5610 Μπαταρία???

[alfisti156]

Το έδεσα χτες βράδυ στην κουπαστή του μπαλκονιού που βλέπει Ανατολή και κατά τις 12.00 που το μάζεψα σηκώθηκε η μπαταρία.
Ίσως να πήρε και βιταμίνες D. Τώρα βλέπουμε πότε θα χρειαστεί πάλι δέσιμο στην κουπαστή.

[Giorgos_I]

Το έδεσα χτες βράδυ στην κουπαστή του μπαλκονιού που βλέπει Ανατολή και κατά τις 12.00 που το μάζεψα σηκώθηκε η μπαταρία.
Ίσως να πήρε και βιταμίνες D. Τώρα βλέπουμε πότε θα χρειαστεί πάλι δέσιμο στην κουπαστή.

Ειδες τι προκάλεσες με την ερώτησή σου ? 

Και που να δείς τι ..............έρχεται.

Αν έχεις φιλότιμο, πρέπει να .........................

[Giorgos_I]

What Kind of Light Does a Solar Cell Need?

Solar radiation in the red to violet wavelengths blast a solar cell with enough energy to create electricity. But solar cells do not respond to all forms of light. Wavelengths in the infrared spectrum have too little of the energy needed to jostle electrons loose in the solar cell’s silicon, the effect that produces electric current. Ultraviolet wavelengths have too much energy. These wavelengths simply create heat, which can reduce a cell’s efficiency. Solar cells require certain wavelengths in the light spectrum to generate useful amounts of electricity.

[Giorgos_I]

Effect of Brightness

Brightness or luminosity is the amount of light that shines on a solar cell. In total darkness, a cell produces no electricity. As the amount of light increases, so does the cell’s current. At a certain level of brightness, however, the cell’s output reaches a limit; beyond this point, more light gives no additional current. A solar cell’s specifications include a nominal voltage and current rating which is the cell’s output under direct bright sunshine.

[Giorgos_I]

Spectrum, Wavelength and Color

Visible light is part of the electromagnetic spectrum, a form of energy that also includes radio waves, ultraviolet and X-rays. The colors of the rainbow contained in visible light represent different wavelengths; the wavelength of the color red, for example, is about 700 nanometers, or billionths of a meter, and 400 nanometers is the wavelength for violet. Solar cells respond to many of the same wavelengths detected by the human eye.

[Giorgos_I]

Sunlight or Artificial Light

Solar cells generally work well with natural sunlight, as most uses for solar-powered devices are outdoors or in space. Because artificial sources of light such as incandescent and fluorescent bulbs mimic the Sun’s spectrum, solar cells can also work indoors, powering small devices such as calculators and watches. Other artificial sources such as lasers and neon lamps have very restricted color spectra; solar cells may not work as effectively with their light.

[Giorgos_I]

Silicon’s Response to Light

In complete darkness, a solar cell produces no current. As the amount of light increases, so does the cell’s output. The cell’s maximum current is limited, however; any additional light beyond a maximum brightness produces no increased electrical output. In addition to brightness, the wavelength of the incident light also matters. A typical silicon solar cell responds to most of the visible and infrared parts of the sun’s light spectrum, but some wavelengths in the yellow and red regions are absorbed poorly. Some of the infrared and all of the longer wavelengths pass through the solar cell and don’t produce electricity.

[Giorgos_I]

Can Solar Batteries Charge Using Incandescent Light?

A solar cell can charge a battery from natural sunlight or from artificial lighting like an incandescent light bulb. A solar cell responds in much the same way to either kind of light; you can use incandescent light with a solar cell to charge a watch or calculator battery, provided the light is bright enough. The cell converts a range of light wavelengths into electrical energy; both sunlight and incandescent light contain these wavelengths, so the solar cell charges the battery from both sources.

[Giorgos_I]

Incandescent Vs. Solar Spectrum

Incandescent lights, the Sun and all other light sources produce what scientists call a “spectrum” – a spread of light wavelengths including long infrared waves, visible light, short ultraviolet waves and X-rays. ............ A solar cell responds to light wavelengths in different ways, converting some wavelengths to electricity while ignoring others. The cell roughly matches the Sun’s spectrum; it processes visible light colors but cannot use the longest infrared waves. Because the spectrum of an incandescent light is close to the Sun’s, a solar cell has no problem running on its light.

