Solar Energy in India
India being a tropical country receives adequate solar radiation for 300 days, amounting to 3,000 hours of sunshine equivalent to over 5,000 trillion kWh. Almost all the regions receive 4-7 kWh of solar radiation per sq mtrs with about 2,300–3,200 sunshine hours/year, depending upon the location. Potential areas for setting up solar power plant can be analyzed using Solar irradiation map of India.
The generation of solar electricity coincides with the normal peak demand during daylight hours in most places, thus mitigating peak energy costs, brings total energy bills down, and obviates the need to build as much additional generation and transmission capacity as would be the case without PV.
Large scale PV plants are used for electricity generation that is fed into the grid. Such systems typically consist of one or more photovoltaic (PV) panels, a DC/AC power converter/inverter, racks, mounting fixtures, and electrical interconnections. Additionally, such systems could also include maximum power point trackers (MPPT), battery systems and chargers, solar trackers, software for energy management, solar concentrators etc. The electricity generated is either stored, used directly for self-consumption, or is fed into large electricity grids.
Grid connected projects may be either i) Ground Mounted PV or ii) Rooftop PV
- i) Ground Mounted PV
SECI has been designated as the nodal agency for the implementation of 750 MW of Solar PV Projects under JNNSM Phase II, Batch-I, wherein SECI has been entrusted with the responsibility of projects selection, monitoring and timely execution, handling VGF funds and trading of the power generated. 750 MW of projects have been selected through a transparent process of VGF-based reverse bidding, 50% of which have the mandate of domestic content requirement (DCR).
A Solar Park is a concentrated zone of development of solar power generation projects, by providing to developers an area that is well characterized, properly infra-structured and where the risk of the projects can be minimized as well as the facilitation of the permitting process.
MNRE plans setting up 25 solar parks, each with a capacity of 500 to 1000 MW; thereby targeting around 20000 MW of solar power installed capacity. These solar parks will be put in place in a span of 5 years and the solar projects may then come up as per demand and interest shown by developers.
Roof-top solar PV installations are becoming a popular green energy option for not only meeting own electricity load but also injecting surplus generation into the grid. Schools, hospitals, storehouses, bus stations, railway stations etc.provide ample spaces to set up PV projects. There is a high possibility of natural load-generation balance if roof-top PV solar systems are installed.
The Ministry of Shipping (MoS) has undertaken an initiative to implement utility-scale Solar Photovoltaic Power Plant projects at various major ports across the country. The Solar Energy Corporation of India (SECI) has been appointed as the overall project management consultant for these projects. An MoU has been signed in this regard between SECI and the Indian Ports Association (IPA), on behalf of the individual port trusts, to implement the solar energy projects. As part of this activity, installation of grid connected solar power plants in the following ports is underway. In addition, installation of rooftop solar power projects at various ports is also undertaken and the related processes has been started.
Concentrating Solar Power (CSP) technologies use systems of mirrored concentrators to focus direct beam solar radiation to receivers that convert the energy to high temperature for power generation. There are four main configurations that are commercially available- Parabolic Trough, Linear Fresnel Reflector, Parabolic Dish and Central Receiver Tower – with Parabolic Trough being the most prevalent.
SECI is developing Pilot Concentrated Solar Power Projects to establish new technologies on commercial scale. Two CSP Plants, of 50 MW each, are being developed with the following parameters:
- Project 1: 50 MW capacity project on Parabolic Trough technology with hybrid cooling and 3 hours Thermal storage, using up to 15% auxiliary fuel. It would reduce water consumption to 25% of a conventional CSP plant.
- Project 2: 50MW capacity project on Solar tower technology with a provision of high (>470 deg. C) operating temperature and 3 hours Thermal storage, using up to 15% auxiliary fuel.
