<br /> Renewable energy resources will play an important role in the world’s future. The energy resources have been split into three categories: fossil fuels, renewable resources and nuclear resources. Renewable energy sources are those resources which can be used to produce energy again and again, e.g. solar energy, wind energy, biomass energy, geothermal energy, etc. and are also often called alternative sources of energy. Renewable energy sources that meet domestic energy requirements have the potential to provide energy services with zero or almost zero emissions of both air pollutants and greenhouse gases. Renewable energy system development will make it possible to resolve the presently most crucial tasks like improving energy supply reliability and organic fuel economy; solving problems of local energy and water supply; increasing the standard of living and level of employment of the local population; ensuring sustainable development of the remote regions in the desert and mountain zones; implementation of the obligations of the countries with regard to fulfilling the international agreements relating to environmental protection. Development and implementations of renewable energy project in rural areas can create job opportunities and thus minimizing migration towards urban areas. Harvesting the renewable energy in decentralized manner is one of the options to meet the rural and small scale energy needs in a reliable, affordable and environmentally sustainable way.<br />Solar energy : <br />1. Solar thermal application <br />As far as renewable energy sources is concerned solar thermal energy is the most abundant one and is available in both direct as well as indirect forms. The Sun emits energy at a rate of 3.8 × 1023 kW, of which, approximately 1.8 × 1014 kW is intercepted by the earth. There is vast scope to utilize available solar energy for thermal applications such as cooking, water heating, crop drying, etc. Solar cooking is the most direct and convenient application of solar energy. Solar energy is a promising option capable of being one of the leading energy sources for cooking [8-10]. Various types of solar cookers are available, out of them box type solar cooker (Fig. 1) is widely used all over the world. A study was conducted in Costa Rica and in the world as a whole, and then compared the advantages and limitations of solar ovens with Esraa Hussein Al-fatlawi <br /><br />conventional firewood and electric stoves. The payback period of a common hot box type solar oven, even if used 6–8 months a year, is around 12–14 months, roughly 16.8 million tons of firewood can be saved and the emission of 38.4 million tons of carbon dioxide per year can also be prevented. Solar water heater of domestic size, suitable to satisfy most of the hot water needs of a family of four persons, offers significant protection to the environment and should be employed whenever possible in order to achieve a sustainable future. It is estimated that a domestic solar water heating system of 100 l per day capacity can mitigate around 1237 kg of CO2 emissions in a year at 50% capacity utilization and in hot and sunny region it is about 1410.5 kg [13,14]. A schematic of solar water heater is illustrated in Fig. 2 Solar-drying technology offers an alternative which can process the vegetables and fruits in clean, hygienic and sanitary conditions to national and international standards with zero energy costs. It saves energy, time, occupies less area, improves product quality, <br />makes the process more efficient and protects the environment. Piacentini and Mujumdar estimated CO2 production for a drying system using 100 kWh day−1 of electricity, over 25 days per month in 11 months of operation per year. It came to around 14.77 tons of CO2 year−1. Further study was conducted on solar crop drying and CO2 emission potential. It was estimated that 1m2 aperture area can save 463 kg of carbon dioxide in life cycle embodied <br />3. Solar photovoltaic system <br />Electrical energy is the pivot of all developmental efforts in both the developed and the developing nations because conventional energy sources are finite and fast depleting. In the last decades, energy related problems are becoming more and more important and involve the ideal use of resources, the environmental impact due to the emission of pollutants and the consumption of conventional energy resources. Direct solar energy conversion to electricity is conventionally done using photovoltaic cells, which makes use of the photovoltaic (PV) effect. PV effect depends on interaction of photons, with energy equal to, or more than the band-gap of PV materials. Some of the losses due to the band-gap limitations are avoided by cascading semiconductors of different band-gaps.. PV modules generate electricity directly from light without emissions, noise, or vibration. Sunlight is free but power generation cost is exceptionally high, although prices are starting to come down. Solar energy has low energy density: PV modules require a large surface area for small amounts of energy generation. The primary component in grid connected PV systems is the inverter, it convert DC power produced by PV array into AC power consistent with the voltage and power quality requirement of the utility gird as illustrated in Fig. 4. Silicon solar cells are perhaps the simplest and most widely used for space and terrestrial applications. The PV system is promising source of electricity generation for energy resource saving and CO2 emission reduction, even if current technologies are applied Further the development in efficiency of solar cells, amount of material used in the solar cell and the system design for maximum use of recycled material will reduce the energy requirement and greenhouse gas emissions [28]. Net annual CO2 emission mitigation potential from 1.8 kWp solar photovoltaic pump at an average solar radiation of 5.5 kWh m−2 is about 2085 kg from diesel operated pumps and about 1860 kg from petrol operated pumps. The CO2 emissions mitigation potential is higher in the case of diesel substitution <br />Fig. 4. Grid connected photovoltaic system <br />compared to the petrol substitution. This is primarily due to low efficiency of fuel utilization in the diesel engine pump<br /><br /><br />Esraa Hussein Al-fatlawi <br /><br />2. Solar thermal power <br />Solar energy is a very important energy source because of its advantages. There are many remote areas in the world where electricity is not available, but solar irradiation is plentiful, thus the utilization of solar energy to produce electricity in these areas is quite possible [18]. Solar thermal electricity power system is a device which utilize the solar radiation for the generation of electricity through the solar thermal conversion; basically collected solar energy is converted to electricity through the use of some sort of heat to electricity conversion device as shown in Fig. 3 [19,20]. The major component of any solar thermal system is the solar collector. Solar energy collectors are special kind of heat exchangers that transform solar radiation energy to internal energy of the transport medium. A historical introduction into the use of solar energy was attempted followed by a description of the various types of collectors including flat-plate, compound parabolic, evacuated tube, parabolic trough, Fresnel lens, parabolic dish, and <br /> <br />heliostat field collectors . Electricity production cost through solar energy is quite higher than that of conventional power station.<br /><br />Esraa Hussein Al-fatlawi <br />