What future for solar energy?

Between hopes, disappointments and spectacular advances, research around photovoltaic solar energy is progressing fast. Overview of the most promising trends with Daniel Lincot

and Pere Roca i Cabarrocas, CNRS research directors and photovoltaic specialists.

The photovoltaic effect, discovered in the nineteenth century, is based in part on the properties of semiconductor materials present in solar panels. How do you work to improve them?
Daniel Lincot1: Research on solar photovoltaic energy is a team effort. The goal is to make more efficient solar cells that better convert sunlight into electricity at lower cost. To increase the efficiency of the photovoltaic cells, it is necessary to improve the semiconducting properties of each of the materials present in the cell, such as silicon, but also their combinations. A photovoltaic cell is a bit like a football team! It must form a whole: there is the individual and the collective. The materials must be better at personal titles, but also able to pass electrons between them.

Pere Roca i Cabarrocas2: When trying to improve performance or cost, every small detail counts. Photovoltaic solar research is truly an open and dynamic branch that integrates physics, electronics, chemistry, materials science and optics. To improve solar cells, we need this multidisciplinary approach.

D. L.: And research is moving fast. When the first silicon cells were developed in the 1950s, their efficiency dropped in the space of a few years from almost 0% to more than 10%. Today, theoretically, it is estimated that it could one day reach 85%! This proves that, in terms of photovoltaics, we are still under foot …

Every day, the sun supplies Earth with an average of 3 kilowatt hours per square meter. This energy seems inexhaustible. So what are the locks that still limit its development on a large scale?
P. R. C.: Contrary to what we think, solar energy is already viable and competitive. In France, EDF is pushing its consumers to become themselves producers of solar electricity. And in many other countries, solar is competitive with other energies.

D. L .: Locks are almost all lifted on a global scale. With Solar Impulse alone, we have shown that we can alternate day and night, and solve some energy storage problems. All these locks simply stand up by the demonstration. The only obstacle is that we would have to go even further … In France, we are still confronted with economic, political and cultural obstacles.
In contrary
to what we think,
solar energy
is already viable
and competitive.

P.C .: Solar Impulse has illustrated that there are solutions and that with intelligent energy management, we can do it. There are even more convincing examples, but less media, that prove the potential of photovoltaics. With solar, we can imagine creating wealth in the countries of the South, which would sell their solar energy. It is a utopia that becomes achievable.

Silicon, used since the 1960s to power space satellites, is still today the flagship material of solar panels. Why is he still not perfect?
D.L .: The silicon industry accounts for 90% of the solar energy market. Its principle is simple. It consists of cutting silicon ingots into wafers to then form photovoltaic cells capable of transforming the energy of the sun into electricity. The problem is that silicon needs a lot of thickness to fully absorb sunlight.

P. R. C.: The record yield of silicon is 26.33% in the laboratory, we must do more! We know that we can go beyond 60% yield with advanced concepts such as multijunctions. In any case, no principle of physics prevents us. The better the photons are trapped, the better the yield is.
Silicon wafer, solar energy, photovoltaic
Silicon wafer which, after various operations, will be transformed into a photovoltaic cell.

To improve the performance of solar panels, should we consider finer materials?
D. L.: It’s not really a question of performance but rather of process and cost. This is the challenge of the so-called thin film sector, which accounts for around 10% of the market share. It is composed of three types of semiconductor materials: cadmium telluride, Cigs3 and silicon in thin layers. This consists of covering a support with a thin layer of one of these materials. Photovoltaic cells become 100 times thinner


Plaquette de silicium, énergie solaire, photovoltaique


Have some lines of research been abandoned over time?
D. L .: Yes, there are almost extinct channels. A few years ago, it was believed, for example, copper sulphide, because it is abundant in nature, non-toxic and absorbs light in a remarkable way. In the 1980s, it was the Grail. Except that the cells were not stable enough and degraded in a few days.

P. R. C.: Other areas are a little overdue, like that of organic photovoltaic cells. There was a boom in the 2000s, which quickly fell. In fact, the researchers who worked in this branch abandoned it in favor of the perovskites. It is true that some organic cells still have problems of stability, yield and cost. But this is not a sector to avoid, because it concerns specific markets.

Are the recycling and lifespan of photovoltaic cells also part of the specifications for solar research?
D. L.: This is very important. We analyze the life cycle of cells, from the mine to recycling. We expect lifetimes of twenty to thirty years or more. So we could even consider bequeathing solar panels legacy!

P.C .: The recycling market is developing very well. The “energy return time” of a cell is only one or two years. That is, in that time you will have produced the same amount of energy that you spent on making the cell. You will have “paid off” the energy. The twenty or thirty years of life after, it’s a bonus!