Solar Thermal systems have the flexibility of being used for off-grid applications too. Industrial process heat (IPH) applications below 250°C, for example, contribute to about 15 to 20% of India’s total oil consumption (almost 80%-90% of which is imported). SECI envisages tremendous potential in the field of off-grid solar thermal application and is in the process of drawing specific plans for implementation and facilitation of projects throughout the country. Such decentralized systems not only empower the customers by granting energy-independence but also have immense potential of scalability. Commissioning of Decentralized Solar Thermal applications is, therefore, going to be a prominent strategy towards achievement of these targets.
Other significant off-grid applications include solar water heaters (using both Flat Plate Collectors and Evacuation Tube Collectors), solar mass cooking and comfort cooling applications.
The mission is setting an ambitious target for encouraging solar thermal applications in domestic and industrial segment. The key strategy is
- To make solar heaters mandatory, through building bye-laws and incorporation in the National Building Codes
- To ensure effective mechanism for certification/rating of manufacturers
- To promote such thermal applications through local agencies/power utilities, and
- To support the upgrading of technologies and manufacturing capacities through concessional funding.
Applications of Solar Power
- Solar Water Pumps: In solar water pumping system, the pump is driven by motor run by solar electricity instead of conventional electricity drawn from utility grid. The pumping system draws water from the open well, bore well, stream, pond, canal etc
- Solar Photovoltaic (PV): Photovoltaic solar cells, which directly convert sunlight into electricity, are made up of semi conducing materials. The simplest PV cells-power are watches and calculators, while more complex systems can light houses and provide power to the electrical grid. Some applications for PV systems are lighting for commercial buildings, outdoor (street) lighting, rural and village lighting etc. Solar electric power systems can offer independence from the utility grid and offer protection during extended power failures.
- Solar Water Purifier: Solar water decontamination system is a water purification system at household level based on solar radiation treatment and water distillation with additional use of solar heating. It is a combination of two water purification processes, the Solar Water Disinfection System (SODIS) and the solar distillation process. For the cases where low turbidity water is not available, contaminated water will be distilled to drinking water using the solar heated still to remove any non-volatile solid impurities such as salts, sediment, heavy metals and microorganisms. The solar water purification system uses only solar energy and can be built using recycling materials, thus, the system is environmentally sustainable.
- Solar collector with optical efficiency: Solar thermal collectors are not 100% efficient. Losses come from several sources, heat losses – solar radiation that is converted to heat, but lost before it can be used. Losses are due to three modes of heat transfer; and Optical losses – solar radiation incident upon the collector that is not converted to heat energy. Procedures have been developed to characterize the performance of flat plate, evacuated tube, and CPC evacuated tube solar thermal collectors. An explanation is as follows:
- Solar Air Heating: The applicability of the solar air heater depends on various factors like high efficiency, low fabrication cost, low installation and operational cost and some other specific factors regarding specific uses. Extensive work in solar air heaters has been done. Various geometries have been proposed and their theoretical investigation is carried out. But it needs commercial exploitation.
- Solar cooling
Concentrating solar collectors use mirrors to focus the sun’s energy on a tube containing fluid. The mirrors follow the sun, heating the fluid to very high temperatures. Absorption chillers operate by using this solar-heated fluid, rather than fossil fuels or electricity, to drive the refrigeration process. Using solar energy with absorption chillers reduces site-generated greenhouse gases as well as the emissions created when fossil fuels are burned to create electricity.
There are multiple alternatives to compressor-based chillers that can reduce energy consumption, with less noise and vibration. Solar thermal energy can be used to efficiently cool in the summer, and also heat domestic water and buildings in the winter. Single, double or triple iterative absorption cooling cycles are used in different solar thermal cooling system designs. The more cycles, the more efficient these systems are.
The term solar architecture refers to an approach to building design that is sensitive to Nature and takes advantage of climatic conditions to achieve human comfort rather than depending on artificial energy that is both costly and environmentally damaging. Unlike the conventional design approach that treats climate as the enemy which has to be kept out of the built environment, solar architecture endeavours to build as part of the environment using climatic factors to our advantage and utilising the energy of Nature itself to attain required comfort levels. Nature’s energies can be utilised in two ways – passiveand active and consequently solar architecture is classified as passive solar and active solar architecture.
