SCIENCE MATTERS - Public must understand nature of energy sources

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How energy needs are met in the future will determine the health of our economy and quality of life for generations to come. Understanding the basics can help in understanding issues surrounding energy generation and the consequences of poor choices.

There are only a few primary (sometimes called renewable) energy sources that are effectively unlimited. Secondary sources are derived from primary sources. Secondary sources are best thought of as conduits, perhaps storing energy for some time before delivering it where it is needed.

The inexhaustible, primary energy sources are solar (sunlight), gravitational, geothermal and nuclear.

Ultimately the sun is provider for most of the energy sources we tap. Photovoltaic cells convert sunlight directly to electricity. Storing the resulting electrical energy for around-the-clock use is a substantial problem.

An alternative method uses large mirrors to focus sunlight on heat reservoirs from which heat is extracted. That heat can be used at night or when there are overcast skies, and could be used to generate electricity.

Wind turbines are designed to capture kinetic energy from wind. Air mass movement ultimately comes from the sun differentially heating different surface areas on the planet. This is an indirect means of exploiting solar energy.

It might prove feasible to attach generators to large blades submerged in the midst of oceanic currents. Such currents are generated from a number of sources, but are primarily caused by winds, solar heating and tidal effects. Again, we are back to the sun as the principle driver of this energy source.

A variant on these ideas proposes filling inland basins at high tide. Then the trapped water is release as the tide recedes and is use to drive generators. This idea exploits gravitational effects of the sun and moon on oceans. It has limited potential and significant logistical and environmental implications.

Hydroelectric dams derive their energy from the gravitational potential energy of water held behind a dam above a river's natural elevation. Of course, the water was originally elevated and redistributed by evaporation and winds, each of which has solar origins.

Geothermal plants use heat from hot geological formations near the Earth's surface to heat water in a turbine that runs a generator. This is a desirable source, but is unlikely to significantly impact our needs.

By a process called photosynthesis, chloroplasts in cells of plants convert and store energy from sunlight. In doing so, they build hydrocarbons from carbon dioxide extracted from the air. We then use those hydrocarbons as fuels.

Harvesting fuels from plants returns carbon sequestered by the plant to the atmosphere on a short time line. In the end, this simply recirculates greenhouse gases into the atmosphere.

One such fuel, ethanol, is produced from things like corn. It is very inefficient, requiring nearly as much energy in its production as is made available as a fuel. Clearly, energy generation from crops on land needed for growing food is short sighted.

Nuclear fusion power is very promising and effectively unlimited, but technologically very difficult. Nuclear waste issues from such reactors are easily addressed. Raw fuels are readily available and practically inexhaustible. At our present pace, however, commercial power plants of this type are decades away.

Since nuclear fission energy depends on finite resources, it is not unlimited. However, its contribution can be substantial. Its environmental impact can be small, provided reactors are well designed and sited. Waste storage has proven to be a formidable problem and must be resolved.

Often "new energy sources" are really just new methods of energy distribution. Maybe they are important, but not for the reason they are truly new sources. Typically, the ultimate source of that energy is not identified.

Electric cars are a great idea, not because electricity is a primary source of energy. Rather, because instead of having millions of vehicles spewing carbon dioxide into the atmosphere, there are many times fewer large electric power plants.

Potentially, those plants could use renewable energy sources, though today that is rarely the case. Even when plants burn fossil fuels, they could be designed to sequester their carbon dioxide. This is more easily done at centralized plants than at the exhaust pipe of every car.

Hydrogen-powered cars or machinery do not exploit a new primary energy source. Hydrogen is no more a primary energy source than power lines running into our homes are primary energy sources.

Hydrogen must be made, and that takes energy. Typically, that energy comes from power plants burning fossil fuels. As with any conduit, hydrogen transports energy from one site where it is generated to another location where it is used.

Today, most of our energy comes from finite reservoirs of fossil fuels: coal, oil and natural gas. Power companies and natural gas producers would like us to believe natural gas is a clean energy source. But, even if its use releases fewer pollutants such as sulfur, it still produces carbon dioxide, the primary greenhouse gas.

Fossil fuels originate from plants that existed several hundred million years ago. At that time, vast tracts of vegetation existed in tropical regions. Those plants extracted huge quantities of carbon dioxide from the atmosphere.

Subsequently, this plant matter was buried by natural processes. Under varying conditions, all of which included great heat and pressure, the hydrocarbons making up this material became coal, petroleum or gas.

Though fossil fuels were created long ago, over the course of millions of years, we are likely to have completely exhausted them in a few centuries. The wisdom of doing this while releasing large quantities of CO2 back into the atmosphere is dangerous.

We must ask ourselves, "Would the planet have been a hospitable place for humans before plants arose and extracted large quantities of carbon dioxide from the atmosphere?" We won't like the answer.

It is best if we leave as much of the fossil fuels sequestered as possible. Better we develop means to extract our energy needs from primary, renewable sources. It won't happen until the public understands the nature of all energy sources.

Steve Luckstead is a medical physicist in the radiation oncology department at St. Mary Medical Center. He can be reached at steveluckstead@charter.net.

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