Photovoltaic Energy

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Overview of Photovoltaic Energy and its uses.

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  • Photovoltaic Energy

    Paolo Abagar, Mario Miguel Celdran, Arjan Delos Santos, Keno Hibaya, Kevin Richard Miraflores, Lovely Jane Vallinas

    EE 147

    Energy Conversion EECE Department

    Mindanao State University Iligan Institute of Technology Iligan City, Philippines

    I. INTRODUCTION

    The term "photovoltaic" has two parts: (phs) a Greek word meaning light, and volt, a word

    coined in honour of the inventor of the electric battery,

    Alessandro Volta ( 1745-1827). It is produced when

    sunlight is converted into energy with the use of solar

    cells or semiconductors.

    -Photovoltaics is the field of technology and

    research related to the practical application of

    photovoltaic cells in producing electricity from light,

    though it is often used specifically to refer to the

    generation of electricity from sunlight.

    Photovoltaics (PV) is a method of generating

    electrical power by converting solar

    radiation into direct current electricity using

    semiconductors that exhibit the photovoltaic effect.

    Photovoltaic power generation employs solar

    panels composed of a number of solar cells containing a

    photovoltaic material. Materials presently used for

    photovoltaics include monocrystalline

    silicon, polycrystalline silicon, amorphous

    silicon, cadmium telluride, and copper indium gallium

    selenide/sulfide. Due to the increased demand

    for renewable energy sources, the manufacturing of

    solar cells and photovoltaic arrays has advanced

    considerably in recent years .

    II. HISTORY

    Photovoltaic energy has been discovered for

    almost two centuries. Photovoltaic effect was first

    discovered by a 19 year old French experimental

    physicist named Edmund Becquerel while he is

    experimenting with an electrolytic cell made up of two

    metal electrodes. Until in 1954, Bell Labs researchers

    Pearson, Chapin, and Fuller reported their discovery of 4.5% efficient silicon solar cells. Then in 1964 the

    Nimbus spacecraft was launched with a 470-W PV

    array which was its first practical application.

    However, it was not until 1940 that the first

    modern solar cell manufacturing began. This used

    silicon as the semiconductor material, patented by the

    American inventor, Rusell Ohl. In 1955, the American

    utility, Western Electric, began to market solar cell

    arrays.

    The first practical applications for these

    devices were in artificial satellites. They were an

    efficient way of providing electricity to remote bodies.

    Vanguard 1 thus became the first satellite to use a

    photovoltaic module to feed the transmitter, which

    consumed a mere 5 milliwatts. By the mid-70's,

    photovoltaic modules began to be used in different

    terrestrial applications. These included clocks, games

    and calculators.

    Over recent decades, photovoltaic technology

    has continued to advance, leading to the development

    of photovoltaic systems connected to networks. This

    has triggered an industry whose main objective is to

    supply modules for large photovoltaic farms to generate

    electricity on a quite different scale. In this market, T-

    Solar has become the byword for excellence.

    III. PROCESS

    Photovoltaic (PV) cells are made up of at least

    2 semi-conductor layers. One layer containing a

    positive charge, the other a negative charge.

  • The photovoltaic process converts sunlight,

    which is the most abundant energy source on the planet,

    directly into electricity. The sun emits photons (light),

    which generate electricity when they strike a

    photovoltaic cell. So in the same way a photovoltaic

    cell, made from a semi-conducting material, is a device

    that converts light into electricity.

    Sunlight consists of little particles of solar

    energy called photons. As a PV cell is exposed to this

    sunlight, many of the photons are reflected, pass right

    through, or absorbed by the solar cell.

    When sunlight strikes the solar cell, electrons

    are knocked loose and move toward the treated front

    surface of the solar cell. This creates an electron

    imbalance between the front and back of the cell and

    causes electricity to flow the greater the intensity of light, the greater the flow of electricity.

    Solar cells are made of silicon, a special type

    of melted sand, consisting of two or more thin layers of

    semi-conducting material, usually silicon. The layers

    are given opposite charges one positive, one negative.

