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.

Happy New Solar 2014!

Happy new year. 2013 is done and gone. The sun celebrated by flipping. And here on earth it was a pretty good year for solar, the best yet, as we will see in the coming months when all the numbers are tallied and investigated. But now its 2014 and if you thought solar power was slowing down, it’s just getting warmed up like a concentrating solar power system in the desert and the industry is looking forward to another record year as solar continues to evolve. 

Analysts are predicting another year of double-digit growth for the solar industry with roughly 40 gigawatts of new photovoltaics at the low end of most analysts’ expectations. There will be a shift away from Europe as the leading market for solar to Asia. The U.S. will also become a much more prevalent market for solar power in 2014 with more homes businesses and utilities adding solar. 

To help accommodate the demand for solar policies will have to be modified in certain markets. Barry Cinnamon, CEO of Cinnamon Solar and founder and former CEO of Westinghouse Solar, told GTM Research that policy changes suggested by utility commissions will be timid, but coming. “The irresistible force of cheaper solar technology is stronger than the immovable object of a high guaranteed rate of return for utilities,” he wrote. The push from commissions won’t be stronger because “utilities have money, political clout and legions of lawyers to effectively lobby to retain their business model.”

One of the most attractive policies for solar are net-metering programs, which allow solar owners and users to sell electricity produced, but not used, by the system owner back to the grid. These policies have come under fire in some markets as widely reported. “The debate over net metering will intensify, but many traditional power companies, which operate both regulated and deregulated businesses, will begin to invest in distributed solar, both outside and inside their territories,” observed Clean Power Finance CEO Nat Kreamer, also writing for GTM Research. “Solar is too profitable a business for utilities to ignore,” he added.

Kreamer’s company is a third-party ownership (TPO) company that provides solar financing services for home and business owners through solar installers. TPO options are popular in states where they’re offered. Looking forward to 2014 he anticipated that more companies will offer such services. “Marketing companies from outside of residential solar will enter the market, driving growth up and customer acquisition costs down,” he said. “Competition and cost structure will push existing solar sales and installation companies to focus on their strengths.”

It will also be a good year for solar installers. “Small solar companies will co-exist with large downstream installers,” Cinnamon predicted.  “Small installers will thrive because their overall operating costs are low and their service levels are high. New financing options, including bank loans and credit unions, will make it easier for local installers (as well as electricians, roofers and HVAC contractors) to compete with ‘no-money-down, free solar’ offers,” he said.

While the solar manufacturing part of the solar industry will remain focussed on balancing manufacturing with demand and producing more efficient, lower-cost modules, solar experts are predicting more emphasis will be placed on reducing costs in other aspects of the solar industry. While policy can help by speeding up the permitting and installation process there’s also a large opportunity to reduce the time it actually takes to install the system itself. For instance, last year TPO solar installer SolarCity signed an agreement to purchase Zep Solar, which developed a mounting and racking system that speeds the installation process, reducing the cost of installing. 

Cinnamon said these “mundane” parts of the rooftop solar array, including solar roof flashings, grounding, racking, job preparation and supply chains, will be a target for cost reductions. “RMI and Georgia Tech just released a terrific time-and-motion study of rooftop solar installations. Their conclusion: the biggest cost reduction opportunities are with integrated racking, and in eliminating the array of little nuts, bolts, wires, clips, pieces and parts that don’t add any functional value to the system, but still need to be assembled on the rooftop.”

One of the interesting companies to watch in 2014 will be First Solar, observed Motley Fool contributor Travis Hoium. The company is the world’s major producer of Cadmium Telluride (CdTe) thin-film photovoltaics, which are cheaper but also significantly less efficient than silicon PV modules (meaning they might be cheaper but they need more space to produce power). “The low cost, low efficiency modules that brought the company to solar dominance are slowly becoming obsolete, and efficiency needs to be improved quickly,” Houim said. 

Indeed, the company has been wildly successful at developing some of the world’s largest PV projects but isn’t very competitive in rooftop sector where space is, at best, limited. It’s becoming a more important market to be in and last year the company purchased silicon PV manufacturer TetraSun. “TetraSun's technology could allow for an entry into the residential and commercial markets where First Solar has so far been shut out,” Hoium said.

Source:- Solar reviews