Biogas based Electricity generation plant

Even today in 2013, over 400 million people in India have no access to electricity. Because of the remoteness of much of India’s un-electrified population, renewable energy can offer an economically viable means of undoing this undone. And what better than a biomass power plant. Today, about 32% of the total primary energy use in the country is still derived from biomass and more than 70% of the country’s population depends upon it for its energy needs in some way or the other. Biomass power generation in India is an industry that attracts investments of over Rs.600 crores every year, generating more than 5000 million units of electricity and yearly employment of more than 10 million man-days in the rural areas. We can divide the biomass power plant market in India into 3 categories. Biogas based power projects Present. The current availability of biomass in India is estimated to be approximately640 million metric tones per annum. This converted to cubic meters of biogas comes to 12800 million cubic meters per annum (@ 20 cubic meters of biogas per metric ton of biomass). • This should lead to both electricity and heat generation of 25600 GWh and 51200 GWh per annum respectively (@ 2 KWh of electricity and 4 KWh of heat energy per cubic meter of biogas). • The Government of India has estimated this availability of biomass to a corresponding potential of about 18000 MW generation capacity. • If the above two statements are combined, it comes to around 4 hrs of electricity generation for 365 days a year. Some case studies displayed at MNRE website talk about 6-7 hours of electricity daily in villages using a 10 KW plant. • A total of around 130 biogas power projects have been installed in the country as on date for feeding power to the grid aggregating to 1176.10 MW of generation capacity. Biogas technology, the generation of a combustible gas from anaerobic biomass digestion, is a well-known technology. There are already millions of biogas plants in operation throughout the world. Whereas using the gas for direct combustion in household stoves or gas lamps is common, producing electricity from biogas is still relatively rare in most developing countries. In Germany and other industrialised countries, power generation is the main purpose of biogas plants; conversion of biogas to electricity has become a standard technology. This document will discuss the potentials, obstacles and necessary framework conditions for the utilisation of biogas for small and medium scale electricity generation in developing countries. This paper will not address the biogas production process in general but focus uniquely on electricity generation. The findings presented here are based mainly on available experience from GTZ-related pilot biogas power plants in different countries. They focus on more or less well-documented existing country cases even though little extensive documentation of practical long term operat-ing experience is available. Besides the cases described here, we know of further examples from other GTZ projects (e.g. Bolivia, Tunisia and the Ivory Coast). However, there is not yet sufficient information concerning these to merit inclusion in this assessment. Biogas is gas resulting from an anaerobic digestion process. A biogas plant can convert animal manure, green plants, waste from agro industry and slaughterhouses into combustible gas. Biogas can be used in similar ways to natural gas in gas stoves, lamps or as fuel for engines. It consists of 50-75% methane, 25-45% carbon dioxide, 2-8% water vapour and traces of O2 N2, NH3 H2 H2S. Compare this with natural gas, which contains 80 to 90% methane. The energy content of the gas depends mainly on its methane content. High methane content is therefore desirable. A certain carbon dioxide and water vapour content is unavoidable, but sulphur content must be minimised - particularly for use in engines. The average calorific value of biogas is about 21-23.5 MJ/m³, so that 1 m³ of biogas corre-sponds to 0.5-0.6 l diesel fuel or about 6 kWh (FNR, 2009). The biogas yield of a plant depends not only on the type of feedstock, but also on the plant design, fermentation temperature and retention time. Maize silage for example - a common feedstock in Germany - yields about 8 times more biogas per tonne than cow manure. In most cases, biogas is used as fuel for combustion engines, which convert it to mechanical energy, powering an electric generator to produce electricity. Appropriate electric generators are available in virtually all countries and in all sizes. The technology is well known and maintenance is simple. In most cases, even universally available 3-phase electric motors can be converted into generators. Technologically far more challenging is the first stage of the generator set: the combustion engine using the biogas as fuel. In theory, biogas can be used as fuel in nearly all types of combustion engines, such as gas engines (Otto motor), diesel engines, gas turbines and Stirling motors etc.

Gas turbines are occasionally used as biogas engines, especially in the US. They are very small and can meet strict exhaust emissions requirements. Small biogas turbines with power outputs of 30-75 kW are available on the market, but are rarely used for small-scale applications in developing countries as they are expensive. Furthermore, due to their spinning at very high speeds and the high operating temperatures, the design and manufacturing of gas turbines is challenging and maintenance requires specific skills. External combustion engines such as Stirling motors have the advantage of being tolerant of fuel composition and quality. They are, however, relatively expensive and characterised by low efficiency. Their use is therefore limited to a number of very specific applications. In most commercially run biogas power plants today, internal combustion motors have become the standard technology either as gas or diesel motors.

