Right, on with the blog. I am going to assume the lowest common denominator for those that read this blog and that assumption is that:
a) everyone has a reasonable grasp of GCSE or equivalent maths (A's not needed, just provided you can do basic calculations)
b) no one has a clue about physical science or engineering
I hope you find this interesting whether you fit into the above categories or not.
Ok, where to begin?
Ah yes - what is energy? It's probably good to start with the basics and work upwards...
If one were to go searching for what the definition of it on the internet then it would take a long time to reach a conclusion and the final result would probably be wrong in as much as it would be mixed up with a hundred other concepts and quantities. Energy has such a broad meaning these days that it is quite often thrown in to various casual conversations when it's referal is only metaphorical.
Let's get down to business then - energy is, for our sake of understanding, something which has the potential to do some work in a physical sense. This means it has a reaction and a potential to change things as we see them in the everyday universe. It can come in various forms: chemical, electrical, thermal, potential, kinetic etc. I think for the purposes of this article we will keep it simple. Let's imagine that any quantity of energy can be equated to a match...
A match has a certain amount of chemical energy locked up inside it. When it is ignited (and let's ignore the energy required to do that for the time being) then the chemical energy is converted into heat, light and sound. That is another factor that we should consider - energy cannot be created or destroyed it can only be converted from one form to another.
Anyway, back to the match, when we think about energy we should think about matches because energy is a term used for a quantity of this stuff. Any quantity of energy is unchanged unless we convert it into something else, we add to it or we take something away from it. We can think about the amount of energy locked up in a match or we can think of a larger amount of energy in terms of how many matches it is equivalent to. Energy is not and should not be referred to as a rate, as a force or anything like that - it is a quantity of the potential to do something.
Now of course we don't usually measure energy in terms of numbers of matches of equivalent energy. The normal unit we use for energy (in the ISO system at least) is the Joule. Please think of Joules as being a measure of a quantity, similar to an amount of money in your bank or a number of acorns in your hand (that one was for Lukasz Machura). One can find how much energy, in Joules, is in one match and in fact I just looked it up and it was about 2000 Joules. That means when a match is lit, if you were able to capture all the heat, light and sound that it released it would come to about 2000 Joules.
Writing Joules down every time is a bit tiring so instead of Joules we can merely write "J" as the unit. Therefore:
Energy is a quantity and is measured in Joules (J)
All right so far I hope.
Ok if all that's clear maybe we can move away from matches in order to think about different measurements of energy flow and quantity. I try to use everyday household objects when I try to explain difficult physics concepts to my tutored students. In the next case I would like you to imagine your bath and the taps. If we can stick with this then you can understand almost all there is to know about thermal and electrical energy.
I want us to think about energy as being a quantity of water. Maybe one Joule is, say, one litre of water. If that doesn't help then think of the water as being petrol instead and the concept might stick a bit easier. Anyway, I hope the majority of you non-arsonists will stay with the water image.
Your bath will contain a certain amount of water (or energy) when you turn the taps on. You can turn the taps on quickly and fill the bath quickly or slowly to fill the bath over a longer duration. In any case, once the bath is full it is full. The quantity of water in there will be the same whether you filled it quickly or slowly.
Now back to the taps. You are sitting there with a one-litre jug (representing one Joule of energy). You run the taps and it fills up the jug. If you have big taps in a house with a high water pressure then you might be able to fill up the jug in just one second. This would mean your taps are delivering water at one jug per second. Let's flip this over for a moment and think back to energy.
If a jug full of water represents one Joule of energy and it takes one second to fill the jug, this means that the taps are delivering one Joule per second. That makes sense doesn't it? One jug per second = one Joule per second. We are now defining a rate of energy transferred or in the example the rate of water transferred from the taps to the jug. One Joule per second is a measurement of Power and is measured in a term I think will be familiar to you all, the Watt.
Let's just clarify everything then:
Power is the rate of energy transferred. This rate is Joules per second or Watts.
1 Joule per second = 1 Watt
Again, writing Watts each time is tiring so we just write the capital letter "W" meaning Watts. Why do scientists and engineers abbreviate everything? Is it just to confuse the public? No, it's to save valuable ink, paper and time especially if you have to write words like "Capacitive Reactance" when just writing "Xc" will do.
So if we're happy to continue and just get back to some simple equations (yuck!):
Power (P) = Energy (E) rate of transfer = Joules (J) per second (s) = J/s = Watts = W
Don't worry about it all too much, just stick with the taps, the jug, the bath and the water. If you turn the taps on full then you might get one jug per second (or one Joule per second = 1 watt). If the taps are only turned on slightly then you might one jug per 10 seconds (which would be 0.1 jug or 0.1 Joule per second = 0.1 watts). Remember that the amount that you turn the taps on determines the rate of flow or Power measured in watts. The amount of water that collects in the bath is the quantity of energy or Joules.
