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Power 2 – Overview of Terms

A guest post by Skvez.

Part 1 of this series is ‘Choosing your back-up/off-grid power source’

Before we get into generating your own electricity and storing this electric power; I think it is worth doing an article on the terms used when discussing electricity and power. It’s easy for those not immersed in the terms to get confused.

This is the electrical potential that exists between two points, it’s the force that tends to drive current to flow and power to be transferred. The greater the Voltage; the greater the tendency for current to want to flow. The symbol for Voltage is ‘V’ and it is measured in Volts (V).

This is the amount of electricity that flows as a result of a Voltage being applied and an electrical path existing for the current to flow along. The Symbol for current is ‘I’ and it is measured in Amps (A)

This is the electrical resistance impeding the flow of current in an electrical path that’s trying to flow due to a Voltage. The symbol for Resistance is ‘R’ and it is measured in Ohms (Ω)

To give an analogy: If we have water flowing in a stream, the stream is our ‘circuit’ the Voltage is the height between the top and bottom of the stream, the current is the amount of water that flows and the resistance is the sum of the terrain the stream flows through, a polished steel tube would be a low resistance (it’s easier for water to flow), a high resistance would be very boggy ground (harder for water to flow).

The relationship between Voltage (V), Current (I) and Resistance (R) is V = I * R

Power is a measurement of Work. It has the symbol ‘P’ and is measured in Watts (W).
The Power is the Voltage times the Current.
P = V * I

But Power is a measurement of instantaneous Work, if we want to know the total work done we need to measure Power over time. Watt-hours are simply the power in Watts times the time (in hours) that that work is done for a total measurement of energy.

Your electricity bill charges you per kWh you consume (the k is kilo, short for 1000 to keep the numbers manageable), probably about 15p/kWh at the minute. When we get into generating your own power, you’ll see that that’s actually really, really cheap compared to the alternatives (!)

The third part of the series is Power 3: Off-grid power system, 12V or 230V?

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