Technologies & systems to make photovoltaics economical

Code No: TMS092 Price: Rs1400/- Category: Energy: Generation

Technologies & systems to make photovoltaics economical

 

SCOPE AND OBJECTIVE OF THE STUDY

As the title itself indicates, the main objective of this study is to find out the ways and means to utilize the photovoltaic technologies and system for power generation in the most economical way. The scope and objectives of the study may be summarized as follows:

i) Relationship and importance of the specific topic to the broad area to which it belongs.

ii) The current status of the technology in the world and in the country. Market (domestic/export) sizes and their potentials. (use existing information/reports to the maximum extent possible.)

iii) Assessment of the technology, resource parameters such as energy, raw material, infrastructure and manpower etc., to arrive at preferred technology options available to the country.

iv) Short term & long term economic aspects of preferred options alongwith their feasibilities.

v) Impact of the preferred option(s) by itself and its spin offs.

vi) Recommendations:

For implementations of preferred technology option(s) indicating critical inputs such as raw material, capital goods and human resources required and their availability, investments required to commercialize, and benefits/returns expected. Maximum possible quantification is required.

For R&D / Technology development indicating the requirement of inputs and expected benefits.

vii) Action Plan for implementation of recommendations alongwith identification of:

List of available technologies for Indian industry and

The agencies/groups/individuals for implementation.

viii) Expected impact of recommendations, if implemented.

METHODOLOGY

• Survey conducted on status of technology in different countries and details obtained through designed questionnaire for the purpose.

• Data complied and evaluated by contacting manufacturers and other agencies, who are involved in promotion of technologies through questionnaire designed for the purpose.

• The designs, characteristics and suitability with reference to Indian conditions, compared on the basis of available data.

• Various R&D organization of government/quasi government and private sector were contacted for various technologies developed/under development with them.

• Desk research conducted on the available information to evaluate the efficiency to the present technologies and improvements required in the technologies for implementation.

• Facts found during the study were summarized and given recommendations including suggestive action plan.

• In addition to the desk study, questionnaires were mailed to various organizations of power industry to obtain their views on the subject.

• We have also consulted the experts in the field during the preparation of this report like IIT, Delhi, Delhi Engg. College, BHEL, REIL, CEL, Siemens etc.

The continuous supply of solar energy to the earth’s surface is equivalent to about 100000 TW. Approximately one-fifth of the radiation impinges on land are and should, accumulated over two hours, suffice to cover the entire primary energy demand by man for the period of one year.

The only relevant chemical process harvesting solar energy is photosynthesis. The energy converted and stored this way accounts for less tan a 0.1% of the original insolation, yet it is essential to all plant and animal life on earth. Solar radiation may be collected as visible light and also as heat. Technical systems described in the following try to mimic photosynthesis, both for electricity generation through direct conversion technologies, and fuel production in order to achieve energy storage.

Photovoltaic Technology enables direct conversion of sunlight into electricity. This is achieved through the use of a semiconductor solar photovoltaic cell which when exposed to sunlight, produces electricity at its terminals.

The present installed power plant capacity (conventional thermal, renewable and nuclear) is about 2.7 TW world-wide. Estimating a mid-term technical potential of solar systems, we may assume that 1% of power capacity to be replaced would be solar and for a relatively long useful life of say 50 years, market demand for solar power plants (including small solar generators) would exceed a 500 MW production capacity pa. Since total power plant capacity is expected to rise beyond today’s level by another 50-80% by the year 2020, with an increasing share of renewable technologies, it seems quite realistic to assume a demand for an annual production capacity for solar systems of at least 5 GW pa production capacity, it would be possible to a solar share of just 2.8-3.5% of the total power plant capacity installed by the year 2020.

Since sunshine at a particular site is available only for a limited period in a whole day, storage batteries are needed for use during off sunshine hours. It is necessary to invest in not only the PV modules but also in storage batteries and associated control systems for optimal use of the available solar energy. This makes generation of electric power quite expensive as compared to other forms.

Solar technology at present is photovoltaics with integrated battery storage. In highly insolated countries, about 2 DM/kWh must be projected, with half of the cost being due to battery storage. The high investment, however, may be compensated in the long run by virtually maintenance free operation. At present, small-scale PV power generation systems are most suited for remote areas, where electricity grid does not exist.

Though the cost of power from PV is high as compared to the cost by conventional sources, there are many attractive features of the PV that makes it an inevitable choice for generation of electricity, particularly in rural villages, which are far away from the main grid lines and provision of extension of the grid lines may not be economically viable. Another factor of importance is that, the existing central power plants feeding to the grid are already overloaded and are not in a position to meet the existing load and thus it may mot be feasible to supply sufficient grid power even to nearby areas.

The state of the art of battery technology is barely satisfactory. Compared to liquid fuels and the use of internal combustion engines, the energy and power densities of all battery systems are small and the costs high.

Following are the attractive features of photovoltaics:

It can be used to generate electricity at the site of requirement itself and hence cost of transmission is avoided.
It being modular in nature, any required capacity can be installed with flexibility.
It has no moving parts and is very reliable. Once installed, it needs almost no inputs for operation and maintenance for a long time.
Once installed, it is free from all types of pollution including noise pollution.

