How does a solar panel work?

solar pannels, solar cells, silicon, energy efficiency, solar radiationPhotovoltaic technology harnesses the energy the sun emits towards the earth to generate electricity. This energy source has a number of well-known assets: it is available “for free”, in huge amounts, and it is totally renewable and non-polluting. Besides, although sunshine is far from being constant across the globe, solar energy is profitable everywhere. Here is an overview of the main advantages of a booming technology whose potential hasn’t been fully exploited.

Operating principle

Photovoltaic panels, also known as solar panels or solar modules, consist in several cells capturing sunlight. These cells include thin layers of silicon, which is both an important element of the earth’s crust and a semiconductor widely used in the electronics industry. Solar radiations emit photons which hit the silicon layers, which in turn absorb them and set electrons in movement, thus generating electrical tension harnessed by thin metal wires.

Efficiency depends on technology

There are different sorts of solar cells: monocrystalline, polycrystalline and amorphous cells. These terms refer to the silicon structure used in each kind of technology. A solar cell’s yield corresponds to the proportion of solar energy it transforms into electricity. A solar cell with a 10% yield, for instance, converts 1kWH of solar energy into 100Wh of electricity.

Monocrystalline silicon, that is one single chunk of crystal, is the most efficient technology with a yield of 12 to 20%, but it is still expensive. Polycrystalline silicon (several smaller crystals) is cheaper but only 11 to 15% efficient. Finally, amorphous silicon (a layer of silicon gas sprayed onto a glass layer) has the lowest production costs but yields a paltry 5 to 9%; it can be found in pocket calculators and “solar watches”. Manufacturers usually mention the optimal power a solar module can yield, that is under ideal conditions, which include not only sunlight (fine weather, little shade) but also direction and angle of the panel.

Solar radiation: a colossal and inexhaustible energy source

Annual solar radiation worldwide is a significant energy source: an estimated 1.6×1018 kWh, that is 15,000 times as much as worldwide energy consumption. Obviously sunlight is not uniform across the globe: it depends on how close to the equator you are and what the climate is like. In France for example, average annual solar radiation is about 1400 kWh per m2, compared to 2300 kWh per m2 in the hottest parts of the world.

There are significant differences in solar radiation within a country the size of France: less than 1220 kWh per m2 in the north-eastern Alsace, compared to over 1760 in the south-easternmost corner (French Riviera). The more south you go, the more solar radiation there is and therefore the less solar panel surface area you need to generate a given amount of electricity. On the contrary, heating needs in the north are more important while solar radiation levels are lower, which is why initial investments are higher; however they quickly pay for themselves and solar modules remain profitable all over the world. This is why although Germany enjoys less sunlight than France, it is the world’s first solar energy producer.

Innovation to sustain fledgling industry

In our electrical efficiency magazine, we have already mentioned the quantum dots technology, which consists in tweaking the microscopic structure of solar cells to improve their efficiency. Three-dimensional solar cells are another promising lead.

Manufacturers in Europe strive to produce more efficient and cheaper modules, pursuing the double goal of improved energy efficiency and higher competitiveness in the face of international competition. Indeed, the solar energy sector has been in the doldrums lately, especially in Germany and in France. However, these economic difficulties have little to do with an alleged intrinsic lack of profitability of solar energy; rather, they are due to competition from China and cuts in government subsidies.

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