The direct conversion of light into electricity called photovoltaic (PV) effect was discovered by Antoine Cesar Bequerel in 1839. The photovoltaic technology really took off with space applications in the 1940s. The terrestrial applications started developing with the oil crisis of the 1970s, launching a real technological boost. Photovoltaic technology is one of the most reliable and efficient off-grid solution to get electricity in remote places. Due to increasing demand and consecutive industrial development, the photovoltaic technology has grown today to maturity and is ready for a number of applications.
The challenges remain in getting the cost lower and the efficiency higher, in order to be more competitive when compared with fossil fuels. Other components coming along with solar panels in a photovoltaic system have also shown tremendous development, especially batteries. In order to get the maximum out of a photovoltaic setup it is necessary to select the load as efficient as possible. This is another way of achieving a lower cost of photovoltaic electricity.
The calculation of the cost of a photovoltaic system will not only be ‘‘how much to pay up front'' but also ‘‘how much energy can be converted and for how long?''; the capital investment. Solar cells can be wafer-based or thin-film-based, each technology with its pros and cons. Wafer-based solar cells generally made of silicon are more expensive but offer higher efficiencies. Thin film solar cells on the other hand are cheaper to fabricate but present lower efficiencies. Nevertheless, they present the advantages of being suitable for different other applications as the possibility of making them on flexible substrates.
Photovoltaic electricity is one of the main tools to achieve successful rural electrification in developing countries when the cost of expansion of the grid is much higher than the available budgets. It is a vector to improve the living and health conditions; it is also a great asset in environment protection by limiting the rejection of greenhouse effect gases. Among the numerous applications of photovoltaic electricity the most appealing are certainly for low power electrical appliances.
Among those low power appliances, domestic lighting is certainly one of the most demanded. Lighting technology has known an important evolution from the carbon arc to the filament light bulb, the fluorescent tubes to the light-emitting diodes (LEDs) that are top of the line today. LEDs can cover a number of applications that were not covered before; especially because of the geometry and color range they can reach, and their power efficiency and life span which are continuously increasing.
In the following we will present the application of photovoltaic for lighting and the consequences of the choice of technology when sizing a photovoltaic standalone system.
The Photon: Energy, Wavelength and Frequency
Light can have a wave or particle behavior and will manifest in one form or the other depending on the experimental situation. In interference experiments light behaves as a wave while in photoelectric experiments light has a particle behavior; a light beam will behave as a bundle of particles.
When light or an electromagnetic radiation in general behaves as a stream of particles, these particles are called photons, while a wave is primarily characterized by its wavelength or frequency and its amplitude. Each photon in a monochromatic radiation will have an energy related to the wavelength or the corresponding frequency (the color) of the radiation. The photon energy is given by the Planck equation
E = hv = hc/?
where h is a universal constant called Planck's constant:
h = 6.625 x 10-34J s-1
v is the frequency
? is the wavelength.
The velocity of light in vacuum, generally symbolized by c, is a universal constant:
c = 3 x 108m/s.
Thus, the above equation allows an inter-conversion between the frequency or wavelength and energy of a photon for electromagnetic waves. The Planck equation gives the energy of a single photon when the color of the radiation (wavelength or the corresponding frequency) is known. The Planck equation also informs about light and semiconductors' interaction. By the band gap of a semiconductor one can know the corresponding color of light needed in order to send electrons from the valence band to the conduction band.
The intensity of a light beam is the number of photons it contains. Thus, for a given wavelength increasing the intensity of the light will not change the energy of the individual photons but will just increase their number. The correspondence between energy in (eV) and wavelength expressed in (µm) is given by:
? = [1.24/ hv(eV)] (µm)
Solar Spectrum
The electric power generated by a solar cell is proportional to its area. The irradiance of the sun at the Equator level is about 1 kW/m2 at 90 degrees, in other words a 1 cm2 solar cell will receive about 10 mW. This irradiated power by the sun is not equally distributed for the different wavelengths composing the solar spectrum. The solar spectrum shows a maximum intensity at the wavelength ? = 0.5 µm, this intensity falls to half at ? = 1 µm.
The absorption spectrum of a semiconductor depends on its band gap. If the band gap is bigger than the energy of the incident photon, there will be no transmission of an electron from the valence to the conduction band. If the energy of the photon is bigger than the band gap an electron will be transferred from the valence to the conduction band and the remaining energy will be released in the form of heat.
