The primary goal of renewable energy is to provide an energy service to our society at an acceptable price. But also the cost of this service has an impact on the local economy, environment and society in general. Compared with conventional solutions, development of renewable energy creates more jobs, strengthen the local economy, reduces environmental impact and reduces the desire on the stocks of energy and thus is a source of peace.
On the environmental point of view, renewable energies contribute to reducing emissions of greenhouse gases, reduce air pollution, water, soil and biosphere, limit the risk of accidents (oil spills, explosions …), and preserve the natural resource stocks. However, they can have local environmental impacts specific to each application and location (land, landscape, noise, changes in the ecosystem). In most cases, however, a local environmental assessment can implement appropriate solutions.
On the economic point of view, renewable energy guarantee a stable price of energy, much less sensitive to market fluctuations of fossil fuels and decrease our energy dependence. Under current conditions, the cost of renewable energy may be higher than that of fossil fuels. This additional cost, however small it may be a loss of competitiveness in the international market. But the government, it is important to keep in mind that the development of renewable energy is conducive to local economic development to the extent that the total expenditure related equipment or services (and employment). Unlike conventional systems using fossil fuels, where up to ¾ of the cost resulting from the purchase of imported fuels (natural gas, oil or coal).
From a social point of view, renewable energies are usually accompanied by the creation of sustainable jobs and insensitive to offshoring. Their decentralized nature also enables local companies to appropriate the production of energy for their needs, while providing a potential shift in economic activity. In the field of wood energy, for example, showed that the wood industries can generate from 10 to 28 times more direct jobs than oil sector, according to their degree of mechanization.
A large-scale, energy independence and reduce international tensions can solidarity between peoples.
Usually when we talk about renewable energy, there is an overview of eight main sectors, namely, wind energy, photovoltaic, solar thermal, small hydro, biogas, solid biomass, biofuels and geothermal . While there are other forms of renewable energy coming to complete the task, and they are considered emerging industries.
In this report, we will be interested in these courses rather old, experiencing a revival due to the ‘decline’ costs, the depletion of fossil fuels, improved technologies and policies for the environment.
These emerging networks are saying that we chose the name of Postclassic, ocean energy concern called again the Thalasso-Energy and the Helio-thermodynamic and we will try to end a look at other trends exploitation of new resources or to improve the technology of the old energy sources (especially the sun) to be a contributory renewable energy in sustainable development.
2. The Thalasso-Energy
In a context of scarcity of fossil fuels and taking into account environmental issues, marine energy, also known as thalasso-energy, certainly have a future in the global energy landscape. They must indeed be conjugated in the plural because the energy sector covers the operation of all energy flows specifically provided by the seas and oceans, waves, tidal currents, ocean currents, osmotic pressure (the difference salinity of ocean currents can create a flow that will be used to generate electricity), and the thermal gradient.
Today, it is the tidal currents and waves (waves) that for the majority of efforts, both in research and development (R & D) in experimental implementation.
The converters can transform the flows of electricity are of astonishing diversity: there are over thirty. The most effective solutions should be required as and when the maturing of the industry.
2.1. The tidal energy:
The strength of the sea is a valuable resource to generate energy. Indeed, the currents are a fabulous contrast to the energy winds are constant and predictable. It is a decisive advantage over other intermittent renewable energy.
There are two major types of currents: the currents located more or less off the coast and the tidal (or tidal) which are found in river mouths and near the coast.
To capture this energy, place the propellers or turbines in the axis of the motorways of the sea, this is called the tidal (There are also names as well as wind hydrohélienne underwater).
Favorable sites are coastal sites for the inking of the propellers. There are two possibilities to fix the turbines. Or propellers are mounted on vertical supports resting on the bottom (which looks like the wind) or is attached by cables together a generator / turbine that floats at mid-depth to capture the most energy of the current and not interfere with navigation surface.
