MATERIALS DEVELOPMENT FOR SOLAR ENERGY APPLICATION By Dr. S.O.O. Olusunle, R.Eng., MASME, FMSN Ag Director/Chief Executive, Engineering Materials Development Institute, Akure at a Public Lecture organized by The Metallurgical, Mining and Materials Division of the Nigerian Society of Engineers 21/02/2011 OUTLINE Background Introduction Solar Energy Harvesting Solar Energy EMDI Effort on Solar Energy Development Available Facilities @ EMDI Conclusion Background About 80% of Africa’s 1 billion population is engulfed in abject poverty and is lacking virtually in all areas of human development Access to energy plays a central role in solving the poverty debacle Africa is referred to as a “dark continent” because about 70% of the population do not have access to electric lighting. Over 1.6 billion people in developing countries do not have access to electricity and have no hope of being connected to the national grid in the near future (World Bank, 1996). Introduction Fossil fuels provide around 66% of the world's electrical power, and 95% of the world's total energy demands. Global warming (green house effect) and climate changes are due to the use of these fossil fuels like coal, oil and gas. by-products of fossil fuels such as carbon dioxide, sulfur and nitrogen oxide may result in acid rain Sourcing for clean, efficient, and sustainable energy is therefore a necessity solar energy stands out because the source is unlimited and available everywhere Solar Energy Solar energy is the energy directly from the sun which is one of the most important non-conventional energy sources available for man’s use. It is clean, renewable and free source of energy largely available in sufficient quantity Man can harness the energy for useful purposes by means of active and passive devices among which are solar cells and photothermal converters. However, the challenges of solar power generation are its production cost and storage. The primary objective of the worldwide research and development is to reduce the cost of generating solar energy to a level that will be competitive with conventional ways of generating power. History Humans have harnessed the power of the sun for millennia. In the fifth century B.C., the Greeks took advantage of passive solar energy by designing their homes to capture the sun’s heat during the winter. Later, the Romans improved on solar architecture by covering south-facing windows with clear materials such as mica or glass, preventing the escape of solar heat captured during the day In the 1760s, Horace de Saussure built an insulated rectangular box with a glass cover that became the prototype for solar collectors used to heat water. The first commercial solar water heaters were sold in the U.S. in the late 1890s In the late 19th century, inventors and entrepreneurs in Europe and the U.S. developed solar energy technology that would form the basis of modern designs Production Sunlight can be converted into heat and electricity in a number of ways. A variety of solar technologies are in production, and many companies and researchers are pursuing efforts to develop devices that convert the sun’s energy more efficiently Energy from the sun is harvested using either photothermal conversion system which converts solar radiation into heat energy or solar cell which convert radiation from the sun directly to electricity. Materials for Harvesting Solar Energy Energy from the sun is harvested using either photothermal conversion system which converts solar radiation into heat energy or solar cell which convert radiation from the sun directly to electricity. The development of materials for solar energy harvesting is based on the use of solar radiation and profound understanding of the materials properties at the atomic scale levels. Material structure-property relations enable the evolution of tailored-made materials for these applications. To achieve this objective, it requires the combination of experiments (i.e., materials synthesis, characterization of structural and processing of thin film for both solar cells and photo thermal conversion), theoretical analysis which cover modeling of the entire system. Development of Photo thermal Converter Photothermal converter is device developed using special materials that absorb solar radiation and convert it to heat energy. The high efficiency photothermal material implies maximum absorption of incident solar radiation with a minimum thermal and optical loss. The temperatures ranging from ambient to 1000°C are achievable in a photothermal converter made of good selective materials, such as black nickel, black chrome, multi-layer tandem stacks and some other composite semiconductor materials which are good absorber (low reflection) of solar radiation and poor emitter of thermal radiation. The temperatures above ambient are used in various applications such as space heating, water heating, and distillation and drying. Solar water heater Solar Box cooker Solar furnance at Odeillo, France Max Temp 3800°C Solar Cell Development A solar cell is a semiconductor device that converts sunlight directly into electric current using the principle of photovoltaic (PV) effect. The effect is made by partnering p-type and n-type semiconductor. The semiconductors are selected such that they absorb significant portion of the solar spectrum. The absorbed photon gives rise to Electron-Hole pairs. These excess carriers are swept across the junction by the electric field and are collected at the contacts. This gives rise to photocurrent and can be made to deliver power to a load. Thus the important steps in solar energy conversion are absorption of radiation, generation of carriers, diffusion of majority carriers, separation of minority carriers by the electric field and collection of carriers at the contact. Historically, solar cells are used as an alternative source for generating electric power, such as remote area power systems, handheld calculators, and water pumps. However, a major barrier impeding the development of large-scale power application of PV systems is the high price of commercially available solar cell modules. Photovoltaic Energy • Silicon based photovoltaic cells represent 90% of the photovoltaic panels presently sold in the world. • More than