Now before anyone makes you believe anything else, when you pay your electricity bills, the consumption part of your bill is a measurement of energy (that's the stuff in Joules) that you have actually used or imported into your house. You pay for the number of Joules that you used for any given period (assuming that someone comes and reads the meter rather than just assuming that you leave the lights on all day). It's a bit like someone coming along and seeing how much water you have run into your bath tub. The amount of water in there is checked and measured and you pay for the amount. How the bath got so full of water is determined by of course two things:
1. How much you turned the taps on (power).
2. How long you left the taps on (time).
Energy = Power x Time
Now we could of course carry on using Joules but unfortunately it is quite a small unit of energy. Remember the match? That in itself contains an incredible 2000 Joules of energy - just in one match!
What about that old light bulb that you keep on under the stairs? Think how much heat comes off that and how many matches that would equate to in 3 months and how many Joules that would be. Well if it was a 60 watt lamp and it was left on for three full months it would be:
60 watts x 3,600 seconds in an hour x 24 hours x 90 days = 466,560,000 Joules!
That's quite a lot of figures to write on your electricity bill for just one light bulb. So instead of using Joules we use a much larger (and more familiar) unit, the Kilowatt Hour.
Let's just unpack that term a little bit. A Kilowatt is one thousand watts (or one thousand Joules per second - that's a big tap!). Remember that this is a unit of power or rate of energy use. If we left the one kilowatt tap on for one hour then that would be one kilowatt hour. Breaking this down further:
1000 Joules per second x 60 seconds in a minute x 60 minutes in an hour = 3,600,000 Joules
OR one kilowatt hour.
See how easy it is. The term kilowatt hour is a bit long as well so it is often abbreviated to kWh.
1 kilowatt hour = 1 kWh = 1000 watts on for one hour = 1000 Joules per second for 3,600 seconds = 3,600,000 Joules
All of your electricity bills will probably be based on the number of kWh you used in any given period. As kWh are a quantity of energy, like matches or apples, you pay a certain amount of money per kWh used. At the current date this ranges from about 10 to 20 pence per kWh of electricity.
Electrical appliances are rated in watts or kilowatts. The amount means "if you switch me on then this is the rate of energy I will use but you can decide how long you use me for". Let's look at an example to finally put all this terminology to bed (don't be scared of the maths, it's only multiplication).
If I use my 1200 watt hairdryer for 15 minutes every day, what will be my annual electricity bill be for the hairdryer alone assuming that my electricity supply company charges me 20p per kWh
> Daily energy used = 1200 watts x 15 minutes (or 0.25 of an hour)
= 1.2 kilowatts (kW) x 0.25 hours = 0.4 kilowatt hours (kWh)
> Annual energy used = 0.4 kWh x 365 days per year
= 146 kWh per year
> Annual energy cost = 146 kWh x 20p
= £29.20 per year
There, that wasn't so bad was it. If you've got this far then you probably understand energy better than 75% of the people around you. That's the Primer for Energy finished for now, let's look at why you should change your lights...
There are many lighting technologies available these days, most people have a mix of
- incandescent GLS (general lighting service) lamps (the old traditional light bulbs)
- tungsten halogen spot lighting (popular in kitchens and bathrooms)
- compact fluorescent (or energy-saving light bulbs as they are known)
- LED (or light emitting diode)
I want for this article to focus on two of the lights above: incandescent vs compact fluorescent. That is old style lightbulb versus energy saving lightbulb.
Most people tend to wait until their old light bulbs go pop before changing over to energy saving lightbulbts as it seems to be the most cost-effective thing to do. It might seem amazing at first that this isn't actually the most cost-effective way to do things until you consider another analogy: if you wanted to drive a more fuel-efficient car would you wait for your 3 litre Volvo to explode before you bought a Prius? This is essentially what people are doing while they wait for their old lightbulbs to blow - and I will prove it here in a way that you will be able to prove it too; not by being super clever but just using some simple maths and....shock, horror - STATISTICS!
