Pakistan is most suitable for solar power:

As solar power does not make sense for all locations in the world. The initial cost of installing solar panels or other sources of solar energy is high, and that is not easy for most people to get around. No matter how much some people would like to get involved in the movement to independent energy, it is cost prohibitive.To achieve the highest level of efficiency, which is the entire point of going solar in the first place, you need the proper amount of roof space to support the panels your house may require. Not only how much space is available, but also the location of your home is also relevant to whether or not you can maintain solar energy. Some houses simply do not receive enough sunlight to produce substantial energy. This could mean that either your house is not positioned favorably in relation to a tree or other house.
As you can see, the cons of implementing solar power in your home are primarily cost and location related, but if those two items do not pose issues for you, the good news is…

If solar power is looked at through a long-term lens, you will eventually make back what you originally spent, and possibly start saving money on your investment

Let’s not forget that solar energy increases the value of your home too. Solar power is not subject supply and demand fluctuations in the way that gas is. Silicon, the primary component of solar panels, is also being more widely produced, therefore, less and less expensive with each passing year.

Solar power is independent, or semi-independent. This is great because you can supply your home with electricity during a power outage. Solar power can also be used in remote locations, places where conventional power can’t be reached. On a larger scale, solar power also reduces our need to rely on foreign sources for power.

And last, but certainly not least, it’s good for our planet! Solar energy is clean, renewable and sustainable. It does not fill our atmosphere with carbon dioxide, nitrogen oxide, mercury or any other pollutants. It is a free and unlimited source of power, unlike expensive and damaging fossil fuels.

Solar cell applications

Applications for solar cells are varied, but often involve instances where normal power sources are not available, for example in space probes. More prosaically, they are also used in calculators and wrist watches.

When used in combination - solar modules, or photovoltaic arrays - they can help provide alternative power sources in combination with the electricity grid.

Solar Cell history
The photovoltaic effect was first discovered by Edmond Becquerel in 1839, and the likes of Albert Einstein continued his work. In 1921 Einstein was awarded the Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect".

The first silicon p-n junction (a combination of N-type and P-type semiconductors) solar cell was made at Bell Labs in 1954, with solar cells first being used to power satellites, such as the Vanguard I, in 1958.


In the following, we bring together resources from Electronics Weekly and UK and EU governmental bodies to provide detailed reference information about solar cells.

Manufacturing solar cells

In general, solar cells are made from thin flat layers of semiconductor that include a p-n junction across the whole area of the cell.

A photon hitting the structure creates an electron-hole carrier pair (an exciton) which is separated by the junction. This develops a potential difference between the front and the back of the cell which can produce a current externally.

There is a relationship between the energy in the photon and the bandgap of the structure which governs the success rate of photon to exciton conversion.
Essentially: a particular semiconductor will only efficiently convert one colour of light - or more accurately, light between two wavelengths with sensitivity peaking somewhere near the middle.

For example, 'single junction' silicon solar cells can only absorb the near-infra red part of the sun's spectrum and have a light to electricity conversion efficiency somewhere around 20 per cent.
GaAs and other compound semiconductors can be used to form junctions with other bandgaps, and these junctions can be stacked to harvest a broader range of wavelengths - or photon energies - depending on whether you are thinking classically or in quantum terms.

Providing they are stacked in the right order so the top layers pass unused light through to lower layers, efficiencies of around 40 per cent can be achieved. The current record is almost 50 per cent.

Double and triple junction cells very expensive, and are found on satellites and transcontinental solar racing cars.

Single crystal junctions achieve the efficiencies mentioned above, but are not the cheapest way to produce solar cells.

Amorphous silicon deposited on glass offers around six per cent efficiency at far lower cost than single crystal silicon, and is frequently seen on solar-powered calculators.
Polysilicon on glass is between amorphous and single crystal silicon in both cost and efficiency.

It is widely believed that, depending on latitude, a minimum efficiency of 10 per cent is required to make cost-effective large-scale solar power installations - and the raw materials will have to be cheap.

Researchers are looking at alternative materials to achieve these aims.

For example: single crystal solar cells are made from IC-grade silicon wafers, whereas less pure silicon could be used with negligible loss in efficiency.

The question of whether an industry will form to produce these less pure wafers remains to be answered.

Organic semiconductors can be used to make solar cells, dopes with materials including carbon nanotubes.

Currently efficiency is a few per cent at most and the cells degrade rapidly in sunlight, but some predict organic solar technology will be the one to take off. In the mean time, these cells are likely to develop enough to be used in solar-powered portable electronics.

Out in the far field are solar cells based on structures that mimic photosynthesis, and various liquid and solid bulk technologies, such as the dye-sensitised solar cells in which the excitons form in dye; titanium dioxide pulls away the electrons; and an electrolyte takes away the holes.

