Solar cell by definition is a cell or an electrical device which transforms solar energy into electrical energy. A solar cell is primarily a photovoltaic cell which produces electricity directly from light through the photovoltaic effect. This cell when subjected to light can create and maintain an electric current without being connected to any outer source of voltage. A solar cell produces direct current (DC) which can be used to operate DC motors, light bulbs, charge batteries, etc.
Sunlight consists of photons that can be directly converted into electricity. Photons create free electrons that travel through the wires and generate electricity. Light is emitted when the photons come in contact with the solar cells. The amount of photons that come into contact with the cells directly governs the quantity of light emitted. The greater the amount of light greater is the number of photons striking the cells and greater is the power ultimately generated.
In order to generate valuable power, it is essential to link a number of cells together so as to form a solar panel, which also goes by the name of a photovoltaic module. The minimal output voltage of a solar panel is customarily 12 Volts and they may either be used individually or wired together in a group. The number and size needed are governed by the quantity of light available and the amount of energy necessary.
Types of Solar Cells
Solar cells are created out of silicon, same material which is also a major component of integrated circuits as well as transistors. Silicon is subjected to a treatment of ‘doping’ or nobbling, thus enabling light to convert into electricity once the electrons are discharged. There are several different kinds of solar cells:
- Monocrystalline Cells — These cells are chiseled out from a single silicon bar that has been raised from a solitary and large-sized silicon rock.
- Polycrystalline cells — These cells are also cut from a silicon bar. However, the bar itself consist of various smaller crystals of silicon.
- Amorphous Solar Cells — These are also referred to as thin film cells as these are comparatively thin in width. Amorphous (or thin film) technology is generally observed in smaller solar cell panels — for example, it can be found in garden lamps or calculators. Amorphous panels also have their wide usage for larger solar applications. A film is placed on a sheet of special materials such as steel to create amorphous models. The section is shaped as a single piece and its unique cells are a lot less visible compared to the other kinds. Amorphous panels have been found to be not much efficient as compared to that of individual cells. Their efficiency has been found to be lower than those created from singular solar cells. However, there has been considerable improvement over last few years to the extent of these being a realistic and useful substitute for panels created out of crystalline cells. The biggest benefit from this is their cost effectiveness. This result in comparatively low-cost per every single Wattage of power produced and this is its most important advantage. This issue can be counter balanced, however, by keeping density of power to lower level; more number of panels are required for an equal amount of power production and so greater space is consumed.
- Crystalline Solar Cells — These are held together in series mode to generate solar panels. Since every cell produces different range of voltages ranging from 0.5 to 0.6 Volts, a total of 36 individuals cells are used for creating open-circuit 20 volt voltage system. Generally, a 12 volt battery can be charged easily with the extent of power generated.
Even though monocrystalline cells have greater efficiency viz-a-viz polycrystalline cells, they do reflect only slight difference in the performance. Apart from that, crystalline cells usually have a greater shelf life than that of amorphous cells.
Although photovoltaic is mostly used to refer particularly to the production of electricity from sunlight, it can also refer to those cells that make use of any other form of artificial light and not just the sun. This is when the cell is used as a ‘photodetector’ (as in the case of infrared detectors) which identifies light or any other electromagnetic radiation close to the perceptible range, or determines intensity of light.
A photoelectrochemical cell is either a variation of photovoltaic cell or a mechanism that directly breaks water into hydrogen and oxygen using only solar illumination.
The first experimental proof of the photovoltaic effect was made by A. E. Becquerel, the French physicist in 1839. It was to be many years after the invention and constant upgrades of many more versions of the photovoltaic cell before the first realistic cell was designed at the Bell Laboratories in 1954 by Gerald Pearson, Calvin Souther Fuller and Daryl Chapin. The cells achieved 6% efficiency and were primarily used for small scale purposes like toys.
Solar cells came out of anonymity and achieved popularity when they were used to power a small part of the satellite Vanguard I also in 1958. Initially, when only batteries were used to fuel the satellites, they would invariably suffer from shorter life span. When cells were attached to the external surface of the body, it resulted in longer mission time without requiring any major changes to the satellite or its systems. Following its success, solar cells gradually began to be incorporated into satellites like the Telstar manufactured by Bell Laboratories.
Several separate cells go into making a solar battery. In a lead-acid battery, each cell generates about 2 Volt DC. Therefore, 6 cells are needed for a complete 12V battery. A battery’s life cycle is determined by the number of periods it can be charged successfully. The life cycle of a battery indicates its utility with solar panels. Generally, for solar power applications, a solar battery should be capable of charging and discharging hundreds and thousands of times. There are several types of batteries:
- Leisure Batteries — These are also known as caravan batteries and are among the cheapest deep-cycle batteries. They often resemble car batteries, but differ in the sense that their plate construction is more complex. Their competence range is normally between 60 – 120 Ah at the capacity of 12 Volts, which makes them perfect for small-scale systems. Since the life cycle of these batteries is restricted to a few hundred, they are usually adapted to systems that are not meant for everyday use, like caravans or holiday homes.
- Traction Batteries — Most commonly, these are the solar batteries being used to power electric vehicles. The vehicles can be scooter-like or even bigger ( a fork-lifting truck, for example) within capacities ranging from 30 – 40 Ah to several hundred. Capacity of small traction batteries hovers around 6 – 12 Volts. They are perfect for solar power functions because they are easily dischargeable and rechargeable on a daily basis. Larger traction batteries are good for thousands of discharging cycles. Semi-traction batteries are high quality leisure batteries, displaying a greater life cycle.
- Sealed Batteries — They mostly range in capacity starting from as low as 1 Ampere-hour to as high as hundreds of Ah. These batteries are known for their minimal maintenance needs (as they are spill-proof). Their major drawbacks are that they are costlier than others; they require more precise charging control system and have shorter shelf-life, particularly at higher temperature ranges. They are most suitable when the installed solar power generating systems require long hours of operation without maintenance.