Renewable energy

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Introduction to renewable energy.

  1. Hydroelectricity
    1. Hydroelectric dams
    2. Three gorges dam
    3. Tidal power stations
    4. Ocean thermal energy
    5. Marine current turbine
  2. Biomass
    1. World production
    2. Ethanol and biodiesel
  3. Wind power
  4. Solar
  5. Geothermal


Hydroelectricity is the fourth power used in the world covering 16 % world electricity production.


Two kinds of dams:

- power stations, said gravity stations, for which inflows into the reserve are solely gravity water
- pumped Storage Power Stations (PSPS), also called pumped reserve hydraulic power plants, for which an artificial device enables to pump water from a lower basin to a higher basin. These often include a gravity part.

Hydroelectric power principle:

Hydroelectric power or hydroelectricity is an electric power obtained by converting hydraulic power of different water flows (streams, rivers, waterfalls, sea currents.). Kinetic power of running water is transformed into mechanichal power by a turbine, then into electric power by an alternating current generator.

hydroelectricite hydroelectricity hydraulique energie

These power plants have two basins, a higher basin and a lower basin. A reversible hydroelectric machine is placed between them. The hydraulic part may operate as well as a pump as a turbine and the electric part as well as an engine as an alternating current generator (synchronous machine). In accumulation mode, the machine uses the power supplied to make water from lower basin to arise to the higher basin. And in production mode, the machine converts water gravitational potential power into electricity.

Turkey, Brazil and South East Asia are the main electricity producers via a hydroelectric system.

I take the example of the famous Three Gorges Dam in China.

Three gorges dam:

Yang-Tse-Jiang hydrographic basin occupies almost 20 % China territory.

bassin hydrographique hydrographic basin

The three Gorges dam construction started in 1993. It has three functions : to regulate stream flow against floods, to produce power, to allow a more regular navigation between Shanghai and Chong Qing.

The three Gorges on Yang-Tse are called Gutang, Wu and Xiling.

The only Yang-Tse basin concentrates half Chinese hydroelectric potential.

The dam is 2.5 kilometers long and 185 meters high.

It is composed of locks to cross it and of electric power stations downstream. The dam is associated with two hydroelectric power stations, one on the right bank of the stream with 12 turbine-alternators and the other one on the left bank with 14 turbine-alternators. Each turbine develops 700 MegaWatt, i.e. 20 nuclear power plants equivalent.

In 2015, power plants will supply with almost 10 % Chinese global electricity consumption, what should replace the annual combustion equivalent to 50 million tons coal in power stations.

Furthermore, the dam enables to welcome ships having a tonnage over 3 000 tons, with the possibility of reaching 10 000 tons.

Yang-Tse and its tributary streams represent 80 % Chinese navigable potential. It is a central artery with harbors handling 30 % water tonnage transported each year in China.

These dams represent the most important ship conveyor in the world (ship capacity 10 000 tons).

In 2003, over 1 600 dams were in construction in the world.

Then there are tidal power stations in the broad sense of the term.

- tidal power stations, in the broad sense of the term, which use sea movement including alternate flood tides (tidal power in the strict sense of the word), permanent sea currents (marine current turbines in the strict sense of the word) or wave movement.

Tides kinetic power:

Seas and oceans water can be used to produce electricity.

Two methods may be used:

- wave application, where tide power is used
- heat application, where differences in water temperatures at different depths are used

Tidal power stations:

Tidal power is issued from water movements created by tides, caused by the joint effect of Moon and Sun gravitational forces. It is used either as potential power, or by elevation of the sea level, or as kinetic power, tide currents.

energie maremotrice tidal power mecanism

As you know, the tide phenomenon is due to the differential of rotational delay between Earth (24 hours) and Moon (28 days) which is then stationary compared to it. The result is that the terrestrial globe turns inside a sea water globe lengthened in both ways by lunar attraction. This rotating power can be used, causing the effect (in very tiny proportions, although definite) of slowing down Earth and expelling Moon for safekeeping reasons of the kinetic moment of the bundle.

In a simple way, the so-called tidal power then constitutes a recovery of the kinetic power coming from Earth rotation.

The order of magnitude of the power naturally dissipated annually by tides is estimated at 22 000 TWh, i.e. a combustion equivalent reaching less than 2 Gtep. This figure has to be compared with the world energy consumption, amounting to 10 Gtep.

As only one fraction of this power is recoverable, the tidal power will be able to contribute for the future in a low part only, to meet world requirements.

