Energy Management Chapter 9: Alternative Energy Sources

Energy Management 1 AU 2nd Term Spring 2024

• Chapter 9 is about alternative energy sources
• Alternative energy sources are non-depleting or renewable
• Examples include solar, wind, and others that replace traditional fossil fuels
• Government funding and tax incentives for alternative energy reduced in the 1980s and 1990s
• The MENA region receives high solar irradiance globally

Solar Thermal Systems

• Introduction to the topic
• Solar Irradiance details
• Solar Thermal Collectors
• Thermal Storage Systems
• Surface temperature (Tsurface) = 5778 K (5505°C)
• Core temperature (Tcore) = 15.6 × 10⁶ K
• Power = 3.85 × 10²⁶ Watts
• Energy = 3.37 × 10²⁷ KW⋅hr/yr
• Annual Energy Intercepted on Earth: 1.5 × 10¹⁸ KW⋅hr/year (0.000000045%)
• World Energy Demand: 1.4 × 10¹⁴ KW⋅hr/yr (0.0093%) - Total: 4.2 × 10⁻¹² %

Solar Irradiance (Distribution)

• The MENA region receives the highest solar irradiance globally

Solar Irradiance (Orientation)

• Designers should estimate the solar radiation angle to remain perpendicular to it for maximum energy collection

Solar Thermal Collectors (Non-Concentrating)

• Flat plate collectors
• Evacuated tube collectors
• Volumetric air collectors
• The flat-plate collector typically faces south in the Northern Hemisphere
• These collectors bring the temperature of a liquid or air up from ambient conditions
• Tracking-type collectors used when high temperatures (over 120°C) are required

Solar Thermal Collectors (Concentrating)

• Parabolic Trough collectors
• CSP collectors
• Fresnel collectors
• Solar Power Tower
• Solar Dish Sterling Engine

Solar Irradiance (Numerical Facts)

• Solar energy arrives at the Earth's atmosphere at a rate of approximately 1353 W/m² (428 Btu/hr ft²)
• This value is the solar constant
• Part of this is reflected, absorbed and scattered in the atmosphere
• When at 40° North Latitude, the noontime radiation rate on a flat surface normal to the sun's rays around 946 W/m² (300 Btu/hr ft²) on a clear day
• A solar collector should track the sun to remain normal to the incoming rays at all times
• A perfect collector may only capture 70% of the energy
• The realistic area to generate 293 kWh(16 million Btu) of energy per day is around 53 m²(567 ft²)

Volumetric Air Collector

• An alternative to liquid solar systems
• Freezing is not a concern with volumetric air collectors
• Leaks are less detrimental than with liquid systems
• Corrosion is less likely to occur

Parabolic Trough

• Temperature range: 250-450°C
• Concentrating collectors for high temperatures (like power generation)
• Cannot use diffuse or scattered radiation, must track the direct sun

Compound Parabolic Concentrator (CPC)

• Used in residential and commercial heating applications

Fresnel

• Composed of multiple smaller flat mirrors to concentrate radiation like parabolic troughs, but simpler and cheaper

Solar Power Tower

• Uses a set of two-axis tracking mirrors (heliostats) to reflect sunlight to a central tower
• Uses molten salt (Sodium Nitrate NaNO₃) as a coolant

Thermal Storage Systems

• Energy demand isn't always tied to solar availability, so storage is needed
• Water is the most common storage, often in tanks, but water freezes and therefore antifreeze may be required.
• Rock-bed storage is used with air-type collectors.

Solar Cells (Photovoltaics)

• The electronic properties of a semiconductor converts sunlight to electricity
• Most solar cells are p-n junction diodes (composed of p-type and n-type materials)
• p-n junctions have electronic asymmetry
• N-type regions have high electron densities and low hole densities. Electrons move easily; holes move with difficulty
• P-type materials are the opposite
• Excess electron-hole pairs are generated when illuminated
• Electrons move from p-type to n-type, and holes move in the opposite direction