In an ideal world, all of our electrical energy would be generated from fully renewable resources, the process would be pollution and loss free, and the original source, the sun, lasts forever. However, until we approach this theoretical ideal, it is important to make our domestic electricity consumption as efficient as possible, use our electrical and electronic products in a manner that minimises power use (thus energy), and be aware of where the power losses are taking place.
We can make a significant difference by moving on to more energy efficient products, correctly timing when we use certain products and taking advantage of using low-energy products and lower power settings. It also helps to understand the association between energy and power, and energy transfer efficiency.
Making Sense of Power Rating
LEDs are the brighter choices.
LEDs are the brighter choices.Electrical appliances and light bulbs are marked with an electrical power rating. For example, an electric kettle may require 2 kilowatts of power (2kW), whereas an electric light bulb only 100 watts (100W). The unit of power is the Watt. It is a unit that indicates the rate at which energy conversion or energy transfer takes place. Consequently, the unit of power can also be expressed as the amount of energy transferred from one form to another per unit of time, therefore power can be expressed as being Joules per Second (J/s). Transferring energy at a rate of one Joule per Second is exactly equal to one Watt.
A 100W light bulb will convert 100J/s of electrical energy into light and heat energy. After ten minutes, or 600 seconds, 60000 Joules of energy will have been converted from electrical energy to light and heat energy. If left for two hours, or 7200 seconds, the same electric light bulb will have transferred 720000 Joules of energy. In other words, the amount of energy transferred is directly related to the rate of energy transfer, and the duration over which that energy transfer is applied.
Why Bother with Energy Transfer Efficiency
Energy transfer efficiency is defined as how much of the original input energy is converted into the next source of energy required. With reference to a basic tungsten filament light bulb, about 95% of the electrical energy is converted into heat, as the filament is literally white hot. That’s why a working filament light bulb is so hot to touch. Even fluorescent light bulb replacements waste about 75% of the electrical energy.
A kettle, on the other hand (until it generates noise) is much better at converting electrical energy into heat. But as noise develops this means that some of the electrical energy is now being converted to sound energy. Finally, the best example is an electric heater, where this can be almost 100% efficient in converting electrical energy into heat energy, provided that the heating elements do not become too hot so that they glow, as this means that some of the electrical energy is now being converted into light energy.
Increasing Electrical Efficiency
In the United Kingdom, all electrical products designed for domestic use have to be marked with an 'Energy' rating, where the letters 'A' to 'G' are shown to indicate the relative energy efficiency. The letter 'A' is the most efficient rating and 'G' the lowest. For the domestic customer, they no longer have to understand how the appliance works as the letter marking provides an instant reference to how energy efficient the product will be.
There are now two basic methods that can be used to reduce the amount of electrical energy consumed and its environmental impact. They are energy transfer efficiency, and how they are used.
Returning to the domestic light bulb example, where the following makes a significant contrast:
Filament Light Bulb: 5% efficient, lasts about 1000 hours.
Fluorescent Light Bulb: 25% efficient, lasts about 10000 hours.
Light Emitting Diode Light Bulb: 50% efficient, lasts about 100000 hours.
Clearly, the Light Emitting Diode or LED Light Bulb is a significant improvement, while remaining as a direct replacement for both standard tungsten filament and fluorescent light bulbs. In addition, it removes the risks associated with fluorescent a light bulb, which is Ultra Violet radiation, and the internal use of mercury, a distinct health and environmental risk.
This LED light bulb replacement (see picture) only consumes 2.5W of electric power to match a conventional 30W tungsten filament light bulb. Use three, which replaces one 100W conventional light bulb with a light source that only consumes 7.5W, or 7.5 Joules per Second, that is over thirteen times less electrical energy for the same level of light.
Assuming that we have followed the process of selecting the most energy efficient 'A' rated products, there are other methods that can be applied to assist in reducing the use of electrical power thus energy. Read on.
Next: How to be smart and use electrical energy efficiently at home by Andrew Porter