PV

::Photovoltaic Technology::

Photovoltaics (PV) is the field of technology and research related to the application of solar cells for energy production by converting sun energy (sunlight, including sun ultra violet radiation) directly into electricity by the photovoltaic effect. The latter refers to the process of converting light (photons) to electricity (voltage). Solar cells are photovoltaic devices that use semi-conducting materials to convert sunlight directly into electricity. When sunlight is absorbed by these materials, it causes electrons to flow through the material generating electric currents. Solar cells produce direct current (DC) electricity. There are two broad categories of solar cells; thin film and crystalline.

The key components of a photovoltaic power system are the photovoltaic cells (also called solar cells) interconnected and encapsulated to form a photovoltaic module (the commercial product), the mounting structure for the module or array (several modules mounted and interconnected together to produce a desired voltage and current (power capacity)), the inverter (essential for grid-connected systems and required for many off-grid systems), the storage battery and the charge controller (for off-grid systems only). Solar cells are typically combined into modules that hold up to 40 cells to generate substantial voltages (typically 12 V or 24V) and currents that can be used to power various devices. The power output of a module is measured under standardized test conditions in Watt Peak (Wp).

Performance of PV modules depends on the amount of solar irradiation received which varies by location and season. For this reason, systems normally need to be carefully designed. A typical commercial solar cell has an efficiency of 15%. The first solar cells, built in the 1950s, had

Applications and Efficiency

PV technology can be employed in a variety of applications: Typical applications of PV technology include remote telecommunications, cathodic protection of pipelines, PV home systems, vaccine refrigeration, water pumping, grid connected or building integrated systems, miniature electronic devices and toys:

*Off-grid domestic PV systems like solar home systems:

Provide electricity to households and villages that are not connected to the utility electricity network (also referred to as the grid)
Provide electricity for lighting, phone charging, refrigeration and other low power loads
Are often the most appropriate technology to meet the energy demands of off-grid communities

*Off-grid non-domestic PV installations:

Are used in locations where small amounts of electricity have a high value
Were the first commercial application for terrestrial PV systems
Provide power for a wide range of applications, such as telecommunication, water pumping, vaccine refrigeration and navigational aids
Make PV commercially cost competitive with other small generating sources

*Grid-connected distributed PV systems:

Provide power to grid-connected customers or directly to the electricity network (specifically where that part of the electricity network is configured to supply power to a number of customers rather than to provide a bulk transport function)
May be on or integrated into the customer's premises, often on the demand side of the electricity meter, on public and commercial buildings, or elsewhere in the built environment

*Grid-connected centralized PV systems:

Perform the functions of centralized power stations
Supply power that is not associated with a particular electricity customer
Primarily supply bulk power, rather existing on the electricity network to perform specific functions.

To design a system for PV application the following information is required: daily energy requirement, voltage and current draw of appliances, average insolation (kWh/m2 day), the yearly variation in insolation levels for the specific area and the equipment type, availability and costs to enable appropriate selection.

Capability and Limitations

The number and type of appliances that can be used with SHS is limited. Lights, TVs, sound systems and low-wattage DC appliances are appropriate.

Costs of well designed, installed and maintained systems are relatively high on a cash basis although the life cycle cost of PV is often less than comparison technologies.
Sales, installation and support infrastructure for systems is largely underdeveloped leading to higher delivery and maintenance cost.
Experiences show that security is essential for most PV installations. In remote unguarded locations, there is risk of the modules and other system components being stolen or vandalized.

Photovoltaic technology is particularly suitable for small power requirements and remote area applications. The provinces of Sindh and Balochistan, and the Thar Desert are specially suited for the utilization of solar energy through photovoltaics. Balochistan, the largest province of Pakistan area-wise, has a population density of just 21 persons per square kilometer, with 77% of the population living in rural areas. About 90% of the villages are yet to be electrified. Large distances with absolutely no approach roads separate these villages. The houses are mostly 'kacha' hut type with walls and roofs made with a combination of mud and straw. Light is the main requirement for these houses. Most of the houses consist of only one room. The electric requirement for each house varies from 50 to 100 W maximum. Transmission lines are very expensive to build in these areas and there is only a remote possibility of grid connection in the near future. Also, the extension of grid lines for such small power requirements is very uneconomical. Local power generation is a possible solution to these problems. When considering diesel generators, transportation of fuel to such remote areas and maintenance are again a costly proposition, therefore, solar energy looks like the best (and only) option for these areas.

In Photovoltaic technology PCRET has photovoltaic device fabrication facilities. Six main labs have been established within PCRET. These Labs are:

· Crystal Growth Lab

· Wafering Lab

· Cell Process Lab

· Test and Measurement Lab

· Lamination Lab

· Solar Testing Lab

· Analysis Lab

The Crystal Growth Lab is equipped with two Czochralski Crystal Puller of Model CG 300 and CG 6000 from Hamco USA. Silicon Single Crystal ingots of diameter 4” to 6” can be grown in this Lab. Photograph of the The grown ingots are sliced in wafering Lab which is equipped with ID Saw, Wire Saw, Squarer and Cutter machinery.

The Silicon cut Wafers are then processed in the cell fabrication lab for making of Solar Cells. For this purpose etching, polishing, junction, formation, alloying, masking and contact making are performed in this Lab. Some of the systems/equipments of cell processing Lab. In this Lab heat resistive and electron beam high vacuum systems are also available, which can be used to grow thin films for research study and making of thin films solar cells

The fabricated solar cells are interconnected in the lamination Lab for PN module making. Three Laminations are available in the Lamination Lab to produce Photovoltaic Panels of various dimension and ratings, Solar cells can be cut to small pieces using Nd-YAG laser cutter for fabrication of small size solar panels for low power applications. The facility of Laser cutter exists within Photovoltaic Division.

The cells and PV Panels are tested in Test and Measurement Lab as per International Standards. The Following facilities exist:

Ø Solar Cell Testing

Ø Photovoltaic PV Panel Indoor Testing

Ø Photovoltaic PV Array Outdoor / Field Testing

Ø PV Panel Environmental Testing

Ø PV Panel Insulation Testing

Ø Solar Cell Contact Adhesion Testing

Ø Inverter Testing

Ø Battery Testing

Ø Solar Flat Plate Collector Testing

Ø Solar Water Heater Testing

Whereas in the Analysis Lab, the spectroscopic analysis of the semiconductor and other geological materials is done for detection of metallic and non metallic impurities up to the level of parts per million (PPM) and parts per billion (PPB) level. The Lab is equipped with Inductively Coupled Plasma (ICP) Spectrometer and Gas Chromatograph (GC). ICP detects impurities using options of Atomic Absorption, Atomic Emission and Flameless Techniques whereas gas chromatograph GC analyses gases using FID and TCD detectors. The photograph of such systems installed within PCRET analysis Lab.