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Sunday, November 16, 2008

Cooking: Lid on, Lid off? Kettle, Hob? and other unanswered mysteries of our time

I imagine that you have, like me, wondered what is the most efficient way of cooking some pasta and what is the cheapest way. Well after years of waiting your prayers have been answered and I have determined the cheapest, the most energy efficient and the quickest way of cooking 0.5 kg of good quality dry pasta.
{I am probably alone in the world in this, but hey, isn't the internet great, I can ramble on about things that nobody cares about and pretend it is all very important, so back in the reality distortion field}

I know you are excited about this, but calm down and refrain from just reading the conclusion, hundreds of man hours have gone into this research, don't you think that it deserves your full attention?

I have systematically measured the amount of time 2.5 Kg of water take to boil, using different methods. Note that it is assumed throughout that the density of water is equal to 1kg per liter (an error of 0.02%). The main gas meter has been used to measure the amount of gas used for the different conditions and where appropriate a Brennestuhl BS-PM230 has been used to measure the electricity used. Gas cost is 4.44p/kWh and Electricity cost is 11.57p/kWh.
It was not possible to measure the water temperature before starting each measurement, but it can be estimated that a variance of no more than 2 K occurred ( Did you notice that? I'm using Kelvin instead of degrees celcius to give the impression that this is a serious piece of research)

Without Lid

The first experimental condition I wanted to test was to cook the pasta on the gas hob without a lid covering the pan.

It took 1073 s for the water to be boiling, an error of ± 60 s has been estimated. The error is chiefly due to the observer deciding when the water is boiling "enough" for the pasta to be dropped in.

The total gas used was 0.08 m³.This is equivalent to 0.89 kWh and I payed 3.93 pence for the privilege.

With Lid

I then repeated the same experiment, but this time the pan had its lid, which completely covered the pan.

It took 993 s for the water to be boiling, an error of ± 60 s has been estimated. The error is chiefly due to the observer deciding when the water is boiling "enough" for the pasta to be dropped in.

The total gas used was 0.06 m³. This is equivalent to 0.67 kWh and the total cost was 2.95 pence.

I should comment that after the water boils, it only takes about 12 minutes for the pasta to be ready. When cooking with a lid, the gas used is reduced as a lot less heat is necessary to keep the water boiling. The difference here is small, but I hypothesize that it will be much more significant for beans or chickpeas that take about 1 hour to be ready.

Kettle Assisted Without Lid

In this case, I filled up the kettle with 1.8 Kg of water and the remaining 0.7 kg were placed in the pan, which was left uncovered. The kettle and the pan were simultaneously boiled.

The kettle took 353s to trigger the automatic stop and the water in the pan took a further 120s to boil, therefore the total time for the water to be ready for the pasta to be dropped in was 473 ± 60 s. The total amount of gas used was 0.048 m³, this is 0.54 kWh. The total amount of electricity was 0.19 ± 0.005 kWh. Therefore the total energy used was 0.75 kWh, for a cost of 4.56 pence (2.2 pence in electricity and 2.36 in gas)

Kettle Assisted With Lid

In this case, I filled up the kettle with 1.8 Kg of water and the remaining 0.7 kg were placed in the pan, the pan was covered with its lid. The kettle and the pan were simultaneously boiled.

The kettle took 343s to trigger the automatic stop and the water in the pan was ready by then, therefore the total time for the water to be ready for the pasta to be dropped in was 343 ± 60 s. The total amount of gas used was 0.032 m³, this is 0.36 kWh. The total amount of electricity was 0.19 ± 0.005 kWh. Therefore the total energy used was 0.45 kWh, for a cost of 3.77 pence (2.2 pence in electricity and 1.57 in gas)

With all this in mind, we can clearly declare that kettle assisted cooking with the lid on is the quickest and less energy consuming way of cooking pasta.

The cheapest way is to cook with the lid on, entirely on the cooker. This method will take an extra 10 minutes and will save you around 0.82 pence a pop. While it might be a pitiful amount, you only need to plan ahead a little bit or wait an extra 10 minutes for your pasta to be ready. After all, you know what Tesco says: Every little helps.

Incidentally, the most environmentally friendly way of cooking your pasta is a toss up between kettle assisted and gas only. Assuming a rather generous 40% efficiency for electricity generation, those 0.19 kWh are actually 0.475 kWh of coal, gas or nuclear and assuming 10% transport cost for gas, it is 0.4 kWh, so in total 0.875 kWh are needed to generate the energy needed to cook the pasta for the kettle assisted cooking with lid on. A similar calculation shows that gas only with the lid on is 0.74 kWh. Gas will also heat up your kitchen which is a nice by-product in winter but might not be so good in the summer.