There are two areas of application of the turbine to produce energy-spa:
Offshore: for the exploitation of deep sea currents (at least 40m deep, the flow is 1.5 to 2 m / s), whose powers are greater than tens of Mega Watts;
Coastal: using tidal currents (at least 25m deep, and flows 12 to 18 km / h), the powers are between one and several Mega Watt.
In such extreme conditions, it is difficult or impossible to install and maintain energy converters with divers or underwater. Thus the small turbines are mechanisms for the turbines back to the air in case of breakdown or for works of maintenance. Maintenance is done so on the surface, removing the need for underwater costly and dangerous.
The main problem is caused by corrosion of seawater It has, however, anti-rust coatings and high performance technology that dream could become reality in no time!
The potential impacts of these sensors are not well known, and concern particularly the fishermen who work in areas of interest under certain assumptions, the turbines would create turbulence, preventing the deposition of sediment and thus the development of the flora, and creating long-term dead zone. The currents are accelerated and small animals would be difficult to move without providing substantial effort. The turbines could also throw in their blades a few marine animals that have not stood the suction created by the turbine.
According to other assumptions, the capture of energy currents slowed the flow velocity in the axis of the turbine which causes currents bypass the fish follow (venturi This is natural when the water passes along a rock, the fish avoid obstacles along the lines of higher speeds). On the other hand, the rotation of the blades is limited by the speed of cavitation at the blade tip, it has less than 10 m / s. And the blades of large turbines that can turn rate of 15 revolutions per minute and their effects would be limited to turbulence at the exit of the turbine. The sediment does not settle around the turbine avoid siltation and facilitate maintenance. In addition, a speed low enough not disturb the fish.
We must also consider that the preferential sites for the installation of turbines are sites of high to very high currents, where conditions are unfavorable to the development of the fauna and flora. The charts show that these areas are exclusively composed of rock or gravel of large caliber.
The environmental impact of tidal energy is currently being investigated in many research and development in Europe in the English Channel, North Sea and Baltic Sea.
According to industry experts, the cost of electricity from turbines would be equivalent to that of wind (one euro watt) and significantly lower than nuclear (about 1.4 euro watt, according to the few available estimates). Productivity hydrohélienne technology is superior to that of wind turbines. The production quality allows easier operation. The visual impact is not commensurate with the wind, and social acceptance would be greatly facilitated.
2.2. Wave energy and wave:
The waves at the sea surface are created by the wind. The amount of energy generated is low (1 W / m² / year, or 200 times less than solar energy directly). But as the waves move in a very efficient, we can hope to recover most of the energy created on large marine surfaces, installing sensors along the coast. Theoretically recoverable power is estimated at 50 kilowatts per meter of coastline. The problem is that the energy tends to dissipate when approaching the coast: for 50 kW / m at 20 km from the coast, it may fall to only 20 kW / m to 1 km of it. We must find a compromise between the distance from the coast (the cost increase when we move away) and the recoverable energy (which decreases when one comes close). Wave energy is not the same everywhere (between 40 ° and 60 ° latitude, wave power is maximum), and varies with the seasons.
Numerous devices have been tried with two broad categories: coastal systems and devices at sea (offshore). The first use the breaking waves, the latter using variations of sea level during the passage of the swell.
The former are easy to build and maintain but their performance is significantly worse than devices that operate off-shore waves more powerful and more regular.
As an illustration, we give here below three types of devices to recover energy from the waves:
Buoys in motion, up, down and sway with the waves. Anchored on the bottom, their movement drives a piston, sucking seawater through a turbine or compressed air or oil will run an engine;
Oscillating columns: at the end of the race, the waves come in a box where they compress the trapped air. This compressed air drives a turbine;
The overflow channel: the waves rush in a channel that narrows more and more. They swell and spill over the dam of a reservoir that fills slowly. The water tank back to the sea through a turbine that spins.
Between 1970 and about 1990, countries such as Japan, Norway, England built the first prototypes. Since then, India, Sweden, Spain, Ireland, Denmark, Greece have joined them and after a few setbacks, the search is distributed from the 90’s.
