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Renewable energy

Table of contents

1 General Information 2 Pros and cons of renewable energy 3 Renewable energy history 3.1 Wood 3.2 Animal traction 3.3 Water power 3.4 Wind power 3.5 Solar power 3.6 The renewable energy movement 4 Renewable energy today 5 Modern sources of renewable energy 5.7 Smaller-scale sources 5.8 Renewables as solar energy 5.9 Solar energy per se 5.9.1 Solar electrical energy 5.9.2 System problems with solar electric 5.9.3 Solar thermal electric energy 5.9.4 Solar thermal energy 5.9.4.1 Solar water heating 5.9.4.2 Solar heat pumps 5.9.4.3 Solar ovens 5.10 Wind energy 5.11 Geothermal energy 5.12 Water power 5.12.5 Electrokinetic energy 5.12.6 Hydroelectric energy 5.12.7 Tidal power 5.12.8 Tidal stream power 5.12.9 Wave power 5.12.10 OTEC 5.13 Biomass 5.13.11 Liquid biofuel (Biodiesel or bioalcohol) 5.13.12 Solid biomass 5.13.13 Biogas 6 Renewable energy storage systems 6.14 Hydrogen fuel cells 6.15 Other renewable energy storage systems 6.15.14 Pumped water storage 6.15.15 Battery storage 6.15.16 Electrical grid storage 6.15.17 Flywheel storage 7 Renewable energy use by nation 8 Renewable energy controversies 8.16 Lack of motivation for funding 8.17 Centralization versus decentralization 8.18 The nuclear "renewable" claim 9 Renewable Energy Support Mechanisms 9.19 Tariff Mechanisms 9.19.18 Advantages 9.19.19 Disadvantages 9.20 Quota Mechanisms 9.20.20 Advantages 9.20.21 Disadvantages 9.21 Contract Bidding Mechanisms 9.21.22 Advantages 9.21.23 Disadvantages 10 External links 11 References

General Information

Most renewable forms of energy, other than geothermal, are in fact stored solar energy. Water power and wind power represent very short-term solar storage, while biomass represents slightly longer-term storage, but still on a very human time-scale, and so renewable within that human time-scale. Fossil fuels, on the other hand, while still stored solar energy, have taken millions of years to form, and so do not meet the definition of renewable.

Renewable energy resources may be used directly as energy sources, or used to create other forms of energy for use. Examples of direct use are solar ovens, geothermal heat pumps, and mechanical windmills. Examples of indirect use in creating other energy sources are electricity generation through wind generators or photovoltaic cells, or production of fuels such as ethanol from biomass (see alcohol as a fuel).

Pros and cons of renewable energy

Renewable energy sources are fundamentally different from fossil fuel or nuclear power plants because of their widespread occurrence and abundance - the sun will 'power' these 'powerplants' (meaning sunlight, the wind, flowing water, etc.) for the next 4 billion years. The primary advantage of many renewable energy sources are their lack of greenhouse gas and other emissions in comparison with fossil fuel combustion. Some renewable sources do not emit any additional carbon dioxide and do not introduce any new risks such as nuclear waste. In fact, most biomass actively sequesters carbon dioxide while growing.

A visible disadvantage of renewables is their visual impact on local environments. Some people dislike the aesthetics of wind turbines or bring up nature conservation issues when it comes to large solar-electric installations outside of cities. Some people try to utilize these renewable technologies in an efficient and aesthetically pleasing way: fixed solar collectors can double as noise barriers along highways, roof-tops are available already and could even be replaced totally by solar collectors, amorphous photovoltaic cells can be used to tinge windows and produce energy etc.

Some renewable energy capture systems entail unique environmental problems. For instance, wind turbines can be hazardous to flying birds, while hydroelectric dams can create barriers for migrating fish - a serious problem in the Pacific Northwest that has decimated the numbers of many salmon populations.

Another inherent difficulty with renewables is their variable and diffuse nature (with the exception being geothermal energy, which is however only accessible where the earth's crust is thin, such as near hot springs and natural geysers). Since renewable energy sources are providing relatively low-intensity energy, the new kinds of "power plants" needed to convert the sources into usable energy need to be distributed over large areas. To make the phrases 'low-intensity' and 'large area' easier to understand, note that in order to produce 1000 kWh of electricity per year (a typical per-year-per-capita consumption of electricity in Western countries), a home owner in cloudy Europe needs to use eight square meters of solar panels (assuming a below-average energy efficiency of 12.5%). Systematic electrical generation requires reliable overlapping sources or some means of storage on a reasonable scale (pumped-storage hydro systemss, batteries, future hydrogen fuel cells, etc.). So, because of currently-expensive energy storage systems, a small stand-alone system is only economic in rare cases, or in applications where the connection to to the global energy network would drive costs up sharply.

The geographic diversity of resources is also significant. Some countries and regions have significantly better resources than others in particular RE sectors. Some nations have significant resources at distance from the major population centres where electricity demand exists. Exploiting such resources on a large scale is likely to require considerable investment in transmission and distribution networks as well as in the technology itself.

