In order to do anything, energy has to be expended. And, of course, we humans do a lot. In this exercise we will examine some of the energy sources that people use, and the impact of their use on the world around us.
Some terms to remember:
- In Physics, energy is measured in joules (symbol J). The energy it takes to lift a small apple one meter is about 1 J.
- Power (energy expended per unit time) is expressed in watts (symbol W). 1 W = 1J/s. Walking up stairs requires work of about 200 W; a typical incandescent light bulb uses 25-100 W, while the compact fluorescent (i.e., "energy saver") bulbs use about 5-30 W.
- In the metric system, we add prefixes based on powers of 10 (orders of magnitude). So 1 kW (1 kilowatt) = 103 W = 1000 W,
while 1 MJ (1 megajoule) = 106 J = 1,000,000 J. The standard prefixes that you might encounter in discussions of energy resources
are shown below:
- k (kilo-) = 103
- M (mega-) = 106
- G (giga-) = 109
- T (tera-) = 1012
- P (peta-) = 1015
- E (exa-) = 1018
- Z (zeta-) = 1021
- Y (yotta-) = 1024
By definition, we need to expend energy to do work. For most of history, the only energy resource (other than fire for cooking and heating) was muscle (human and animals (for cultures with beasts of burden). Some cultures also used wind (sailing, windmills) and water (boating, water wheels). But these latter two are limited in availability (either time or place).
Steam power was known since at least classical time: heat up water, and it turns to steam, which can push against surfaces or wheels to move gears and levers. Later, use steam to turn turbines and generate electricity: this is how coal and nuclear fission plants work, for instance. Burning wood is sufficient for low level steam activity, but really effective steam power needs greater concentrations of energy.
Coal, fuel of the Industrial Revolution:
- Actually is still one of the most important energy resources in modern times, too!
- Produced where abundant plant matter was buried faster than it could decay (generally, ancient swamps)
- Therefore, limited to places where such swamps were extensive. Most coal was deposited in the Carboniferous Period in the once low-lying regions of what is now North America, Europe, and Asia.
- Consequently, these regions were able to take advantage of the Industrial Revolution, while southern nations could not (even though they had the know-how, they didn't have the coal!)
- Easily mined, easily stored, easily transported, easily burned
- Burning produces ashes, smoke, smog, and carbon dioxide and other greenhouse gasses
- Geological surveys and studies of the historic and predicted rate of coal use suggest that we have many centuries worth of coal yet.
- However, like all geological resources, the rate at which it forms is VASTLY slower than the rate at which humans are using it up.
Petroleum (gasoline and natural gas resources), fuel of the modern age:
- Primary fuel for modern transportation, via the internal combustion engine
- Produced in environments in which vast amounts of organic matter (such as decaying plankton) gets
buried, distilled, and the organic goo is trapped
- Typically requires ancient warm conditions and subsequent development of features (like reefs and salt deposits) that trap the petroleum
- Examples of this environment was the hot equatorial seas of the Cretaceous Period, in which buried organic material got trapped in reefs of rudist clams and underneath salt layers
- These conditions were common in what is now the American Southwest and Gulf Coast, parts of South America, northern Africa, and the Middle East. However, a related set of conditions were also present in the North Sea and what is now northern North America (Does that list sound at all familiar with regards to the distribution of petroleum today?)
- Easily drilled, stored, transported, and burned
- Burning produces smoke, smog, and carbon dioxide and other greenhouse gasses
- Surveys and studies show that known and predicted petroleum supplies will run out in the late 21st or early 22nd Century.
Renewable Resources (solar, wind, water, geothermal, etc.):
- Energy density far too low (many orders of magnitude!) to handle transportation requirements of modern world
- Also, most are only available for use in localized spots: not an exportable resource
- However, using such systems might take some of the load off of the non-renewables.
- FAR more energy per unit mass than chemically-based systems!!
- Essentially just a steam-powered turbine to generate electricity, using radioactive materials to heat the water.
- However, fission plants are expensive to maintain.
- Nuclear waste is locally far more dangerous than coal or petroleum waste, but is globally far more benign!
Potential future resources
Fuel Cell technology:
- Not a different energy resource per se, but a different approach
- Combine a hydrogen-rich fuel through a series of special sheets to generate electricity
- Waste product is just water, if pure hydrogen is used as fuel (other products as well if hydrocarbons are used)
- However, currently requires a lot of energy to break water to make hydrogen, so have to generate energy in the first place!
- Also, storage requirements for pressurized or liquid hydrogen limits size and range of fuel cell vehicles.
Nuclear Fusion, Energy of the Future (and may always be!):
- Dwarfs the energy potential per unit mass of fission
- REAL solar power (i.e., this is how the sun works!)
- "Waste" material of fusion reaction would be helium, an inert (and useful!) gas
- Problem: currently, requires more energy to maintain a fusion reaction than we can get out of it
We will come back to the issue of future energy resources and utilization in far more detail in the third semester.