Photovoltaic Systems

Solar Photovoltaic Systems

Photovoltaic (PV) or solar cells are used for generation of power from solar light. Solar cells convert light energy into electrical energy; but do not store the same. Whenever solar radiation is available, solar cells can produce electrical current. To get electricity needed at night, a battery is included in the circuit which stores the energy generated during the day. Several materials are used to make solar cells; the most common being silicon. Typical solar cells are 3 – 6 inches in diameter and are available in various shapes such as circular, square etc. The conversion process occurs instantly whenever light falls on the surface of a cell. The output of the cell is proportional to the light input.

Photovoltaic ( PV ) effect was first described in 1839 by a French physicist Edmond Becquerel. It was further studied by Heinrids Hertz in 1870s. Initially, selenium PV cells were used for converting light to electricity at 1 to 2 % efficiency. PV was first used commercially in 1940s. In the early 1950s, Czochraiski process was developed for producing highly pure crystalline silicon. The first crystalline silicon PV cell was developed in 1954 with 4 % efficiency. The PV devices used now have efficiencies in the range of 13 – 16 %.

How is electricity produced ?

When the light rays fall on a solar cell, they penetrate into the solar cell and create a flow of electrons throughout the crystal structure. The crystal structure of silicon contains empty spaces ( hole ) which accept these electrons. As one electron moves to fill a hole, it creates another hole and it is this flow of electrons which produces electricity.

Cells, Modules, Arrays

There are different types of silicon cells such as:

  • (a) Mono crystalline silicon
  • (b) Poly crystalline silicon
  • (c) Amorphous silicon

The most common types of silicon cells are mono crystalline with efficiency of about 12%.

Since typical silicon solar cells produce only about 0.5 V, many cells are connected together to give higher and useful voltages. Usually 30–36 cells are connected together in a circuit to give a final voltage of about 15 to 17 V, which is sufficient to charge a 12 V battery. If the voltage or current from one module is not enough to power the load, then modules can also be connected together, just as the cells. Manufacturers usually build modules with convenient junction boxes that allow inter connection in series or parallel.

Module: refers to set of solar cells connected in series and parallel for required power (voltage and current).

Array: refers to set of modules connected in series and parallel for higher power output especially in kilowatts.

Different methods of use of solar PV

(i) Instantaneous:

Under this method, electricity is produced whenever there is sunshine and is used instantaneously and no storage is involved in this mode. This mode is useful only when there is sunlight and can not be used at night.

Example : Solar water pumping

(ii) Store and Use

In this method, electricity produced during day time is stored in a battery and used either simultaneously or at night for lighting applications or traffic signals.

Example : Solar home lights, street lights, radio, traffic signals etc.

(iii) DC to AC conversion

Solar module produces DC electricity, which is stored in the battery and converted as AC electricity through an inverter and used for domestic AC appliances such as conventional lights, fans, TV etc.

(iv) Hybrid systems

SPV power plant in conjunction with a diesel generator set or small aerogenerators could be used as hybrid system to increase the availability of power during day and night.

Components of the Solar PV system

The SPV systems generally consist of the following components :

(i) SPV Modules / Panels

SPV module / panel is made of number of solar cells connected together in parallel and series to produce electricity from sun light.

(ii) Battery

D.C. electricity produced during day time is stored for use at night. Mostly, lead acid batteries are used. Nichel cadmium batteries are also suitable but are expensive. All batteries used for P.V. applications are deep cycle i.e. designed to discharge down to 50 % or more without damage so that they can supply power over a long period of time unlike a car battery which is usually discharged to about 3 - 5 % only. The life time of battery varies depending on factors such as usage, maintenance and proper charging. Normal life is about 5 years.

(iii) Balance of System / Power Conditioner

It helps maintain the battery at as high a charge as possible and provides the required quantity of electricity, at the same time protecting the battery from deep discharge or over-charge. Power conditioners consist of

  • 1. Charge controllers which limit the current and voltage to maximize power output.
  • 2. Inverter ( for AC applications ) to convert DC power to AC power.

(iv) Power/electrical load

Luminaires or electrical appliances such as fan, TV, pump etc. form the electrical load in S.P.V. system.

Types of Solar PV System

1 Solar Lantern
2 Solar PV Home Lights / Office Lights
3 Solar PV Street Lights
4 Solar Water Pumps
5 Solar PV Power Plant
6 New and Emerging uses of Solar PV Systems

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