There are many technologies available for making solar PV cells. Each one of them have their own advantages and limitations and it is not a very easy to arrive at a straight forward conclusion about the suitability of a particular technology. Every aspect of various available technologies/systems have to be analysed before selecting technologies/systems that will make the use of photovoltaics most cost effective and economical for our country.

There are currently seven alternative solar cell technologies that are in various stages of commercialization internationally. These can be categorized into non-thin film and thin film. The non-thin film will include concentrator, wafer silicon, grown silicon sheet and deposit silicon sheet. The tine film category includes single junction amorphous silicon, multi junction amorphous silicon and polycrystalline thin film based on cadmium telluride and copper indium diselenide.

Developments have taken place in solar cells over the years resulting in increased efficiency and lowering of cost. Out of the various technologies, crystalline silicon (single crystalline and multi crystalline) and amorphous silicon have been commercialized.

The developments in single crystalline have reached a stage where efficiency of 24% has been achieved on small area cells. The most advanced developments are in the form of PERL (Passivated emitter rear locally diffuse) cell. The other promising development related to the concept of laser grooved buried contact cells. On commercial scale, the cell efficiencies of 14% and above routinely attained. Against this the developments in India have achieved commercial efficiencies upto 11 to 12 and need still higher levels of quality control.

In multicrystalline cells, the highest efficiency achieved till date is of about 17.8% (2x2 cm area) using high quality cast substances. In India, multicrystalline cells of acceptance quality are yet to be manufactured.

Amorphous silicon technology developments have revolved around quality manufacturing technology, low cost production and improvements in cell reliability. High film production type of machines have resulted in almost continuous feed through of the substrate materials. Single junction cells have reached efficiencies of 12 to 12.5% in small areas and 10.5% on 30x40 cm. Multi junction devices have reached efficiencies of 13.7% and large sub modules have surpassed 9% efficiency levels. Currently starting efficiencies of 10% after degradation can be realized on stacked cell structures.

In polycrystalline thin film cells, the most advanced are cadmium telluride and copper indium diselenide. The highest totals area efficiency of 13.6% 1.08 cm2 has been achieved on cadmium telluride internationally. In the case of copper indium diselenide the highest active area cell efficiency of 14.1% has been reported 3.5 cm2). The recently concluded agreement with Deutche Aerospace would bring the latter technology to India.

For concentrator cells research results have indicated efficiencies of 34% for mechanically stacked GaAs-on GaSb Cells operated at 100 X. in silicon concentrator cell development, stable efficiencies of the order of 26% have been achieved at 100x1x1.2 cm2) important progress has been made in the development of concentrator components. The latest development is in the design of point focused concentrator modules.

The low-cost photovoltaic modules require much less silicon, with a silicon layer being 20-30 microns thick rather than 300-400 microns, typically used in the conventional commercial cells. Also the material quality can be 100-1,000 times poorer than the worst material presently used, as a consequence of the improved cell design. Instead of the basic production module being a cell of approximately 100 cm2 area, the basic unit with the new approach might typically be 1 m2 in area, larger by a factor of 100.

Low material quality is a result of uniformly distributed defects. These defects may be chemical defects due to the use of less pure source materials or crystallographic defects such as due to dislocations. Another important type of defect is low quality material arises from grain boundaries t very tolerant or such grains. between individual grains within the material. Conventional solar cell design is no

It must be recognized that the photovoltaic industry is very immature in terms of production capacity at this time, with little more than 100 MW of photovoltaics installed worldwide. To place this in perspective, today’s total installed capacity of photovoltaic systems is about 5 percent of the installed capacity of wind electric systems. At these low production levels, user acceptance is restricted to a few. The low production levels also have impact on the prices of the technology, both through manufacturing cost and market supply and demand. Without needing any breakthroughs, today’s photovoltaic technology appears capable of reaching the manufacturing cost levels necessary for widespread utility applications. This progress can be achieved through use of optimized manufacturing processes that are cost-effective at high production levels. Lowering of production cost, price reduction through supply increase, and significant installed capacity levels would make photovoltaics to have an impact by the next decade.

For CO2 reduction, energy conservation together with the broad-scale implementation of renewable technologies, including the combined use of solar-thermal and PV systems, become indispensable. But the question of energy storage has to be addressed. Present battery concepts are based mostly on the lead-acid accumulator, a mass product for which a further significant cost reduction is required but seems unlikely. The development of alternative storage systems should thus be supported further.

A significant reduction in the cost of PV systems as already been achieved, but further reductions are still necessary. For a large-scale use in the power sector, production processes must be developed for efficient thin layer modules requiring less energy than the presently prevailing crystalline silicon technology. PV components should preferably be integrated into existing structures of buildings, thus reducing or avoiding the need for investment in components such as supporting structures of foundations. In addition, feeding power into the electricity grid would reduce emissions and limit the need for expensive batteries.

