System Testing and Commissioning – SS1 Solar Photovoltaic Installation & Maintenance Lesson Note (Third Term)

System testing and commissioning is the set of checks an installer carries out on a solar photovoltaic (PV) system before handing it to the customer.

• Dead tests: checks done with the power off.
• Live tests: checks done with the power on.
• Performance checks: checks that confirm the system does its job under load.
• Handover: showing the customer how to use the system.

Behavioural objectives

1. State three reasons for testing and commissioning a solar system.
2. Carry out the dead tests: visual inspection, continuity test and polarity check.
3. Carry out the live tests: open circuit voltage, battery voltage and charging current.
4. Describe the load test, inverter output check and temperature check.
5. Explain to a customer how to read the system’s lights and alarms.

What are the key terms in testing and commissioning?

These are the words used throughout this lesson.

• Testing: measuring and inspecting a system to find out whether it is safe and working.
• Commissioning: the final stage of installation, when the system is switched on, proved to work and handed over.
• Multimeter: a meter that measures voltage, resistance and continuity, and sometimes current.
• Clamp meter: a meter that measures current by clamping round a wire without cutting it.
• Continuity: an unbroken path for current along a wire or joint.
• Polarity: the positive (+) and negative (-) sides of a circuit.
• Open circuit voltage (Voc): the voltage of a panel when nothing is connected to it.

Why do we test and commission?

We test and commission a solar system to prove that it is safe, performs well and can be supported by a warranty.

• Safety: to make sure no one gets shocked and nothing catches fire.
• Performance: to make sure the customer gets the power they paid for.
• Warranty: a company may ask for your test records before it replaces a faulty part.
• Car comparison: a builder checks the brakes and engine oil before giving a car to a driver. An installer checks the system in the same way.

The Golden Rule: always test before you put the final covers on the wires. It is easier to tighten a loose screw now than to repair a burnt wire later.

What safety steps come before testing?

Safety steps protect the installer and the equipment before any meter touches a wire.

• Protective wear: wear safety shoes, gloves and goggles.
• Jewellery: remove rings and metal watches, because metal can cause a short circuit.
• Isolation: switch off the breakers and switches for the panels, battery and inverter before dead tests.
• Panels: a panel produces voltage whenever light falls on it, so treat its wires as live in daylight.
• Meter setting: set the multimeter to the correct function (DC volts, AC volts or continuity) before you touch the probes to a wire.
• Dry hands: never work with wet hands or on a wet floor.

What are the “Dead” tests (power is OFF)?

Dead tests are checks done before the system is switched on, to make sure the wires and joints are safe and correct.

1. Visual inspection

• Check that no wire touches metal edges.
• Check that all screws and terminals are tight.
• Look inside the inverter box for rubbish such as metal filings.
• Check that cables are fixed neatly and not hanging loose.

2. Continuity test

1. Switch the system off.
2. Set the multimeter to continuity mode.
3. Touch one probe to each end of the cable, for example the wire at the roof and the end at the controller.
4. A beep or a very low reading shows an unbroken wire. No beep shows a break or a loose joint.

3. Polarity check

• Positive (+) must connect to positive (+), and negative (-) to negative (-), at every joint.
• Check the cable colours and the labels on the terminals. Red is usually positive and black is usually negative.
• A multimeter on DC volts shows a positive number when the red probe is on positive. A minus sign shows reversed polarity.
• Reversed polarity can blow a fuse or damage the controller or inverter. Find it before you switch on.

What are the “Live” tests (power is ON)?

Live tests are measurements taken with the system switched on, to see what is really happening in the circuit.

1. Open circuit voltage (Voc)

• Measure the panel voltage before the panel is connected to the controller.
• Compare the reading with the Voc written on the panel label.
• A reading close to the label value shows a healthy panel. The reading changes a little with sunlight and heat.
• A very low reading points to a faulty panel, a broken wire or heavy shade.

2. Battery voltage

• A healthy 12V battery shows about 12.6V when full and not charging.
• A reading of about 10V is too low. The battery needs charging or may be faulty.

3. Charging current

• Connect the panels, then read the current in amps.
• On a sunny day the current should be close to the panel rating.
• If a 10A panel gives only 1A in bright sun, look for a loose wire, a shaded panel or dirt on the glass.

What are the performance checks?

Performance checks are tests that run the system under load to confirm it works well for the customer.

1. Load test

• Switch on the fans, TV and bulbs together.
• Listen to the inverter for a loud “struggling” noise.
• Watch the battery voltage for a sharp drop.
• A good system carries the load smoothly.

2. Inverter output

• Set the multimeter to AC volts and measure at the inverter output.
• In Nigeria the mains supply is nominally 230V, and the reading should be about 220V to 230V.
• A much lower reading means appliances may not work properly.

3. Temperature check

• After about 30 minutes of running, touch the plastic insulation of the wires. Never touch bare metal.
• The wires should feel cool or slightly warm.
• A wire as hot as a cup of tea is a warning. The wire may be too thin for the current, or a joint may be loose.
• Switch off and correct the fault at once.

What is the difference between dead tests and live tests?

Dead tests are done with the power off and check the wiring. Live tests are done with the power on and check voltage and current.

What is the order of commissioning?

Commissioning follows four stages in a fixed order.

1. Carry out the dead tests with the power off.
2. Switch on one part at a time and carry out the live tests.
3. Run the load test, inverter output check and temperature check.
4. Record the results and hand over to the customer.

What should go in the logbook of tests?

The logbook is a written record of each test, the tool used and the result expected.

What are common faults found during testing?

Most faults found during testing come from loose joints, wrong connections, shade or wrong wire size.

How do we hand over the system to the customer?

Handover is the last part of commissioning, when you teach the customer how to read and use the system.

The “User Manual” talk

• Charging light: show the customer the “Charging” light and what it means.
• Low battery alarm: let the customer hear what the alarm sounds like.
• Red light: tell them, “If you see a Red Light, switch off the system and call me.”
• Load limit: explain which appliances the system can carry at the same time.
• Panels: advise keeping the panels clean and free from shade.
• Records: give the customer a copy of the test results.

Class practical activity

1. The “Fake Fault” Game: the teacher leaves a screw slightly loose or puts a shadow on a panel. Students use meters to find the problem.
2. Fill the Form: each student writes the “Test Results” for a 12V system they just “installed”.
3. The Customer Talk: one student plays the installer and another plays the house owner. The installer explains how to know if the battery is full.

Evaluation

1. Give three reasons for testing and commissioning a solar system.
2. Why are the visual inspection, continuity test and polarity check called “Dead” tests?
3. What happens if positive is connected to negative by mistake when the system is switched on?
4. What voltage should a healthy 12V battery show when it is full and not charging?
5. What does it mean if a wire feels hot like a cup of tea during the temperature check?

Assignment

List the three live tests and the three performance checks. For each one, write one sentence to say what you measure or observe and what a good result looks like.