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From the photovoltaic effect to the complete solar module
The solar cell consists of a positive and a negative silicon-layer. By solar irradiation the current of electrons is started to run.
Enlarge ImageMost solar cells consist of sillicon, which is extracted from plain sand. First of all, sillicon must be purified. For the sunlight can make run the current of electricity, you still need some more things: you must lock in some foreign atoms into the sillicon-crystalls. To understand easily, check the graphic nearby. There you can see two layers. One layer is populated with foreign atoms (to be exact: Boron-atoms) to generate (by the lack of electrons) a positive charge. That’s called the p-layer. In the second layer different foreign atoms (namely Phosphorus) generate a negative charge because they import electrons. That’s the n-layer.
Only the interaction of the (n)-layer and the (p)-layer permits the photovoltaic effect. With constant irradiation, a solar cell works like a battery.
The solar cells get connected to add up the voltage of the single cells.That’s how a solar module generates with a voltage of 24 volts in most cases.
On today’s market there are two kinds of solar cells available. The mono-/poly-crystalline and the amorphous solar cells. The difference lies mainly in the coefficient and the cost of production. The coefficient, that is the part of irradiating energy which can be transformed into electricity, can be measured under standard conditions (vertical irradiation of 1000 W/m2 at 25°Celsius).
The production of mono- and polycrystalline solar cells is still very laborious and therefore expensive. The amorphous solar cells (sillicon without a crystalline structure) are much more cheaper to produce. For a while, they have been used in watches, calculators and other small devices. Larger applications are coming up slowly – the rising cost of sillicon favours sillicon-poor cells.
Theoretically to substitute the annual average consumption of nuclear power in Switzerland, you would need about 21 m2 per head of the most efficient solar cells available on the market (mono- crystalline cells of SUNPOWER, counted on an annual demand of 8000 kWh of final consumption per head – 40% of this supplied by atomic power, a coefficient of the solar cells of 20%, a global irradiation of 1200 W/m2 and an output of 850 kWh/kWp). The 21 square meters should only give you an idea what dimensions we are discussing. Practically, you would need more solar space per head, because the problem of energy-storage for the balance of day/night, summer/winter and the meteorological changes are not solved yet. Ideas, in fact, on how the problem could be solved exist already! More on this: the sun as a part of a future energy-system.
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Only the interaction of the (n)-layer and the (p)-layer permits the photovoltaic effect. With constant irradiation, a solar cell works like a battery.
The solar cells get connected to add up the voltage of the single cells.That’s how a solar module generates with a voltage of 24 volts in most cases.
Different kinds of solar cells and coefficient
On today’s market there are two kinds of solar cells available. The mono-/poly-crystalline and the amorphous solar cells. The difference lies mainly in the coefficient and the cost of production. The coefficient, that is the part of irradiating energy which can be transformed into electricity, can be measured under standard conditions (vertical irradiation of 1000 W/m2 at 25°Celsius).
The production of mono- and polycrystalline solar cells is still very laborious and therefore expensive. The amorphous solar cells (sillicon without a crystalline structure) are much more cheaper to produce. For a while, they have been used in watches, calculators and other small devices. Larger applications are coming up slowly – the rising cost of sillicon favours sillicon-poor cells.
Can the sun substitute atomic power?
Theoretically to substitute the annual average consumption of nuclear power in Switzerland, you would need about 21 m2 per head of the most efficient solar cells available on the market (mono- crystalline cells of SUNPOWER, counted on an annual demand of 8000 kWh of final consumption per head – 40% of this supplied by atomic power, a coefficient of the solar cells of 20%, a global irradiation of 1200 W/m2 and an output of 850 kWh/kWp). The 21 square meters should only give you an idea what dimensions we are discussing. Practically, you would need more solar space per head, because the problem of energy-storage for the balance of day/night, summer/winter and the meteorological changes are not solved yet. Ideas, in fact, on how the problem could be solved exist already! More on this: the sun as a part of a future energy-system.
Read More