Solar energy is the greatest source of energy for earth. Solar energy is clean, renewal and accessible all over the world. Fossil resources limitation and environmental changes make solar energy feasible in comparison with fossil fuels especially in regions with high solar radiation.
Solar technologies are divided to two min categories: Thermal Power Plants and Non- Power plants application
Solar Thermal power plants utilize Direct Normal Irradiation (DNI). Direct Normal Irradiation is deflected by clouds, steam, smoke and dust. Thus, solar thermal power plants have to be installed in locations with high irradiance. Sites with more than 2000 kWh/m2 per year are suitable for solar thermal power plants. Sites with 2800 kWh/m2 per year are more appropriate for these power plants. These sites have to be located in places which climate and plant can not affect atmosphere by producing humidity and dust. These locations are steppes, shrubberies, semi-deserts and deserts which are placed in less than 40 degree north or south altitude. High potential locations are United State of America south west, Mediterranean European countries, Middle East and Near East, Iran and India deserts, Pakistan, China and Australia.
Solar thermal technologies produce 100 to 300 GWhe per one square kilometer in most areas. This capacity is equal to annual electricity production of a 50 MW capacity fossil fueled power plant in average load.
A solar thermal power plant is including equipments which produce super heat by collecting and focusing solar energy. The collected energy convert to electricity through heat exchangers, turbine generators or steam motors. Solar thermal power plants are divided to three categories based on the concentrator types:
1- Parabolic Trough Collector
Parabolic trough solar thermal power plants are including long rows of concentrators. Concentrators are parabolic reflectors are made of glass mirrors and installed on a supportive structure. Receivers are made of tubular tubes covered by selective surface through a pyrex tube and placed in the focal point. The receiver installed on two poles at its end points. The tracking device is one axial and tracking path is rotational from east to west on one axis, thus solar irradiance focus on focal point during the tracking period. Heat transfer fluid oil flow in the absorbing tube with 400 ◦C and exchange water into vapor through the heat exchanger and the super heat vapor during Rankin cycle generate electricity by turbine and generator.
2- Power Tower
Solar power tower is a type of solar furnace using a tower to receive the focused sunlight. It uses an array of flat, movable mirrors that each focus the sun's rays upon a collector tower (the target). The number of these mirrors which called heliostats comes to hundreds and thousands pieces. The reflector plates designed to focus solar irradiance to the central receiver which is the power tower.
3- Dish Stirling
Dish stirling is a heat-mechanical motor which converts heat to mechanical power with higher efficiency in comparison with diesel and gasoline motors. Nowadays these motors are used in specified applications. Stirling motor uses stirling cycle which differs from the conventional cycle in other motors. This motor uses external heat sources like gasoline, solar energy or biomass fuels and there is no combustion in the motor cylinder. A reflector dish is required for utilizing solar energy in this motor. This reflector focuses solar irradiance n the stirling motor directly. And the motor starts to generate electricity.
Solar energy has different non-power plant applications in industrial, commercial and residential. These applications are:
1- Water heating (Solar water heater for homes, buildings, mills and pools)
Solar water heaters absorb solar energy by absorber plate (collector) with different efficiency in different seasons. Hot water tank saves the hot water for using during the day and night with a minimum energy loss. The gas, gasoline and electricity cost will decrease by using solar water heater. In large scale projects the reduction of energy cost is significant. After 4 or 5 years utilizing solar water heater and energy cost reduction will amortize initial investment. Operation and maintenance of these systems are very low and the standard operational lifetime about 15 years.
2- Space heating in buildings
Space heating is the first and the most practical application of solar energy in building. Solar heating systems based on the fluid type (gas or liquid), which heated in solar collector, is divided in two categories. Both types collect and absorb solar energy and transfer heat directly into building space. One the most advantages of this system is substitution clean and renewable energy for conventional fuels as a threat for environment.