How to set energy use targets


Saving energy is a worthy aim but like most goals it is better if you have a measurable target to aim for. How should you go about setting an energy use goal? I am particularly fond of the Wheaton Eco Test.  The test (or target) is really simple. You find out what the average spending is for a particular commodity and then use less than that. If you have time I would recommend that you go and read the essay.

In the past I have received utility bills where the bill includes a little graph showing how much I use in relation to other people in the same area. I was always shocked to see how my two person household uses less than other single person households! I guess it’s easy to waste mindlessly if you aren’t paying attention.

Comparative usage from an electricity bill
Comparative usage from an electricity bill. Note that the usage was in conjunction with gas.
Comparative usage from a water bill
Comparative usage from a water bill

Now I will conceded that it can be difficult to find out what these averages are. Here are some of the values I was able to find for Melbourne and/or Australia.

The point is not the accuracy of the averages, the aim is to find some reasonable average and then aim to use less than that average. Not doing anything less than the average is just kidding yourself.

How to use a plug-in power meter

Energy Meter Header

In my post on Dollars and Fridges I referred to the use of my MS6115 plug-in power meter to measure the power consumption of my fridge. I wanted to discuss this tool as well as it’s advantages and shortcomings.

The MS6115 is a $22 device that is similar to the US Kill-a-Watt. The basic operation is really simple. You plug in the MS6115 into a power outlet and then plug the device you want to investigate into the MS6115. It then tells you the power usage of the connected device. There are a few more advanced features where you can include your electricity price as well as dates and times but the menu’s are difficult to navigate and I prefer to only use the basic features. Let’s have a look at the menu’s


When you first turn the device on it shows all the display elements at once.


The different features we have are WATT, kWh, SET, AMP, VOLTac, COST/kWh, some warnings, various date and time related features, POWERFACTOR and Hz (frequency). You cycle through the menus by pressing the FUNC button below the screen.


The first page shows your AC line voltage and frequency. This is interesting but does not tell us much regarding the power usage. For more information have a look at Table of mains voltages and frequencies.


The next page shows us the amperage and power factor. Keep going.


Here things get interesting. The WATT page shows us the power usage of the connected device.


Finally we get to the energy used menu, the kWh display.


The last menu before we start at voltage again shows us the total price. This will only show the correct values if you entered the electricity price during the initial setup.

How to perform a measurement

The types of devices we want to measure fall into two rough categories. The one type of device is under our control like a floorlamp or a TV set. The other type of device can turn on and off by itself like a fridge or a electric hot water heater.

For the first type of device it is sufficient to just write down the power usage on the WATT screen. Since we know, or can estimate, the time the device is on we can multiply the power usage with the time in use to obtain the energy usage. So for example:

If we have a floorlamp and we measure its power usage as 120 watt and we know we only use it for about 2 hours per day, we can work out that the floorlamp uses 87.6kWh per year.

87.6\ kWh = \frac{120W}{1000W}\times{2\ hours}\times{365\ days}

For the second type of device I do the following. Firstly plug in the device and then take note of the time, or even better set an alarm for the next day at the same time. Then you let the device run. The next day just navigate to the kWh menu and write down how much energy was used for the past day. So for example:

I measured my fridge and it showed that it used 1.4 kWh  per day. I just multiply it out with the days in the year to determine that it used roughly 511 kWh per year.

511\ kWh = 1.4\ kWh\times{365\ days}

Note that the second method does not account for human behaviour or seasonal changes. For example if you open the fridge more often or if it needs to work harder during the summer. It does however give you a good approximation of the average usage.


If you are interested in any of the other features have a look at the manual.

MS6115 Manual


The MS6115 is a very cost effective way of getting a handle on the flows of energy in your house. It is simple to use and has very few limitations. It can measure the power usage for any device that has a plug.

Dollars and Fridges


I’m using a really old fridge/freezer. Really old. I wanted to investigate if it would be worthwhile replacing it with a more energy efficient model. After the hot water heater this is one of the bigger power users in the apartment. I have been measuring the power use over the past few days using an MS6115 plug-in power meter. I will elaborate more on it in a later post.

I worked out the average daily power use for this fridge to be about 1.4 kWh. This does not take into consideration how many times the door was opened, if new items were stored or what the ambient temperature is, but it gives me a good idea to work from.

I received this fridge for free so it cost me nothing apart from transport. If I take a look at a similar fridge a few minutes of research comes up with the Samsung SR227MW. This fridge uses 280 kWh per year, or about 0.8 kWh per day. This is approximately an 80% improvement in efficiency. For this improvement I need to pay $566 and get a 2 year warranty.

Is it worthwhile replacing my fridge with the more efficient new one? I have the following information:

Current fridge usage 1.4 kWh per day
Electricity price 23.8 c per kWh
New fridge usage 0.8 kWh per day
Cost of new fridge 566 Dollars

With this information I can workout the payback period. The formula to determine this is reasonably simple.

Break\, even\,(days) = \frac{Cost\, of\, new\, fridge}{(Current\, fridge \, usage-New\, fridge \,usage)\times Electricity\, Price}

This gives me a total of 3970 days or 10.9 years before the savings of the new fridge have paid for itself. If I consider that my current fridge is possibly older than I am and is still working, compared to a new unit that only has a 2 year warranty this does not seem like a good idea.

What people often don’t realise is that all objects have another energy aspect attributed to them. This is called embedded energy. This refers to the energy needed to manufacture the item in question. The diesel to mine the steel, the coal to melt the steel etc. I will discuss this in a future post.

With all this taken into account replacing my working fridge just does not make sense.