With some forms of organic solar cell, as well as solid dye-sensitised cells, it may be possible to make large areas very cheaply on printing presses.

As the manufacture of nano-scale material powders becomes possible, researchers are not only reviewing existing solar cell types, but looking at schemes in which the light is absorbed by particles of similar size to its wavelength.

Solar Cell in spotlight

Taking light energy and converting it into electrical energy, the solar cell is an ecological device. The light absorbing material of a solar cell will lead to photogeneration of charge carriers and a conductive contact will carry off the electrons into another wire or circuit.

Solar cells are made up of thin layers of silicon, and when sunlight strikes a cell's light absorbing material, chemical reactions release electrons, generating an electric current.

For example, they can be constructed with sequential layers of thin film semiconductor materials, which are usually only micrometers thick. According to Sharp Electronics, a specialist in this area, such thin-film technologies account for around 12 percent of all solar modules sold worldwide.

The manufacturers of solar cells boast that they are cost-effective, quiet, safe, and reliable, and only require minimal maintenance over a long operational life.

Note that the term photovoltaic cell is sometimes used when the cell's light source is not explicitly sunlight. Also, the study of solar cells is known as photovoltaics.

Developing Technologies: Electrochemical PV cells

Unlike the crystalline and thin film solar cells that have solid-state light absorbing layers, electrochemical solar cells have their active component in a liquid phase. They use a dye sensitizer to absorb the light and create electron-hole pairs in a nanocrystalline titanium dioxide semiconductor layer. This is sandwiched in between a tin oxide coated glass sheet (the front contact of the cell) and a rear carbon contact layer, with a glass or foil backing sheet.

Some consider that these cells will offer lower manufacturing costs in the future because of their simplicity and use of cheap materials. The challenges of scaling up manufacturing and demonstrating reliable field operation of products lie ahead. However, prototypes of small devices powered by dye-sensitised nanocrystalline electrochemical PV cells are now appearing (120cm2 cells with an efficiency of 7%).

Developing Technologies: Concentrators

Solar cells usually operate more efficiently under concentrated light. This has led to the development of a range of approaches using mirrors or lenses to focus light on to specially designed cells and use heat sinks, or active cooling of the cells, to dissipate the large amount of heat that is generated. Unlike conventional flat plate PV arrays, concentrator systems require direct sunlight (clear skies) and will not operate under cloudy conditions. They generally follow the sun's path through the sky during the day using single-axis tracking. To adjust to the sun's varying height in the sky through the seasons, two-axis tracking is sometimes used.
Concentrators have not yet achieved widespread application in photovoltaics, but solar concentration has been widely used in solar thermal electricity generation technology where the generated heat is used to power a turbine.

Crystalline silicon solar cells

Historically, crystalline silicon (c-Si) has been used as the light-absorbing semiconductor in most solar cells, even though it is a relatively poor absorber of light and requires a considerable thickness (several hundred microns) of material. Nevertheless, it has proved convenient because it yields stable solar cells with good efficiencies (11-16%, half to two-thirds of the theoretical maximum) and uses process technology developed from the huge knowledge base of the microelectronics industry.

wo types of crystalline silicon are used in the industry. The first is monocrystalline, produced by slicing wafers (up to 150mm diameter and 350 microns thick) froma high-purity single crystal boule. The second is multicrystalline silicon, made by sawing a cast block of silicon first into bars and then wafers. The main trend in crystalline silicon cell manufacture is toward multicrystalline technology.

For both mono- and multicrystalline Si, a semiconductor homojunction is formed by diffusing phosphorus (an n-type dopant) into the top surface of the boron doped (p-type) Si wafer. Screen-printed contacts are applied to the front and rear of the cell, with the front contact pattern specially designed to allow maximum light exposure of the Si material with minimum electrical (resistive) losses in the cell.

The most efficient production cells use monocrystalline c-Si with laser grooved, buried grid contacts for maximum light absorption and current collection.

Some companies are productionizing technologies that by-pass some of the inefficiencies of the crystal growth/casting and wafer sawing route. One route is to grow a ribbon of silicon, either as a plain two-dimensional strip or as an octagonal column, by pulling it from a silicon melt.

Another is to melt silicon powder on a cheap conducting substrate. These processes may bring with them other issues of lower growth/pulling rates and poorer uniformity and surface roughness.

Each c-Si cell generates about 0.5V, so 36 cells are usually soldered together in series to produce a module with an output to charge a 12V battery. The cells are hermetically sealed under toughened, high transmission glass to produce highly reliable, weather resistant modules that may be warrantied for up to 25 years.