- Wavelength
k - Boltzmann constant
T - Absolute temperature
1.5.3 Wien’s Displacement Law
The relation between maximum emissive power wavelength and temperature of black body in given by the following expression:
1.6 Solar Energy Conversion
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].
| Energy | From light | From chemical | From electrical | From mechanical | From heat |
| To Chemical | photo-synthesis | foods | electro-plating | Digestion of food | Gasifier |
| To Electrical | Solar cells | Powered torch light-battery Fuel cell | Transformer | Wave power Electric generator Windmill | Thermo-electric Geothermal Ocean-thermal power Thermo-couple |
| To Mechanical | photoelectric | Adenosine triphosphate hydrolysis Chemical Nutrients | Power drill | flywheel | Heat engines |
| To Light | laser | Most flame-characterized combustions Radium used to be painted | Electric lamp | spark | Match box |
| To Heat | Solar cells | Burning of wood Firing | Electric heater | Rubbing of hands together | Heat exchanger |
1.6.1 Sources of Renewable and Non-Renewable Energy
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.
1.6.2 Differentiate Between Renewable and Non-Renewable Energy Sources
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.
| S.No | Aspects | Renewable energy | Non-renewable energy |
| 1 | Origin | Earth’s atmosphere— Not human made | Underground layers of Earth-Natural resources |
| 2 | Restrictions | Eco-friendly to use | Serious impact on environment leads to climatic change |
| 3 | Skills | Interdisciplinary | More awareness link with engineering terms |
| 4 | Life of Resources | Finite | Infinite and vanish |
| 5 | Scale | Small | Large |
| 6 | Impacts on environment | 3%–4% of CO2 | 91%–94% of CO2 |
| 7 | Harmful to environment | Less harmful | More polluted to air, water |
| 8 | Requirements of area | Larger | Smaller |
| 9 | Maintenance cost | High | Low |
| 10 | Safety Precaution | Less | More |
| 11 | Examples | Solar, tidal energy, ethanol, biofuels, methanol, biodiesel, etc. | Oil, natural gas, minerals, etc. |
1.7 Photo-Thermal Conversion