Passive solar architecture:
It relies upon the design or architecture of the building itself to ensure climate control by way of natural thermal conduction, convection and radiation. The rudiments of solar passive design were developed and used through the centuries by many civilisations across the globe; in fact, many of these early civilisations built dwellings that were better suited to their climatic surroundings than those built today in most developed and developing countries. This has been largely due to the advent of cheap fossil fuels that allowed for artificial temperature and light control at the cost of natural light and cooling.
A substantial share of world energy resources is therefore being spent in heating, cooling and lighting of such buildings. The use of solar passive measures such as natural cross ventilation, sufficient day-lighting, proper insulation, use of adequate shading devices coupled with auxiliary energy systems that are renewable and environment friendly can considerably bring down the costs as well as the energy needs of the building.
Solar detoxification uses the ultraviolet energy in sunlight to destroy contaminants. The contaminated medium is mixed with a catalyst (e.g., titanium dioxide) and fed into an illuminated reactor. Ultraviolet light activates the catalyst, forming reactive chemicals known as “radicals.” These are oxidizing agents. When they come into contact with contaminants, they break them down into non-toxic byproducts such as carbon dioxide and water.
For contaminated soil, vacuum extraction is used to remove contaminants from soils. After the contaminants are condensed, they are fed into the reactor. For contaminated groundwater, the groundwater passes over the catalyst. An advantage of this system over conventional treatment processes, such as those using granular activated carbon or air stripping, is that it destroys the toxic compounds.
The process can only be used effectively during the daytime with normal sunlight intensity. Weather changes affect destruction rates. Large spaces are required for the reactor. The larger the reactor, the more efficient the process.
Solar detoxification is used for the destruction of volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and pesticides in soil and groundwater.
Solar Cooking Systems
- Solar Cookers
A solar cooker lets UV light rays in and then converts them to longer infrared light rays that cannot escape. Infrared radiation has the right energy to make the water, fat and protein molecules in food vibrate vigorously and heat up. It is not the sun’s heat that cooks the food, nor is it the outside ambient temperature, though this can somewhat affect the rate or time required to cook, but it is the sun’s rays that are converted to heat energy that cook the food; and this energy is then retained by the pot and the food by the means of a lid. An effective solar cooker will use the energy of the sun to heat a cooking vessel and efficiently retain the energy (heat) for maximum cooking effectiveness.
Akshay Urja shops
The Akshay Urja shops have been constituted to carry out the following functions:
- Sale of different renewable energy and energy efficient devices;
- Repair and servicing of renewable energy devices;
- Dissemination of information on renewable energy devices/systems; and
- Facilitate individuals/companies to go in for renewable energy devices.
Passive solar heating
Passive solar heating uses free heating direct from the sun to dramatically reduce the estimated 40% of energy consumed in the average Australian home for space heating and cooling.
Passive solar heating is the least expensive way to heat a home. Put simply, design for passive solar heating aims to keep out summer sun and let in winter sun while ensuring the building’s overall thermal performance retains that heat in winter but excludes it and allows it to escape in summer. Passive solar design also depends on informed, active occupants who remember to open and close windows and isolate zone spaces, for example, each day.
Passive solar heating requires careful application. It maximises winter heat gain, minimises winter heat loss and concentrates heating where it is most needed.
Solar radiation is trapped by the greenhouse action of correctly oriented (north-facing) glass areas exposed to full sun. Window orientation, shading, frames and glazing type have a significant effect on the efficiency of this process. The trapped heat is absorbed and stored by materials with high thermal mass (usually masonry) inside the house. It is re-released at night when it is needed to offset heat losses to lower outdoor temperatures.
There are different possibilities to achieve solar cooling. It can be achieved either by generating electricity and operating a compressor or by using the solar heat directly to operate a heat-driven cooling cycle. Of the above possibilities, the ones using thermal energy directly to produce cooling are more efficient as they do not have other intermediary conversion processes.
The solar cooling system can be divided into three major components; solar energy collecting element, refrigeration cycles, and the application at different temperature ranges.