I am happy that with the above I have answered one of the last remaining unanswered questions troubling mankind.

Monday, November 10, 2008

Changing Suppliers

You've finally had enough of your current supplier and have decided to switch suppliers.
I have done it myself many times and I would agree it is the best way to save money.
I have found four different comparison sites:

I'm sure there are a few more out there, but they probably use the same search engines, therefore I'll stick to these.

The good news is that all of them recommend the same tariff as being the cheapest:

Npower's Sign On-Line 14 Paperless Billing

This is good news. Unfortunately SimplySwitch tells me it is actually more expensive than my current tariff. LIES!!!
Simplyswitch, simply have not updated their tariffs for ScottishPower, not very good, not very good at all. I can only presume that they haven't updated the tariffs for Southern Electric either.

Second on my target list, is MoneySuperMarket. They suggest that British Gas Click Energy 6 is almost as cheap as Npower's Sign On-Line 14 Paperless Billing. I can't be too harsh this time, as British Gas Click Energy 6 is a fiendishly complicated tariff, but I make it almost £120 more expensive. They say it is only £20 more expensive. They also get EbiCo wrong, which is an amazing achievement, given that they only have one rate and no standing charge. It seems they don't use Yorkshire rates, but South of Scotland rates which happens to be the highest electricity rate that EbiCo do. This is a bit suspicious, but before I don my tinfoil hat, I enter a postcode in London and they do provide the correct tariff. At any rate they are also out, too many wrong tariffs.

Uswitch and EnergyHelpLine provide pretty much the same information. Incidentally, they quote British Gas Click Energy 6 as £90 more expensive than Sign On-Line 14 Paperless Billing, and happen to get my current tariff wrong. They don't use the Yorkshire tariff for Scottish Power. I know we are in the third world and all that, but do make an effort.

So all in all I have reached the conclusion that you cannot trust neither of the four websites completely. My advice is to do a comparison using either uswitch or energyhelpline and then double check the calculation yourself between the cheapest tariffs. The one thing to bear in mind is that the calculations assume equal energy use throughout the year which is very, very Wrong.
This tends to underestimate the amount of tier 2 gas usage, which results in larger bills. This is because most people tend to use most of their gas during the winter quarter and hardly any during the summer quarter ( I'm guessing none if your cooker is electric).

To give you an idea, I have estimated my usage as follows:

Gas: Winter 47% of total, Spring 24%, Summer 3%, Autumn 26%
Electricity: Winter 29% of total, Spring 23%, Summer 23% and Autumn 25%

This means that on Scottish Power's discounted Dual Fuel Online tariff, the equi-use way of calculating energy costs is £10 more expensive than my more realistic estimate and for British Gas' Click Energy 6, the equi-use way favoured by the sites is £16 more expensive than my more realistic estimate.

As you can see, while it does not vary much it can skew comparisons even further, which unfortunately means that if you are serious about finding out the cheapest tariff you are going to need realistic quarter by quarter estimates of your usage and will need to do the maths yourself.

Finally, while it might run counter to a lot of advice around, it might actually be cheaper to have two different suppliers, even if you forgo the dual fuel discount. For instance while Npower's Sign On-Line 14 Paperless Billing is indeed the cheapest in my case, it does rely on £100+ of discounts that I'll get after being on that tariff for 12 months. This means that I would be stuck with npower for 12 months regardless of any price increases, as changing suppliers before I get the discount will mean losing it completely, which means that I would have been paying quite a bit more than necessary, which brings me to my second best option: electricity from Scottish power on my current tariff and gas from EbiCo. Yes, I won't get a dual fuel discount (£15.25), but gas works out ~£40 cheaper, so I will be ~£25 better off.

Wednesday, October 29, 2008

Energy Saving Tips -- TV

The bulk of electricity in many households is used by entertainment devices, e.g. TVs, computers, game consoles.

The easiest way to cut down electricity is not to use these devices at all. Easier said than done, so the second best thing is to use them less, which again is obvious, but also easier said than done, the last thing that you can do is use devices that are not so power hungry. Do not rush to the shops yet, it might be in your best interest to hang on to your old power hungry appliance, I'll explain below.

