Photovoltaics cells: working principle

Photovoltaics (PV) or solar cells as they are often called, are semiconductor devices that convert sun energy into direct current (DC) power. Gatherings of PV cells are electrically arranged into modules and arrays, which can be used to charge batteries, operate motors, and to power any number of electrical loads. With the appropriate power conversion equipment, PV systems can produce alternating current (AC) compatible with any conventional appliances, and can operate in parallel with, and interconnected to, the utility grid.

History of PV cells

The first conventional photovoltaic cells were produced in the late 1950s, and throughout the 1960s were principally used to provide electrical power for earth-orbiting satellites. In the 1970s, improvements in manufacturing, performance and quality of PV modules helped to reduce costs and opened up a number of opportunities for powering remote terrestrial applications, including battery charging for navigational aids, signals, telecommunications equipment and other critical, low-power needs.

In the 1980s, photovoltaics became a popular power source for consumer electronic devices, including calculators, watches, radios, lanterns and other small battery-charging applications. Following the energy crises of the 1970s, significant efforts also began to develop PV power systems for residential and commercial uses, both for stand-alone, remote power as well as for utility-connected applications. During the same period, international applications for PV systems to power rural health clinics, refrigeration, water pumping, telecommunications, and off-grid households increased dramatically, and remain a major portion of the present world market for PV products. Today, the industry’s production of PV modules is growing at approximately 25 percent annually, and major programs in the U.S., Japan and Europe are rapidly accelerating the implementation of PV systems on buildings and interconnection to utility networks.

working principle of Photo Voltaic cell

A typical photovoltaic cell is called a PN junction composed of a thin wafer consisting of an ultra-thin layer of phosphorus-doped (N-type) silicon on top of a thicker layer of boron-doped (P-type) silicon. An electrical field is created near the top surface of the cell where these two materials are in contact. When sunlight strikes the surface of a PV cell, this electrical field provides momentum and direction to light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electrical load




Regardless of size, a typical silicon PV cell produces about 0.5 – 0.6 DC volts under open-circuit, no-load conditions. The current (and power) output of a PV cell depends on its efficiency and size (surface area), and is proportional to the intensity of sunlight striking the surface of the cell.

For example, under peak sunlight conditions, a typical commercial PV cell with a surface area of 160 cm^2 (~25 in^2) will produce about 2 watts peak power. If the sunlight intensity were 40 percent of peak, this cell would produce about 0.8 watts.

The Sun is by far the most abundant form of renewable energy available on our planet. The amount of energy that Earth receives from the Sun is immense, in fact, it has been calculated that the amount of solar energy that Earth receives in one minute from the Sun would be enough to satisfy the energy needs of entire human population for one year. The world, however, uses only a tiny fraction of totally available solar energy, primarily because solar power technologies need to improve their cost-effectiveness (solar panels cost a lot and they are not that efficient).

When explaining the working principle of photovoltaic (solar) cells we first need to know that sunlight is made out of tiny energy pockets called photons and that each individual solar cell is designed with a positive and negative layer thus being able to create an electric field (similar to the one in batteries). As photons are absorbed in the cell their energy causes electrons to get free, and they move to the bottom of the cell, and exit through the connecting wire which creates electricity (flow of electrons). The bigger amount of the available sunlight the greater the flow of electrons, and the more electricity gets produced in the process.

Photovoltaic or solar panels are devices that are used to convert sunlight into electricity. Photovoltaic panels consist of numerous solar cells. By combining these individual solar cells into photovoltaic panels we can produce enough energy to power our homes as well as for many other purposes (space satellites). 

Photovoltaic cells are usually made of expensive materials such as silicon, thus explaining the high costs of solar panels. However, solar panel prices have decreased by approximately 70% in the last three years, meaning that they are becoming more competitive with fossil fuels in terms of economics.

Installing solar panels on the rooftops of your home is not that complicated, primarily because solar panels do not have moving parts. Once installed, they operate very silently, and with enough available sunlight will provide emission-free source of renewable energy.

The electricity generated by photovoltaic panels is direct current. This means that there is a need for installing inverter. With the installation of inverter this direct current can be converted into alternating current so it's in sync with mains electricity, and can be used normally.

As already said above, the amount of sunlight at your location plays key role in determining the economics of your solar power installation. Some areas receive more sunlight than other, and in these areas installing solar panels is more economically viable.