The proper cycle for each application mainly can be selected based on cooling demand and required temperature ranges. Some applications require different range of cooling which cannot be achieved by any single refrigeration cycle.
Solar electrical cooling system consists of a photovoltaic panel and an electrical refrigeration device. Photovoltaic cells transform light into electricity through photoelectric effect. Many of the solar electrical refrigeration systems are made for independent operation.
Solar cells, also called photovoltaic (PV) cells by scientists, convert sunlight directly into electricity. PV gets its name from the process of converting light (photons) to electricity (voltage), which is called the PV effect. The PV effect was discovered in 1954, when scientists at Bell Telephone discovered that silicon (an element found in sand) created an electric charge when exposed to sunlight. Soon solar cells were being used to power space satellites and smaller items like calculators and watches.
Traditional solar cells are made from silicon, are usually flat-plate, and generally are the most efficient. Second-generation solar cells are called thin-film solar cells because they are made from amorphous silicon or nonsilicon materials such as cadmium telluride.
Thin film solar cells use layers of semiconductor materials only a few micrometers thick. Because of their flexibility, thin film solar cells can double as rooftop shingles and tiles, building facades, or the glazing for skylights.
Third-generation solar cells are being made from a variety of new materials besides silicon, including solar inks using conventional printing press technologies, solar dyes, and conductive plastics. Some new solar cells use plastic lenses or mirrors to concentrate sunlight onto a very small piece of high efficiency PV material. The PV material is more expensive, but because so little is needed, these systems are becoming cost effective for use by utilities and industry. However, because the lenses must be pointed at the sun, the use of concentrating collectors is limited to the sunniest parts of the country.
Solar Photovoltaic Technology is employed for directly converting solar energy to electrical energy by the using “solar silicon cell”. The electricity generated can be utilized for different applications directly or through battery storage system. Solar PV has found wide application in rural areas for various important activities besides rural home lighting. Remote villages deprived of grid power can be easily powered using the Solar Photovoltaic technology. The economics of rural electrification can be attractive considering the high cost of power transmission and erratic power supply in the rural areas.
A roof top SPV system could be with or without grid interaction. In grid interaction system, the DC power generated from SPV panels is converted to AC power using power conditioning unit and is fed to the grid either of 11 KV three phase line or of 220 V single phase line depending on the system installed at institution/commercial establishment or residential complex. They generate power during the daytime which is utilized fully by powering the captive loads and feeding excess power to the grid as long as grid is available.
The grid- interactive rooftop SPV systems thus work on net metering basis wherein the beneficiary pays to the utility on net meter reading basis only. Ideally, grid interactive systems do not require battery back up as the grid acts as the back-up for feeding excess solar power and viceversa. However, to enhance the performance reliability of the overall systems, a minimum battery-back of one hr of load capacity is strongly recommended.
Non-grid interactive systems ideally require a full load capacity battery power back up system. However, with the introduction of advanced load management and power conditioning systems, and safety mechanisms, it is possible to segregate the day-time loads to be served directly by solar power without necessarily going through the battery back-up.
There have been several initiatives from the Government of India to promote solar PV applications. From time to time the Ministry has implemented various schemes for demonstration and promotion of solar energy devices.
The National Solar Mission program was initiated by the Government as one of the eight programs under the National Action Plan for Climate Change by the Prime Minister of India in 2008. In the month of November 2009, the Mission document was released as the Jawaharlal Nehru National Solar Mission (JNNSM) and the Mission was formally launched by the Prime Minister of India on January 11, 2010. Apart from solar PV, the already existing technology in India, JNNSM also has the provision to develop solar thermal technology for large scale grid connected power plants.The proposed roadmap is as follows:
- Systems mainly for electricity conservation:
- Solar street lights
- Solar traffic signals
- Solar blinkers
- Solar power packs/inverters
- Solar illuminating hoardings/ Bill boards
- Other systems of community use as felt necessary by Implementing Agencies
- Systems for abatement of diesel & other fuel oil
- Roof top SPV systems with or without grid interaction