I would strongly suggest that you get a plug in electricity meter. I personally use a Brennenstuhl PM 230 Power and Energy Monitor, but there are other models


This can be one of the main drivers of electricity consumption. I can be quite smug here as I don't own a television, which enables me to save not only loads on electricity but £140 pounds a year on TV license fees. Enough of my smugness.

I do however have a 20" monitor. This uses 70-90W, depending on brightness and the amount of white displayed on the screen.

It's hard to do an apples to apples comparisons of TV technologies, but the image below can be taken as an average guide of what each type of technology uses and how much it would cost you yearly to run it (1 kWh @ 11.57p). I don't have exact model numbers for the TVs used, so I won't post them. The plasma TV was measured by a friend with a different power meter.

I can hear you say how the screen sizes are not the same, that is true but nigh on impossible to find a CRT that is 42".

While it is possible to calculate an average power usage per square cm, this can be misleading as there isn't a linear scaling.

The same friend that measured the plasma TV, also measured his 5.1 surround system that uses a whooping 130 W, which means that it uses the same amount of power as a 32" CRT TV.

Perhaps the most important figure is the stand by figure, which unfortunately I only have for the plasma TV, 30 W. While this might not sound like much, if you leave it on standby for 20 hours and use it for 4 every day you are looking at £76 of electricity in total, 25 of those pounds for the TV to be warming up air.

You might have heard many times on the media how you should not leave appliances in standby, I've just given you 25 reasons not to, unless you've got shares in your utility company.

There are also digital tuners and DVD/Blu-Ray Players. Unfortunately I don't have data for these. Sony quotes 8w for its DVP-NS39 model (dvd player) and 26 W for its BDP-S350 Blu-ray (Blu-Ray player). Standby figures are below 1W.

Humax quotes 10W in use, 5W in standy by for its F2-FOXT set top box (freeview digital tuner)

As you can see it pretty soon adds up, with a maximum power of 440W for watching freeview, 438 W watching DVDs and 456 W watching Blu-Ray discs on the plasma TV. While you are unlikely to watch 4 hours daily of blu-ray discs, it is not outrageous to think that you will use your 5.1 surround system while watching telly, were you to do this, you are looking at an extra £22, which brings your maximum consumption up to £98 and this is only to watch television.

A word of warning to people thinking about using a PS3 as a blu-ray player. The PS3 uses around 170 W, which is incidentally about as much power as it uses while idling PS3. Leave your PS3 idling 24/7 and you are looking at a whopping £172 a year, but I am getting ahead of myself

Sunday, October 26, 2008

Energy Saving Tips -- Lighting

I guess I should go over the basics when it comes to energy saving.

Incandescent lights are out. No ifs, no buts. If you want to save energy and money they have got to go. Light is the byproduct of heating up the tungsten coil, which is why they are so inefficient.
See a comparison below of how much it costs to run a 100 watt tungsten light bulb versus how much it costs to run an equivalent CFL. (kWh @ 11.57 pence)


At the time of writing Tesco quotes £2.94 for a 20 W CFL, which means that even with an average use of one hour it is better to use a CFL. If you then take into account that CFLs can last 6000-15000 hours vs 1000-2000 hours for incandescent light bulbs, then the total cost of ownership is so high for incandescent light bulbs that it is simply a no brainer to use CFLs.

At an average of 4 hours a day and assuming 8000 hours lifetime, a CFL will cost you:


£18.58 in electricity + £2.94 to buy the CFL

Assuming a lifetime of 2000 hours for incandescent lights, 8000 hours will cost you:


£92.91 in electricity + 99p to buy a pack of four incandescent light bulbs

CFLs are not the panacea. They do contain mercury, so it is advisable not use them where kids can knock them down and break them. They also emit more UV light. This is only a concern if you are sensitive to UV light AND are very close to the CFL. On a more mundane level they don't work with dimmer switches and can take time to switch on.

I can't think of any real reason for using dimmer switches, so it is not a problem for me. If you have a hallway that you need to light quickly I suggest using Halogen lights, while they are in essence incandescent lights they are brighter (in lm/W terms) and therefore need less energy than normal incandescent lights.

The SI unit of luminous flux is the lumen, unfortunately the lumen is not a common day unit and unlike the kilogram or the metre it is hard to have a feel for what a lumen actually is. You can get an idea by looking at the graph below, linked from Wikipedia, that shows a plot of Power vs Luminous Flux. An incandescent light bulb (red line) has approximately 1250 lm @ 100 W, if you look at a 100 W incandescent light you are looking at approximately 1250 lumens of luminous flux. I don't expect that you will need to be able to estimate luminous flux of light bulbs by looking at them, but this should give you an idea of what a lumen, or 1250 lumen look like.

