Comprehensive Revision I – SS3 Solar Photovoltaic Installation & Maintenance Lesson Note (Third Term)

A solar photovoltaic (PV) system turns sunlight into electricity, then controls, stores and delivers it safely to appliances.

Behavioural objectives

By the end of the lesson, students should be able to:

1. explain how a silicon solar cell produces electricity and name the main types of solar panel;
2. state the functions of the charge controller and the inverter, and the types of each;
3. define deep cycle, State of Charge and Depth of Discharge, and connect batteries in series and in parallel;
4. describe the three parts of the safety triangle and the correct way to put out a solar fire;
5. state the environmental and economic benefits of solar energy and the aim of the “30:30:30” policy.

What are the main parts of a solar PV system?

A solar PV system has five main parts: solar panels, charge controller, battery, inverter and load.

• Solar panels: change sunlight into DC electricity.
• Charge controller: protects the battery from overcharging.
• Battery: stores power for use at night or on cloudy days.
• Inverter: changes DC to AC for household appliances.
• Load: the appliances that use the power, such as bulbs, fans, TVs and fridges.
• Safety devices: fuses, breakers, earthing and isolation switches keep the system safe.

What are the types of solar PV system?

There are three types of solar PV system: off-grid, grid-tied and hybrid.

• Off-grid: works alone with batteries and has no link to the national grid.
• Grid-tied: connects to the grid and has no battery storage.
• Hybrid: uses batteries and also connects to the grid or a generator.

How do solar cells and panels produce electricity?

A solar cell is a silicon device that changes sunlight directly into DC electricity.

How does a silicon solar cell work?

1. Sunlight (light energy) falls on the silicon cell.
2. The light energy frees electrons in the silicon.
3. The built-in electric field of the cell pushes the freed electrons in one direction.
4. The moving electrons flow through the external circuit as electric current (DC).
5. Many cells are joined in series to make a panel with a useful voltage.

• Silicon: the material used in almost all solar cells, and it comes from sand.
• Electricity: the movement of electrons through a circuit.

What are the types of solar panel?

There are three common types of solar panel: monocrystalline, polycrystalline and thin-film.

• Monocrystalline: made from a single pure silicon crystal, dark black in colour and the most efficient.
• Polycrystalline: made from many silicon crystals melted together, blue and “marbled” in look.
• Thin-film: made by spreading thin layers of material on a surface, light and sometimes flexible, but less efficient.

Why is there glass on top of a solar panel?

• Protection: the glass guards the cells from rain, wind, dust and bird droppings.
• Light passing: the glass lets most sunlight reach the cells.
• Exam tip: if asked why glass is used, answer “protection”.

What do charge controllers do?

A charge controller is a device between the panels and the battery that stops the battery from overcharging.

• Prevents overcharging: reduces or stops charging when the battery is full.
• Prevents deep discharge: disconnects the load when the battery is too low.
• Blocks reverse current: stops power flowing back to the panels at night.

What are the types of charge controller?

There are two types of charge controller: PWM and MPPT.

• PWM (Pulse Width Modulation): a simple, cheap controller that switches the charging current on and off to suit the battery.
• MPPT (Maximum Power Point Tracking): a smarter controller that finds the panel’s best working point and turns extra voltage into extra current.

What does an inverter do?

An inverter is a device that changes DC from the panels or battery into AC for appliances.

• DC (Direct Current): flows in one direction, as from panels and batteries.
• AC (Alternating Current): changes direction regularly, as from the national grid, and is needed by fans and fridges.

What are the types of inverter?

There are two common types of inverter by output: pure sine wave and modified sine wave.

• Pure sine wave: gives clean power like the national grid, so it suits fridges, fans and computers.
• Modified sine wave: gives rougher power, which is fine for bulbs but can make fans hum or harm sensitive electronics.

How do solar batteries store power?

A solar battery is a rechargeable battery that stores the electricity from the panels for use when there is no sun.

What are the key battery terms?

• Deep cycle: a battery built to be drained and recharged daily for years, unlike a car battery that gives a quick burst to start an engine.
• State of Charge (SoC): how full the battery is, like a phone’s percentage. 100% means full.
• Depth of Discharge (DoD): how much of the battery’s capacity has been used.
• Relationship: SoC + DoD = 100%.
• Lead-acid rule: do not discharge a lead-acid battery below 50% SoC (past 50% DoD), or its life becomes shorter.
• Capacity: measured in amp-hours (Ah).

How do we connect batteries?

Batteries are connected in series to raise voltage and in parallel to raise capacity.

Series connection

1. Join the positive (+) of the first battery to the negative (-) of the second.
2. Take the load from the free positive and free negative terminals.
3. Voltage adds up. Capacity stays the same.

Parallel connection

1. Join positive (+) to positive (+) and negative (-) to negative (-).
2. Take the load from one positive and one negative terminal.
3. Capacity adds up. Voltage stays the same.

How do we protect a solar system and stay safe?

Safety in a solar system means preventing fire, shock and equipment damage.

What are the parts of the safety triangle?

The safety triangle has three parts: fuses and breakers, earthing, and isolation.

1. Fuses and breakers: the deliberate weak point in a circuit. When too much current flows, the fuse blows or the breaker trips, so the inverter is spared.
2. Earthing (grounding): a copper rod buried in the ground is joined to the metal frames of the panels. Fault current then flows safely into the earth.
3. Isolation: a disconnect switch between the panels and the controller lets you cut the power completely before repairs.

How do we put out a solar fire?

• Never use water: the system carries live electricity, so water can cause shock.
• Use CO2: a carbon dioxide extinguisher is safe on electrical fires.
• Use dry powder: a dry powder extinguisher is also suitable.

What other safety rules apply on site?

• Isolate first: switch off before touching any wiring.
• Insulated tools: use them to avoid shock.
• Protective gear: wear gloves, safety shoes and a helmet.
• Panels stay live: they produce voltage whenever light falls on them.

How do we maintain a solar PV system?

Routine maintenance keeps a solar system working well and extends its life.

• Panel cleaning: remove dust and droppings with a soft cloth and clean water, when the panels are cool.
• Shading check: cut back branches or remove objects that shade the panels.
• Connections: check cables, terminals and fuses for looseness, heat marks and corrosion.
• Battery care: keep terminals clean and tight, and avoid deep discharge.

Why does solar energy matter for the environment and policy?

Solar energy is clean, renewable power that cuts pollution and brings electricity to places the grid does not reach.

What are the benefits of solar energy?

• Zero emissions: solar produces no smoke, which helps reduce the greenhouse gases that cause climate change.
• Decentralisation: every house can be its own power station, with no long wires from a distant city.
• Rural electrification: decentralised solar brings power to villages without grid supply.
• Economic growth: barbing salons and tailors can work at night without buying petrol for generators.

What is the “30:30:30” policy?

• Aim: Nigeria’s goal is to reach 30,000 MW of power by 2030.
• Renewable share: 30% of that power should come from renewable energy.

Evaluation

1. State two differences between monocrystalline and polycrystalline panels.
2. Explain the difference between a PWM and an MPPT charge controller.
3. What voltage and capacity result when two 12V batteries are connected (a) in series and (b) in parallel?
4. Why should you never use water to put out a solar fire? Name two suitable extinguishers.
5. What is the aim of Nigeria’s “30:30:30” policy?

Assignment

1. Name the three parts of the safety triangle and explain how each one protects a solar system.