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.