What is energy?

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I was recently asked what energy was, to which I spouted out the school textbook definition I had learned many years ago: “the ability to do work.” But after a few follow up questions from my friend I concluded to myself that I did not really know what energy was. And given that I work in the energy industry I decided I better find out what energy actually was! The answers I found out surprised me! And the good news for my own sanity is that I found out that wiser and smarter people than me didn’t know what energy was either, but the good news is that all agree on one thing that is that it all useful energy comes back to the sun.

Someone told me that a good starting point to learn about energy was the Nobel Price winner Richard Feynman. He put it very succinctly in his classic textbook Lectures on Physics: “It is important to realize that in physics today, we have no knowledge of what energy is.” The good news is that he and physics can tell us a lot about how energy behaves, how it flows and interacts with things and how it can be used. The behaviour of energy is primarily governed by two laws, the First and Second Laws of Thermodynamics.

The First Law is commonly known as the law of energy conservation and tells us that energy cannot be created or destroyed but just goes from one form to another. The Second Law tells us that if no energy enters or leaves a system, then the potential energy in that system – the potential to do work – cannot increase. In other words, whenever anything happens at all, the amount of useful energy falls. This of course leads to the question what is ‘useful energy’?

Energy usefulness is all about what we can do with energy. And each energy source has different levels of usefulness. So for instance, a stone in your hand has potential energy caused by gravity which will pull it to the ground when you let go of it. That is somewhat useful but oil, for instance, is even more useful. It can be burned for heat or used with an internal combustion engine to move a car. Interestingly, the most useful form of energy known to us is electricity. There is no source of energy which can be controlled and used in such a wide variety of ways as electricity. In fact, none of the digital devices that make up our modern world would be possible without electricity which is why it is not only the most useful form of energy but the most important!

The other thing to realise about energy is that the source of nearly all useful energy on our planet, with very minor exceptions, is the sun. Without the sun we would have no food, no animals, no trees and no biomass feedstock. In addition, the process of photosynthesis, taking place over many millennia of Earth’s history, has left us with a valuable legacy of fossil fuels like coal, oil and natural gas. But the interesting thing is that enough energy falls on the surface of our planet each day to surpass our current energy needs by 10,000 times! The issue for all of us is how best to extract and use that energy. The answer to that is increasingly clear, solar photovoltaic. Taking the sun’s energy of the sun and converting it directly into electricity gives us the most useful form of energy we know. And that is the reason why there will be more solar panels installed this year than any other source of power generation. It is also why China investing more in new solar installations than Saudi Aramco, the biggest oil producer in the world is in new oil projects!

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