Renewable energies (ENR), the future of energy storage
Producing electricity in an infinite manner is possible thanks to renewable energies (ENR ). This has become a major issue today. But how can we use the sun, water or wind to generate energy in a stable manner? Here are some explanations to better understand how renewable energies are the future of electricity and our country's energy transition, but knowing how to store them to use them better.
What are the renewable energy sources?
For a long time, man has used what we call “stock” energies. These are deposits of fossil fuels such as oil, coal, gas and even uranium. Not only are these raw materials not inexhaustible but their use generates pollution, unlike “flow” energies.
There are 5 renewable energies (ENR). They all have in common that they use inexhaustible resources and generate very little pollution. They are all receiving special attention from the French and interesting developments. They are sources of great hope for the energy production of our country.
Wind energy: the force of the wind
Wind energy is partly due to solar energy. In fact, wind appears under the effect of temperature and pressure differences. But to transform the kinetic energy of the wind into mechanical energy, which is itself converted into electricity, we need a wind turbine.
How does a wind turbine work?
It is thanks to the force exerted by the wind on the propeller blades that wind energy is produced. The rotor, which is the element that holds the blades, rotates around a horizontal axis. It can be made up of two or three blades whose diameter determines the power of energy production. When the blades rotate, they drive a generator that produces electricity. This device most often includes a multiplier between the propeller and the electric generator. The system works by ensuring that the propeller is always facing the wind which must blow between 10 and 90 km/h.
The rotor, propeller and multiplier constitute the nacelle which is installed at the top of a mast. It measures between 50 and 100 meters high.
The electricity produced by the generator is carried by cables to the transformer.
Onshore wind turbines and off-shore wind turbines
The first wind turbines installed in France to produce electricity date from the 1970s. These were land-based wind farms. We also talk about wind farms.
Alongside onshore wind farms, off-shore wind turbines are developing. They are installed at sea where the winds are more constant and also stronger.
They can be installed or floating, even if the latter solution is more expensive.
Advantages and limitations of wind energy
Wind turbines produce energy with a resource that is inexhaustible and has a low impact on the environment, without greenhouse gases.
Despite this, the installation of wind turbines is subject to technical and societal constraints. Indeed, the installation of wind farms is generally poorly received by residents and often gives rise to complaints concerning visual and noise pollution. The maximum power rarely exceeds 3 to 4 MW for onshore wind turbines.
Off-shore wind turbines can provide double the energy and this can be problematic for integrating it into the electricity grid.
Electricity storage could be a means of ensuring the continuity of distribution of this energy with intermittent production. This provides a significant advantage to wind energy which could continue to grow with this new argument.
Water provides hydraulic energy
It is the most important source of renewable energy in France. Hydroelectricity has been exploited since the end of the 19th century , thanks to hydraulic power stations. Using the power of water is a technique known since the beginning of electricity with water mills. Hydraulic power plants are designed on the same concept with a turbine and an electric generator.
Advantages and limitations of hydraulic energy
There are more than 2,500 hydroelectric plants of all sizes throughout the country. It is a known technology, which is largely mastered. It also has the advantage of not emitting greenhouse gases, while producing a large quantity of electricity. Its management is also much more flexible than the others. There is no need to wait for the sun or the wind to produce electricity in a very safe way.
But there are of course limits to hydraulic production. The first is obvious, it is the cost of the investment: it is very important.
What is also not negligible are the environmental impacts of hydraulic power plants. The construction disrupts the entire ecosystem around the dam, not forgetting the nearby power line networks. Moreover, the number of sites no longer changes because the particular conditions for installing a power plant are very specific. There are not many possibilities left on French territory.
Finally, climatic hazards can also disrupt the performance of hydraulic energy production. Drought should not be neglected, especially in recent years when we have noticed more climate changes. The storage of electricity from hydraulic sources makes it possible to compensate for the drop in production.
