowatt hours (kWh).
Currently, the amount of energy used every 15 minutes is recorded and transmitted to the distributor (Jemena for Alphington).
If you have a solar PV system with a computer interface or phone app (a very good idea), the inverter may also be able to communicate and display in real time the instantaneous power in kilowatts (kW) being imported, or exported, as well as the household
consumption in kilowatts (kW). A small current transformer needs to be installed in the meter box to permit this final level of monitoring, which is probably worth the extra investment.
A phone app is a great way of developing an understanding of exactly how much each appliance at your home is using, by turning things on and off to monitor the changes in consumption. I have attached screenshots of our 10kW solar system at around 11am on a cold cloudy winters day with the hot water heat pump and the space heating heat pump running on economy settings. You can see that our consumption matches our (solar generation) production so we are not importing or paying for energy from the grid at that time. The second charts show the total energy used on the previous day, which had followed an overnight temperature of - 2 C.
