Solar energy could be harvested by two major solar technologies: photovoltaic (PV) and concentrating solar power technologies (CSP). While PV technology converts the global solar irradiation directly into electrical current, the CSP technologies convert the solar direct normal irradiation into thermal energy that could be utilized in conventional power generation plants. This could be used also as process heat for industrial applications and for cooling purposes. A Brief description about these two major technology categories is to be found below:
Concentrating Solar Power (CSP) (click to expand)
The working principle of CSP technology is based on generating heat by concentrating the direct normal sun beam and derives that heat into a conventional power block, which in turn produces electricity. The CSP plants comprise usually integrated thermal energy storage (TES) system that enables the provision of high quality dispatchable power to support grid stability as well as sustain isolated grids at reasonable costs. This makes CSP technology advantageous over other renewable energy technologies since they can overcome the fluctuation of electricity generation and allow the dispatchibilty of electricity on a 24/7 basis.
Generally CSP plants have two major elements: a solar field to concentrate the collected solar energy and a power block, which represents the conventional part. There are two types of concentration techniques in solar fields: the line focusing and point focusing. Most common technologies of these types are parabolic trough and solar tower plants respectively.
For parabolic trough power plants, the solar field consists of special arranged loops of parabolic shaped reflective concentrators that focus the direct sun beam onto absorber tubes mounted exactly in the focal line of the parabola. The heat captured at the absorber is transferred into the heat transfer fluid (HTF), normally synthetic thermal oil, which is heated up to 390 °C. This heat could be used either to generate steam for steam turbines connected to an electrical power generator or to generate heat to be used directly for industrial processes.
CSP systems size can be dimensioned from a few kilowatts to utility scale Megawatts plant. Integrated Solar Combined Cycle (ISCC) is an attractive hybrid option for CSP plants that combines natural gas co-firing to produce dispatchable power.
The amount of generated power from a CSP plant differs from one location to another, due to different Direct Normal Irradiation (DNI) values for each site. The so called Sun Belt zone of the world, e.g. MENA desert, is the largest potential solar site and the most attractive region to host future CSP plants.
Photovoltaic (PV) (click to expand)
Photovoltaic technology is the most common way to harvest sunlight to produce electricity. A PV cell consists of semi-conductor material, normally silicon, where electrons will be freed if sufficient amount of solar irradiation (photons) are absorbed. Subsequently, these electrons flow from the negative to the positive layer of the cell creating a voltage differential. Several PV cells are combined together to give a PV module; the basic unit of the PV system. Depending on its desired size, a solar PV system could have a few of such modules up to hundreds of thousands.
In recent years, with large installed capacity, PV technology became so reliable that it can produce power at competitive costs in comparison to conventional power generation technologies. The PV industry is growing at a rate of 40% per year and creates thousands of jobs at the global and local levels. Furthermore, its supply chain is optimized for a fast and efficient project development worldwide.
Photovoltaic systems have no moving parts and therefore produce no noise and require minimum maintenance and operation efforts. Since they only utilize the sunlight as fuel, they do not emit pollutants into the environment. Thanks to advances in manufacturing a typical cell efficiency reaches 15% and has a lifetime of more than thirty years.