Photovoltaic energy from the sun
It was Alexandre Edmond Becquerel who discovered the photoelectric effect in 1839. This physical phenomenon makes it possible to directly transform radiation into electricity, without the intermediate use of heat, for example. These energy sources have experienced great development in several countries.
The operating principle of a photovoltaic cell
Photovoltaic cells use the photoelectric effect to produce current by absorbing solar radiation. The properties of the semiconductors, struck by the photos of light, set in motion a flow of electrons. The different layers of silicon create an electric field. It should be noted that silicon is a very easy element to find : it is even the most abundant element after oxygen! This is also an almost inexhaustible source.
The efficiency of photovoltaic cells, the limit of solar energy
To calculate the quantity of energy produced by the cell, it is necessary to take into account the efficiency, the average level of sunshine in the region over a year and the installation conditions of the cells. Thus incident solar energy is 1MWh/m2/year in the Paris region, it increases to 1.7 in the south of France and reaches 3 in the Sahara desert.
The installation of photovoltaic parks is decisive for the profitability of energy production. Not all regions that do not experience consistent and significant sunshine are candidates for solar energy. Its productivity is also reduced and the panels have a lifespan reduced to 25 years.
But it still remains a renewable energy source that will continue to grow in importance, especially if we can store it for use when we need it . It will not be able to compete with nuclear energy production for the moment, but the energy transition is very present in France. Prices can be adapted for consumption intended for the general public.
Biomass, biological energy
It is certainly one of the energy sources least known to the general public and yet many French people have adopted the composter in their garden or on their balcony.
Energy comes from biological materials: this is household waste or even agricultural waste. They are burned and we speak of biomass by combustion. And it is the oldest form of energy production since it dates back to the invention of fire!
The other solution which is experiencing great development is biomass by methanization : the fermentation of organic waste produces a gas which is not far from natural gas. This biogas is essentially composed of methane. It is made from household waste, manure or even sludge from sewage treatment plants.
Biogas, in development for energy production
The biogas sector contributes to the objectives of the energy transition by adding an element that is not always present: the circular economy . In fact, it is the recovery of waste from methanization in agriculture. We are talking about digestates.
At the end of 2016, more than 450 installations produced electricity from biogas . But the prospects are interesting since it is estimated that the overall deposit in 2030 for methanization is 130 million tonnes of raw material , composed of 90% agricultural materials.
The objectives of this sector are in accordance with the national action plan for renewable energies (ENR) of 2009. It is also interesting to be able to store this energy to benefit from biomass on a continuous basis.
Geothermal energy? The power of the soil
The last of the renewable energies makes it possible to produce different types of energy depending on the temperature of the heat drawn from the subsoil. Hot water is used for heating or air conditioning installations for individual homes but also for buildings. It is also possible to produce electricity.
It is of course a renewable energy, with low greenhouse gas (GHG) emissions.
There are different types of geothermal energy and the recovery of geothermal heat.
Surface geothermal energy is also called very low temperature or very low energy geothermal energy. In this case, the heat from the ground that is exploited is only found at a depth of 200 meters. The temperature is below 30 degrees.
For low temperature or low energy geothermal energy, the exploited water deposits are located at a depth of a few hundred meters to around 2000 meters. The temperature rises to 90 degrees.
Finally, high temperature geothermal energy, also called high enthalpy, concerns temperatures above 150 degrees. In this case, for such production, it is necessary to drill to a depth of more than 1,500 meters.
A still marginal source of renewable energy
The investments for a geothermal installation as well as the amortization period are very high. Projects must be well studied and above all obtain support from the Heat Fund (Ademe) and the Geothermal Guarantee Fund for deep aquifers. We must ensure that production prices can be adapted for consumption by the general public.
Other systems exist as the constraints are numerous and the risks high. But the desire is to help projects that arise to use this resource which exists in an inexhaustible manner. And of course the storage of this energy is essential for its development.