In order to get 1250 lm with a CFL ( green line) it takes approximately 18 W. It takes a Halogen light bulb approximately 40 W to reach 1250 lm.

Friday, October 24, 2008

Measuring Energy (2)

Now it's time for the hard part: To measure energy usage regularly.

At the very least you should take meter readings once every quarter, this way you will be paying what you use rather than estimates. Feel free to lie to your utility company if you reckon that they will increase your monthly direct debit during the winter. This is essentially an interest free loan to your utility company. It's a shame that ofgem is such a gutless regulator. Again EbiCo has it right and doesn't provide discounts for receiving interest free loans from its customers (i.e. discounts for paying by direct debit).

You should aim to take meter readings every month. If you are really committed, like myself, you can take them every week. Make sure you take them at the same time each time (this is only relevant for weekly meter readings), as a couple of hours of heavy electricity or gas usage can skew your meter readings significantly.

Once you start taking readings, it is a good idea to put them in a spreadsheet. I personally use OpenOffice, it's free and can handle Micro$oft Office documents. The best idea is to create a plot like this one:

Energy Use

This way you can easily see how much energy you are using and with the plot above as a basis you can create a plot like the one below, which tells you how much it costs.

Energy cost

Tuesday, October 21, 2008

Measuring Energy

The first step in saving energy is to measure how much energy one uses. You might think that your utility company already does that, and you would be right, but I am talking about taking control here. If you were to ask yourself how much energy you use a year, it is possible that you know how much you paid for that energy but it is unlikely that you know how much energy you have used and this is what is important, the amount of energy that you use, if you don't know how much you use you'll never know how much energy you are saving. It seems unlikely that prices will be coming down soon or ever for that matter (I'll rant about that in another occasion), therefore any savings are going to have to be made by you, but before you make any savings you need to know how much energy you have used.

In a country like the UK, heating during winter is essential, particularly given the age of the housing stock, and air conditioning in the summer is a luxury. If you, like me, heat your house using gas (LNG) then your gas bill is going to be determined to a large extent by the weather. If you don't use gas, your electricity bill will be affected by the weather, but there is plenty of scope for reducing it.

At any rate, grab your old utility bills and get counting. Go back as far back as possible and look at the kWh figures. You want to compare like for like, therefore if you have made substantial changes to your house, e.g. doubled glazed windows, insulation or added an extension or conservatory, get your bills from after the change, that way you can measure exactly how much energy you use in your house as it is now. What you want to arrive is at a yearly usage figure for both electricity and gas. This will be your baseline energy use, your target as it were.

This is all well and good, but I appreciate that with utility companies relying more and more on estimates, the figure you arrive at might not be very accurate, that's true, you could try going back a couple of years and calculate the average energy use per year, that should iron out inaccuracies due to poor estimates.

Armed with this figure(s) (My figures below)

7500 kWh for gas
1900 kWh for electricity

You are ready to start saving.

It might be due to my scientific background but I like talking of energy use in kWh rather than how much it costs. This approach is more transparent as the savings or otherwise are not dependent on the whims of the utility companies. It is also fiendishly hard to calculate how much you are actually paying because of the many discounts and tariff tiers, kudos to EbiCo for having a simple tariff.

In order to simplify the calculation of how much energy you pay for during a year, I suggest you do the following:
  • Ignore discounts (Dual fuel, online, special rates, etc)
  • Calculate an average electricity and gas price tariff.
In order to calculate an average tariff one needs to calculate the relative weight of each tariff, so in my case my supplier (Scottish Power) charges anything above 4572 kWh p.a. at a lower rate, talk about madness, the more you use the less expensive it is, comparatively. Anyway back to my calculations:

4572/7500 ~ 0.61

So 60% is at the higher rate (4.860p per kWh), 40% at the lower rate (3.837p per kWh)

My average gas tariff = 0.6*4.860 + 0.4*3.837 = 4.497p per kWh

Doing the same for electricity I get an average rate of:

11.57p per kWh

(The cut-off for higher rate is 900 kWh p.a. for electricity)

Just bear in mind that the lower your energy use the higher your average rate will be. However, do not be deceived into thinking that you are not saving money, you are. Think about it this way, If I were to use 4000 kWh of gas a year, it would cost me £194.4, however if I were to use 5000 kWh I would pay £238.6.

So armed with these figures on to the energy saving sunset we ride