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Basics of Solar Power Generation
04/30/2013
By R C Sabarish
Being a tropical country, with an average intensity of solar radiation received in India is 200 MW/ km2 with 250-300 sunny days in a year, India has a huge potential for solar power generation. At present, the government and private sector are currently busy with the development of a large number of solar power projects in India under the central government's most ambitious Jawaharlal Nehru National Solar Mission (JNNSM).
Under this mission, the country aims to generate 1,000 MW to 2,000 MW energy on utility grid power by the year 2013, which includes rooftop power generation. India targets to generate utility grid power of 20 GW and off -grid solar power of 2,000 MW by the year 2020.
The plan is envisaged to tame the current power shortages that the industries across all sectors are facing. As per the Central Electricity Authority (CEA) report, the peak electricity demand in December 2012 was 1,28,689 MW, of which 1,16,394 MW was met in the country. Southern region, comprising Andhra Pradesh, Karnataka, Kerala, Tamil Nadu, was the worst hit with a shortage of 17.4 percent or 6,120 MW during the month.
Coal and gas shortage, delay in commissioning of plants and delayed monsoon in South India are the main reasons for power shortage in the region. Considering southern states, Tamil Nadu is the worst hit of all, the state being a developing hub for automobile and other industries, it is forecasted by experts that the demand will exponentially increase in years to come.
The Government of Tamil Nadu has taken steps to resolve the issue of power shortage by investing in renewable energy, mainly solar. Tamil Nadu in its solar energy policy has made it mandatory for large-scale power consumers to meet 6 per cent of their energy requirements from solar power by 2014. As per the policy, it will be mandatory for high-tension consumers in SEZs, IT parks, telecom towers, colleges and residential schools, industries guaranteed with round the clock power supply and buildings with 20,000 sq mt built up area to go in for 6 per cent Solar Purchase Obligation (SPO). Solar power being an expensive source of electricity ranging from Rs. 10 to Rs 15 per KWh as of 2009, has become economical power source, thanks to the international trade which has brought the cost down drastically.
The solar system consists of three main parts: 1) Panel 2) Inverter 3) Battery. Combining these three elements, solar energy can be converted into electrical energy, which can be further used in both households and industries.
PHOTOVOLTAIC SYSTEM
The traditional stand alone system consists of the following:
* PV modules, connected in parallel or series - parallel;
* Charge controller;
* Battery or battery bank;
* Inverter;
* Switchgears and metering;
Solar modules (Solar PV collector) work through, what is called a photovoltaic process - where radiation energy is absorbed from sun by semiconductor cells - normally silicon and transformed into electricity (voltaic).
The electric current then goes to an inverter, which converts the electric current from DC (direct current) to AC (alternating current).The system is then connected to the mains power with battery backup (Fig 1.0) or electricity grid (Fig 2.0).
PV modules
A solar cell, or photovoltaic module (PV), is a device that converts light into electric current using the photoelectric effect.
PV modules are of two types: Crystalline silicon cells, Thin layer cells.
Crystalline Silicon Solar Panels
Traditional systems, called crystalline silicon solar modules, involve wafers of refined silicon beneath sheets of glass. The panels are surrounded by a metal frame. A solar panel installer connects crystalline silicon panels - made with silicon wafers, glass paneling, and a frame. These are by far the most common solar panels. If you've come across a solar panel installation, chances are it uses crystalline silicon technology.
Crystalline silicon technology has been used for around 50 years, and was first developed for powering satellites in space. Crystalline silicon systems are generally capable of converting up to about 18 % of solar radiation exposure into useable electricity. This is termed as a photovoltaic efficiency of 18%. The main complaint of crystalline silicon is that the systems are expensive and bulky.
Thin film solar panels
A new breed of solar technology is thin-film solar panels. Thin film is less bulky than crystalline silicon and increasingly cheaper to produce. Thin-film solar energy systems currently have a lower photovoltaic efficiency than crystalline silicon - converting around 9% to 11% of radiation exposure.
Thin-film solar panels work in the same photovoltaic manner as crystalline silicon modules, without the bulky wafers and glass paneling. Amorphous silicon is a material used in some thinfilm flexible solar panels, which can be moulded in any surface such as roofs or walls.
The main disadvantage of the thin film panels is lower efficiency and its installation requires a large space, to generate the same power installed with crystalline modules.
Solar inverters
Solar inverters may be classified into three broad types: Stand-alone inverters, used in isolated systems where the inverter draws its DC energy from batteries charged by photovoltaic arrays. Many stand-alone inverters also incorporate integral battery chargers to replenish the battery from an AC source, when available. Normally these do not interface in any way with the utility grid, and as such, are not required to have antiislanding protection.
Grid-tie inverters, which match phase with a utilitysupplied sine wave. Grid-tie inverters are designed to shut down automatically upon loss of utility supply, for safety reasons. They do not provide backup power during utility outages.
Battery backup inverters
Battery backup inverters are special inverters which are designed to draw energy from a battery, manage the battery charge via an onboard charger, and export excess energy to the utility grid. These inverters are capable of supplying AC energy to selected loads during a utility outage, and are required to have antiislanding protection..
(The writer is Managing Director, Aeon Renewable Energy Solution Pvt Ltd)
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