Materials for Solar Energy Conversion

In account of solar energy always should starts with the energy source as the sun. The mass of the sun is approximately 10 24tonnes, a diameter of 1,392,082 km, and energy radiation takes place at the extend of 3.8 × 10 20megawatts [9]. For a billion of years, the stated results remain unchanged in a present scenario, but definitely from time to time, there are minor changes occur in the radiation of sun energy. Based on these factors, we have been considering the constant solar energy.

Solar constant may be as the average of incoming solar energy per unit area, and it has been measured on outer surface atmosphere in a plane perpendicular to the rays with a numerical value of 0.1353 W/cm 2. Solar Constant (S) = 1350 W/m 2(approximately) [10].

Heat transfer is one of the energy transfers from high body region to a lower body region due to the potential difference of temperature gradient. There are numerous applications involved under this disciplines, which are as follows:

✓ Internal combustion engines

✓ Refrigerators and air conditioning systems

✓ Heating and cooling of fluids

✓ Radiators, etc.

The heat transfer is classified into three various modes: heat conduction, convention, and radiation. The same has been depicted in Figure 1.1.

Heat conduction is a mechanism of heat transmission that takes place from one part of a material to another part of same material or from one region to another region through some physical contact that extends it. Pure conduction heat transfer takes place only in solids.

Convection heat transfer takes place between a solid body and fluid medium where the temperatures are different. Convection process always involves in case of fluid medium.

Radiation is a process of heat transfer that will occur between two different body temperatures without a solid or a fluid medium as transmitting medium. The example of this process is electromagnetic waves where no medium is mandatory for its propagation.

Figure 1.1 Various modes of heat transfer.

All the electromagnetic waves are categorized in terms of wavelength and it travels at a rate of speed as light which is C = 2.998 × 10 8m/s.

Properties of emission: The emission radiation depends on the following aspects by a body:

✓ Surface temperature

✓ Nature of surface

✓ Radiation frequency/wavelength

The following are the important parameters to deal the emission properties that are noted as emissive power (E b), monochromatic emissive power (E bʎ), emissivity (€), radiation intensity, radiosity, density, and pressure.

Concept of Black Body

A black body is an object which absorbs all the energy radiation from outer atmosphere to its receiving surface. A black body is a perfect emitter. For a black body α = 1, α = 0, and τ = 0.

Black body is an ideal surface that has the following properties:

✓ Black body absorbs all incident radiation irrespective of wavelength and directions.

✓ At a prescribed temperature, it emits larger amount of thermal radiation.

The Stefan-Boltzmann law is as the emissive power of a black body that is directly proportional to fourth power of its absolute temperature.

where E b- Black body emissive power (W/m 2)

σ - Stefan Boltzmann constant—5.67 × 10 –8W/m 2K 4

T - Absolute temperature (K)

Plank’s Law states that spectral distribution of radiation intensity of perfect black body is expressed by the following equation:

where

(Eb)λ - Single wavelength emissive power of a body

c - Light velocity

h - Planck’s constant

ʎ - Wavelength

k - Boltzmann constant

T - Absolute temperature

The relation between maximum emissive power wavelength and temperature of black body in given by the following expression:

Solar energy can be converted into some other useful form of energy sources using different conversion technologies as in Table 1.4. The methods are photoelectric, photoelectric-photothermal, photothermal, photochemical, photocatalytic, and photo-electrochemical conversion.

Table 1.4 Energy conversion [11].

Renewable and non-renewable energy are of two types, in general, on the planet earth used by living organisms.

Renewable energy sources: Renewable energy sources are defined as the energy achieved from natural sources that are continuously produced by themselves for a day-to-day activity usage in a periods of time. These energy systems comprise sun, ocean waves, biomass (wastage of vegetable materials), hydel-power plants, and also some other such resources. This type of energy is also stated as green or sustainable or nonconventional energy sources.

Non-renewable energy sources: Non-renewable energy sources are defined as the fuel that do not rejuvenated itself continuously once utilized on the scale of levels that sustain its rate of consumption. These resources are presented in a larger amount of fixed quantities and used quickly as faster than nature could produce. Some best suitable instances are coal, nuclear energy, fossil fuels, natural gas, petroleum products, uranium, etc.

The difference in renewable and non-renewable energy sources was explained in Table 1.5.

Table 1.5 Difference in renewable and non-renewable energy sources.