Subsidies for the build up of large-scale production lines for PV components may be one option to enhance the dissemination of solar energy systems. On a shorter time scale, however, major worldwide demonstration programmes for remote applications, are for feeding solar electricity into the public grid by means of decentralized and large-scale central systems, seem more appropriate to improve our understanding of PV systems thus stimulating, at the same time, the demand for building large-scale PV factories.

It is not realistic to assume utilities will purchase massive quantities of photovoltaics when some price threshold is reached. Introducing new products there has been a need to find a way to build production capacity and user acceptance simultaneously.

National photovoltaic programme should be to supply of power of photovoltaic in all non grid connected villages. As cost of transmission, distribution, losses and supply equals the cost of photovoltaic supply at such places. The national programme should be to generate among the manufacturers that there is a demand and products will be adsorbed by the consumers. The plans should clearly demonstrate that the annual need of photovoltaics would be 10 MW and might be doubling in each coming year to reach an annual target of 50 MW by the year 2000. This will set in motion the manufacture and the supply products based on photovoltaics. Large size industrial houses should be encouraged to utilize a part of their energy needs by photovoltaics.

Although, the report is mainly concentrated on cell manufacturing technologies, economics of photovoltaic appliances have also been discussed. The advantages of the PV systems, various types of applications in the fields like Rural, health care, communications, corrosion protection are detailed and few examples of the cost for water pumping with diesel or kerosene have been compared. To PV systems, life time system cost is very important.

Initial costs are always very high in case of PV appliances. Success of PV is completely dependent upon PV appliances’ relative merits on life time of the equipment as well as availability in comparison to kerosene based appliances. In the areas where desalination can be the only source of water supply and power is not available the water purification can also be done with the helpof PV based equipments. Tere are other agricultural applications like electrified cattle fencing, grain milling or cold storage etc. are also feasible. Fishery industry has got brief application for PV as shore based navigation aid and light on fishing boat.

India has been importing PV cells and systems in the last few years but recently production patter has improve and import will become somewhat limited if country follows the National Photovoltaic Programmes as proposed and established extensive production facilities. India is technically competent to produce superior quality products which can compete with any Western appliances and can find a good export market specially in the East Asian and African countries where health care programmes are being aided by WHO, UNICEF and other International Agencies. USAID/NASA/CDC Programmes shave established based on the field trials performance of PV based refrigerators and the availability over 95% of the time has boosted use in health care programmes of vaccination and animal husbandry in remote areas.

The report also discusses certain relevant topics like cost reduction, storage of energy solar thermal power through paraboloidal dish and various hybrid options for mass production of PV power and their ownership or cost effective alternatives from transmission distribution or maintenance of line considerations, off-grid customer owned or utilization owned systems and finally outlines on implementation plan for developing PV in overall national perspective and investment of 2000 crores and action plan for R&D estimates specific topics to concentrate and a decision to mass production of PV power and supply resources need ed should not be from Govt. This has to be industry oriented and publicly contributed but National Programmes are to be outlined by the government.

The relevant topics have been added for utilizing solar energy by several other means. Various solar power technologies have been discussed and comparisons made. The LUTZ/Solel is already established and functioning very well in a number of plants in USA. Te Australian technology based on parabolodial dish and two way tracking system can generate high temperature ad process of steam supply as well as power generation. Processes are so automated that minimum manpower is required. These have been compared along with carbon emission level and land use pattern, and efficiency of production.

Report concludes with recommendations, implantation and suggested action plan. Some important recommendations are summarized below.

National photovoltaic programme should be formulated with a view to supply power through photovoltaic in all non-grid connected villages.

The national programme should be framed to create a demand for products.

Large sized industrial houses should be encouraged to meet a part of their energy needs by photovoltaics.

This will generate interest among scientific institutes and laboratories to work on and find out solutions to cut cost of various stages of production, and set a healthy competition to improve quality among the manufacturers.

Research on photovoltaic technology in India is still limited to few centres without much interaction with the industry. The govt. supported research much be for industries sponsored problem solving.

Existing manufacturing plants should be encouraged to double their capacity in the first phase.

As the amorphous technology has a cost advantage for specific use, and it will enhance usability as well as cut down the cost for user and supplier on total system basis.

Business should jump small and medium sized enterprise to large complexes comprising integrated solar grade silicon production plants and possible also float glass factory.

The industrial or in-house use of photovoltaics can be promoted during the day time without much storage and other auxiliaries to supplement at least day time requirement in a planned manner which will cut down the cost of use of photovoltaics by 50%.

The manufacturers are to use engineering techniques to cut down the manufacturing cost. Some suggested actions are:

• Enhancement of solar grade production facilities techniques and cost reduction methodologies.

• Method for Utilization of poor grade silicon material with high efficiency.

• Getting the most in the use of amorphous silicon cell’s technology as the Japanese have done.

• Comparative evaluation of see-though solar cells for mass utilization in cars, doors, windows, roofs and all other possible exposed parts to sunlight, to generate power.

• Research to develop the technology for concentrator solar cells.

• Research on alternative materials which may eventually lead to cost effective methodology, development and production of large size silicon ingots and their slicing techniques for this solar cells.

Technologies should be developed for production of PV cells for Megawatt generation and not for kilowatt generation only.