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Skip to 0 minutes and 5 seconds We ended last week with a discussion about renewable energy and the transformation of energy from one form to another. We can trace the transformations backwards and usually end up at the Big Bang or some other event in the universe. This week, I’d like to return to focus on the energy used by human society. Governments in many countries track the sources of energy and consumption of energy. For instance, the Lawrence Livermore Laboratory in the United States produces this energy flow chart each year. In the United Kingdom, the Department of Energy and Climate Change produces this similar one. It’s apparent from both these countries that they heavily depend on fossil fuels.

Skip to 0 minutes and 56 seconds The combustion of fossil fuels, including coal, oil, or petroleum and natural gas, supports the generation of electricity, controls the climate in our homes, factories and offices, and powers our transportation system. It’s interesting to look at the national energy efficiency. If we define efficiency as what we want divided by what we have to supply, in the UK, energy inflow - that’s imports and indigenous production - is about 290 million tonnes oil equivalent. And our final consumption is about 150 million tonnes’ oil equivalent. This is what we want. So the national energy efficiency is 150 divided by 290, or about 51%. And this energy efficiency figure will be about the same for most countries.

Skip to 2 minutes and 0 seconds So it would appear that we waste about half our energy - not very impressive. But the second law of thermodynamics implies that it is inevitable. We will explore this in more detail in week four. First, we’re going to explore how we apply the first law of thermodynamics to a system. A system might be the steam used as the working fluid in the power station behind me to transmit heat from the coal-fired boiler to the turbines that generate shaft power and turn the generators. Or the system might be the cyclist pedalling uphill while eating a banana that we considered last week.

Skip to 2 minutes and 41 seconds Remember, in thermodynamics we can define our system as the part of the universe that we’re interested in, and everything else is the surroundings. More formally, a thermodynamic system is a well-defined quantity of matter which can exchange energy with its environment. In the next video clip, I will talk some more about system boundaries and the transfer of energy and matter across the boundaries.

Where does our energy come from?

Eann talks about the energy transformations leading to the delivery of energy to everyone’s home and estimates the resulting national energy efficiency.

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This video is from the free online course:

Energy: Thermodynamics in Everyday Life

University of Liverpool