Don't run away, this is going to be easy-peasy stuff. Let's start off by looking at each lamp in turn and what their vital statistics are:
Incandescent Lightbulb
Power rating = 60 watts
Average life = 1000 hours
Unit cost = 50 pence (about 60 Eurocents)
Light output = about the same as the lamp below
Energy utilisation = they convert about 95% of the energy they use into heat and only 5% as light
Compact Fluorescent Lamp
Power rating = 11 watts
Average life = 6000 hours
Unit cost = £3 (about 4 Euros)
Light output = about the same as the lamp above
Energy utilisation = they convert about 90% of the energy they use into light and only 10% as heat
I'm not going to argue here about light quality or rendering, we can save that for another day.
Now let's think about your house full of these old incandescent lightbulbs. Over the last few years you have changed them when they have popped so that now all their lives are mixed up, some might pop tomorrow, some still have a few more months in them. We can assume that their remaining lives are randomly distributed between 0 hours and 1000 hours.
Now let's do a bite-sized bit of simple statistics. If you threw a six-sided dice and kept a record of your scores you would find that the average score would tend towards 3.5 - why is this? It is because you are scoring with equal frequency between 1 and 6. That is you are scoring roughly the same number of ones as two and threes etc. If you threw 600 times you would expect to score around 100 ones, 100 twos, 100 threes etc. Therefore your total score would be:
100 x 1 = 100
100 x 2 = 200
100 x 3 = 300
100 x 4 = 400
100 x 5 = 500
100 x 6 = 600
Total 2,100
So if you threw 600 times then your average score would be 2,100 divided by 600 which is 3.5. It is the number exactly halfway between 1 (the lowest number on the dice) and 6 (the highest number).
Let's now return to the world of lightbulbs. If the individual lives of all the lightbulbs in your house was randomly distributed between 0 and 1000 hours then the average life of your lightbulbs would be the point exactly halfway between 0 and 1000, namely 500 hours. We can then assume that on average any lightbulb in your house has a remaining life of 500 hours. I will also assume (probably accurately) that you don't remember which bulbs you changed most recently so you can't go and be selective with your lamp changing.
If every light bulb has an average of 500 hours left in it then how much electricity are you going to have to pay for until one lightbulb goes pop?
Well the calculation is quite easy and let's assume that your electricity unit rate is 20p per kWh (about 25 Eurocents):
Cost of remaining life = 0.06 kilowatts x 500 hours x 20p
= £6.00 (about 8 Euros)
Now let's see how much money you would spend in
a) paying for a new energy-saving lightbulb and
b) paying for the electricity use of that new lightbulb for the exact same amount of time (i.e. let's ignore the extended lamp life of these new types of light)
Ok, here goes...
a) A new compact fluorescent lamp may cost around £3, some are more expensive, some are cheaper but let's stick with £3 (about 4 Euros) for now.
b) The electricity cost for the same 500 hours is:
= .011 kilowatts x 500 hours x 20p
= £1.10
So the total cost would be £3 + £1.10 = £4.10! This is of course cheaper by about 30% than keeping your old lightbulb until it goes pop.
The warning sign with statistics is that they are best applied to large populations of data rather than one or two data points (or light bulbs) so we would be best to apply this to all the light bulbs in your house. Assuming that you have about 10 lights in your house:
- Staying with your old lights until they all go pop will cost you about £60 in electricity.
- Replacing your old lights with new ones right now will cost you about £41 total in both electricity and buying new lamps.
- Therefore, spending some money today to replace your lights will save you a net £19 over the next 500 hours of using lights in your house.
This saving doesn't even take into consideration that energy saving lights will last you about six times as long as old fashioned light bulbs.
Now I expect that most people are not at the stage of being between replacing between old-fashioned lightbulbs and energy saving lamps but are more likely to be on the fence between changing from tungsten halogen spots to LED spotlights. If so then you are probably blown away by costs such as £12 for one LED spotlight! And you would be right to do so. When compact fluorescent lamps came out they were similarly very expensive and it has taken a few years and some forward-thinking companies like IKEA to drive the prices down. When I did a similar calculation between halogen and LED's I came up with a cost of £15 per light for the remaining life of a tungsten halogen compared to £16.80 to replace with an LED - it's pretty much well balanced at the moment and based on cost it might be wiser to wait for your halogens to fail before replacing. I have recently replaced a halogen downlighter with an LED spotlight and was impressed with the light intensity and the light quality though. Also they seem to last forever so maybe you'll take the plunge especially if you can buy LED lights for cheaper or your electricity unit rate is higher. That's all it comes down to! If you give a damn about climate change then you might go and change them after work tomorrow...
There, I hopefully just showed that being sceptical means being honest with data and not bending experiments and calculation to serve your argument.
I hope you have found this article technical, sceptical, interesting and useful but I guess I would be happy with just two of the above. Please comment if you would like to give me some feedback.
Thanks for reading, back soon with more.