Solar Ponds A solar Thermal Energy Collector

A solar pond is a pool of saltwater which acts as a large-scale solar thermal energy collector with integral heat storage for supplying thermal energy. A solar pond can be used for various applications, such as process heating, desalination, refrigeration, drying and solar power generation. A solar pond is simply a pool of saltwater which collects and stores solar thermal energy. The saltwater naturally forms a vertical salinity gradient also known as a "halocline", in which low-salinity water floats on top of high-salinity water. The layers of salt solutions increase in concentration (and therefore density) with depth. Below a certain depth, the solution has a uniformly high salt concentration. There are 3 distinct layers of water in the pond: • The top layer, which has a low salt content. • An intermediate insulating layer with a salt gradient, which establishes a density gradient that prevents heat exchange by natural convection. • The bottom layer, which has a high salt content. If the water is relatively translucent, and the pond's bottom has high optical absorption, then nearly all of the incident solar radiation (sunlight) will go into heating the bottom layer. When solar energy is absorbed in the water, its temperature increases, causing thermal expansion and reduced density. If the water were fresh, the low-density warm water would float to the surface, causing a convection current. The temperature gradient alone causes a density gradient that decreases with depth. However the salinity gradient forms a density gradient that increases with depth, and this counteracts the temperature gradient, thus preventing heat in the lower layers from moving upwards by convection and leaving the pond. This means that the temperature at the bottom of the pond will rise to over 90 °C while the temperature at the top of the pond is usually around 30 °C. A natural example of these effects in a saline water body is Solar Lake in the Sinai Peninsula of Egypt. The heat trapped in the salty bottom layer can be used for many different purposes, such as the heating of buildings or industrial hot water or to drive an organic Rankine cycleturbine or Stirling engine for generating electricity. Salinity-gradient solar ponds can collect and store solar heat at temperatures up to 80 °C. As a result, these water bodies act as a renewable source of low grade heat which can be utilized for heating and power generation applications. In this paper, design and test result of the combined system of thermosyphon and thermoelectric modules (TTMs) for the generation of electricity from low grade thermal sources like solar pond is discussed. In solar ponds, temperature difference in the range 40–60 °C is available between the lower convective zone (LCZ) and the upper convective zone (UCZ) which can be applied across the hot and cold surfaces of the thermoelectric modules to make it work as a power generator. The designed system utilizes gravity assisted thermosyphon to transfer heat from the hot bottom to the cold top of the solar pond. Thermoelectric cells (TECs) are attached to the top end of the thermosyphon which lies in the UCZ thereby maintaining differential temperature across them. A laboratory scale model based on the proposed combination of thermosyphon and thermoelectric cells was fabricated and tested under the temperature differences that exist in the solar ponds. Result outcomes from the TTM prototype have indicated significant prospects of such system for power generation from low grade heat sources particularly for remote area power supply. A potential advantage of such a system is its ability to continue to provide useful power output at night time or on cloudy days because of the thermal storage capability of the solar pond. Advantages and disadvantages • The approach is particularly attractive for rural areas in developing countries. Very large area collectors can be set up for just the cost of the clay or plastic pond liner. • The evaporated surface water needs to be constantly replenished. • The accumulating salt crystals have to be removed and can be both a valuable by-product and a maintenance expense. • No need of a separate collector for this thermal storage system. Efficiency The energy obtained is in the form of low-grade heat of 70 to 80 °C compared to an assumed 20 °C ambient temperature. According to the second law of thermodynamics (seeCarnot-cycle), the maximum theoretical efficiency of a cycle that uses heat from a high temperature reservoir at 80 °C and has a lower temperature of 20 °C is 1−(273+20)/(273+80)=17%. By comparison, a power plant's heat engine delivering high-grade heat at 800 °C would have a maximum theoretical limit of 73% for converting heat into useful work (and thus would be forced to divest as little as 27% in waste heat to the cold temperature reservoir at 20 °C). The low efficiency of solar ponds is usually justified with the argument that the 'collector', being just a plastic-lined pond, might potentially result in a large-scale system that is of lower overall levelised energy cost than a solar concentrating system.

Design of Solar Wind hybrid grid connected power system Project

Both Solar & Wind power are used in remote areas for charging a battery and delivery of grid quality electricity through large capacity sine wave inverters. In areas where wind speeds are above 5.4 m/s, our 1 Kw wind turbine will deliver more than 5Kwh of energy everyday as against maximum 4 Kwh delivered by 1 Kw solar panel. Our 3.2 KW Whisper 500 wind turbine delivers 16 KWH of energy per day at 5.4 m/s annual wind speed average. When the wind speed is above 6.3 m/s average, our 1 Kw wind turbine delivers 8 Kwh of energy/day. Wind turbines are less expensive than solar panels of the same capacity. Therefore, in places where wind speeds are above 5 m/s it is advisable to use a combination of wind and solar power for optimum investment & maximum output. It is also to be noted that wind power and solar power complement each other. During monsoon months solar power generation is reduced to a large extent due to cloudy skies, during the same period, the wind speeds are much higher than rest of the year. During monsoon, wind turbines generate extra power to compensate for the loss of solar power.