Economy experts call into question the cost related to this kind of production. The estimated cost of the electricity produced by these power stations is expected between 4.7 and 12 pence/kWh, what is more onerous than nuclear or wind powers.

Ocean thermal energy:

Ocean Thermal Energy (OTE) or Ocean Thermal Energy Conversion (OTEC) is produced by operating the temperature difference between ocean surface waters and deep waters.

On the surface, thanks to solar power, the water temperature is high (it may exceed 25°C in inter-tropical zone). And deeply, not having solar radiation, the water is cold (approx 2-4°C). Cold layers do not mix with warm layers. Indeed, the water density increases as temperature lowers down, what prevents deep waters to mix and to warm up. This temperature difference may be operated by a solar powered machine, as this latter requires a cold source and a warm source to produce power.

energie marethermique ocean thermal energy

This energy is only exploitable in inter-tropical zones. Elsewhere, the temperature difference between the surface and the floor is not sufficient to obtain a sufficient output and then a sufficient power to pump the cold water in deep and feed a solar thermal machine. These facilities are only possible in a zone covering from Tropic of Cancer to Tropic of Capricorn, i.e. between 30 and -30° latitude.

OTE (Ocean Thermal Energy) produces power thanks to a working fluid (sea water, ammonia (NH3) or another fluid, the dew-point of which is approx 4°C). This fluid switches from liquid state to steam state in the evaporator by contact with warm water taken out of the surface. The pressure produced by steam goes through a turbo-generator to operate a turbine and produce electricity. After the gas has lost its pressure, it goes into a condenser to go back to the liquid state by contact with cold water taken out of the floor.

OTE operates with a temperature differential of 20°C. The higher the temperature differential is, the higher the production is. By getting down to the floor, colder water is taken out and equal volume production increases.

The theoretical maximum output is really low compared to the traditional output of solar thermal machines (40 % for a natural gas turbine). Moreover, this latter does not take into account the work necessary for pumping deep waters.

Output varies according to the plant power : the more powerful it is, the higher the output is and this also depends on the cycle used. The output will be highest for a maximum temperature difference between the surface and the floor.

Let me take as an example NELHA organization in Hawaii. Nelha owns an immense site equipped with 3 types of canalizations : one surface canalization and two deep canalizations. Concerning the surface canalizations, they are located in a perimeter of 180 meters away from coasts, 13.5 meters deep. They are placed at an accurate distance from sea floor so that sand, corals and aquatic life are not sucked off. Here, their canalizations were placed 13.5 meters deep.

Concerning deep canalizations, two exist, a recent one and an old one. The old canalization pumped 6°C water by 600 meters deep. And nowadays, OTE from Hawaii pumps 4°C water by 900 meters deep from 55 assembled pipes.

Marine current turbine power:

A marine current turbine (or underwater, or placed on water and half submerged) is a turbine which uses sea currents or streams kinetic power, such as a wind power plant uses air kinetic power.

The marine current turbine enables the transformation of hydraulic power into mechanical power, which is then transformed into electrical power by an alternator.

marine current turbine power energie hydrolienne

Marine current turbine advantages are due to the fact that they are far smaller than wind power plants for an equal power. This is due to the water density (approx 800 times higher than that of air). Moreover, marine currents are predicted and allow to evaluate accurately the electricity production. Potentials of marine currents are very high, the French company EDF (Electricity of France) believes that 3 GW (i.e. approx 2 PWR type nuclear reactors) can be installed close to French coasts. The marine current turbine power uses a renewable energy (marine current) and does not pollute, in terms of wastes issued from combustion, such as CO2 or radioactive wastes. However, these facilities cost a lot of money to be installed and to be maintained.

The European potential of marine current turbine energy is evaluated at approx 12.5 GW which might produce 48 TWh annually, what represents the capacity of three recent power generating plants.

world oil consumption country countries


Biomass is the sixth energy used in the world, behind nuclear energy.

World production:

world biomass consumption energy

Ester production:

world ester production

Ethanol production:

world ethanol production

Oil substitutes : the alternative

The etymology of “biocarburant” (oil substitute) comes from the Greek language, “bio” means life, living, and “carbo” means coal in Latin. So, biofuel comes from biomass, having then a vegetal origin. So, by chemical processes, fuel is produced from organic materials.

Two main branches are presently used :

Ethanol : it is obtained from sugar plants, such as sugar cane or beet, or from starch extracted from wheat, rye, potato and mainly corn ; also from fibrous materials (vegetal wastes or wood extracts). Following fermentation, ethanol is obtained, to be used pure or mixed in variable proportions with regular gasoline.

