Since the days when we humans learned to use fire and developed six simple machines, we have progressed a lot in our ability to harness external sources of energy. In fact, we have defined and redefined its use. But what is energy? Scientists define it as “the ability to do work” — anything from manufacturing a box to carrying it, for example. The most important aspect of energy is that it enables some kind of change.
Mechanical energy usually comes to mind first. There are two different forms of it: kinetic (energy that is actually doing something, like running a machine) and potential (capable of running the machine, but currently at rest).
To understand the distinction further, think of the energy involved in riding a bike. As you pedal along on a flat surface, you use your own kinetic energy (pedaling) to make the bicycle move forward. Going up a hill, you use more kinetic energy than when you’re on the level, but you also build up potential energy in terms of the gravity you overcome. When you’re stopped up at the top of the hill with the brakes on, you’re not using any energy at all. Heading down, you use both your kinetic energy and your gravitational potential. Think “battery” when you think of potential energy: it’s just kinetic energy that is stored.
Some examples of energy at work:
- Wind, river, and tidal are all forms of kinetic energy. Dams and reservoirs are valuable as a potential energy source from moving water.
- Light produces radiant energy, which we transform to create passive, photovoltaic, and concentrating solar power.
- Heat from either artificial or geothermal (renewable) sources is called thermal energy and is often transferred from one material to another, as in boiling.
- Energy can also come from sound (microwaves, for example).
- We use chemical energy in batteries to store electricity.
- Nuclear energy exists in potential at the atomic level and transforms to kinetic energy through a chain reaction.
Electricity is the premier form of energy in today’s world. Over the past 150 years, people have become accustomed to generating power by applying a spark to a fuel and burning it to run machines. This method itself consumes a lot of energy, because it depends on seeking, extracting, processing, transporting, and consuming fuels (primary energy) to achieve secondary energy. The secondary energy comes in the form of either electricity from a power plant, or steam and thermal power. Fuel burning also creates unwanted byproducts (pollution, harmful to biological life) along every step of its supply chain.
Technically, electric energy starts as potential energy, measured in volts. When switched on, an electric circuit generates power. We measure power by combining how much electric energy is transferred and how fast the transfer happens (in joules per second, or watts). Most circuits transform the electric energy into mechanical or some other form of energy.
A watt (or kilowatt, megawatt, gigawatt, or terawatt) expresses how much electricity can be generated at a specific moment by a power plant, or how much is needed to power something (like a light bulb). We rate power plants in watts (or, more likely, kilowatts, megawatts, or gigawatts) to indicate the maximum amount of power a plant can put out at a given point in time. The (soon-to-be) largest solar PV power plant in the world has a rating of 379 megawatts, and the smallest US nuclear plant has a capacity of 502 MW. The largest single nuclear plants are three times that size, while nuclear stations go up to about 8,000 MW, or 8 GW (7 reactors). Three Gorges Dam (hydroelectric) in China is the largest electric power plant in the world, with a 22,500 MW (22.5 GW) electricity generation capacity.
Watt-hours indicate how much electricity is produced over time. What you see on your electric bill indicating electricity usage for the month is in watt-hours (or, more likely, kilowatt-hours).
To get electrical energy from power plants to consumers, we send it through a system of interconnected wires: the electric power grid. We use resistors to standardize (rate) that power. However, each resistor lets a little power escape in the form of heat. We also lose power through transmission: estimates of grid loss are anywhere from 5-7% in most parts of the US and Canada. And when we convert direct current that’s originally generated to alternating current (AC), used for home and office outlets, we lose even more.
All the infrastructure used to handle the process and the energy lost in transformation, conversion, and distribution further diminish power. At the same time, the grid itself is limited to preplanned paths that limit access to power, especially in less “developed,” rural, and island areas. And consumers of power have become so distant from its source that they do not understand what’s necessary to provide it.
In the days of Edison, Westinghouse, and other electricity pioneers, power sources, availability, and losses did not mean as much as they do today. Increased population, debates over fuel costs and utility functions, and links with climate change have begun to cause considerable friction. We are transitioning from nonrenewable (fossil-fuel based) to renewable technologies, from older to newer sources of power. The structure of energy production and distribution is changing as well, beginning with the fuels we use to generate power.
Coal, oil, and natural gas, all nonrenewable resources, were abundant and accessible in the 19th century. We have used up the handiest sources, so these fuels have begun to require extraordinary effort to obtain. They are also becoming more expensive to convert to energy. Too, the process of generating power releases quantities of pollutants harmful to biological life. We can see a change in energy sources as developed countries begin to reduce or halt the use of coal — the “dirtiest” fossil fuel — and developing nations plan to use it only on the road to cleaner energy sources.
Biomass (wood, animal waste, nonfood vegetation) is intermediate. It belongs on the “renewable” list, but when burned inefficiently, it causes considerable pollution, especially in particulate form.
Cleaner sources include passive solar, windmills, dams and running water, and the like, which we once used but abandoned for the convenience and strength of electric power from fuels. Modern versions like giant wind turbines and photovoltaic panels provide much greater efficiency than our first efforts did. Geothermal, wave, and tidal energies are also showing promise. Nuclear power, used for over half a century, has proven “clean” at the power plant, but not in the uranium mining, transportation, and waste disposal, let alone in how its byproducts can be widely fatal and virtually ineradicable.
For a final snapshot of energy and power use in one of the most industrially developed nations of the world, here’s a look at all the energy sources and power use in the United States around the year 2013. Two and a half centuries ago, Americans would never have understood it. And it, too, must change to match the needs of the times.
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