Renewable energy
From RationalWiki
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.
Contents |
[edit] Solar energy
Solar energy is the energy of the sun shining on the earth, originating from entropic fusion reactions at the heart of the star. It can be tapped in many different ways, directly & indirectly.
Direct methods usually reffer to either solar panels or passive heat absorbion.
Indirect methods would include: Hydroelectric power & Wind Power. In Hydro, the sun provides the energy from the water to evaporate, so it can begin its travel from a highground anew. In Wind power, solar radiation is often the prime cause behind the kinetic energy of air molecures. Plants also utilize solar energy in order to perform many energy costly chemical reactions, which later in the food chain are broken down by life for energy.
[edit] Direct solar
"Direct" solar power means capturing the energy in sunlight and converting it to a usable form via various technologies.
There are three main ways of doing this:
- Photovoltaic cells
- Heat capture cells
- Concetration towers
Sometimes space-based solar collection systems have been proposed, but these will probably not be built in the foreseeable future.[1]
Photovoltaic cells[2] convert solar radiation into electricity through the use of the photovoltaic effect. Although the Earth's surface receives daily about 4.2 kilowatt-hours per square meter, most solar panels are not perfectly efficient (and they can never be for thermodynamics reasons) and in reality most of them struggle to get over 20% efficiency (8%-15& being more common, even for commerical uses).
Heat collection cells take many forms. The one encountered most often is used for water heaters[3], which might look like Solar Panels, but in reality at no points is a conversion to electricity taking place. Other forms of heat collection are greenhouse structures, as well as passive heating architectural schemes making use of either controlled glazed surfaces or a material's native thermal capacity. Since such systems only try to convert into heat (so any "heat losses" are actually aiding them), for their specific applications they are actually far more efficient than solar panels with conversion rates of over 60%. (The reason for this being that they don't work equally well in the entire spectrum).
Concentrations towers are essentially a specialized heat capturing system where a lot of mirrors aim thermal energy into a central point. Pretty much utilizing the same mechanism Archimedes did when he (allegently) burned a Roman fleet. In a solar tower's focus point there is usually some kind of heat absorbing liquid, which is heated and used to turn turbines, similar to the way conventional power plants generate electricity. The advantages of that approach, is that, while solar panels are expensive objects, each and everyone one requiring electrical installations & maintance, mirrors are ... just dumb mirrors which you could clean with a hose. In addition, because the important energy conversation takes place en mass at the central focus points, such facilities only have to improve on that one, vs photovoltainc ones which would have to do so over their entire area. Heat storage strategies, can also allow such a plant to maintain generation during brief interruptions (ie, clouds) or even for a significant part of the night.
Experimental 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. Were the US to switch into a centralized solar generation from sunlit states, it would require the overhowling of the current, decades old energy distribution systems. A first step towards that would be a nationwide direct current backbone.
Project Desertec[4] is a similar scheme involving huge solar arrays in the Sahara desert which would then transmit low-loss DC power to Europe.
[edit] Spain
Spain has more available sunshine than any other European country. Its government is committed to achieving a target of 12 percent of primary energy from renewable energy by 2010 with an installed solar generating capacity of 3000 megawatts.[5]
[edit] 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.
[edit] Disadvantages of direct solar
- Photovoltaic cells are, as of now, still very inefficient.
- Photovoltaic cells degrade through time, making "break even" calculations not so obvious.
- Many highly populated parts of the world don't get consistent high levels of sunlight.
[edit] 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.
[edit] 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.
- water power is a renewable energy
[edit] 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.[6]
- Hydroelectric dams pose barriers to migrating fish.
[edit] 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%[7]
[edit] Advantages of wind power
- Once the infrastructure is in place, it is very clean.
- The technology is now well established.
[edit] Disadvantages of wind power
- Unpredictable output as the wind does not always blow. Many turbines are required over a large area to compensate for this.
- Changes from single, concentrated sources of energy (power stations) to multiple low power sources (hundreds of turbines) may be incompatible with current electricity distribution networks.
- Environmental damage while the wind farm is being built.
- Wind farms built on peat may release more CO2 than they save.[8]
- Most "anti wind" groups, however, tend to focus on the following, which aren't particular good reasons against wind power really, but they're easy to understand.
- Bird kills - although they are very minimal compared to cars, cats and flying into windows.
- Visual impact.
- Noise generation.
[edit] 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.
[edit] 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.
[edit] Disadvantages of plant energy
- It competes with food production and could lead to significant price increases.
- 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.[9]
- Where wood is burnt directly for heat it can present a fire risk.
Note: almost all of the above can be countered by using industrialized (non-THC variant) hemp for plant energy. The process for making it is very efficient, it doesn't compete with food production much or at all (even though you can make food out of it), and is one of the fastest-growing biomasses on the planet, capable of producing 10 acres of biomass per month[10]. In fact, it should be noted that this is what Henry Ford had originally planned to use for his model T.[11]
[edit] 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.
[edit] Advantages of geothermal energy
- Very high energy densities may be naturally available.
- In practical terms the environmental impact is low.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] Footnotes
- ↑ New Scientist Space energy
- ↑ http://en.wikipedia.org/wiki/Solar_panel
- ↑ http://en.wikipedia.org/wiki/Solar_water_heater
- ↑ http://www.desertec.org/]
- ↑ Spain expects 3,000 MW in Solar Plants by 2010
- ↑ http://www.newscientist.com/article/dn7046.html
- ↑ http://www.cleanpowernow.org/index.php?name=News&file=article&sid=202
- ↑ New Scientist - Hidden cost of wind turbines
- ↑ http://www.newscientist.com/article.ns?id=mg18825265.400
- ↑ http://www.hempcar.org/hempfacts.shtml
- ↑ http://www.hempcar.org/ford.shtml