The atmosphere attenuates the sun's radiations before they reach the Earth's surface, mainly because of the absorption of infrared by water vapor and the absorption in the ultraviolet by the ozone layer. The air mass is defined as the level at which the atmosphere affects the sunlight received at the Earth's surface. The lower the air mass, the less will be the influence of the atmosphere. If you find this post useful, please help by sharing it with your friends. To find out more, you can check out How Can I Use Solar Energy At Home.
The challenges remain in getting the cost lower and the efficiency higher, in order to be more competitive when compared with fossil fuels. Other components coming along with solar panels in a photovoltaic system have also shown tremendous development, especially batteries. In order to get the maximum out of a photovoltaic setup it is necessary to select the load as efficient as possible. This is another way of achieving a lower cost of photovoltaic electricity.
The calculation of the cost of a photovoltaic system will not only be ‘‘how much to pay up front'' but also ‘‘how much energy can be converted and for how long?''; the capital investment. Solar cells can be wafer-based or thin-film-based, each technology with its pros and cons. Wafer-based solar cells generally made of silicon are more expensive but offer higher efficiencies. Thin film solar cells on the other hand are cheaper to fabricate but present lower efficiencies. Nevertheless, they present the advantages of being suitable for different other applications as the possibility of making them on flexible substrates.
Photovoltaic electricity is one of the main tools to achieve successful rural electrification in developing countries when the cost of expansion of the grid is much higher than the available budgets. It is a vector to improve the living and health conditions; it is also a great asset in environment protection by limiting the rejection of greenhouse effect gases. Among the numerous applications of photovoltaic electricity the most appealing are certainly for low power electrical appliances.
Among those low power appliances, domestic lighting is certainly one of the most demanded. Lighting technology has known an important evolution from the carbon arc to the filament light bulb, the fluorescent tubes to the light-emitting diodes (LEDs) that are top of the line today. LEDs can cover a number of applications that were not covered before; especially because of the geometry and color range they can reach, and their power efficiency and life span which are continuously increasing.
In the following we will present the application of photovoltaic for lighting and the consequences of the choice of technology when sizing a photovoltaic standalone system.
The Photon: Energy, Wavelength and Frequency
Light can have a wave or particle behavior and will manifest in one form or the other depending on the experimental situation. In interference experiments light behaves as a wave while in photoelectric experiments light has a particle behavior; a light beam will behave as a bundle of particles.
When light or an electromagnetic radiation in general behaves as a stream of particles, these particles are called photons, while a wave is primarily characterized by its wavelength or frequency and its amplitude. Each photon in a monochromatic radiation will have an energy related to the wavelength or the corresponding frequency (the color) of the radiation. The photon energy is given by the Planck equation
E = hv = hc/?
where h is a universal constant called Planck's constant:
h = 6.625 x 10-34J s-1
v is the frequency
? is the wavelength.
The velocity of light in vacuum, generally symbolized by c, is a universal constant:
c = 3 x 108m/s.
Thus, the above equation allows an inter-conversion between the frequency or wavelength and energy of a photon for electromagnetic waves. The Planck equation gives the energy of a single photon when the color of the radiation (wavelength or the corresponding frequency) is known. The Planck equation also informs about light and semiconductors' interaction. By the band gap of a semiconductor one can know the corresponding color of light needed in order to send electrons from the valence band to the conduction band.
The intensity of a light beam is the number of photons it contains. Thus, for a given wavelength increasing the intensity of the light will not change the energy of the individual photons but will just increase their number. The correspondence between energy in (eV) and wavelength expressed in (µm) is given by:
? = [1.24/ hv(eV)] (µm)
Solar Spectrum
The electric power generated by a solar cell is proportional to its area. The irradiance of the sun at the Equator level is about 1 kW/m2 at 90 degrees, in other words a 1 cm2 solar cell will receive about 10 mW. This irradiated power by the sun is not equally distributed for the different wavelengths composing the solar spectrum. The solar spectrum shows a maximum intensity at the wavelength ? = 0.5 µm, this intensity falls to half at ? = 1 µm.
The absorption spectrum of a semiconductor depends on its band gap. If the band gap is bigger than the energy of the incident photon, there will be no transmission of an electron from the valence to the conduction band. If the energy of the photon is bigger than the band gap an electron will be transferred from the valence to the conduction band and the remaining energy will be released in the form of heat.
The atmosphere attenuates the sun's radiations before they reach the Earth's surface, mainly because of the absorption of infrared by water vapor and the absorption in the ultraviolet by the ozone layer. The air mass is defined as the level at which the atmosphere affects the sunlight received at the Earth's surface. The lower the air mass, the less will be the influence of the atmosphere. If you find this post useful, please help by sharing it with your friends. To find out more, you can check out How Can I Use Solar Energy At Home.
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