Plans are well underway to create a capacity of 10MW in the next 5 years. Advanced prospects are risky but many companies already have plans to install several MW / year. Assessments of market potential have been made which show that the contribution of wave energy could exceed 2000TWh/an which is the same order of magnitude as the energy of large hydro in the world.
3. The Helio-thermodynamics
Long locked in its development, the thermodynamic solar-industry is now undergoing a revival thanks to declining costs, more efficient technologies and policies are sensitive to environmental issues.
Technically, the helio-thermodynamics is to focus the sunlight to heat a fluid to a temperature sufficient to generate electricity.
The exploitation of solar energy in this way requires sunlight conditions that are specific to only certain parts of the world. The best areas are the Sahara, the deserts of Australia or California, but also the Mediterranean areas such as Spain, Italy, occupied Palestine or North Africa.
It is considered that plants are only conceivable in the regions of the world where the direct solar radiation exceeds 1900 kWh / m² / year, and where the atmospheric transparency is good (so in arid and mountainous).
The three main types of solar power plants are distinguished mainly by how you focus the sun’s rays:
Parabolic trough collectors: they are parallel rows of long semi-cylindrical mirrors (a “U”), which rotate around a horizontal axis to follow the path of the sun. The sunlight is concentrated on a horizontal tube, which circulates the coolant to be used to transport heat to the plant itself. The fluid temperature can rise to 500 ° C. This type of plant is the most common.
The power towers: A set of movable mirrors (heliostats) located on the ground all the concentrated solar radiation precisely at the same point: a boiler at the top of a tower. The temperature thus obtained is 600 ° C.
The parabolic collectors: They have the same shape as our satellite dishes, but bigger! The parables have a diameter of from 10 to 20 m and are adjustable. Solar radiation is focused on the focal length of the parabola, where a mini-power plant. The temperature reached 800 ° C. obtained
These solar only works during the day. To ensure a continuous operation, you can store the hot coolant that will be used at night, or burn traditional fuels (gas, coal …) once the sun goes down. In addition they can not be installed anywhere, so they are profitable, you must:
– Lots of sun for most of the year;
– Good transparency of the air (and therefore in an unpolluted area);
– Lots of free space to install the mirrors and parables (2 ha / MW);
– A flat area if possible (to save the coolant pump);
– A grid not too distant to make electricity.
The United States, the country home of the industry, now concentrated almost all thermodynamic solar-power installed worldwide, with 355 MW. Four U.S. states are particularly involved in the development of new projects with 64 MW Nevada, California, where two contracts were signed to develop 800 MW between 2008 and 2011, Arizona and New Mexico.
But the revival of the industry is now driven by Spain, which has set a target of 500 MW for 2010.
The side of Germany, several industrial and engineering firms working on techniques to be developed in the South and is participating in the parabolic collector EuroDish, seven copies of 10 kW operating in Europe and India. Ten solar thermal power projects are being studied around the world (Iran, South Africa, Egypt, occupied Palestine, Morocco …). In France, the sector continues to mobilize actors even if all sites developed in the early 80’s have now been renovated and research centers.
4. Postclassic ideas!
4.1. Solar Tower:
The tour will start at the center of a structure made of glass or plastic with an area of 350 hectares, acting as a solar collector. The heated air at the collector is transferred to the interior of the tower where it drives turbines connected to generators that produce electricity. Estimated the power generated by such a facility of 750m to reach 40 MW and will cover the electricity demand of 120,000 people. It will provide the energy equivalent of 140,000 barrels of oil and prevent the emission into the atmosphere of 78,000 tons of carbon dioxide.
The field-collector may also be used as a greenhouse. An area of 250 hectares will be devoted to growing fruit and vegetables.
Telecommunication systems and monitoring against fire will be mounted at the top of the tower. A watchtower and a public access are also planned and converted the building into a tourist attraction.
The initial budget for this project amounts to 240 million euros. The construction of the tower for three years.
The solar technology has already proven itself in Spain in 1982, where a tower of 195 meters was built in Manzanares (Madrid). She had a field collector with a diameter of 240 meters and was capable of providing 50 kW