You are both involved in the IPVF, which will bring together more than 200 researchers around solar energy. What are his ambitions for the future?
P. R .: Research on solar photovoltaic in France is among the best in the world, but we have little visibility. IPVF brings us a spotlight. And it also makes it possible to bring together the different sectors: thin layers, silicon, perovskites …

D. L.: The creation of the IPVF makes it possible to prepare the future for our country. We believe that the key decade is 2020-2030. It will be the solar years, the switchover. It is estimated that, during this period, the solar power generation capacity will exceed the terawatt! The flagship “30/30/30” goal of the IPVF would be to achieve 30% return at 30 cents per watt in 2030. For this, this structure offers remarkable opportunities for public-private synergies, in associating at the same time academic partners such as the CNRS or the École Polytechnique, major industrialists, such as EDF, Total and Air Liquide, but also smaller ones like Horiba Jobin Yvon or Riber. The CNRS is at the heart of this construction, it is a great pride for us and also a great responsibility.

Energie solaire, photovoltaiqueSolar panels covering roofs of homes in the Deer Valley neighborhood, in Phoenix, Arizona.
J.LOTT / New York Times-REDUX-REA
Today, solar energy represents only 1% of the energy produced in the world. In time, will solar manage to surpass fossil energies?
P. R. C.: Of course, yes! While coal seems cheaper, it is because we do not take into account all the long-term costs of health and the environment. Solar is already largely competitive in many parts of the world, like Arizona. The future is not in fossil energy, although the transition will obviously not happen next year. Solar energy can charge the battery of a laptop as well as provide the energy needed for an entire village, it is extremely flexible. And solar is an unlimited and cheap resource.
D.L .: In about twenty years, solar energy will most likely supplant conventional energy systems. Already today, photovoltaics is approaching in some countries the 10% of electricity supply. We will learn how to adapt our energy production to the seasons, for example by promoting solar in summer and wind or hydro in winter. The system is finally balanced … When we work on solar energy, we are necessarily guided by the idea that it is good for humanity.

source: https://lejournal.cnrs.fr/articles/quel-futur-pour-lenergie-solaire


What is renewable energy?

An energy is said to be renewable when it comes from sources that nature is constantly renewing, as opposed to non-renewable energy whose stocks are depleted….

Renewable energies come from 2 major natural sources: the Sun (at the origin of the cycle of water, tides, wind and plant growth) and the Earth (which gives off heat).

Nicknamed “clean energies” or “green energies”, their exploitation generates very little waste and polluting emissions but their energy power is much lower than that of non-renewable energies.

From 2000 meters altitude to 2000 meters underground, discover some of the renewable energies.



source: https://www.edf.fr/groupe-edf/espaces-dedies/l-energie-de-a-a-z/tout-sur-l-energie/le-developpement-durable/qu-est-ce-qu-une-energie-renouvelable

What is solar energy?

Solar energy is a source of energy that depends on the sun. This energy makes it possible to manufacture electricity from photovoltaic panels or solar thermal power plants, thanks to the sunlight captured by solar panels.

The sun, although distant more than 150 million kilometers from us, remains our largest source of energy even if it is intermittent.

It is a clean energy that emits no greenhouse gases and its raw material, the sun, is available all over the world, free and inexhaustible.

How does a solar installation work?

Three elements are needed for a photovoltaic system: solar panels, an inverter and a meter.

These three elements make it possible to recover the energy transmitted by the sun, to transform it into electricity and then to distribute it to all the customers connected to the network.

integrated into the roof, the solar panels convert the light directly into direct electrical current
the inverter then transforms the electricity obtained into ac compatible with the network
the meter measures the amount of current injected into the network


What is wind energy?

Wind energy is a source of energy that depends on the wind. The sun heats the Earth unevenly, creating zones of different temperatures and atmospheric pressure all around the globe. From these pressure differences arise air movements, called wind. This energy makes it possible to manufacture electricity in wind turbines, also called wind turbines, thanks to the force of the wind.

A wind turbine is composed of 4 parts:

the mast
the nacelle that contains the generator generating electricity
power lines that evacuate and carry electrical energy (when connected to the grid)

Descending from the windmill of the Middle Ages, the first wind turbine was commissioned in France in Dunkerque in 1990.

At the end of 2012, France has about 4 500 wind turbines.

It is an energy that emits no greenhouse gases and its raw material, the wind, is available all over the world and totally free.

There are 2 types of wind farms, depending on their geographical location and the available area.

Shut in

A wind farm, or wind farm, consists of 3 to 10 machines at least 200 m apart. Electricity generation, most of the time purchased by EDF from its producer, is channeled by cable to the grid. Given the size of wind turbines, a large area is required to install a significant wind farm.

It is a wind farm located at sea, about 10 km from the coast, at depths of up to 25 to 30 m. It is connected to the terrestrial network by an underwater cable.


Source: https://www.edf.fr/groupe-edf/espaces-dedies/l-energie-de-a-a-z/tout-sur-l-energie/produire-de-l-electricite/les-differents-types-d-eoliennes

What is hydropower?

