The ability of a system ‘to do work’ is energy. It sounds odd, but just think about it; all kinds of ‘systems’ such as plants, animals, machines, the human body, our natural environment and all the various technologies we use (radio’s, mobile phones, TV’s, cars and aeroplanes) do work and they can only do work if they have energy. You unplug your TV, and it stops working. You stop watering your plants and they die. Without energy, there can be no life.
The universe is imbued with energy; it is everywhere. Some energy is stored and others are energy in motion.
For example, sunlight, as one source amongst many others such as gravity, plant mass, geothermal, wind and waves, produces 3,766,800 exajoules of energy each year. This is only a small proportion of the sun’s energy that actually reaches the earth. An exajoule is a billion billion joules. With one joule of energy I can lift my hand to drink my coffee. All the plants on this earth use about 3,000 exajoules per year and humanity spends about 500 exajoules per year.
Energy cannot be created or destroyed. The first law of thermodynamics states that: “energy can be transformed from one form to another, but cannot be created or destroyed”. This is a really strange idea. We often think that when we make a fire, we have ‘used up’ the energy. Not really. All we have done is to transform the potential energy (biomass) into another form of energy called heat. A dramatic example is lighting. In a typical lightning strike, 500 megajoules of electric potential energy is converted into the same amount of energy in other forms, mostly light energy, sound energy and thermal energy.
Not all energy is available to us to use. Science and technology enables us to harness and use this energy. It was at first the use of fire by us as cave people and later followed by the burning of coal and oil that propelled humankind on the industrial revolution. This revolution was not possible without the invention of, for example, the steam engine, electricity, the internal combustion engine and splitting of the atom. We did use muscle power and wind to discover the oceans by sailing ship and water (gravitation) to irrigate our plants and to mill our flour, it was only very recently that we started to harness all sorts of energy and more efficiently. The old watermills, for example, had a power rating equal to an electric hand-drill that you buy off the shelf in the store today!
Energy is a quantity and power is the rate at which we use the energy. (Hyperlink to video – http://blogs.scientificamerican.com/plugged-in/the-essentials-of-energy/). Energy is a quantity that can ‘do work’, as we have seen above. We measure energy in joules or calories. When we convert energy, we create power. Power is the rate at which energy is used. One joule of energy used per second is a watt of power. Energy = power X time. Put simply; a 100 Watt light bulb uses a hundred joules of energy every second. An adult male eats about 2 500 calories of food a day (10.5 joules of energy). Burning this energy over twenty four hours gives us about 121 Watts power (per hour). 24 Watts are used by our brains to think, dream, decide, plan and operate all our systems. So we can only use energy by converting it into power. This conversion could be anything from converting mechanical energy to electrical power, chemical energy to heat, atomic energy to bomb blasts, sunlight to food through photosynthesis, and so on.
But, the second law of thermodynamics says that these processes of conversion are often irreversible. Once you have had your ‘braaivleis’ from your wood fire (converting biomass into heat), you cannot convert that heat back to biomass again. Many sources of energy are of this kind – especially those that we relied upon mostly. And that is fossil fuels. We call these sources of energy ‘non-renewable’ energy. That is why our earth’s energy sources are bound to decline.
Non-renewable energy is not only limited, but the processes for converting it into power is harmful to our climate, environment and our own health. We need only to look at global warming as a result of, what some scientists call ‘humankind’s fossil fuel burning orgy over the last few centuries’, to realise that the use of fossil fuels is not sustainable.
Luckily, earth is not a closed system. There is so much energy in the universe and the tiny bit that reaches us is unimaginably bountiful, that we need not worry that we will run out of energy. All we need to do is to turn to the sun. The sun won’t burn up soon; it is estimated to remain stable for another 7.5 billion years. It gives heat which causes wind and drives sea currents and produces rain and drives a great number of biological, chemical and mechanical processes. The sun is our most reliable and most powerful source of energy. And sunlight is a renewable source of energy.
We waste energy. For every 100 units of energy produced presently, only 40% reaches our homes. Whilst it is important to move to renewable energy, it is equally important to become more efficient in the way we use energy (hyperlink to energy cooperatives).