What are kWh and Ah?
One of the difficult things with electric vehicles is the terminology and jargon associated with them. Kilowatts, charging connectors, inverters, rates of charge and discharge are all new concepts for car buyers who previously had to only worry about whether their motor uses diesel or petrol.
However, anyone with a background in electronics or electrical engineering will soon spot that the terms used are nothing new. The technical terminology revolves around the notion of kilowatts and amperes.
What is an ampere and ampere-hour?
Both kilowatts and amperes are units of measurement. Ampere is a unit of measure of the rate of electron flow (think electricity) or the flow of current in a conductor – something that conducts or controls electricity – in the space of one second.
Electrons are tiny, negatively charged particles. Because they are negatively charged, they are negatively attracted, meaning if one moves closer to another, the other electron will move further away from it. Move one electron in a line and the others will move. This is the basic behind current or electricity. The measure of this current is known as ampere.
One ampere (A) has a standard definition of 6.24 x 10 to the power of 18 electrons flowing through a second. The more amps you have, the higher the current.
As an example, a typical laptop has a current of about 3A (three amps).
An amp hour (Ah) is a different unit to amps, and is used to define capacity. It’s used to estimate the amount of energy a battery can hold. In simple terms, it’s used to define the amount of current a battery can supply in an hour until it runs out of current.
Amp hours are therefore used to determine battery life. Amp hours divided by amps tell us the battery life in hours.
So a 2Ah battery can draw two amps for one hour before it runs out, or four amps for half an hour, or one amp for two hours.
What is a kilowatt and kilowatt-hour?
Watts on the other hand are a definition of power. A watt is a measure of both the amps and voltage combined. Voltage can be thought of the amount of electrical pressure a conductor or circuit has - the force that pushes the electrons along the circuit. Amps are the speed at which electrons move past a given point.
Power is then a relation of both force and speed. The formula runs as:
Power (Watts) = Amps x Volts
Watts are used to define the amount of power that runs through a given power supply. A kilowatt (kW) is simply a thousand watts.
A kilowatt hour (kWh), much like an amp hour is different from a watt. A kilowatt hour is a measure of energy, so how much energy is consumed in a given period.
Kilowatt multiplied by an hour give you an indication of how much energy you use in an hour. A battery capacity is always given in kWh, and is used to measure the charge in a battery. So a 40kWh battery can discharge 40kW in an hour, or 20kW in two hours.
Importantly, electricity supplied to a battery is always given in kW, with the battery capacity registered in kWh. Similarly, an electrical motor’s power is always listed in kW.