    When enough photons are absorbed by the

    negative layer of the photovoltaic cell, electrons are

    freed from the negative semiconductor material. Due to

    the manufacturing process of the positive layer, these

    freed electrons naturally migrate to the positive layer

    creating a voltage differential, similar to a household

    battery.

    When the 2 layers are connected to an external

    load, the electrons flow through the circuit creating

    electricity. Each individual solar energy cell produces

    only 1-2 watts. To increase power output, cells are

    combined in a weather-tight package called a solar

    module. These modules (from one to several thousand)

    are then wired up in serial and/or parallel with one

    another, into what's called a solar array, to create the

    desired voltage and amperage output required by the

    given project.

    Due to the natural abundance of silicon, the

    semi-conductor material that PV cells are primarily

    made of, and the practically unlimited resource in the

    sun, solar power cells are very environmentally

    friendly. They burn no fuel and have absolutely no

    moving parts which makes them virtually maintenance

    free, clean, and silent.

    Illustrations:

  • Photovoltaic effect was first observed by

    French physicist A. E. Bacquerel in 1839. Photovoltaic

    effect is directly related to the photoelectric

    effect.When the sunlight or any other light is incident

    upon a material surface, the electrons present in

    the valence band absorb energy and, being excited,

    jump to the conduction band and become free.

    Illustration:

    These highly excited, non-thermal electrons

    diffuse, and some reach a junction where they are

    accelerated into a different material by a built-in

    potential. This generates an electromotive force, and

    thus some of the light energy is converted into electric

    energy.

    IV. TYPES OF PV CELLS

    Monocrystalline Silicon Cells

    These are made using cells sliced from a single

    cylindrical crystal of silicon, this is the most efficient

    photovoltaic technology, typically converting around

    15% of the sun's energy into electricity. The

    manufacturing process required to produce

    monocrystalline silicon is complicated, resulting in

    slightly higher costs than other technologies.

    Polycrystalline Silicon Cells

    Also sometimes known as multicrystalline cells, these

    are made from cells cut from an ingot of melted and

    recrystallised silicon. The ingots are then saw-cut into

    very thin wafers and assembled into complete cells;

    they are generally cheaper to produce than

    monocrystalline cells, due to the simpler manufacturing

    process, but they tend to be slightly less efficient, with

    average efficiencies of around 12%.

    Thick-film Silicon

    This is a variant on multicrystalline technology where the

    silicon is deposited in a continuous process onto a base

    material giving a fine grained, sparkling appearance. Like

    all crystalline PV, it is normally encapsulated in a

    transparent insulating polymer with a tempered glass

    cover and then bound into a metal framed module.

    Other Thin Films

    A number of other materials such as cadmium telluride

    (CdTe) and copper indium diselenide (CIS) are now being

    used for PV modules. The attraction of these technologies

    is that they can be manufactured by relatively inexpensive

    industrial processes, certainly in comparison to crystalline

    silicon technologies, yet they typically offer higher

    module efficiencies than amorphous silicon. Most offer a

    slightly lower efficiency: CIS is typically 10-13%

    efficient and CdTe around 8 or 9%. A potential

    disadvantage is the use of highly toxic metals such as

    Cadmium with the need for carefully controlled

    manufacturing and end of life disposal, although a typical

    CdTe module contains only 0.1% Cadmium which is

    reported to be a lower quantity of the metal than is found

    in a single AA-sized NiCad battery.

  • V. ADVANTAGES

    1. Available nearly everywhere

    2. Inexhaustible and abundant

    3. Clean energy

    Solar power is clean energy with little

    environmental impact, and does not release air

    pollutants or noise while it is being generated.

    Compared to other means of generating power

    (hydraulic, nuclear, thermal), it demands little in

    terms of installation condition or scale. The

    distance between the point where the energy is

    generated and consumed is therefore short and

    keeps power loss minimal during supply. With few

    moving parts in its system it has no mechanical

    corrosion and long life. Above all, it benefits from

    an infinite source of energy.

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