[By Eng Chisakula Kaputu]
SO what is energy? Simple question that is rather difficult to answer satisfactorily.
Truthfully, all matter is energy at rest. Simply, energy is the ability to do work. The rate at which we convert this energy is what is known as power. And just for completeness, work done is as scientifically defined distance travelled x force applied. So, in just one paragraph, we have defined energy, power and work, so we have done some ‘powerful energising work’ already.
We are going to talk more about energy in the form we are all most familiar with. But before that, here is some trivia; when a human is dancing quite vigorously as one would during a chikokoshi, they can produce almost 400Watts of thermal energy or crudely known as heat (often showing as chibe). Not so trivia is the fact that all forms of energy can be turned into thermal energy or heat. And definitely not trivia; the unit of power called horsepower was James Watt’s way of ensuring that people were satisfied that his steam engine replacing harnessed animals (horses in this case) had the equivalent in power to that of the horse (1 horsepower = 746Watts).
And here is something wrongly accepted as fact: energy consumption isn’t really consumption but conversion because energy can never be consumed but merely changed into another form. No energy is ever lost in any of these conversions. And this is the first law of thermodynamics (Thermo- what? Simply, law of Conservation of energy). There is also what is known as the diminishing utility of converted energy, meaning that as energy is converted from one form to another, the usefulness diminishes through conversion losses (this essentially is the second law of thermodynamics), e.g. a light bulb converts electrical energy to electromagnetic energy (light) as the useful part but also as thermal Energy (the useless part) in the case of lighting purpose only.
Energy comes in many forms and is reported by many different units of measure (UOM). Energy can also be classified as either a primary or secondary energy source. The different types of energy include: electromagnetic energy, chemical energy, nuclear energy, thermal energy, gravitational energy (potential), mechanical energy (kinetic), electrical energy, etc.
And the different units of measure include: Horsepower (hp), Watt (W), Joules (J), Calories (Cal), British Thermal Unit (BTU), etc. And all units of measure can be stated in another unit merely by applying a conversion factor. Examples;
1 kilowatt hour (kWh) = 3600 kilojoules (or 3.6MJ)
1 kilowatt hour (kWh) = 859 kilocalories
1 calorie (cal) = 4.184 J
1 British thermal unit (BTU) = 1055 J
But we are not going to overwhelm ourselves with knowing all of this. We are, after all, just interested in electrical energy/electricity as we continue to discuss and get to understand climate change and energy in light of the current load shedding. Remember though that all forms of energy are important for human existence.
So, electrical energy/ electricity is what we are going to unpack. To start with, electricity is simply the flow of electrons, electrons being negatively charged subatomic particles (oh no, we are not starting with definitions again!). Alright then, we all know what electricity is from seeing its applications/uses, so we shall proceed on that basis.
Electricity is often described either as energy or power, and these two are not the same thing at all. Power and energy are not interchangeable terms; simply, power is the accumulation of energy over time or the rate of conversion of energy or the demand for energy at any given instance. Conversely, energy is power measured over time or the amount of work done over a given period of time. In an electrical system, at any given moment in time, the system demands a certain amount of energy and this demand is what is called power. These moments in time intervals or periods are typically 15 or 30-minute durations. So, demand and power are one and the same (consumption is synonymous to energy).
Mathematically, power (in Watts) = energy (in Joules) divided by time (in seconds) (W=J/s). Energy (J) = Power (W) x Time (s). So the familiar term of a kilowatt-hour (kWh) is a unit of measure of energy in terms of watts ‘consumed’ over a specific time interval. One kWh is equivalent to one kilowatt (1000 watts) of electrical demand in use for one hour.
1 kWh = 1000W x 1 hour = 3600,000Ws = 3600 000J = 3.6MJ. Note: 1kW = 1000Watts, 1 hour = 60 x 60 =3600 seconds; Watt x second (Ws) = Joule (J), Mega = 106).
Power/electric utilities use the Kilowatt-hour (kWh) as the standard unit of measure for energy ‘consumption’ and is measured by an electric meter for billing purposes. Other Electric meters also measure demand (kW), power factor (pf), etc.
Electricity is generated from primary energy sources such as water, fossil fuels, wood fuels, etc., through some elaborate conversion processes and applied technologies. For our example, water (an indirect primary energy source) is used as a prime mover to generate electricity in many different ways, applying different conversion processes and technologies. At an elevated height, water has potential energy which is converted to kinetic energy as it is allowed to free fall as in a hydropower plant. The waters’ kinetic energy is converted to mechanical energy to turn the turbine that is coupled to a generator that in turn through the turning of the generator converts mechanical energy into electrical energy.
The same water, through the application of another energy source such as coal (direct primary energy source) to heat the water, turns the water into steam that is used to turn the turbine in a Thermal Power plant. The highly pressurised steam uses its inherent Kinetic energy to turn the turbines by conversion from Kinetic energy to mechanical energy. As with the hydropower conversion process, the turbine is coupled to a generator that turns and, thus converts mechanical energy into electrical energy.
You can see now how the same water is used to generate electricity in two different forms (as liquid and using its potential energy and as steam using its kinetic energy). We also see how in a Thermal Plant, we use another energy source (a fossil fuel such as coal or HFO or LNG, etc.) to heat up the water into steam. Electricity is also generated from other sources such as the sun (radiant solar energy or electromagnetic energy to photovoltaic), wind (mechanical to electrical), etc. Solar and wind are examples of renewable energy sources. They are renewable energy sources because they are naturally replenishing and virtually inexhaustible, unlike the fossil fuels that do not replenish within human timescales.
The electricity thus generated at a generating plant has to be transported/transmitted through a series of wires (overhead line conductors and underground cables) and associated equipment to a plug point in our home, and this entails a lot of losses along the way. Typically, the energy conversion efficiency of such a system (from primary energy sources like coal, natural gas, petroleum or nuclear to water as prime mover to a turbine to a generator to a step-up transformer to a step-down transformer) is such that for every 1 unit of energy at input, we would get 0.35 of a unit at output (i.e. 35 per cent energy conversion efficiency). The 65 per cent loss is attributed to sound energy, electromagnetic radiation and thermal energy or heat, mostly. That is energy for us; we cannot live without it; we need it and we are it.
The next articles shall explore these issues/themes listed below so keep reading and giving us feedback: Climate change – energy correlation, Energy-Water-Environment nexus, Economic-Energy-Socio-Political nexus.
The author is an energy expert and sustainability practitioner with over 25 years experience (Industrial Mining, Academia, Power Infrastructure/ESI, Electrical consultancy and energy advisory & consultancy). Reproduction of this article in full or in part without express permission from the author is forbidden.
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