Sabtu, 27 Desember 2008

Fisika Energi

What of nuclear power?

Radioactive materials dispersed within the Earth’s structure, produce sufficient heat to prevent the inner core from cooling; however this important flux of heat is much less than solar heat. The dispersed and buried nature of the material overwhelmingly prevents the radioactivity from affecting organic life. Likewise the relatively small amounts used so beneficially in medicine and instrumentation may be controlled and used safely. However if the radioactive material has a long lifetime (perhaps many thousands of years) and is concentrated, as with a significant fraction of nuclear ores and wastes, biological organisms cannot continue in its presence.

Discarded radioactive material is likely to eventually ‘leak’ into the biosphere, to be absorbed and concentrated into food chains, with the higher forms of life accumulating radioactivity with subsequent danger of genetic harm. There is no known and certain way to safeguard radioactive waste from ultimately entering and harming the biosphere. To date, no form of containment is reliable against ingress of water over the thousands of years needed before the radioactivity becomes negligible.

When extracted, nuclear energy is used only for nuclear weapons and/or centralised electricity generation. Usually, as in the UK, these activities have been associated, so causing concern that weapons proliferation and terrorism may stem from nuclear power. In commercial terms, nuclear generated electricity is expensive and only undertaken with considerable government funding. Nuclear accidents are of major concern.

Nevertheless, a significant advantage of nuclear power is the significant abatement of CO2 and other emissions that might otherwise come from fossil fuels. Continued R&D on the political and technical difficulties and opportunities of nuclear power is justifiable, but only in relation to similar effort on fossil fuel and renewable energy. All such effort should be transparent and open to public scrutiny.

Discussion: What are the benefits and disbenefits of utilising nuclear ores? Have these factors changed over the last 20 years? Who needs to use nuclear power; when and how much?

Brown versus Green energy supply

Therefore it is helpful to make 2 classifications of energy supply

(1) brown energy, derived from the underground sources of nuclear ores and fossil fuels, and

(2) green energy, derived from ongoing energy supplies available in the natural environment.

One view from ecology is that Brown Energy sources are effectively ‘removed pollution’, so such fuels are, ab initio, already concentrated pollution. Clearly there is a duty to process and use such fuels efficiently with the minimum of adverse impacts (as is indeed is increasingly practised and the declared aim of ethical business). Nevertheless, the final emissions remain pollution, which is discharged wholly or in part into the air and water of our immediate environment. In contrast, Green Energy supplies at source are intrinsically non-polluting, since life depends upon them. Most categories of Green Energy technology, as explained below, do not emit pollution. Clearly, as we move from Brown to Green energy, the efficient use of present energy and the minimisation of emitted pollution is vital.

iconDiscussion: Where does the ‘natural environment’ start and stop? Is the human economy part of ‘nature’ or separate from it?

Renewable (Green) energy

Renewable energy is energy supplied from the natural and persistent flows of energy in the immediate environment. Obvious examples are sunshine that heats glasshouses and hydropower that generates electricity. Such technologies are called ‘renewables’ and are, by definition, sustainable. The generally benign ecological and environmental impacts of renewables contrasts with the adverse impacts of Brown Energy. By using Renewable Energy instead of Fossil Fuel Energy, buried carbon remains underground (its use is abated). Using carbon that is already circulating in the ecology of the biosphere, e.g. in plants, does not produce ‘extra carbon’ and so does not threaten long-term harm.

The total energy passing through our environment is enormous and predominantly arrives form the Sun; in one hour as much solar energy arrives as is used by the world economy in one year. In addition there are relatively smaller energy fluxes from tides and geothermal heat.

Sunshine transforms into most of the renewable supplies.

Thus sunshine:

  • heats the surface (solar water heaters, cookers, dryers, buildings);
  • causes wind (wind turbines and pumps) which in turn causes sea waves (wave energy devices);
  • evaporates water giving rainfall (hydropower);
  • powers photosynthesis in plants (biomass, biofuels, gasifiers, landfill gas) from light (photovoltaic electricity);
  • and, via plants, provides animals with food (hence biogas, sewage gas).

In addition tides (tidal power) and subterranean heat (geothermal power stations, heat pumps) give occasional and locally important energy supply possibilities. There is no shortage of renewable energy; the challenge is to develop, manufacture, and utilise the associated technology.

Left to rot, biomass decays to CO2 with slow heat emission. When burnt as fuel, a similar process occurs, but the heat can be used to substitute for Brown Energy, thus abating fossil CO2 emission. Therefore using sustained biomass for energy does not introduce extra carbon into the Atmosphere, as does the combustion of fossil fuels.

Compared with brown energy, renewables harness mild forms of energy and so the equipment is relatively large and visible. It tends to require expensive capital items, though the energy harnessed is free. The visual impact, in contrast to the ecological impact, can be considered adverse.

The more efficient the renewable energy systems, the smaller the equipment and therefore the cheaper the energy supplied; moreover, the visual impact is reduced. With Brown Energy, both the adverse impacts and the costs are reduced if the systems are efficient. Therefore, energy efficiency is of prime importance for both renewables and non-renewables.

iconDiscussion: What benefits do we have, or have we experienced, from forms of renewable energy?

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