Renewable energy

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=== Hydroelectric energy ===
 
=== Hydroelectric energy ===
Hydreoelectric power, or water power in general, involves taking advantage of water that has been raised due to evaporation by the sun, and deposited on high ground.  As it then flows back towards the ocean, its potential energy can be tapped by turbines or water wheels, which are usually built into dams to increase the drop.
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Hydreoelectric power, or [[water]] power in general, involves taking advantage of water that has been raised due to evaporation by the sun, and deposited on high ground.  As it then flows back towards the ocean, its potential energy can be tapped by turbines or water wheels, which are usually built into dams to increase the drop.
  
 
Many hydroelectric schemes are also designed to store energy, as water is pumped into the dam when energy is cheap at night and then allowed to run out when demand is higher during the day. Although not particularly efficient it is perhaps the only commonly used method of "storing" significant amounts of electrical energy.  
 
Many hydroelectric schemes are also designed to store energy, as water is pumped into the dam when energy is cheap at night and then allowed to run out when demand is higher during the day. Although not particularly efficient it is perhaps the only commonly used method of "storing" significant amounts of electrical energy.  

Revision as of 18:11, 30 April 2008

Renewable energy sources are energy sources which theoretically are constantly being renewed. The name may be a bit of a misnomer and perhaps ambient energy sources might be a better term. They include:

Contents

Solar energy

Solar energy is the result of the sun shining on the earth. It can be tapped in many different ways.

Direct solar

"Direct" solar power means capturing the energy in sunlight and converting it to a usable form via various technologies.

Two main ways of doing this are photovoltaic cells and panels containing a liquid, which is warmed and moved to where heat is needed.

Sometimes space-based solar collection systems have been proposed, but these will probably not be built in the foreseeable future.[1]

Slightly more practical suggestions have been made involving huge solar arrays in the Sahara desert which would then transmit low-loss DC power to Europe. [2]

Installations like this are already in place in the Southwestern desert in the United States, which are in reasonably close proximity to large cities in California and Nevada. They are simply heat-to-energy collectors, however, rather than the more "high-tech" photovoltaic type systems.

Advantages of direct solar

  • If the technology works well, it can be scaled up to huge production levels quite well.
  • Relatively little maintenance is required.

Disadvantages of direct solar

  • Photovoltaic cells are, as of now, still very inefficient.
  • Many highly populated parts of the world don't get consistent high levels of sunlight.

Hydroelectric energy

Hydreoelectric power, or water power in general, involves taking advantage of water that has been raised due to evaporation by the sun, and deposited on high ground. As it then flows back towards the ocean, its potential energy can be tapped by turbines or water wheels, which are usually built into dams to increase the drop.

Many hydroelectric schemes are also designed to store energy, as water is pumped into the dam when energy is cheap at night and then allowed to run out when demand is higher during the day. Although not particularly efficient it is perhaps the only commonly used method of "storing" significant amounts of electrical energy.

Advantages of water power

  • It is relatively clean, once the equipment has been built and installed.
  • Creation of artificial lakes upstream of the dams, to be used for recreation, wildlife preserves, or potable water supplies.

Disadvantages of water power

  • Flooding of landscapes, reducing ecological niches.
  • Displacement of residents.
  • Burial underwater of important cultural landmarks.
  • Limited options for use (there is only so much rain to capture as it flows downhill).
  • Many areas simply have no substantial water flow to tap near them.
  • The lakes behind dams convert large amounts of CO2 to methane, a far worse greenhouse gas, which causes further global warming.[3]
  • Hydroelectric dams pose barriers to migrating fish.

Wind energy

This is one of the more developed forms of renewable energy and major projects are underway worldwide.

Although only 1% of the world's power comes from the wind, some European countries produce a lot more. For example 20% of Denmark's energy comes from the wind and and 9% of Spain's. European targets are also very ambitious, with Spain planning to obtain 15% of its power from wind by 2010. In general, annual wind power growth in Europe is a surprising 32%[4]

Advantages of wind power

  • Once the infrastructure is in place, it is very clean.
  • The technology is now well established.

Disadvantages of wind power

  • Unpredictable output as the wind does not always blow.
  • Visual impact.
  • Bird kills.
  • Noise generation.
  • Environmental damage while the wind farm is being built.
  • Wind farms built on peat may release more CO2 than they save.[5]

Plant based energy (biofuels)

Plant based energy consists of allowing plants to fix carbon in sugars and cellulose via sunlight, and then to either produce liquid fuels (such as alcohol) from them or burn them directly.

Advantages of plant energy

  • It's carbon neutral in the long run.
  • It can produce convenient, high energy density liquid fuel, which is very useful in transportation.

Disadvantages of plant energy

  • It competes with food production and could lead to significant price rises.
  • Some systems, such as making ethanol from corn, are very inefficient.
  • Often, plant matter is harvested without proper concern for replenishment.
  • In some cases tropical rainforest is being cut down to grow biofuels.[6]
  • Where wood is burnt directly for heat in can present a fire risk.

Geothermal Energy

Geothermal technologies tap the temperature difference between the surface of the earth and shallow or deep underground regions. Alternatively they may make use of high-temperature hot springs in geologically active areas.

A heat pump, while expensive to install, uses the relatively constant temperature a few meters below the earth's surface to allow compression/condensation liquid heat transfer technology to heat and cool buildings. They are 3 to 5 times as efficient in their consumption of electricity per BTU produced as direct resistance heating.

Also, it is possible to tap the much higher temperatures hundreds or thousands of meters below the earth's surface.

Advantages of geothermal energy

  • Very high energy densities may be naturally available.
  • In practical terms the environmental impact is low.

Disadvantages of geothermal energy

  • In the very long run, "global cooling". It is not truly renewable.
  • Dangerous deep shafts must be used to access the heat deep in the earth's crust, although existing mines might be useful for this.

Tidal and wave energy

This relatively new technology is designed to obtain energy from tidal movements or from waves. Although the concept seems simple few, if any, commercial installations are in place.

If efficient systems could be built they could provide significant predictable power (at least from tides).

There are essentially two ways to "trap" tidal energy - to build generation plants that are run by large amounts of water flowing in and out of large estuaries, and to build open ocean devices that somehow tap the energy by letting the tides (and perhaps waves, too) force a floating object up and down relative to an anchored one.

Advantages of tidal and wave energy

Whatever we build will provide energy until the moon "runs down".

Power generation systems can be built into, or merged with, flood control systems that protect large cities located on major estuaries, such as London and the Thames. This generates the energy close to a large need for it.

Disadvantages of tidal and wave energy

They would need to be shown not to interfere with fish stocks or fisheries.

The local energy output will wax and wane from maximum to virtually zero four times a day, and this time slowly changes from day to day. This can, however, be mitigated by dammed mill pond type systems.

References and notes

  1. New Scientist Space energy
  2. African solar power to Euroipe
  3. http://www.newscientist.com/article/dn7046.html
  4. http://www.cleanpowernow.org/index.php?name=News&file=article&sid=202
  5. New Scientist - Hidden cost of wind turbines
  6. http://www.newscientist.com/article.ns?id=mg18825265.400
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