Tag Archives: electricity

My First Electricity Calculator

I have built my first online electricity calculator. It’s very simple and there are lots of similar calculators out there but it’s a start.

Behold: Electricity Calculator

Here’s how it works. Let’s say you are wondering how much it would cost to run a nightlight if you leave it on all the time. This nightlight has 0.2 watt LED, so you enter 0.2 as wattage.


Next you enter 24 as the number of hours per day. Here in Australia we pay 30 cents per kilowatt-hour on average. The calculator gives you the result: the running cost would be $0.53 per year.

Electricity Calculator

Another example. We have 6 light bulbs in our kitchen. They are CFLs (of course) and 14 watt each.


So in total they use 6 * 14 = 84 watt. We have them on for about 3 hours per day. We pay 40 cents per kilowatt-hour. According to the calculator the kitchen lighting cost us $3.02 per month or $36.79 per year.


Easy Targets for Saving Electricity

When it comes to saving electricity there are steps that are very easy to achieve. They don’t require a ton of effort. And best of all, they are free.

For example consider a situation: the light is on but there is nobody in the room. The electricity is essentially being wasted. The solution is easy: turn off the light whenever you leave the room.

It pays off to find where in your home the energy is being wasted. Here are some more examples:

  • Heating or cooling empty rooms.
  • Keeping your computer on all the time. Turn it off when not using. Or, better yet, configure it go to sleep automatically.
  • Filling the kettle too full. The water that you didn’t use gets cold again. The energy used to boil it is wasted.
  • A second fridge that is almost empty.

The nice thing about these changes is they would not make any noticeable negative impact on you or others.

How to Measure Your Electrical Use with Electric Meter

The first step to saving electricity is usually to determine what devices in your home use the most energy. If you know your top 5 energy guzzlers you would know what changes will make the biggest difference.

The easiest way to do it is to use a plug-in power meter, similar to Kill-A-Watt.


Sometimes though it is not possible to use it. The device could be located in the hard to reach spot (e.g. whole house air conditioner). Or maybe you don’t have the meter handy.

What you can do in this case is to use your electricity meter, the one that counts how many kilowatt-hours you have used.

Recently I decided to measure how much electricity does our electric oven use. I suspect that it uses the most of the energy on weekends (that’s when my wife cooks).


I guess the oven is hard wired – I couldn’t find the socket for it in any case.

Here is our meter on the side of our house:


As you can see it is a smart meter. I live in Melbourne and we are lucky to get smart meters before the rest of Australia. The meter knows exactly how much energy our household is using right now but unfortunately it wouldn’t tell. All it shows is the total consumption so far and the current date and time.

However our meter has a little red blinking light. The more electricity we use, the more often it blinks. This is similar to the old meters with a spinning disk.

In fact there are two lights on our meter. According to the plate on the meter it turns the left LED lamp on or off every time 1 watt-hour is used. The right light is for var-hours.

So here is the plan:

  1. Calculate how much electricity our home is using with the oven off.
  2. Turn the oven on and calculate again.
  3. Subtract the first figure from the second figure. This will be how much electricity our oven use.

First, I counted beats with the oven off:

It was 4 beats in 38 seconds. This equals to 1 beat every 10 seconds on average. So every 10 seconds one watt-hour was used. Using this formula

watts = watt-hours / hours = watt-hours / (seconds / 3600 ) = watt-hours * 3600 / seconds

… we can calculate that this equals to 379 watts. Cool, we are using less than half kilowatt-hour per hour when the oven is off.

Next, I turned the oven on. I set the temperature to 200°C and the mode to ‘fan forced’. This time, I counted 32 beats in 20 seconds – this equals to 5,760 watts:

So based on that, our electric oven uses 5,381 watts or 5.381 kilowatt-hours per hour. At the moment we pay 40 cents per kilowatt-hour. So if we use our oven for 1 hour every day is would cost us $65 per month.

If you have an old analog electric meter you would count disc revolutions instead of blinks. Michael Bluejay has a great set of instructions and a calculator on his website that can help you.

How to Configure Windows 7 to Put Your Computer to Sleep Automatically

I used to leave my computer on all the time – just so that I don’t have to wait for it to start. Then, I upgraded my computer. As part of the upgrade I switched from Windows XP to Windows 7. What I noticed is now my computer goes to sleep automatically when I don’t use it. I think this is great for saving electricity.

Here is how to make sure that Windows 7 puts your computer to sleep automatically.

Click Start button, open Control Panel.

Open ‘Hardware and Sound’ category.

Open ‘Power Options’.

Click ‘Change when the computer sleeps’.

Set ‘Put the computer to sleep’ to 20 minutes.

The default is 30 minutes which is reasonable; 20 minutes is even better. Click Save Settings. Now if you don’t use your computer for 20 minutes it will go to sleep automatically.

While you there click ‘Choose what the power button does’ …

… and select ‘Sleep’ option.

I like to be able to quickly put my computer to sleep when I know that I finished for today. Also, when my kids were small they liked to press the power button just to see what will happen. Usually this resulted in Windows starting to shut down the computer and closing half of the programs before getting to some editor that would ask if I want to save the document before closing it.

The computer uses very little energy in sleep mode but starts up very quickly and in exactly the same state as you leave it. Another cool benefit is that you can wake it up by pressing any key or clicking the mouse. Keep in mind that you still need to shut down your computer if you want to unplug it. If your desktop computer loses power while it is in the sleep mode it would reset its state: all open programs and documents would be abruptly closed. This is why it’s a good idea to save your work when you step away from your computer – just in case of power outage.

See also: Sustainable Computing: Sleep or Hibernate?