PV System Installation Steps II – SS1 Solar Photovoltaic Installation & Maintenance Lesson Note (Third Term)

PV system installation steps II is the fixed connection order for a solar system: batteries first, then solar panels, then the AC output to the house.

Behavioural objectives

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

1. State the “Battery First” rule and give the reason for it.
2. Connect batteries to an inverter using the correct colour code and a spanner.
3. Describe how solar panels are wired to the charge controller safely.
4. Explain why a change-over switch is used between the inverter and the grid.
5. List the steps for the first start-up (commissioning) of a PV system.

What is the “Battery First” rule?

The “Battery First” rule says always connect the batteries to the inverter and charge controller before connecting the solar panels.

• Controller needs a reference: the charge controller must “wake up” and read the battery voltage (12 V, 24 V or 48 V) first.
• Panels first is risky: the controller has no battery to send energy to, so it may be damaged or behave wrongly.
• Same rule for the whole system: battery first, solar second, AC output last.

What safety steps come before wiring?

Safety steps are the checks you make before touching any cable, so that nobody is shocked or burnt.

• Breakers OFF: keep the battery, solar and AC breakers switched off while joining wires.
• Remove metal items: take off rings, bracelets and watches, because metal can short the battery terminals.
• Use insulated tools: a spanner with an insulated handle lowers the risk of a short circuit.
• Panels make power in daylight: connected panels give voltage even when the breaker is off, so handle the wires with care.

How do you connect the batteries?

Batteries are connected to the inverter with thick cables, because the current is very high.

1. Clean the terminals: remove dust and the “white powder” (corrosion) from the battery heads.
2. Fit the cable lugs: place each thick cable end on the correct terminal.
3. Tighten with a spanner: do not twist wires by hand. A loose connection causes sparks and can melt the terminal.
4. Check the colour code: confirm red is on positive and black is on negative before switching on.

What is the battery colour code?

• Reversed polarity: swapping the cables can cause sparks, a loud bang and serious damage to the inverter.
• Double-check: always look at the markings on the battery and inverter before you tighten.

How do you wire the solar panels to the controller?

Solar panels are wired to the controller through a DC breaker, after the battery has already been connected.

1. Fit the DC disconnect: put a circuit breaker on the panel cables before they enter the controller.
2. Keep it OFF: leave the DC breaker off while you join the wires.
3. Join with MC4 connectors: these “click-and-lock” plugs must click firmly so that rain cannot enter.
4. Check polarity: set the multimeter to DC volts, put the red probe on the wire you think is positive and the black probe on the other.
5. Read the display: a positive reading with no minus sign confirms the polarity is correct.
6. Connect to the controller: join the checked wires to the panel input terminals, positive to positive and negative to negative.

How do you connect the inverter to the house?

The inverter output is the AC side of the system, and it can kill if handled carelessly.

What is a change-over switch and why is it used?

A change-over switch is a switch that lets the house use only one power source at a time.

• Never join sources: inverter output and NEPA (grid) supply must never be connected together.
• Danger of joining them: power can feed back and damage the inverter or hurt people working on the lines.
• How it works: the switch sits between the two sources and the house, and connects only one.

What colours are used for the output wiring?

Why must the inverter not be overloaded?

• Heavy loads: water heaters and air conditioners (ACs) draw a lot of power.
• Design limit: connect them only if the system was designed for them.
• Check the rating: total load must stay below the inverter’s rated power.

How do you start the system for the first time (commissioning)?

Commissioning is the first start-up and testing of a newly installed system, done one switch at a time.

1. Switch 1, the battery breaker: turn it on. The inverter screen should light up.
2. Switch 2, the solar breaker: turn it on. The controller should show “Charging”.
3. Switch 3, the AC output: turn it on to send power to the house.
4. The “smell and sound” test: stand near the system for 5 minutes and watch for a burning smell or strange hissing sounds.
5. Result: if it is silent, cool and clean-smelling, the installation has passed the first check.

• Shutting down: switch off in the reverse order, AC output first, then solar, then battery.

What are the common installation mistakes?

Common installation mistakes are wrong connection order, wrong polarity and loose joints, and each has a simple prevention.

Class practical activity

1. The terminal check: give each group a battery and a thick cable. Let them tighten the bolt with a spanner until it does not move.
2. The multimeter test: show students how to test continuity, to find out whether a wire is broken inside. Do this with the wire disconnected from any power.

Evaluation

1. Why must the batteries be connected before the solar panels?
2. State the colour code for the battery terminals.
3. Why is a change-over switch used between the inverter and NEPA (grid) power?
4. List the three switches in the order you turn them on during first start-up.
5. What two things do you check for in the “smell and sound” test?

Assignment

Design a “Danger: High Voltage” sign for a real solar installation, and include three warnings taken from this lesson.