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Energy sources (FR)

Fossil fuels

It is only since the start of the industrial revolution (ca 1750) that there has been ever increasing use of fossil fuels as these are more concentrated that renewable energy sources. Fossil fuels such as oil, gas and coal are characterised as non-renewable because they were created over very long time periods compared with our current rate of use. In creating useful energy from the combustion of these fuels, a colourless gas called carbon dioxide is created which, being lighter than air, rises and congregates in the upper atmosphere.

Carbon dioxide is one of the six greenhouse gases whose characteristic is that they are able to absorb the heat radiated from the earth’s surface so creating global warming. The world has become very dependent upon fossil fuels as they are easy to extract, transport and utilise and are not dependent upon sunlight, directly or indirectly. However, our increasing use of energy and growing population worldwide has created another global concern which is the finite size of these resources.

Peak oil and gas

All the major models of oil production predict that the world’s oil supply will peak by 2025 and some models predict that the supply has already peaked (Figure 1).

Figure 1: Oil and gas profiles

(Source Colin Campbell)

Switching from oil to gas will only be a short term option as the world’s supply of gas is likely to peak within 20 years. What is of greatest concern is not when the oil or gas peaks occur, but how the world will manage with ever decreasing amounts of liquid or gaseous hydrocarbons. In the accompanying figure, it can be seen that the decline is predicted to vary from between 2% and 7% per year.

Even at the lowest rate of decline, the mismatch between demand and supply is such that it is important to start now to switch from oil to other energy sources preferably renewable as soon as possible. Such a change in energy source will help to limit climate change.

Figure 2 below shows the predictions of the various oil production models. These are summarised in the graph which shows not only the predicted date of the oil peak but the subsequent rate of decline in millions of barrels of oil per day.

Figure 2: Summary of various oil production models

(Source ERC, UK)

Further reading Global oil depletion – an assessment of the evidence for a near-term peak in global oil production, UK Energy Research Centre report August 2009

Renewable energy sources

The sun is the ultimate source of most of our energy either directly through light and heat or indirectly through wind and waves. In addition there are tides created by the rotation of the moon around the earth or geothermal heating from the cooling of the earth’s core. The other source of energy is the conversion of light by photosynthesis into nutrients to enable the growth of plants and trees generally known as biomass.

These sources are renewable, abundant and inexhaustible. Their usage creates little or no pollutants and could be generated or produced on a micro-scale at point of use saving transmission and distribution losses. They have met our energy needs in previous eras and there is no reason why they could not meet our needs today.

The challenge will be to adapt our lifestyle to their variation during the day and to the variation between summer and winter. In this thermal storage and that of electricity will help to overcome the mismatch between supply and demand.

Renewable heating and cooling

The three principal sources of renewable heating and cooling are solar thermal, heat pumps and biomass. Whilst solar thermal panels generally provide only domestic hot water, the other two sources can provide heat for both hot water and for space heating.

Solar thermal panels are generally mounted on the roofs of buildings and should be orientated to have direct sunlight for most of the day. They could supply all of a family’s hot water needs in the summer and up to 40% during the winter.

[ink to the solar thermal page on the KITH website]

Heat pumps do not produce heat, but concentrate low grade heat present in the ground, air or water and convert it into useful heat. Heat pump systems vary in size from small systems for individual homes to large systems for schools, commercial buildings and hospitals. Heat pumps are reversible and so can extract heat from building during the summer.

[link to the heat pump page on the KITH website]

Biomass boilers generally use wood pellets which can be gravity fed or blown into the boiler. Space of 1 to 2 cubic metres is required for storage. The alternative is wood burning stoves which require a source of logs most likely from a nearby forest.

[link to the biomass page on the KITH website]

Renewable electricity
Solar cells and wind turbines are the principal sources of renewable electricity. Solar cells, generally in the form of photovoltaic modules or tiles, are usually mounted on the roofs of buildings that have a suitable south facing orientation, or on a flat roof with a similar orientation. The electricity generated can be used by the occupants and any surplus exported via the electricity grid; conversely electricity can be obtained form the grid if demand exceeds supply.

[link to the photovoltaic systems page on the KITH website]

Wind turbines generate electricity by the movement of air turning the blades to which the shaft of a generator is attached. Large turbines can supply electricity to communities whilst small sized turbines and can be mounted on a pole or on top on ones roof.

[link to the wind turbine on the KITH website]
[link to encouraging renewable energy sources]

Centralised versus dispersed energy production
One hundred years ago all energy production was localised – electricity was generated at point of use primarily by wind turbines whilst oil and paraffin was available in containers. Windmills or watermills were also used to grind wheat to produce flour.

Windmill Watermill

Today most of our energy production is centralised with large electrical power stations situated on or near coal fields or near coal fields or near gas pipelines. This energy is then transmitted and distributed to our homes by electrical cables or pipelines. Whilst this is the most efficient form of generation and supply of energy supplied by fossil fuels, it does require a large infrastructure and leads to substantial losses of the order of 20%.

The reintroduction and uptake of renewable energy sources is most efficiently done at point of use as such sources are widespread and abundant. The losses in transmission and distribution can then be avoided. The electricity grid and pipe lines then perform a different role in which they supply energy if insufficient renewable energy is available locally or transfer energy if supply exceeds demand. In particular the electrical grid lines can link local sources together so that lack of supply in one area can be met by supplies from another area where the wind is blowing or the sun is shining.

In the longer term, we may need to adapt our lifestyle so that we work when energy is available and so this may mean going to school some days and staying at home on other days when no renewable energy is available. This could be quite an enjoyable experience.

[link to CwC activity #4]



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