Jumat, 27 November 2009

Fisika Energi

Renewable technologies

There are many forms and types of renewables technology; most are now established and with rapidly increasing rates of commercial implementation, often at 30 to 40% growth per year. However, even at these rates, it will be 10 to 20 years before renewables become dominant supplies.

Renewables are classified by immediate source, and then by technology and purpose. The energy is used for heat, machines, electricity generation and transport. The variability of most renewables requires integration and storage, including amalgamation using electricity and heat grids.

The following is an approximate guide for use in the UK, with examples orientated to meaningful household use, either on site or via the purchase of electricity from a ‘Green Electricity’ Supplier.

Benefit in the UK is indicated by the number of
This is only general guidance however, since each place has a distinctive environment and opportunities, e.g. with a suitable stream, hydroelectricity can be the best choice, but few places have this.)

Solar heating

Sunshine for heat (a) absorbed directly e.g. passive solar buildings at zero to 10% extra cost of new-build, and opportunistically for building conversions and extensions; saving 50% of conventional heating, (b) transmitted to use e.g. active solar water heaters using ‘solar thermal panels’ at about £2,000 per house, so reducing conventional water heating by 50% in the UK.

So: consider adding a solar water heater to the cost of your home; let sunshine enter your otherwise insulated house.

Solar electricity

Sunshine generating electricity (a) immediately e.g. photovoltaic solar modules or panels that interconnect with the grid or use battery storage, at £15,000 per house for 50% annual electricity, (b) by machines using heat from ‘solar thermal’ devices e.g. concentrating mirrors raising steam, but not sensible in the UK with cloudy skies.

So: plush buildings can be faced with designer solar panels.

Wind power

This is electricity from wind turbines. The industry is growing rapidly at 30 to 40% per year; each year world-wide there is more new wind power than nuclear or traditional coal power. Wind-electricity costs are less than from nuclear, oil or coal, and about equal to gas, even without considering the abatement benefits of CO2 and other pollution. Controversial impacts are mostly visual and sometimes noise. Most machines are large, perhaps to 100 m in diameter and commercially grid-connected. Siting is both on land and offshore at sea. Small machines, diameter 1 to 10 m, may be used for autonomous electricity supply with batteries, perhaps integrated with other renewables. Capital costs are about £700/kW for large machines, and more for small machines.

So: make a conscious decision about the electricity you buy.


This is the generic name for dead and harvested biological matter and its products. There are many opportunities, often complex, for both energy and fertilising nutrients. The use of otherwise waste material, e.g. sewage, gives a cost advantage. Since humans always produce waste, such energy supplies may be considered ‘renewable’. However care is needed to optimise systems and prevent inadvertent pollution. Specific examples are below.

Fire wood

There is a surprising surplus of fallen, waste and scrap wood that can be used dry for domestic, commercial and industrial heating. Purpose-designed stoves and boilers are essential for serious use. Fuel wood and waste is unlikely to be sufficiently ‘smokeless’ in towns and cities. In the country, up to 100% of water and building heat can be supplied, but the supporting effort is significant.

So: if permitted, collect and use firewood efficiently.

Urban waste

On average, at least 5% of a towns energy supply can come from the combustion of local organic wastes, e.g. from ‘rubbish’ collection, industry and agriculture. District heating, combined heat and power, energy efficient buildings and environmental taxes enable such strategies to be successful (as in Denmark and Sweden). However, (i) every opportunity should be taken to recycle actual parts and materials before resorting to combustion, (ii) high quality combustion is needed to minimise pollution.

So: vote for councillors who promote recycling and high-tech use of wastes.

Landfill gas

Purpose built rubbish-pits produce a combustible mix of methane and other gases that may fuel electricity generation at megawatt scale and/or provide commercial process heat. Sewage gas is similar. Likewise Biogas can be collected from animal manure. All such processes support the proper control and treatment of otherwise unhealthy wastes.

So: persuade your sewage company to recover the gas.

Energy crops

Plants may be harvested commercially, dried and then burnt for heat. The heat is used immediately or to generate electricity, hopefully combined with the use of the rejected heat. Partial combustion, in a gasifier, produces a combustible gas to be used as a convenient fuel. High quality equipment minimises smoke emission and ensures optimum combustion. Crop oils, e.g. rape seed, are a basis for transport biofuels at national scale.

So: realise that agriculture provides more than food.


Falling water turns a turbine for electricity generation. (a) Large systems have stored water behind dams that inundates valleys, e.g. for 10% of Scotland’s electricity; (b) ‘Run of the river’ systems without storage have less impact, but are small and less continuous, e.g. electricity generation at some old mill sites.

So: balance human impact and conservation.

Wave power

This is electricity from sea waves. The energy travels in large, long-wavelength, Atlantic sea-waves averages about 50 kW/m, and then reduces as the waves become less extreme near to shore. After many years of ongoing research, commercial devices are now operating into the grid and being built in Scotland. Early machines are relatively small (about 150 kW peak electricity), but this capacity will increase with experience.

So: vote for parliamentary candidates favouring research and development of new renewable energy sources.


This is heat from the earth. Hot aquifers, as in Southampton and Paris, may be tapped for district heating, and some for powering turbines for electricity production, as in areas of Italy, New Zealand and California. In principle, but not yet in practice, heat can be extracted from large volumes of granite.

Tidal range

This is hydroelectricity from the rise and fall of tidal height, as water flows through a tidal barrier. About 15% of UK electricity could come from the tidal range power of the Severn Estuary, and lesser amounts from other estuaries with such enhanced tidal range. However the consequent reduction of mud flats, without compensation, would harm wading and migratory birds. Co-operative benefits can be a road across the barrier, flood prevention, enhanced fisheries and leisure facilities.

Tidal flow currents

This is similar to low-head hydro, but commercially not proven. Medium and small scale developments with low impact.

iconDiscussion: What forms of renewable energy could we implement (I) at home, (ii) at work, (iii) in your locality?

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