Grid-Tied Solar Set-Up – SS2 Solar Photovoltaic Installation & Maintenance Lesson Note (First Term)

The Goal of the Demonstration

In a standard solar setup, the house is an “island”—it stands alone. In a Grid-Tied setup, the house is a “team player.” It stays connected to the street transformer.

What we are demonstrating today:

1. How the Grid-Tied Inverter “listens” to the grid.
2. How the power flows from the panels to the house first, and then to the street.
3. Why the system shuts down if the street power goes off (The “Anti-Islanding” rule).

Safety Warning: In this practical, we are dealing with 230V AC power. You must never touch a bare wire. Always ensure the Main Switch is OFF before we make any connections.

The Components on the Table

Before we wire it up, let’s identify our tools:

• The PV Array: Our solar panels (DC Source).
• Grid-Tied Inverter: This is different from a normal inverter. It doesn’t need a battery to work; it uses the grid as its “reference.”
• AC Discovery/Main Board: This is where the street power enters.
• Bi-Directional Meter: A special meter that can count numbers forward (when you buy power) and backward (when you sell solar power to the grid).

The Connection Steps (DC Side)

First, we handle the power coming from the sun.

1. Mounting: We ensure the panels are facing South at about 15 degrees (for Nigeria’s location).
2. Stringing: We connect the panels in “Series” to increase the voltage. Most grid-tied inverters need a high voltage (like 200V–500V) to start working.
3. DC Isolator: We install a switch between the panels and the inverter. This allows us to “cut off” the sun during maintenance.

Pro-Tip: Always check your polarity with a Multimeter. Red is Positive (+) and Black is Negative (-). If you swap these, you might hear a “pop” and smell smoke from the inverter!

The Connection Steps (AC Side)

This is where it gets interesting. The inverter has to “join” the grid.

1. Synchronization: When we turn the system on, the inverter doesn’t start immediately. It “listens” to the grid for about 60 seconds. It needs to match the grid’s Frequency (50Hz in Nigeria) and Voltage (around 230V).
2. The Connection: We connect the AC output of the inverter to a dedicated breaker in the distribution board.
3. Earthing: We must connect the inverter’s metal casing to the house’s Earth line.

Testing and “Anti-Islanding”

Once the system is running, we perform the Shutdown Test.

The Scenario: Imagine there is a fault on the street, and a technician is climbing the pole to fix it. If your solar system keeps sending power to the street, you could electrocute that technician.

The Test:

1. While the sun is shining and the inverter is working, we flip the Main Grid Switch to “OFF.”
2. Observation: The inverter must shut down instantly (usually within milliseconds).
3. Even though the sun is bright, the inverter stops producing power because it no longer “feels” the grid’s heartbeat. This is called Anti-Islanding Protection.

Conclusion: A successful grid-tied setup is one that provides free energy when the grid is up but stays “dead” when the grid is down for the safety of everyone.