Phantom Power in Practice


The term phantom or vampire power was very newsworthy a few years ago. This concept refers to the small power draw from appliances that don’t turn off fully and use energy even when they aren’t really doing anything useful. An example might be a microwave using power to run it’s clock even when you aren’t using it to heat anything. In my apartment my phantom draw is about 100W. This seems really insignificant until you realise the cost implications.

There are approximately 8765 hours in a year. If we assume that my phantom draw is constant over the span of a year, then the phantom draw is using 876.5 kWh. At a price of $0.2376/kWh the phantom draw is costing me $208! This is almost half of what the Australian government said household’s would save with the repeal of the carbon tax.

In a future post I will attempt to hunt down these phantoms. And kill them.

Electricity Prices Explained


Tariff Price
excluding GST including GST

Peak Step 1

(First 16.45 kWh/day)

16.3000 c/kWh 17.9300 c/kWh
Peak Step 2 17.0000 c/kWh 18.7000 c/kWh
Service to Property 106.0000 c/day 116.6000 c/day
GreenPower 5.3000 c/kWh 5.8300 c/kWh

This is the electricity price breakdown for the area I live in. All prices are in Australian dollar. GST refers to the Goods and Services Tax which is a 10% tax levied by the government.

Lets analyse the different sections. Since I cannot claim back GST like a business, I will only focus on the prices inclusive of GST. The first Tariff, Peak Step 1, shows the price I will pay as long as my daily usage is less than 16.45kWh. This stepped tariff system aims to incentivise people to use less electricity. So for every “unit” or kWh of electricity that I use under the Peak Step 1 tariff I get charged $0.1793. Every unit after the 16.45kWh threshold is charged at the Peak Step 2 rate, costing me $0.187 per unit, 4.3% more.

The “Service to Property” charge is a daily flat rate charge that covers the cost of maintaining the infrastructure to provide electricity to where I live. This charge is paid irrespective of how much you use and even applies to people who have solar energy that they sell back to the electricity company. In some places this is not a separate fee and the charge is incorporated in the electricity unit price.

The last cost, GreenPower, is the premium I choose to pay voluntarily to ensure that my electricity is supplied by renewable energy sources. In the case of this supplier the power is generated using the Snowy Hydro power generation scheme.

So all inclusive I pay $1.166 per day as my connection fee and then $0.2376 per kWh as long as my usage is less than 16.45kWh per day.

Energy & power measurement


How is energy measured? There are various units energy is measured in but they all fall into two categories when applied to energy consumption. The units either describe the total energy used to achieve something or the energy use per unit of time. Lets consider speed and distance. When I travel home in my car I might need to travel 10km. To keep to the speed limit I might need to travel no faster than 60km/h.
The 10km I need to travel is the total distance I need to travel in order to achieve my goal of getting home. The 60km per hour that I am traveling describes the rate of movement per hour.

These two units are related but they are not the same thing. With the information I can calculate that if my speed does not change it will take me 10 minutes to get home. If you knew how long you traveled and the speed you could determine how far you moved.

Lets translate this to energy. The unit that energy is measured in is the joule. One joule is roughly the energy required to lift a small apple 1m off the ground. This is not a scientific definition but makes for a good illustration.  Joule is our distance – the total amount of energy required to do something without any consideration for time.


What would be the speed equivalent? Measuring the rate of change of energy is called power. It is measured in the unit watt. Watt is the same as joule per second. So if you had a basket of small apples and were picking them up one by one, and one per second, the power involved would be 1 watt.

So in the same way as the speed/distance example energy/power and joule/watt are related but they are not the same thing. What gets confusing is that the majority of energy measurements are denoted in watt-hours. This is the same as giving distance in the unit of km/h.h or kilometer per hour hours. These are all the different ways of denoting the same thing. So when people talk about watt-hours remember that they are actually taking about joule, the unit of energy measurement.

Example: If I have a toaster rated at 700W and it takes 2 minutes to toast my bread I can determine that running the toaster for 2 minutes requires 84 000 joules of energy.

It is due to the fact the numbers get big so quickly that a different unit was devised but that still describes the same thing. The standard unit for describing electrical energy consumed is watt-hour or kilowatt-hour (a thousand watt-hours). This is the same as 3.6MJ or 3 600 000 joule.

That is a lot of apples.


Sorted Coins

What is energy? In essence energy is the ability to do work. It is the thing you need to do something useful.  The picture above illustrates this principle. If you have a box filled with a random assortment of coins it will take energy to sort them and neatly stack them on top of each other.

There are two main laws that govern energy. The first law states that Energy cannot be created or destroyed but it can changed from one type to another.
The second law states that “in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state.”

These laws sound complicated but they basically encapsulate that you can’t get energy for free (First law) and that in a closed system energy moves from being concentrated to being dispersed (Second law). The second law also describes another aspect known as entropy (chaos, disorder), and says that entropy will increase over time in a closed system.

To illustrate. A mug of heated tea is standing on a desk. After a few hours the tea is colder and the desk below the mug is a little bit warmer. The mug cooling down has to transfer its heat somewhere (First law) – this heat is transferred to the surrounding air and the desktop. The heat moving from the tea and the mug to the surroundings illustrate the Second law. The heat energy moves from being concentrated in the water to being dispersed in the water, mug, air and desk.

So energy is everywhere and it is more useful to us if it is concentrated than when it is dispersed. Also these laws are laws – so when somebody talks about free energy or things sucking energy from their surroundings to heat up, a mistake is usually being made or something is not being considered. Sadly you cannot get something for nothing.