If you're interested in environmental issues, there's little doubt that you're aware of the links between energy usage and climate change. As a matter of convenience we all tend to waste energy, and as a result we're hurting both our planet and bank accounts. Further to that, fuel prices seem to constantly rise, leaving us even more out of pocket when we get into bad habits.
There are so many ways in which we can save energy, some require a little cash investment, but many just require a change in thinking to tighten up efficiency.
In order to understand how much electricity each appliance uses you'll need to have a basic grasp on how electricity is measured, but don't worry it doesn't get too technical.
Energy consumption is measured in kilowatt hours (kWh). This means that an appliance rated at 1000 Watts, will use around 1 kWh if switched on for an hour.
To calculate the usage of an appliance in kWh, you simply multiply the energy rating of the appliance (normally in Watts) by the time used, and then divide it by 1000 (1000W = 1 kWh).
This makes is particularly easy when using an electrical item that has a fixed power usage, such as a light-bulb.
- A 100W incandescent light-bulb used for one hour uses 0.1 kWh: (100 x 1) / 1000 = 0.1
- A 1500W microwave used for 15 minutes uses 0.375 kWH: (1500 x 0.25) / 1000 = 0.375
- A 1200W dishwasher used for an hour and half uses 1.8 kWh: (1200 x 1.5) / 1000 = 1.8
For appliances with a variable power output (e.g. an oven), you can estimate the power usage by dividing the maximum energy requirement (Watts), by the fraction of the power used (e.g half power = 0.5).
Example: A 4000W oven used at half its maximum temperature would be 4000 x 0.5 = 2000 watts. The oven is therefore using around 2 kWh of energy for each hour it's used on this setting. You can then apply this figure to the above equation to calculate the estimated usage over any period of time
The cost of Kilowatt Hours
Suppliers generally use the kilowatt hour as the standard unit of electricity measurement. Depending on your tariff and provider, the price for a kilowatt hour can vary, but as a general rule of thumb it's around 15 pence. You can find out your exact unit price by checking your last bill, or calling your provider. Alternatively, if you're on a pre-pay meter, you may find the unit price displayed on the meter's interface.
Once you have the pricing details of your tariff you can start calculating how much you could save, or might be wasting by simply multiplying the calculated energy usage by the unit price. For example, if I had a habit of leaving the kitchen light on when not in the room and estimated that this equated to an average of 5 hours a day I could make the following calculations on how much I could save over a year:
- 50W bulb unnecessarily used for around 5 hours per day, all year round
- (50 x 5) / 1000 = 0.25 kWh – daily wastage
- 0.25 x 365 = 91.25 kWh – yearly wastage
- (91.25 x 15 pence) / 100 = £13.69 saving
The same method can of course be applied when calculating how much you might save if replacing electrical items for more efficient counterparts. For more examples of practical applications of this knowledge, please refer to our other guides on cutting your energy bills.