Solar Energy

Renewable Energy Sources | Solar Energy

Solar energy is created in the fusion reactions of our nearest star - the Sun and this energy is the basis for the creation of all other forms of energy and natural processes. According to the available technology today, solar radiation can be used in two ways:

  • The use of solar energy as thermal energy that can be transformed into mechanical or electrical energy. To convert solar radiation into heat energy, flat collectors or vacuum tubes, or CSP are used with systems for thermal accumulation.
  • Direct conversion of solar energy into electricity through a process of photovoltaic (pv) conversion in the photoelectric effect, where the conversion into electricity is done using solar cells.

The total energy from the Sun that comes to the Earth in one year is about 1.6 billion TWh, which is a very great potential, capable of supplying humanity with 10 years of power, but the energy density per unit area is small only 1000W/m2 while for Serbia, the energy density of about 1250 W/m2 higher than the average energy density in EU. This is why Serbia is potentially good location for investment in solar energy systems. Energy density of solar radiation, depends on many factors: sequence of day and night, atmospheric conditions, geographic location, etc. Balance of solar energy as it passes through the Earth's atmosphere: 47% is absorbed in the atmosphere, 30% is reflected, 23% goes to the hydraulic cycle and 0.02% into the process of photosynthesis as a source of biomass.

Function of spectral emmision coeficient compared to wavelength and energy density diagram during apsorbtion in vacuum tubes or in flat solar collectors

Solar systems that are used to convert solar energy into heat:

  • Flat – plate collectors
  • Collectors with vacuum tubes 
  • CSP Concentrated Solar plant – focusing parabolic systems or parabolic through
  • CSP – parabolic dish solar
  • CSP – with heliostats


Pictures from ledt to right: Flat plate solar collectors, Collectors with vacuum tubes, Focusing parabolic systems or parabolic through systems for thermal generation of solar energy


CSP systems, parabolic dish collector and picture on the right is CSP Heliostat system Solar One in US

Storage of solar energy - heat accumulators:
The main problem in the use of solar energy is the uneven flow of energy in relation to the day - night and seasonal changes of the energy needed. In the period of day about 14 hours it is expected a maximum of Sun insolation, while spending is nearly at constant value, and therefore solar energy must be stored. Solar energy is not available at night and in the winter due to low temperature and low yield sunlight needs to be stored in order to be constantly available 24 hours a day, 365 days a year. Methods of storage:

  • Heat - a classic heat storage tank and latent heat,
  • Chemical– storageof thermal energy in chemical bonds and it’s modifications,
  • Thermochemical - includes adsorption and
  • Mechanical


Picture of 50kW solar collector with specific heat accumulator for solar power

pv - Photovoltaic Conversion
For the appearance of the photovoltaic effect PV the most important is the interaction between quantum of electromagnetic radiation - photons with an electron of a conductor or semiconductor. Photodiode is a diode in which the physical environment layer charge can be exposed to the effects of electromagnetic radiation, or light. If the energy of the solar light is greater than or equal to the width of the band gap – forbidden conductor zone of the semiconductor, and leads to internal photo-electrical effect, or there is a breakout of electrons from covalent bonds due to the absorption of photon. In each tear off electrons from the covalent bond, one semiconductor hole is created. This resultsin electrons and holes as charge carriers in non-equilibrium state in comparison to those that are caused by thermal vibration of the crystal grid of semiconductor. When side electric charge particles are crossing the side it comes that opposite parts of the semiconductor is charging with different types of charges. As a result of this charging on the ends of the pn junction, there is the potential difference, called circuit voltage. Short-circuit current and voltage, load depend on the intensity and frequency of light which illuminates the diode and the current is generated in the photovoltaic process.


Parts of pv photoelectric module for conversion of sun light energy directly to electric energy


Picture on the left, outside aperance of pv solar module, in the middle is picture of required parts for supplying domestic electric grid with AC current and on the right is picture of inverter for transforming DC current to AC current

The concept of focusing photovoltaic solar power plant

Photovoltaic solar power plant, also can use a collimator systems, but in this case, solar energy, or photon energy is converted directly into electrical energy in photovoltaic conversion process. With the collimation of the solar energyit is possible to increase degree of flux radiation and photons. Instead of one semiconductor layer that performs the photovoltaic effect, it is possible to manufacture a grid photovoltaic semiconductors where the light penetrates in depth if photovoltaic element allowing a high degree of efficiency. This decreases implementation cost and savesland areas, because it is required smaller areas. The system of focusing mirrors, which are constantly being directed normal to the direction of the sun's rays drastically improves efficiency compared to the static PV –photo voltaic modules. Otherwise a photovoltaic solar power plant installed in the form of a large number of photovoltaic panels, which are routed to their photovoltaic surfaces perpendicular to the direction of solar radiation.


Pictures of pv photovoltaic focused sollar array capacity of 50kW, colimated solar light is focused on pv element and directly turned into electricity

Aditional pictures:


Picture on the left is schematics of vacuum tube element and picture on the right is schematics of flat plate solar collector

Picture of CSP Heliostat - Colimated Solar Power plant with capacity of 5MW. Mirrors focuses sun light to central tower where heat energy is beeing accumulated via working fluid and accumulator of large specific heat capacity

Pronađite nas na: