SSCE Past Questions (Theory) – SS3 Solar Photovoltaic Installation & Maintenance Lesson Note (Second Term)

SSCE theory questions in Solar Photovoltaic Installation and Maintenance test five main skills.

• Energy calculation: finding the energy used by appliances in watt-hours.
• Fault finding: naming the causes of a fault in a solar system.
• Comparison: contrasting components such as PWM and MPPT charge controllers.
• Safety: stating precautions for working with battery banks.
• Policy: explaining how rural electrification helps Nigeria.

Behavioural objectives

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

1. calculate the total energy used by a set of appliances in watt-hours (Wh), showing every step;
2. list possible causes of short battery backup in a solar lighting system and suggest the simplest fix first;
3. compare a PWM charge controller with an MPPT charge controller;
4. outline safety precautions for installing a 24V solar battery bank;
5. explain how rural electrification helps to reduce rural-to-urban migration in Nigeria.

How are SSCE theory questions marked?

Examiners award marks for clear, separate points and for correct working, not only for the final answer.

• Method marks: given for correct steps, even when the final answer has a small error.
• One point per line: write each point on its own line so the marker can count it.
• Units: write Wh, W, V and h correctly in every calculation.
• Number of points: if the question asks for three causes, give three and no more than the question asks.

What do the command words mean?

How do you answer sizing and energy questions?

Energy in watt-hours (Wh) is the power of an appliance in watts multiplied by the hours it is used.

• Formula: Energy (Wh) = Power (W) × Time (h).
• Several appliances: work out each group separately, then add the results.
• Unit conversion: 1000Wh equals 1 kilowatt-hour (kWh).
• Why it matters: panels and batteries are sized to match the total daily energy of the load.

The question: A barber shop uses 2 clippers (15W each) for 4 hours a day and 3 LED bulbs (10W each) for 6 hours. Calculate the total energy used in Watt-hours (Wh).

The worked solution:

1. Clippers: 2 × 15W × 4 hours = 120Wh
2. Bulbs: 3 × 10W × 6 hours = 180Wh
3. Total: 120Wh + 180Wh = 300Wh

• Exam tip: do not just write “300”. Always show your addition and multiplication.
• Method marks: examiners give them even if your final answer has a small calculation error.

How do you answer troubleshooting and maintenance questions?

Troubleshooting is the step-by-step search for the cause of a fault so that it can be corrected.

The question: A customer complains that their solar lights stay on for only 2 hours at night, even though the day was very sunny. List three possible causes.

The worked solution:

1. Old or weak battery: the battery may be “tired” and can no longer hold a full charge (high internal resistance).
2. Dirty panels: dust or bird droppings block the sun, so the battery never gets 100% full.
3. Loose connections: a loose wire between the charge controller and the battery stops power flowing properly.

What other causes can you give?

• Shading: a tree or building shadow falls on the panel during the day.
• Corroded terminals: rust or white deposits on battery terminals block current.
• Faulty charge controller: it may stop charging early or cut the load off too soon.
• Overloading: extra bulbs or appliances were added, so the load is bigger than the system was designed for.
• Undersized panel: the panel is too small to refill the battery in one day.

In what order should you check the faults?

1. Inspect the panels for dirt and shade, and clean them if needed.
2. Check that all wires are tight and the terminals are clean.
3. Check the charge controller display or indicator lights.
4. Check that the load has not been increased.
5. Test the battery last, and replace it only if it fails the test.

• Pro tip: always suggest the simplest fix first (such as cleaning the panels) before expensive fixes (such as buying a new battery).

How do you compare PWM and MPPT charge controllers?

A charge controller is a device that controls the current from the solar panel to the battery to prevent overcharging.

• PWM (Pulse Width Modulation): switches the panel on and off rapidly to hold the battery at the right voltage.
• MPPT (Maximum Power Point Tracking): adjusts voltage and current to take the most power the panel can give.

The question: Compare a PWM (Pulse Width Modulation) charge controller with an MPPT (Maximum Power Point Tracking) controller.

The worked solution:

• Exam tip: when the question says “compare”, give a point about both controllers on every row.

What safety precautions apply when installing a battery bank?

A battery bank is a group of batteries joined together to give the system voltage and storage needed.

• 24V bank: two 12V batteries joined in series give 24V.
• Marks: safety points are easy marks, so learn them well.

The question: Outline four safety precautions a technician must take when installing a 24V solar battery bank.

The worked solution:

1. Remove jewellery: take off metal rings or watches to avoid “short-circuiting” the battery terminals.
2. Use insulated tools: use spanners and screwdrivers with rubber handles.
3. Ventilation: make sure the battery room has fresh air (especially for lead-acid batteries, which can release gas).
4. Terminal covers: always put the plastic caps over the battery terminals after tightening the wires, to prevent accidental sparks.

What other precautions can you give?

• Protective wear: wear safety goggles and gloves to protect the eyes and hands.
• Isolate first: disconnect the panels and switch off the loads before connecting the batteries.
• Correct polarity: join positive to positive and negative to negative where the wiring diagram shows.
• Matching batteries: use batteries of the same type, voltage and capacity in one bank.
• No flames: keep smoking, naked flames and sparks away from the battery room.

How does rural electrification reduce rural-to-urban migration?

Rural electrification is the supply of electricity to villages and other rural communities, often using solar power.

The question: Explain how “rural electrification” helps in reducing rural-to-urban migration in Nigeria.

The worked solution:

• Job creation: with solar power, youths in villages can start businesses such as barbing salons, phone charging centres, and cold-room storage for fish and crops.
• Education: students can study at night, and schools can use computers, which makes village life more attractive.
• Safety: solar streetlights reduce crime at night, so people feel safe staying in their hometowns instead of moving to big cities like Lagos or Abuja.
• Health: clinics can keep lights on at night and run refrigerators for vaccines and medicines.

• Tip for students: think about your own community and use real examples of how light changes a person’s life.
• Structure: give each point a heading and one sentence of explanation.

Evaluation

1. A shop uses 4 LED bulbs (10W each) for 5 hours a day. Calculate the total energy used in Wh, showing your working.
2. List three possible causes of solar lights staying on for only 2 hours at night on a sunny day.
3. Compare a PWM controller with an MPPT controller under four headings.
4. Outline four safety precautions for installing a 24V solar battery bank.
5. Explain two ways rural electrification reduces rural-to-urban migration.

Assignment

1. In your exercise book, write a full answer to this question: Explain how “rural electrification” helps in reducing rural-to-urban migration in Nigeria. Use at least one example from your own community.
2. Write out the troubleshooting question from this lesson again, and list the causes in the order in which you would check them, starting with the simplest fix.