Archive for the ‘alternative power’ Category

Making Sense of your Gas Bill

Saturday, January 30th, 2010

This is how to interpret a British Gas gas bill.

Your gas meter measures cubic metres of gas flowing through it. (The old ones used to measure cubic feet; but the gas companies switched to proper measurements longer ago than the lifetime of a gas meter, so they should all be cubic metres by now.) But your bill is calculated on the number of kilowatt-hours of energy liberated from the gas.

On your bill, there will be a calculation such as this:

metric units used 239 * calorific value 39.3572 * volume correction 1.0226400 / convert to kWh 3.6 = gas used in kWh 2448.43

So what do the figures mean?

  • metric units used is the number of cubic metres of gas measured by your meter.
  • calorific value is the number of megajoules of energy in a cubic metre of gas, at some specified combination of temperature and pressure.
  • volume correction is a “fiddle factor” to account for seasonal variations in air pressure and temperature. When it’s cold, the molecules are more densely packed, so you get more energy in the same space. When the atmospheric pressure is low, the gas molecules are free to jiggle about more, so you get less energy in the same space. Each molecule contains a certain amount of potential energy stored in the bonds between atoms. So the calorific value depends on pressure and temperature, which is why this calculation is required.
  • conversion to kWh is because there are 3.6 megajoules in a kilowatt-hour. (A watt is one joule per second; there are 3600 seconds in an hour. Kilo means * 1 000 and mega means * 1 000 000.)

Given these figures, you can work out how many kWh are in one cubic metre of gas, simply by doing the same calculation for 1 metric unit used. According to the above, it is 11.23 kWh per m; but this figure may well be different for you, as the volume correction is seasonally-dependent.

But that’s not the whole story. The price per kWh depends on how many units you have used, with the first few kWh each day being more expensive. There will be a section like this:

2448.43 kWh used over 103 days
First 756.00 kWh @ 6.846p = £51.76
Next 1692.43 kWh @ 3.275p = £55.43
Total cost of gas used = £107.19

The higher rate applies to 756.00 kWh over 103 days, and adds an extra cost of 3.571p per kWh. As long as we actually use up all the “expensive” kWh, we will end up paying a fixed extra amount each week. If we are allowed 756.00 kWh in 103 days, then that is equivalent to 756.00 * 7 / 103 = 51.38 kWh in 7 days; which will cost us an extra 51.38 * 3.571p = £1.83 on top of what they would have cost if we had only been paying 3.275p for them.

Meanwhile, one cubic metre of gas on the meter gives us 11.23 kWh and so costs us 36.78p. So, our weekly bill will be equal to £1.83 plus 37p for each m of gas used.

Simples! :)

If you ask your gas supplier nicely they will send you a payment card, which can be used at local shops to make payments towards your gas bill. All you need to do is to work out the cost of the gas you have used each week (basing it on the figures from your last bill, which probably won’t be the same as mine), and round it up or down to the nearest whole pound.

The Embargo is Lifted

Tuesday, September 15th, 2009

Now that the person who was not to know about it is safely home, I can finally reveal the home improvement I recently had carried out:

Esse 100 SE

Esse 100 SE


An Idea Whose Time has Been and Gone

Friday, September 4th, 2009

Filament light bulbs — at least the 100W flavour — have been banned. The only question that needs to be asked is, what took the government so long?

Anyone who has ever tried generating their own electricity will know that these bulbs are stupidly wasteful. A 100W bulb kicks out some 95W of heat. It’s surprising really, what with the distinction that has to be drawn between (for example) strawberry flavour, strawberry flavoured and strawberry lest the consumer be unaware how little fruit the product contains, that they’re even allowed to call them “light” bulbs at all! Heat bulb would be a much more accurate description!

Every person who has bought a 100 watt filament bulb to use for general illumination instead of a 20 watt compact fluorescent bulb is needlessly pissing 80 joules of energy up the wall every second the thing is on, using up fossil fuels that won’t ever be available again. Add up all those 80s and you could probably take a whole coal- or gas-fired power station out of service.

Of course, the 20 watt fluorescent is still putting out 15 watts of heat, so there’s room for improvement, and there does need to be a recycling scheme set up — but since compact fluorescent lamps contain enough valuable materials to be well worth recycling if you can get enough of them together, this is pretty much inevitable.

I’m looking forward to seeing the next generation of LED-based lamps.

Thing done

Friday, August 28th, 2009

I have had a home improvement carried out.

Unfortunately, it’s meant to be a surprise for someone, so I can’t mention what it is until that person returns from where they are. I can’t even mention who that person is, or where they might be coming back from, in case they are reading this and work out who I mean and what I’ve had done. In fact, I think I’d better stop now.

Zero Standby Current Timer

Sunday, July 26th, 2009

This is a timer for controlling LED lights powered from a solar-charged battery. It was built to illuminate a passageway between two terraced houses, which is used to move the rubbish and recycling bins from the gardens of both houses to the street on collection days. Power is supplied from a battery charged by a solar panel. To guard against battery wastage due to leaving the lights on, it was desired to have a time switching arrangement where a single push of the switch gives a fixed duration of light before switching off automatically.

The first intention was to use a mechanical time delay switch, but this was found to be a rather costly solution.

The lights themselves were modified from 3-LED, battery powered push lights obtained in packs of two from a pound store (I frequent such places, searching for anything with white LEDs to use in my experiments!) The modification was simple but fiddly; entailing some track cuts to rewire the LEDs from a parallel to a series circuit and bypass the switch, and a resistor change. The timer itself was built inside an MB2 plastic enclosure with a pushbutton switch.


Circuit operation is as follows:

The Proof of the Pudding

Friday, September 5th, 2008

I managed to obtain a suitable donor lamp for my inverter project: £3 from Wilkinsons, plus another £1.99 for the bulb (9W, 14mm. screw base). The hollow china base of the lamp will contain the inverter circuit. When all is finished, you won’t be able to tell that it isn’t an ordinary mains lamp — except for the fact that the power lead will have a 6.3mm. jack plug on the end (this being the connector on which I am standardising for my 12 volt distribution boxes).

Nice hollow base:  Plenty of room for circuit.

Nice hollow base: Plenty of room for circuit.


And another light!

Wednesday, September 3rd, 2008

This is the LED cluster light I was thinking of building before I went ahead with the inverter lamp, and have now completed:

24-LED cluster with 14mm. screw fit base

24-LED cluster with 14mm. screw fit base


Up from the Ashes of Disaster, grow the Roses of Success!

Sunday, August 31st, 2008

I have a working fluorescent lamp inverter!

There’s such a thing as going too far

Monday, August 25th, 2008

Whilst searching for power MOSFETs to build a H-bridge, I noticed this 12V microwave oven for in-car use. And whilst the thought of solar-powered cooking did cross my mind briefly, I had to reject it as being ultimately rather impractical. It needs 20 amps even on its low power setting, which is enough to cane one of my 8Ah batteries in 24 minutes.

If I wanted hot food while out and about, I’d be more inclined to consider a Coleman stove. This one is powered by unleaded petrol. It’s well worth the initial investment; petrol works out cheaper in the long run than butane canisters (not to mention there being several different, incompatible types), and is more widely available.

Or if I just wanted to heat up a Cornish pasty, I’d probably wrap it in foil and stick it in the engine compartment!

Stuff that Doesn’t Work

Wednesday, August 20th, 2008

Behind every great inventor, goes the saying, is a pile of failed experiments. Here I’m going to document some of my cases of finding out the hard way what doesn’t work.