Hydropower makes it possible to manufacture electricity in hydropower plants through the force of water. This force depends either on the height of the waterfall (high or medium-fall power plants), or the flow of rivers and streams (run-of-the-river power stations).

Hydraulic energy depends on the water cycle. It is the largest source of renewable energy.

Under the action of the sun, the water of the oceans and the earth evaporates. It condenses into clouds that move with the wind. The drop in temperature over the continents causes rainfall that feeds the water of lakes, rivers and oceans.

A hydraulic power plant is composed of 3 parts:

the dam that holds the water
the power plant that produces electricity
power lines that evacuate and carry electrical energy

In France, hydroelectricity has been exploited since the end of the 19th century, making it the oldest energy produced by a national resource. EDF operates 640 dams, 150 of which are more than 20 m high.

It is an energy that does not emit greenhouse gases, it can be used quickly thanks to the large quantities of stored water and it is a renewable energy very economical in the long term.

There are 3 main forms of dams:
The dam-weight

In concrete or stone, it is the simplest and heaviest.

It is vertical with respect to the reservoir and inclined with respect to the valley. It relies solely on the ground.

Thus, it opposes all its mass to the pressure of the water.
The arch dam

In concrete, it relies in part on rock walls. Thanks to its curved shape, it postpones the pressure of the water on the banks. It can also be supported by buttresses.

It is inclined relative to the reservoir and vertical to the valley. It is often used in narrow valleys.
The buttress dam

Its triangular concrete buttresses allow it to postpone the pressure of the water towards the ground.

It is very light because its weight is reduced only to the foothills.



Sources: https://www.edf.fr/groupe-edf/espaces-dedies/l-energie-de-a-a-z/tout-sur-l-energie/produire-de-l-electricite/les-differentes-formes-de-barrages

What is biomass?

Energy from biomass is a renewable source of energy that depends on the cycle of living plant and animal matter…

Biomass energy is the oldest form of energy used by man since the discovery of fire in prehistory. This energy makes it possible to manufacture electricity thanks to the heat released by the combustion of these materials (wood, plants, agricultural waste, organic household refuse) or the biogas resulting from the fermentation of these materials, in biomass plants.
Biomass by combustion

The waste is directly burned producing heat, electricity or both (cogeneration). This concerns wood, waste wood processing industries and agricultural plant waste (straw, sugar cane, peanut, coconut …).

The urban waste incineration plant TIRU (a subsidiary of EDF) in Ivry-sur-Seine (Val-de-Marne) treats household waste of more than 5 million inhabitants (more than 690 000 t per year) ).

In France, 10% of biomass electricity production comes from the combustion of biogas.
Biomass by anaerobic digestion

The waste is first transformed into a biogas, by fermentation through micro-organisms (bacteria). The biogas is then burned. This biogas is close to natural gas and mainly composed of methane. This concerns household waste, animal manure and slurry, sewage sludge, paper and cardboard …

In France, several plants produce electricity thanks to biomass, mainly wood. They are most often installed close to the very places where the waste is stored. The wood is also used for collective and industrial heating.

Biomass energy emits almost no pollutants and has no impact on the greenhouse effect. The amount of CO2, a greenhouse gas that it releases, is the amount that plants absorb during their growth.

In addition, upgrading biogas to electricity avoids the emission of methane, another greenhouse gas, into the atmosphere. It represents a very important energy potential, mainly from landfills, but also from sewage sludge and urban and agricultural waste.

Today only 1/4 of this potential is actually used for the production of electricity and / or heat.


Sources: https://www.edf.fr/groupe-edf/espaces-dedies/l-energie-de-a-a-z/tout-sur-l-energie/produire-de-l-electricite/qu-est-ce-que-la-biomasse


The operation of a dam

A hydro plant produces electricity through a waterfall between two levels of different heights, which sets in motion a turbine connected to an alternator.

1. The water retention

The dam retains the natural flow of water. Large amounts of water accumulate and form a reservoir.
2. Forced driving of water

Once the water is stored, valves are opened so that the water rushes into long metal pipes called forced pipes. These pipes lead the water to the hydraulic power station, located below.

Most hydraulic power plants in France are automated. Each plant starts according to a pre-defined program according to the electricity needs.
3. Electricity generation

At the exit of the pipe, in the power station, the force of the water rotates a turbine which in turn operates an alternator. Thanks to the energy provided by the turbine, the alternator produces an alternating electric current.

The power of the plant depends on the height of the waterfall and the flow of the water. The more important they are, the higher this power will be.
4. The adaptation of the tension

A transformer raises the voltage of the electric current produced by the alternator so that it can be more easily transported in very high and high voltage lines.

The turbined water that has lost its power joins the river by a special channel called tailrace.


source: https://www.edf.fr/groupe-edf/espaces-dedies/l-energie-de-a-a-z/tout-sur-l-energie/produire-de-l-electricite/le-fonctionnement-d-un-barrage