If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would no longer be the main distributors of electrical energy but would operate to balance the electricity needs of local communities. Those with surplus energy would sell to areas needing "top ups". That is, network operation would require a shift from 'passive management' - where generators are hooked up and the system is operated to get electricity 'downstream' to the consumer - to 'active management', wherein generators are spread across a network and inputs and outputs need to be constantly monitored to ensure proper balancing occurs within the system. This will require significant changes in the way that such networks are operated.

However, on a small scale, use of renewable energy that can often be produced "on the spot" lowers the requirements electricity distribution systems have to fulfill. Current systems, while rarely economically efficient, have proven an average household with a solar panel array and energy storage system of the right size needs electricity from outside sources for only a few hours every week. Hence, advocates of renewable energy believe electricity distribution systems will become smaller and easier to manage, rather than the opposite.

Renewable energy history

The original energy source for all human activity was the sun via growing plants. Solar energy's main human application throughout most of history has thus been in agriculture and forestry, via photosynthesis.

Wood

Firewood was the earliest manipulated energy source in human history, being used as a thermal energy source through burning, and it is still important in this context today. Burning wood was important for both cooking and providing heat, enabling human presence in cold climates. Special types of wood cooking, food dehydration and smoke curing, also enabled human societies to safely store perishable foodstuffs through the year. Eventually, it was discovered that partial combustion in the relative absence of oxygen could produce charcoal, which provided a hotter and more compact and portable energy source. However, this was not a more efficient energy source, because it required a large input in wood to create the charcoal.

Animal traction

Motive power for vehicles and mechanical devices was originally produced through animal traction. Animals such as horses and oxen not only provided transportation but also powered mills. Animals are still extensively in use in many parts of the world for these purposes.

Water power

Animal power for mills was eventually supplanted by water power, the power of falling water in rivers, wherever it was exploitable. Direct use of water power for mechanical purposes is today fairly uncommon, but still in use.

Originally, water power through (hydroelectricity) was the most important source of electrical generation throughout society, and is still an important source today. Throughout most of the history of human technology, hydroelectricity has been the only renewable source of electricity generation significantly tapped for the generation of electricity.

Wind power

Wind power has been used for several hundred years. It was originally used via large sail-blade windmills with slow-moving blades, such as those seen in the Netherlands and mentioned in Don Quixote. These large mills usually either pumped water or powered small mills. Newer windmills featured smaller, faster-turning, more compact units with more blades, such as those seen throughout the Great Plains. These were mostly used for pumping water from wells. Recent years have seen the rapid development of wind generation farms by mainstream power companies, using a new generation of large, high wind turbines with two or three immense and relatively slow-moving blades.

Solar power

Solar power as a direct energy source has been not been captured by mechanical systems until recent human history, but was captured as an energy source through architecture in certain societies for many centuries. Not until the twentieth century was direct solar input extensively explored via more carefully planned architecture (passive solar) or via heat capture in mechanical systems (active solar) or electrical conversion (photovoltaic). Increasingly today the sun is harnessed for heat and electricity.

The renewable energy movement

Renewable energy as an issue was virtually unheard-of before the middle of the twentieth century. There were experimentations with passive solar energy, including daylighting, in the early part of the twentieth century, but little beyond what had actually been practiced as a matter of course in some locales for hundreds of years. The renewable energy movement gained awareness, credence and strength with the great burgeoning of interest in environmental affairs in the mid-1900s, which in turn was largely due to Rachel Carson's 'Silent Spring'.

The first US politician to focus significantly on solar energy was Jimmy Carter, in response to the long term consequences of the 1973 energy crisis. No president since has paid much attention to renewable energy.

Renewable energy today

Around 80% of energy requirements in western industrial societies are focused around heating or cooling buildings and powering the vehicles that ensure mobility (cars, trains, airplanes). However, most uses of renewable power focus on electricity generation.

Geothermal heat pumps (also called ground-source heat pumps) are a means of extracting heat in the winter or cold in the summer from the earth to heat or cool buildings.

Modern sources of renewable energy

There are several types of renewable energy, including the following:

• Solar power.
• Wind power.
• Geothermal energy.
• Electrokinetic energy.
• Hydroelectricity.
• Biomatter, including Biogas Energy.

• Piezo electric crystals embedded in the sole of a shoe can yield a small amount of energy with each step. Vibration from engines can stimulate piezo electric crystals.
• Some watches are already powered by movement of the arm.
• Special antennae can collect energy from stray radiowaves or even light (EM radiation).

Most renewable energy sources can trace their roots to solar energy, with the exception of geothermal and tidal power -- yet even these can be attributed to the sun's gravity. For example, wind is caused by the sun heating the earth unevenly. Hot air is less dense, so it rises, causing cooler air to move in to replace it. Hydroelectric power can be ultimately traced to the sun too. When the sun evaporates water in the ocean, the vapor forms clouds which later fall on mountains as rain which is routed through turbines to generate electrity. The transformation goes from solar energy to potential energy to kinetic energy to electric energy.