[Giorgos_I]

Energy From Light

In addition to its spectral qualities, solar energy on a sunny day amounts to about 1,000 watts per square meter on the Earth’s surface. However, a typical solar cell receives only a tiny fraction of this because its size is only a few square centimeters. A standard incandescent light bulb produces between 40 and 100 watts total and has most of the energy in the longest infrared wavelengths. If you hold a solar cell a few inches from a light bulb, it will receive a similar amount of light as it does from the Sun; although the Sun is more powerful by far, the close distance of the incandescent lamp makes up for its smaller output.

[Giorgos_I]

Distance,Time and Voltage

The energy received by a solar cell from an incandescent light diminishes rapidly with distance. The less light that falls on the solar cell, the weaker its output, so it takes longer to charge a battery. If the cell’s voltage is lower than a minimum threshold value, it becomes impossible to charge the battery; for example, a 12-volt battery needs 12.9 volts to charge it. As long as light shines strongly on a solar cell, voltage should not pose an issue.

[Giorgos_I]

The Effect of Wavelength on Photovoltaic Cells

Solar cells depend on a phenomenon known as the photovoltaic effect, discovered by French physicist Alexandre Edmond Becquerel (1820-1891). It is related to the photoelectric effect, a phenomenon by which electrons are ejected from a conducting material when light shines on it. Albert Einstein (1879-1955) won the 1921 Nobel Prize in physics for his explanation of that phenomenon, using quantum principles that were new at the time. Unlike the photoelectric effect, the photovoltaic effect takes place at the boundary of two semiconducting plates, not on a single conducting plate. No electrons are actually ejected when light shines. Instead, they accumulate along the boundary to create a voltage. When you connect the two plates with a conducting wire, a current will flow in the wire.

Einstein's great achievement, and the reason for which he won the Nobel Prize, was to recognize that the energy of the electrons ejected from a photoelectric plate depended – not on light intensity (amplitude), as wave theory predicted – but on frequency, which is the inverse of wavelength.

The shorter the wavelength of incident light, the higher the frequency of the light and the more energy possessed by ejected electrons. In the same way, photovoltaic cells are sensitive to wavelength and respond better to sunlight in some parts of the spectrum than others. To understand why, it helps to review Einstein's explanation of the photoelectric effect.

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Sunlight contains an entire spectrum of radiation, but only light with a short enough wavelength will produce the photoelectric or photovoltaic effects. This means that a part of the solar spectrum is useful for generating electricity. It doesn't matter how bright or dim the light is. It just has to have – at a minimum – the solar cell wavelength. High-energy ultraviolet radiation can penetrate clouds, which means that solar cells should function on cloudy days – and they do.

[Giorgos_I]

A factor affecting efficiency is the reflectivity of the solar cell. A certain fraction of incident light bounces off the surface of the cell without encountering an electron. To reduce losses from reflectivity and increase efficiency, solar cell manufacturers usually coat the cells with a nonreflective, light-absorbing material. This is why solar cells are usually black.

[Giorgos_I]

Let There Be Light

Sunlight allows plants to perform photosynthesis, a process which is required for plant growth and health. Photosynthesis allows plants to synthesize glucose from carbon dioxide and water and release oxygen. The blue and red portions of the sun's wavelengths supply plants with their color. The sun naturally provides the plant with the right balance of blue and red rays it needs to survive. Plants that are denied sufficient light will eventually lose their color and die. Plants deprived of light will grow upward, stretching their stems more rapidly that usual, searching for light. This process is known as etiolation and is a survival mechanism that maximizes the plant's chances of getting to light.

Certain plants have the ability to grow and flourish without using the power of the sun. These types of plants are known as low-light plants and medium-light plants. Both of these plant types can survive using artificial lighting sources only. If possible, use fluorescent tubes rather than incandescent light bulbs when lighting a plant with artificial light.

[Giorgos_I]

How Light Diminishes With Distance

For a source that shines equally in radial directions, the amount of light on a unit area decreases by the inverse-square law. If a certain light bulb shines on a spot 1 meter away, the illuminance there might be 900 lux. A spot 2 meters away would be at double the distance and therefore would have only 1/22, or one-quarter the illuminance, which would be 225 lux. A spot 3 meters away would be at triple the distance and would have only 1/33, or one-ninth the amount of light, only 100 lux.

If the light originates from a source that is not a point, such as from a tubular fluorescent bulb, or if the light is manipulated by lenses, mirrors or reflectors, then the inverse-square law may not apply.