Classroom #E1: Introduction to Energy
Energy School
(no test, no worries)
Welcome to classroom #E1:
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Different forms of energyEnergy can be divided into different forms as it can have different caracteristics or properties. Some of the most common are:
We can also choose to divide these types into 2 main categories: Kinetic & Potential All or most of these forms of energy can be found in our everyday life (less so with nuclear) and there are often multiple types involved in any given process. We will not explain them in detail here, but please do research on them for your own for better understanding. Here are some examples of links that can be useful: Level: Basic https://www.youtube.com/watch?v=63t0Y2ACoh4 https://www.solarschools.net/knowledge-bank/energy/types https://www.eia.gov/energyexplained/what-is-energy/forms-of-energy.php |
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Conservation of energyEnergy can not be created, only converter between different forms The amount of energy in the universe is believed to be constant. This means that new energy can not be created nor destroyed, only converted between different form or places, called the conservation of energy. We will now give an example of how this could look: Example: Petrol & combustion engine in a car The energy in petrol has been stored through chemical-bonds that was created many million years ago as plants then absorbed sunlight through photosynthesis and binds carbon with other elements, such as hydrogen. The sunlight in itself is the result of radiation caused by nuclear energy being released by the Sun. As the plants got buried and put under very high pressure from the ground above, for the millions of years, oil and what we now call fossil fuels where created. Light + Gravitational = Chemical When petrol (product from oil) is being used in a car, the combustion engine releases the stored energy as the chemical bonds breaks when it being put under concentrated pressure and fire heat lighted from the spark plugs, releasing N2, CO, CO2, NHx and other compounds from its exhaust. When the chemical bonds break, more heat gets released and expands the gases in the engine's cylinders, which is used to move the car forward as the engine, transmission and other moving part turns part of the heat, or thermal energy, into kinetic (link to quick introduction to ICE - internal combustion engine). Chemical = Thermal + Kinetic + Sound |
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Energy efficiency - there are always lossesEvery energy solution or system can be more or less efficient as every system has losses. Understanding where and how these losses appear is very valuable if we want to improve and optimise the solutions and behaviour.
Example: When the car moves forward, only approximately 20% of the energy in the petrol is being used to move it forward on the road. The rest of the energy turns into: > thermal-energy in the engine and the moving part in the car (driveline, friction between the tires and the road, and more). The engine quickly becomes some hot that it needs to be cooled down by water cooled down by fans. > sound-energy for the same parts in the car and the tires against the road. > thermal-energy from the friction that occurs as wind and air particles collide with the car. From the example above, we see that only 20% of the stored energy in the fossil fuel is being used for meaningful work (some of the heat is also meaningful as it is used for warming up the inside of the car when it's cold). This means that the energy efficiency of that specific system is 20%, with 80% losses. It is basically impossible to change a form of energy from one to another without having losses, but understanding when and where these losses occurs is very valuable in order to create as efficient systems and solutions as possible.
Example of different forms of energy working in hour homes and the losses that might occur When energy is used in our homes, it often means that more than one category is involved. Here is an example: Need: You want to read a book a dark afternoon in January. When you turn on the switch on the wall, light energy spread in the room and over the pages as photons, covering your needs at the moment. This happens because electrical energy is past through a lamp and cables, causing them to warm up slightly, as electrical energy is converted to thermal due to friction as the electrons moves through them. If using an older lightbulb, normally with an efficiency of 10-20% the amount of heat coming from it will be much more than if using a low energy light such as LED, which normally have an efficiency of 45-50% (5-10 times less energy needed for the same amount of light). If the system is off-grid, the electricity is likely coming from a battery, which is storing potential electrical energy. The battery, which if being lead-acid often have an efficiency of 85%, could perhaps have been charged up during the day from light energy through PV-panels (photo voltaic) on the wall or roof. Todays panels often have an efficiency of 25-35%, the inverter that changes the current from AC and DC will likely have 94-97% and the charge controller before the batteries might have 95-99%, with most of the losses occurring through thermal energy. From the example above we can see that there are many losses in the system. If counting in the efficiency of the panels, 12% of the energy in the incoming sunlight gets converter into usable work. If not including the panels, that number increases to 39%, with most losses occurring in the LED as 50% of the reached electricity turns into light and 50% to heat. |
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Class continues..More content in Classroom #E1 is to come.. |
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