Biodiesel : it is obtained from oil contained in plants, such as sunflower, colza, soya, but mainly from palm fruit from which palm oil is extracted. The oil obtained is transformed chemically with alcohols and may then be used pure or mixed with conventional diesel oil. This gives then biodiesel, also called diester (in France), a biodegradable and non-toxic fuel.

Since a few years, oil substitute world production grows in a considerable way (15 %/year since 2002).

biocarburant croissance biodiesel growth

Producing countries:

United States:

The United States are the first ethanol world producer, mainly produced from corn (produced in Middle West “corn belt”). Approx 150 refining plants transform corn into ethanol in the United States.

raffinerie ethanol USA refinery

The country launched American Clean Energy and Security Act (ACES) in 2009, aiming at promoting agrofuel use, a plan similar to that of European Union Emission trading Scheme (EU ETS). Since then, agrofuel production keeps growing in the United States (12 billion gallons in 2010). In spite of these efforts, biofuel only represents 1.5 % energy used in road transports.


Europe occupies the third position (United States first, Brazil second), and the first position if we consider the only biodiesel production (thanks to Germany and to France). Europe then enjoyed a real agrofuel increase between 2004 and 2006.

production agrocarburant europe agrofuel consumption

Indeed, the European Parliament voted for a calendar including the introduction of clean fuel in transport in a ratio of 5.75 % in 2010, 8 % in 2015 and 10 % in 2020, as you can note in the hereunder diagram.

consommation europe carburant propre consumption biofuel

In 2009, the European average is 2 % (ratios vary much according to the States). Let us know that, since 2007, Germany came first biodiesel world producer and France came second. England and Sweden are agrofuel consumers but very little producers. So, they import it. European government also implemented a tax policy very profitable to biofuel in order to develop it at a maximum in Europe. For example, in Sweden, generalization of E85 gasoline in petrol stations makes increase from 150 stations in 2006 to 1000 in 2008 and multifuel cars (said flex-fuel) are exempt from taxation and insurance is cheaper. But Sweden has to import 75 % its ethanol consumption.

As a summary, there is an effort made by more and more states to get out of fossil energy dependence. This aims at limiting greenhouse gas. Actually, with ethanol, 60 % greenhouse gas emissions are reduced for one liter gasoline.

However, I specify that, to produce (in distilleries) this biofuel, power is necessary (gas for ethanol). Obviously, this power releases CO2. There is a paradox as that is what we like to avoid. Let us also note that corn transformation requires a great quantity of herbicides and nitrogenous fertilizers, what results, in the future, in high soil pollution. So, agrofuel production has an impact on the food production by crops assignment. The conflict is clear, because cereal quote used to produce agrofuel is indexed according to oil quote.

indexation softs petrole biocarburant biofuel index

This problem shows that farmers make more profits in cultivating their fields to make biofuel than to make food products.

All these problems incited to create new types of biofuel from lumber, straw, forest residues, all that giving what is called cellulose ethanol.

At last, there are oil companies, as British Petroleum (BP), which carry out research on biofuel produced from microalgae.

Wind power

Wind power energy is the 7th energy used in the world. It represents 0.5 % world electricity.

In 2008, Europe remains the first producer (mainly thanks to Germany and Spain).

wind power world production

The output of wind power plants doubled in 20 years.

In 2050, the wind power area will be multiplied by 10-50 times. This energy is more and more used.


Solar energy is the 8th energy used in the world. Solar energy represents 0.1 % world electricity.

Photovoltaic panel area reached 142 million square meters in the world in 2006.

In Europe, from 2006 till 2008, it rose from 19 to 26 million square meters. In Europe, Germany is the country having most counted on this new energy, but at world level China is far before everybody.

world solar energy production

world solar energy production export


Geothermal energy is the 9th energy used in the world with a total consumption reaching 1 %.

In 2007, the world production remains marginal : 8.5 million megawatt/hr.

The main producing countries are the United States, Mexico and Indonesia, Italy, Japan and New Zealand, Iceland, Australia and South Korea. These countries mine a resource which is present anywhere on the planet.

world solar energy production panel

This source is mainly present in the USA, Greenland, China and Japan where it represents over 4000 MW/hr. Norway, France, Russia, Mexico, among others, which have resources over 1000 MW/hr. Australia, Brazil, Spain, India, United Kingdom, and others which mine a resource under 100 MW/hr.

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