one third of the cost is due to the silicon itself. Indeed, its purification, crystallization and the wafer fabrication have an important energetic and economical cost. • The photovoltaic research community is looking for solar cell structure based on thinner silicon layers. • However, the thinner the material, the lower its light absorption, especially at long wavelengths (near infrared). So the primary objective of solar cell research and development is to reduce the cost of production to a level that will be competitive with conventional ways of generating power. One way to achieve this is to significantly increase the conversion efficiency of solar cell materials and devices. Basically, there are two approaches to increasing the efficiency of solar cells; (1) Selecting the semiconductor materials with appropriate energy gaps to match the solar spectrum (i.e., between 1.1 – 1.8eV) and the optimizing their optical, and electrical properties; (2) Innovative device engineering, which enables more effective charge collection as well as better utilization of the solar spectrum through the use of the emerging advance materials. Advancement in solar cell materials development Polycrystalline Thin Film Solar Cell These are solar cell made by depositing one or more thin film layers of polycrystalline semiconductor materials on the substrate. Polycrystalline thin film solar cells are important because of their low cost of fabrication, large areas, and the possibility of convenient integration with other solar energy conversion devices. Dye-Sensitized Solar Cell Dye-sensitized solar cells are next-generation solar cells based on innovative tech. Unlike conventional silicon-based solar cells, dye-sensitized solar cells consist primarily of photosensitive dye and other substances. Dye-sensitized solar cells are able to generate electricity by converting energy from light absorbed by the dye. Polymer Solar Cell Polymer solar cell is an organic photovoltaic cell that produces electricity from sunlight using polymers. Compared to silicon-based devices, polymers are lightweight, disposable, inexpensive to fabricate, flexible and have lower potential for negative environmental impact. These plastic solar cells are produced by coating or printing polymer and nano-engineered materials onto polyethylene substrate in a continuous roll-to-roll process similar to photographic film. Hybrid solar cell These are solar cells that combine advantages of both organic and inorganic semiconductor materials. EMDI Focus in the Area of Solar Energy Development As part of the effort in developing materials for efficient solar application in Nigeria, EMDI has made significant progress in the following areas (in addition to publications on solar cell production in reputable international journals): Synthesis, fabrication and characterization of ternary compound based solar cell Ternary semiconductors, are compound semiconductor which consist of three elements with a wide range physical properties. The physical Properties which may vary, include band gaps, crystal lattice structures, electron and Hole mobilities, optical properties, thermal conductivity, and so on. By selecting appropriate ternary semiconductor materials, it becomes possible to realize various devices, which cannot be achieved using the main elemental semiconductor material, silicon. E.g CuAlS, CdPbS, CuSnS A student on PhD research is presently working on using the ternary compound for solar cell and other optoelectronic devices. Development of micro processor controlled spin coater for thin deposition EMDI as been able to develop a micro processor controlled spin coater for thin film deposition. NASENI has a 7.5MW solar panel manufacturing plant at Karshi, Abuja through a joint venture project with a foreign partner. The ultimate aim is to develop the technology for solar cell production in EMDI that will feed Karshi Plant preparation and characterization various Nano/ Thin materials for advance energy research Various nano materials are being investigated for their possible application in energy research. materials such as Dilute magnetic semiconductor Materials (Mn: SnO2), Mn: PbO and Fe2O3, Dielectric Material and Piezoelectric material Preparation and characterization of conducting polymer blend for solar cell application and other optoelectronic devices Development of stamping methods for pattern transfer and cold welding for polymer solar cell Research embarked upon by one of our collaborator from Princeton university, USA Synthesis, fabrication and characterization of nanostructures Eu doped ZnS light emitting diode in collaboration with a Researcher from university of Agriculture, Makurdi Solar Paint New 'solar paint' could generate electricity from the roofs and walls of EVERY home without the need for bulky panels 'Nanocrystals' used to generate power Can be painted or printed onto walls or windows So tiny you could fit 250,000,000,000 on head of a pin (The nanocrystals are about 4 nanometers in size) Thin enough to be painted or printed onto walls SOME OF THE FACILITIES AVAILABLE @ EMDI FOR SOLAR-RELATED RESEARCH WORK THE GLOVE BOX Glove Box is a chamber constantly supplied with nitrogen or argon to create the needed inert atmosphere needed for work in an electronic fabrication lab. THE SPIN COATER “EMDI MicroCONTROLLER Spin Coater” – GF-BB-UBmcsc01 “EMDI MicroCONTROLLER Spin Coater” – GF-BB-UBmcsc01 Won 2 awards @ the 5th University of Lagos Research Conference and Fair held between 21st and 23rd October, 2009. First, as the Best Exhibited Project outside the University and the Second-Best of all exhibited projects THE LESKER NANO-38 THERMAL DEPOSITION UNIT Microelectronic Grade Vacuum Oven NanoSpec Film Thickness Measurement System UV-VIS SPECTROPHOTOMETER X-RAY DIFFRACTOMETER MICROPROCESSOR CONTROLLED OPTICAL MICROSCOPES Keithley 4-POINT PROBE SYSTEM Conclusion With the level of human capacity and facilities available at EMDI, the institute is poised to contribute to the rapid development of solar energy generation in Nigeria through impartation of research based knowledge, engineering principles and practices of developing materials for solar energy application which is the one of modern technologies in solving the present energy challenges.