مقالة للتدريسيه في قسم الفيزياء الطبيه م.م ضي علي

تاريخ النشر: 21/09/2019
عدد المشاهدات: 673
تم نشر الموضوع بواسطة: اعلام قسم الفيزياء الطبية
solar energy

Almost all the renewable energy sources originate entirely from the sun. The sun’s rays that reach the outer atmosphere are subjected to absorption, reflection, and transmission processes through the atmosphere before reaching the earth’s surface. On the other hand, depending on the earth’s surface topography, as explained by Neuwirth (1980), the solar radiation shows different appearances. The emergence of interest in solar energy utilization has taken place since 1970, principally due to the then rising cost of energy from conventional sources. Solar radiation is the world’s most abundant and permanent energy source. The amount of solar energy received by the surface of the earth per minute is greater than the energy utilization by the entire population in one year. For the time being, solar energy, being available everywhere, is attractive for stand-alone systems particularly in the rural parts of developing nations. Occurrences of solar energy dynamically all over the world in the forms of wind, wave, and hydropower through the hydrological cycle provide abilities to ponder about their utilization, if possible instantly or in the form of reserves by various conversion facilities and technologies. It is also possible that in the very long term, human beings might search for the conversion of ocean currents and temperature differences into appreciable quantities of energy so that the very end product of solar radiation on the earth will be useful for sustainable development.
The design of many technical apparatuses such as coolers, heaters, and solar energy electricity generators in the form of photovoltaic cells, requires terrestrial irradiation data at the study area. Scientific and technological studies in the last three decades tried to convert the continuity of solar energy into sustainability for the human comfort.
Solar energy is referred to as renewable and/or sustainable energy because it will be available as long as the sun continues to shine. Estimates for the life of the main stage of the sun are another 4 – 5 billion years. The energy from the sunshine, electromagnetic radiation, is referred to as insolation.
Solar energy is radiant light and heat from the Sun that is harnessed using a range of ever-evolving technologies such as solar heating, photovoltaics, solar thermal energy, solar architecture, molten salt power plants and artificial photosynthesis.
It is an important source of renewable energy and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic systems, concentrated solar power and solar water heating to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light-dispersing properties, and designing spaces that naturally circulate air.
The large magnitude of solar energy available makes it a highly appealing source of electricity. The United Nations Development Programmed in its 2000 World Energy Assessment found that the annual potential of solar energy was 1,575–49,837 exajoules (EJ). This is several times larger than the total world energy consumption, which was 559.8 EJ in 2012.
In 2011, the International Energy Agency said that "the development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating global warming, and keep fossil fuel prices lower than otherwise. These advantages are global. Hence the additional costs of the incentives for early deployment should be considered learning investments; they must be wisely spent and need to be widely shared".
The Earth receives 174 pet watts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. Most of the world's population live in areas with insolation levels of 150–300 watts/m², or 3.5–7.0 kWh/m² per day.
Solar radiation is absorbed by the Earth's land surface, oceans – which cover about 71% of the globe – and atmosphere. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis, green plants convert solar energy into chemically stored energy, which produces food, wood and the biomass from which fossil fuels are derived.
The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined.

2.Wind Energy:
Wind energy is not a new form it has been used for decades. A WT consists of a rotor, turbine blades, generator, drive or coupling device, shaft, and the nacelle (the turbine head) that contains the gearbox and the generator drive. Modern wind turbines can provide clean electricity as individuals or as wind farms. Wind turbine blades usually are two or three blades each nearly 10–30m long.
Operation. The wind rotates the windmill-like blades, which in turn rotate their attached shaft. This shaft operates a pump or a generator that produces electricity. a pump or a generator that produces electricity. Although, the energy characteristics of larger wind turbine farms are closer to the centralized energy sources, small wind turbines (working as modules) can be combined with PV and battery systems to serve area of 25–100kW as shown in (figure 1)











Figure( 1)Schematic operation diagram of a wind turbine.










3.Biomass:
Biomass resources include the following: agricultural waste, animal manure, forest waste, industrial waste, municipal waste, sewage sludge, crops, etc. Biomass as an energy source can either be used directly by combustion to produce heat, or indirectly after converting it to discrete forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are loosely classified into: electrochemical conversion methods, thermal, chemical, and biochemical conversion. Another alternative is to convert the solid biomass into a fuel gas. Generally, piston-driven engines are found of using biofuel, high efficiency gas turbine generator as well as fuel cell also use biofuel. Biomass plants typically are of the direct combustion, mixed combustion, or gasification type. With the direct combustion power generation method, steam is produced from the heat generated by the burning of materials such as wood waste, agricultural waste, and livestock waste as shown in (figure 2) above. The steam turns a turbine, which in turn drives a generator that produces electricity.















Figure(2 )Direct/Mixed Combustion Power Generation Methods


4.Small hydropower plant:
All hydropower systems use the energy of flowing water to produce electricity or mechanical energy. Although there are, several ways to harness moving water to produce energy, “run-of-the-river systems,” which do not require large storage reservoirs, are most often used for micro hydropower systems (figure 3) Small hydropower (SHP) is commonly used to refer to hydropower with capacity less than 10 MW. Other terms that are normally used are mini hydropower for SHP with capacity between 100 kW and 1 MW and micro hydropower for SHP with capacity below 100 MW. The power generated from SHP plants is quite large .










Figure) 3)