Energy and Power Fundamentals

Electrical InformationWith all the different terms used to describe electricity and electrical equipment, we thought a quick summary of the basics of off-grid equipment and electrical knowledge will be useful when deciding what equipment is most suitable for your needs.  For further explanations and information, we recommend Google or attending an electrical training course.

Calculating your power and energy requirements

Ensuring you are selecting the correct equipment type, capacity and features for your intended purpose are equally as important as buying quality, brand name equipment and installing it correctly.  If the wrong equipment is selected based on incorrect power and energy calculations, it will either not deliver the outcome you're after, fail prematurely or damage the equipment.

Completing an accurate load profile is an essential part of correctly designing and choosing off-grid solar system equipment. The load profile is a list of all your appliances and utilities that require electricity. An estimate of their usage frequency (e.g. how many days per week, and hours per day) builds a picture of daily kWh usage and kW peak power demand. 

For a copy of an Energy Load Profile template CLICK HERE.


Power relates to the measurement of electrical energy (Amps, Volts, Watts, KiloWatts) at an instant (No time component). Important to understand when calculating 'peak power' for your application. Example - If all your electrical appliances turned on simultaneously, does your equipment have suitable Power capacity to handle it?

A = Amp: a measurement of the rate of electrical flow in a circuit (a component of power)

V = Volt: a measurement of electrical pressure across two parts of a circuit (a component of power)

W = Watt: a measurement of instantaneous power. A watt is a product of multiplying Volts and Amps

kW = Kilowatt: a measurement of true instantaneous power; 1000 Watts make a Kilowatt

kVA = Kilo Volt-Amp: a measurement of apparent power before it is corrected for current and voltage waveform misalignment (power factor or pf ) to make it true power or Kilowatts.


Energy (Amp hour, Watt-hour, KiloWatt hour) is power multiplied by time.  Energy is the same measurement used for standard household electricity bills and is critical to understanding the solar array and battery bank size for your application.  Solar arrays produce 'Energy', Battery banks store 'Energy'.  Example - A 100W LCD TV is used for 1 hour = 100Wh if the same 100W LCD TV is on for 2 hours it would use 200Wh. 

Ah = Amp-hour: the product of multiplying amps and hours; often used to measure the current delivery capacity of battery banks at a specific discharge rate and time period such as 20 or 100 hours etc. (It is only a component part of energy)

Wh = Watt-hour: a measurement of energy; it means watts delivered, calculated over a one hour period.

kWh = Kilowatt-hour: a measurement of energy that is often used for billing purposes for example; it means Kilowatts delivered, calculated over a one hour period. A Kilowatt-hour is the product of Volt x Amps x Hours x 1000. One Kilowatt-hour = 1000 watt-hours. Kilowatt-hours are sometimes used to measure battery energy storage capacity; it is calculated by multiplying Amp-hours by the battery bank nominal voltage (e.g. 1000Ah battery storage capacity @ C100 rating x 48V battery configuration = 48kWh over 100hr rate).

Voltage Classes and Other

LV = Low voltage class: includes mains power and is applicable to all equipment operating above 120 Volts DC or 50 Volts AC and not exceeding 1000 Volts AC or 1500 Volts DC. LV class equipment can only be serviced by a licenced electrician.

ELV = Extra Low voltage: this voltage is typically used in battery banks. ELV class applies to electrical equipment operating below 120 Volts DC or 50 Volts AC

DC = Direct Current: refers to a current that flows in only one direction.

AC = Alternating Current: refers to a system utilising a current that rapidly flows back and forth; for mains power equipment the current typically runs back and forth at 50 times per second.

Hz = Hertz: is the name given to the measurement of the frequency of alternating current reversals or cycles per second. Regarding generator sets the frequency in Hertz usually relates directly to engine speed. For example, a two-pole generator running at 3000 revolutions per minute will deliver a 50 Hz frequency.

M.P.P.T. = Maximum Power Point Tracking: is an advanced method of extracting the maximum possible power from a solar array (usually) within the solar inverter or solar charge controller as opposed to older type basic regulators which do not have this feature.