Q.15 Explain the uses of solar energy. (AKTU. - 2008-09)
Ans. Uses of Solar Energy: - (AKTU. - 2010 - 11)
(1) Solar Water Heating: -
A solar water heater unit comprises a flat plate collector and an insulated storage tank. This system of water heating is commonly used in hostels, hospitals, hotels, guesthouses, etc. as well as domestic and industrial units.
(2) Solar Space Heating of Buildings: -
Solar space heating can be provided passively through the architectural design of the premises. At its simplest, this involves only the orientation of the building and providing large south-facing windows.
Alternatively, an active technology of solar space heating where water is the medium, is essentially an extension of the technology employed in solar water heating except that energy has to be recovered from the tank through a heat exchange surface.
(3) Solar Air-Conditioning: -
Solar air-conditioning includes solar-powered refrigeration systems of Rankine cycle systems, absorption refrigerator systems and solar-regenerated desiccant cooling systems. Out of these, open-cycle absorption desiccant cooling systems seemed to offer the best prospects.
(4) Solar Refrigeration: -
Solar refrigeration is closely related to air-conditioning. It is generally required for food preservation or for storage of medical and biological materials.
(5) Solar Drying: -
Solar drying of agricultural and animal products is the most ancient, traditional and widespread method of utilizing direct solar energy.
The customary technique involves the spreading of the material (to be dried) in a thin layer on the ground to expose it to sun and wind.
(6) Solar Cooking: -
A typical solar cooker is a well-insulated shallow rectangular / square metal box which is blackened from the inner side and fitted with a flat glass cover. When placed in sunlight, the solar radiation penetrates the glass cover (or covers, in case two glass covers are provided for minimizing the heat loss) and are absorbed by the blackened surface; thereby, resulting in an increase in temperature inside the box.
(7) Solar Greenhouses: -
A greenhouse is a closed structure covered with transparent material (glass or plastic) which acts as a solar collector and utilizes solar radiant energy for the growth of plants.
(8) Solar Furnaces: -
Solar furnaces provide a means of generating extremely high temperatures (upto around 3,500°C) under very clean conditions, and can be used to melt refractory materials.
(9) Solar Desalination: -
The use of solar energy for desalting sea-water and brackish well water has been demonstrated in several moderate-sized pilot plants all over the world including USA, USSR, Greece, Australia and several other countries.
(10) Salt Production: -
Solar evaporation of seawater (brine) has been a traditional method of obtaining salt. Latest developments have been concerned with improved pond/pool construction and salt-harvesting techniques.
(11) Solar Electricity-Thermal: -
Solar energy may be used to heat a fluid, which then generates electricity through a conventional heat engine. To obtain an adequate working temperature, some form of concentration of solar energy is required.
(12) Solar Electricity-Photovoltaic: -
Photovoltaics or solar cells are devices which directly convert incident solar radiation to electrical current. It works on the principle of photoelectric effect.
Q.16 What exactly are fossil fuels and why are they non-renewable?
Ans. Fossil fuels (coal, oil, and natural gas) are the remains of organisms that lived 200-500 million years ago. During that stage of the Earth’s evolution, large amounts of dead organic matter had collected. Over millions of years, this matter was buried under layers of sediment and converted by heat and pressure into coal, oil and natural gas.
Once we discovered these fuels, we began consuming them at an ever increasing rate. From 1859 to 1969, total oil production was 227 billion barrels. (In the oil industry, the barrel is the preferred unit and one barrel is equal to 159 liters). Fifty per cent of this total was extracted during the first 100 years, while the next 50 per cent was extracted in just 10 years!
Today, out consumption rate is far in excess of the rate of formation of fossil fuels. We consume in one day what the Earth took one thousand years to form! That is why fossil fuels are considered non-renewable.
Q.17 Describe biomass and biogas energy sources.
Ans. Biomass Sources: -
Biomass is organic matter derived from plants, algae, animal etc. The energy obtained from biomass is called biomass energy. Biomass resources are classified in two groups (i) Biomass from cultivated fields, crops, forests etc. (ii) Biomass from municipal waste, animal excreta/dung etc. Biomass can be considered a renewable energy source. Biomass is heated in absence of air to obtain char. This process is known as phrolysis. Gasification of biomass is done to yield clean and combustible gases.
Currently biomass contributes 15% of the total energy supply worldwide and 40% of this energy is consumed in developing countries, mostly in rural areas.
Biogas Sources: -
The main source for production of biogas are cattle dung, night soil, poultry or piggery dropping. These materials are confined in a place, out of contact with oxygen, give rise to a large number of bacteria. These bacteria convert carbohydrates, proteins, fat into volatile acid and carbondioxide. The process of digestion and gasification occurs better at the temperature about 350C
. When the temperature falls, the process of digestion is retarded. The time for which fermentable material resides inside the digester is called retention period.
In rural areas biogas has many applications such as cooking, lighting etc. The biogas obtained from cattle dung contains methane about 55% to 60% and carbon dioxide about 40% to 45% and negligible amount of H2S and hydrogen etc. However, with night soil the methane content may increase to 60%, CO2 34%,H2S 0.6% and other gases 0.4%.
Q.18 Explain how, ‘hydrogen as an alternative future source of energy’.
Related Questions -
Q. “Hydrogen as an alternative future source of energy, explain it. (AKTU. - 2008-09, 2010 - 11)
Ans. Hydrogen An Alternative Future Source of Energy: -
Many experts believe that, as we run out of fossil fuels, we will move towards using the element hydrogen as the main fuel to run the world’s economy. When hydrogen burns and gives us energy, it combines with oxygen to produce water vapour. In this process, there is no air pollution or emission of carbon dioxide.
Iceland promises to become the world’s first hydrogen economy over the next 25-30 years. For this purpose, the Government of Iceland has teamed up with companies like Diamler-Chrysler, Royal Dutch Shell, and Norsk Hydro. The project is the brainchild of the chemist Bragi Arnason. The project will produce hydrogen from seawater using the country’s abundant renewable energy sources: wind, geothermal, and hydropower. Hydrogen will run buses, cars, fishing vessels, and even factories. Royal Dutch Shell will operate hydrogen filling stations.