Solar energy per se

Since most renewable energy is "Solar Energy" this term is slightly confusing and used in two different ways: firstly as a synonym for "renewable energies" as a whole (like in the political slogan "Solar not nuclear") and secondly for the energy that is directly collected from solar radiation. In this section it is used in the latter category.

There are actually two separate approaches to solar energy, termed active solar and passive solar.

Solar electrical energy

For electricity generation, ground-based solar power has serious limitations because of its diffuse and intermittent nature. First, ground-based solar input is interrupted by night and by cloud cover, which means that solar electric generation inevitably has a low capacity factor, typically less than 20%. Also, there is a low intensity of incoming radiation, and converting this to high grade electricity is still relatively inefficient (14% - 18%), though increased efficiency or lower production costs have been the subject of much research over several decades.

Two methods of converting the Sun's radiant energy to electricity are the focus of attention. The better-known method uses sunlight acting on photovoltaic (PV) cells to produce electricity. This has many applications in satellites, small devices and lights, grid-free applications, earthbound signaling and communication equipment, such as remote area telecommunications equipment. Sales of solar PV modules are increasing strongly as their efficiency increases and price diminishes. But the high cost per unit of electricity still rules out most uses.

Several experimental PV power plants mostly of 300 - 500 kW capacity are connected to electricity grids in Europe and the USA. Japan has 150 MWe installed. A large solar PV plant was planned for Crete. In 2001 the world total for PV electricity was less than 1000 MWe with Japan as the world's leading producer. Research continues into ways to make the actual solar collecting cells less expensive and more efficient. Other major research is investigating economic ways to store the energy which is collected from the Sun's rays during the day.

Alternatively, many individuals have installed small-scale PV arrays for domestic consumption. Some, particularly in isolated areas, are totally disconnected from the main power grid, and rely on a surplus of generation capacity combined with batteries and/or a fossil fuel generator to cover periods when the cells are not operating. Others in more settled areas remain connected to the grid, using the grid to obtain electricity when solar cells are not providing power, and selling their surplus back to the grid. This works reasonably well in many climates, as the peak time for energy consumption is on hot, sunny days where air conditioners are running and solar cells produce their maximum power output. Many U.S. states have passed "net metering" laws, requiring electrical utilities to buy the locally-generated electricity for price comparable to that sold to the household. Photovoltaic generation is still considerably more expensive for the consumer than grid electricity unless the usage site is sufficiently isolated, in which case photovoltaics become the less expensive.

System problems with solar electric

Frequently renewable electricity sources are disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would no longer be the main distributors of electrical energy but would operate to balance the electricity needs of local communities. Those with surplus energy would sell to areas needing "top ups". Some Governments and regulators are moving to address this, though much remains to be done. One potential solution is the increased use of active management of electricity transmission and distribution networks.

Solar thermal electric energy

The second method for utilizing solar energy is solar thermal. A solar thermal power plant has a system of mirrors to concentrate the sunlight on to an absorber, the resulting heat then being used to drive turbines. The concentrator is usually a long mirrored parabolic trough oriented north-south, which tilts, tracking the Sun's path through the day. A black absorber tube is located at the focal point and converts the solar radiation to heat (about 400°C) which is transferred into a fluid such as synthetic oil. The oil can be used to heat buildings or water, or it can be used to drive a conventional turbine and generator. Several such installations in modules of 80 MW are now operating. Each module requires about 50 hectares of land and needs very precise engineering and control. These plants are supplemented by a gas-fired boiler which ensures full-time energy output. The gas generates about a quarter of the overall power output and keeps the system warm overnight. Over 800 MWe capacity worldwide has supplied about 80% of the total solar electricity to the mid-1990s.

One proposal for a solar electrical plant is the solar tower, in which a large area of land would be covered by a greenhouse made of something as simple as transparent foil, with a tall lightweight tower in the centre, which could also be composed largely of foil. The heated air would rush to and up the centre tower, spinning a turbine. A system of water pipes placed throughout the greenhouse would allow the capture of excess thermal energy, to be released throughout the night and thus providing 24-hour power production. A 200 MWe tower is proposed near Mildura, Australia.

Solar thermal energy

Solar energy need not be converted to electricity for use. Many of the world's energy needs are simply for heat; space heating, water heating, process water heating, oven heating, and so forth. The main role of solar energy in the future may be that of direct heating. Much of society's energy need is for heat below 60°C (140°F) - e.g. in hot water systems. A lot more, particularly in industry, is for heat in the range 60 - 110°C. Together these may account for a significant proportion of primary energy use in industrialized nations. The first need can readily be supplied by solar power much of the time in some places, and the second application commercially is probably not far off. Such uses will diminish to some extent both the demand for electricity and the consumption of fossil fuels, particularly if coupled with energy conservation measures such as insulation.

Solar water heating

Domestic solar hot water systems were once common in Florida until they were displaced by highly-advertized natural gas. Such systems are today common in the hotter areas of Australia, and simply consist of a network of dark-colored pipes running beneath a window of heat-trapping glass. They typically have a backup electric or gas heating unit for cloudy days. Such systems can actually be justified purely on economic grounds, particula
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