Unit 3 | MNGT 801 Notes | Solar Energy Technology and Applications Notes | AKTU Notes

3.1 What is Solar PV?

PV stands for PhotoVoltaic — "Photo" means light, "Voltaic" means electricity.

Solar PV is the technology of converting sunlight directly into electricity using solar cells.

3.2 Principle — The Photovoltaic Effect

When light (photons) falls on certain semiconductor materials, it knocks electrons loose. These free electrons flow as electric current. This is the photovoltaic effect.

Discovered by Edmond Becquerel in 1839.

How a solar cell works:

• A solar cell is made of silicon — a semiconductor material.
• It has two layers: N-type (extra electrons) and P-type (missing electrons = holes).
• At the junction of these two layers (P-N junction), an electric field is created.
• When sunlight hits the cell, photons give energy to electrons.
• The electric field pushes electrons in one direction → electric current flows.
• Metal contacts collect this current → we get DC electricity.

3.3 Solar Cell Structure

A solar cell is a thin wafer, usually about 0.2–0.3 mm thick.

Components:

• Anti-reflection coating (reduces reflection, increases absorption)
• N-type silicon layer (top)
• P-N junction
• P-type silicon layer (bottom)
• Metal contacts (top and bottom — collect current)

Output of one cell:

• Voltage: ~0.5–0.6 V
• Current: ~3–4 A (depends on size)
• Power: ~1–3 W

This is too small for practical use. So we combine cells.

3.4 Solar Cell → Module → Array

Solar Cell: Single unit, produces ~0.5V

Solar Module (Panel):

• Multiple cells connected in series (to increase voltage) and parallel (to increase current).
• A typical module has 36 or 72 cells.
• Output: 12V or 24V, 100–400 W

Solar Array:

• Multiple modules connected together.
• Used for large power requirements (homes, factories, power plants).

3.5 Performance Analysis of Solar Cells

Key parameters:

1. Short Circuit Current (Isc):

• Maximum current when output terminals are short-circuited.
• Increases with more sunlight intensity.

2. Open Circuit Voltage (Voc):

• Maximum voltage when no current is drawn.
• Typically ~0.6V for silicon cells.

3. Maximum Power Point (Pmax):

• The point where the product of V × I is maximum.
• Actual usable power from the cell.

4. Fill Factor (FF):

• FF = Pmax / (Voc × Isc)
• Tells how "ideal" the cell is. Good cells have FF of 0.7–0.85.

5. Efficiency (η):

• η = Pmax / (Incident solar power × cell area) × 100%
• Typical silicon solar cell efficiency: 15–22%

Factors affecting performance:

• Temperature: Higher temp → lower voltage → lower efficiency. Cells work better in cold sunny weather.
• Irradiance: More sunlight = more current.
• Shading: Even partial shading reduces output significantly.

3.6 Types of Solar Cells / Modules

1. Monocrystalline Silicon:

• Made from single crystal silicon.
• Highest efficiency (18–22%)
• Expensive, dark black color
• Best for limited roof space

2. Polycrystalline Silicon:

• Made from multiple silicon crystals.
• Efficiency 15–17%
• Cheaper than monocrystalline
• Bluish appearance

3. Thin Film Solar Cells:

• Very thin layers of semiconductor material (like CdTe, CIGS, amorphous silicon).
• Efficiency 10–13%
• Flexible, lightweight
• Used on curved surfaces

4. Bifacial Solar Panels:

• Capture sunlight from both front and back sides.
• 10–20% more output than regular panels.

3.7 Standalone PV Systems

A standalone PV system is one that works without connection to the electricity grid. It is used in remote areas.

Components:

• Solar Panels – Generate DC electricity
• Charge Controller – Prevents overcharging of battery, protects battery life
• Battery Bank – Stores electricity for use at night or cloudy days
• Inverter – Converts DC to AC (for household appliances)
• Load – The appliances that use the electricity

Applications:

• Rural electrification
• Street lights
• Water pumps in villages
• Telecom towers
• Remote weather stations

3.8 Advances in Solar Technologies

Concentrating Solar Thermal (CSP):

• Uses mirrors/lenses to concentrate sunlight on a small area.
• Produces very high temperatures (300–1000°C).
• Used to generate steam and run turbines for electricity.

BIPV (Building Integrated PV):

• Solar panels integrated into building materials — roof tiles, windows, walls.

Perovskite Solar Cells:

• New generation solar cells with efficiency up to 25%+.
• Cheaper to manufacture than silicon.
• Still in development (durability issues).

Hybrid PV-Thermal (PVT) Systems:

• Combined system that produces both electricity and heat simultaneously.
• More efficient use of sunlight.