Starting with the Numbers

Before we can do any of the maths on how much energy we are using at the moment, I need to understand the best units to work in. Luckily my daughter, Devi, and son in law, Matthew, are on hand to make up for the physics lessons I failed to follow at school.

It seems the basic unit of energy is the joule. It’s not a large unit, so we will be thinking in kilojoules and megajoules. Then when thinking of appliances and systems that use energy we need the watt. This is the rate at which the appliance is using the joules. 1 watt equals 1 joule per second. So now to turn this into actual cases:

A hundred watt bulb will use 60 x 60 x 100 joules in an hour. That’s 360 kJoules. Since the electricity meter measures kilowatt hours that’s the equivalent of a tenth of a kilowatt hour. And at around 6p per kilowatt hour, that light is costing us 0.6p for every hour that it’s on.
The television is rated at 67 watts, so it takes about .07 kjoules an hour, which costs us about 0.4p for every hour of viewing.
And the 1 kilowatt electric fire takes 1 kWatt an hour, costing us 6p.

And by the way, the appliances that are left on standby are using around a third of the power. So the television may only be costing 1 or 2p for an evening’s viewing, but it costs an additional 3p for the rest of each day. And that applies to the set-top box, the two screens and the several other boxes. In terms of computers left on, those are figures to find out…

When it comes to oil, there should be a conversion into watts that we can find. But before that there is the simple measure of how many litres of oil we are using, since avoiding burning fossil fuels and producing greenhouse gases is our main concern. But the efficiency of the boiler and the insulation of the house do come into play, since if these were improved we could achieve the same level of comfort for less carbon produced. In this regard, the EU energy efficiency grades are apparently the thing to look at. Anyway, insulation may be boring but it remains the best first way to improve matters.

Calor gas for the cooking is similar, as it the petrol used in the vehicles.

Matthew also introduced me to Good Energy ( which sounds like just what we need. It will supply electricity at a higher rate, but guarantee that it’s all produced from renewable sources. For Hedgerley Wood they will charge 7.85 per KWh plus a standing charge of 12.83 per day. That immediately suggests (and to him as well as to me) that it might be better to heat the water with an immersion heater ultimately powered by GE’s renewables, but to use a smaller amount of oil. Need to check on the logic of this.

Clearly GE can’t at the moment be the answer for everyone, since they don’t produce enough for the needs of the whole country, but the sense is that every household that joins helps them expand their capacity.

They also have on the site a very good first indication of carbon dioxide emissions. The average household, they say, produces 10 tonnes of carbon dioxide a year. And a small car traveling 6 miles produces 1.5 kg.

In the case of Hedgerley, switching to GE for our electricity would, by itself, save around 2,070 kg a year. This is based on the fact that 1 KWh produces 0.43 kg of CO2. When I get back to the electricity bills I should be able to check out our current carbon emissions from electricity.

The other great advantage of GE is that they will buy back electricity that we produce locally. According to the first descriptions of home generation on the site it looks like a much better option that storing locally any energy we produce.

That leads to the question of how we could produce it. The sites to start with (tomorrow) seem to be:
British Photovoltaics Association –
The Energy Saving Trust –

If we start with solar it seems that heating the water is the best, since energy is lost every time you convert between different types. Of course with our amount of sunlight it will only heat the water to a certain level, but that will make the final burst of heating required smaller. Beyond that, how to produce electicity is the next thing to research. We need to know whether the same panels can do both, what it will all cost and what we do about all those water pipes during the freezing months.

For wind energy I’ll have to wait to tomorrow to continue the research. I am after all on holiday and the internet connection here is pretty ropey.

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