Archive for May, 2019

World Metrology Day 2019

May 19, 2019

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Monday 20 May – World Metrology Day 2019 – is a day towards which I have been working for the last 14 years.

Back in 2005, my NPL colleagues Richard Rusby,  Jonathan Williams and I compiled a report on possible methods for measuring the Boltzmann constant. The aim of the measurement would be to obtain an estimate of the Boltzmann constant with sufficiently small uncertainty that the International Bureau of Weights and Measures (BIPM) would feel able to redefine what we mean by ‘one kelvin’ and ‘one degree Celsius’ in terms of this new estimate.

To cut a very very long story short, we succeeded. And tomorrow, that project comes to fruition.

Of course it wasn’t just me. Or even me and my immediate colleagues in the thermal team at NPL. We were helped by colleagues from across the laboratory, and from other institutions. Notably:

  • Cranfield University who manufactured the key component in the experiment,
  • The Korean National Laboratory KRISS and the Scottish Universities Environmental Research Council who helped with isotopic analysis of argon gas.
  • Colleagues helped us from:
    • LNE-CNAM in France,
    • INRIM in Italy,
    • NIST in the USA,
    • PTB in Germany,
    • CEM in Spain.

And I have probably missed an important institution or partner from this list because – frankly – it has been a long haul!

But even this list doesn’t include all the other teams involved in the wider kelvin re-definition project.

Several other institutions also sought to independently measure the Boltzmann constant using a range of different techniques and the value chosen by the International Bureau of Weights and Measures (BIPM) was the weighted average of estimates from this international effort.

In all, hundreds of scientists, engineers and technical staff around the world have supported this effort and I feel humbled to have had the opportunity to take part in a project of this scale.

And it is not just the kelvin, today three other units will also be be redefined – the mole, the ampere and the kilogram.

In this troubled world, it is a real comfort to me to feel the friendships built and professional relationships created during these last 14 years.

I think it shows that the International System of Units is a living international institution which really works; which brings people together from around the globe to make measurements better. The SI is an institution of which the whole world can feel proud.

Happy World Metrology Day 🙂

Should I still be using gas?

May 6, 2019

TL/DR The carbon emissions associated with electrical generation in the UK have fallen so much it is has become greener – but not necessarily cheaper – to cook and heat using electricity.

Electricity Generation

The carbon intensity of a source of electricity is a measure of how much carbon dioxide (measured in kg) was emitted to make one unit of electrical energy: an electrical kilowatt hour (kWe).

The chart below shows the carbon intensity of electricity generated by various techniques. The average carbon intensity depends on generating mix – and how that varies with time.

Carbon Intensity of different generating sources

When I began talking about Climate Change back in 2004, Coal, Gas and Nuclear were the main generating sources for UK electricity. And the average carbon intensity – if I remember correctly – was around 0.50 kg CO2 per kWe.

The generating mix in 2019 is radically different. The carbon intensity varies daily and seasonally between about 0.1 kg CO2 per kWe (at times of low demand and high renewable generation) and 0.4 kg CO2 per kW(at times of high demand and low renewable generation). The average value is less than 0.3 kg CO2 per kWand falling.

The chart below shows how the carbon intensity of electricity varied through the month of December 2018. The average value was 0.243 kg CO2 per kW.and the maximum and minimum values were 0.390 kg CO2 per kWand 0.094 kg CO2 per kWrespectively.

Carbon Intensity in December 2018

In my home

I can choose to heat by using electricity or gas.

  • If I heat using electricity then I can convert electrical energy into heat with 100% efficiency, so for every kW of electrical power I use, I generate 1 kW of thermal power (kWth). And hence release roughly 0.3 kg of carbon dioxide.
  • If I heat using gas then I can convert chemical energy in the gas into heat with high efficiency – but not generally 100%. So (looking at the chart at the start of the article) for every 1 kWth, I emit at least 0.47 kg of carbon dioxide.

Now the price per kWh (one kilowatt hour) that I am charged by EDF, the French government-backed company that supplies my electricity and gas is:

  • 26.6 pence for 1 kWh of electrical/thermal energy during the day.
    • Generally higher carbon intensity ~ 0.4 kg CO2 per kWe.
  • 5.0 pence for 1 kWh of electrical/thermal energy during the night.
    • Generally lower carbon intensity ~ 0.15 kg CO2 per kWe
  • 4.2 pence for 1 kWh of thermal energy (via gas) at any time.
    • Always at least ~ 0.46 kg CO2 per kW

So the reduction in the carbon intensity of the UK’s generating mix means that switching to electricity now makes ‘green sense’. i.e. If I generate 1 kW heat in my house using electricity then less carbon dioxide is emitted than if I just burned the gas directly

But in order to make financial sense I would need to make sure that I didn’t use any ‘daytime’ electricity.

Mmmm. Well at least I have a choice!



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