Advanced PV System Design – SS2 Solar Photovoltaic Installation & Maintenance Lesson Note (First Term)

What is a Hybrid System?

Think of a Hybrid System as a “multitasking” solar setup. In the past, you either had a system with batteries (Off-Grid) or a system connected to the street power (Grid-Tied).

A hybrid system gives you the best of both worlds. It connects to the solar panels, the utility grid, and a battery bank all at once.

Why go Hybrid?

• Security: If the grid goes down at night, your batteries kick in.
• Savings: You can use solar power during the day and only “buy” electricity from the grid when your panels aren’t producing enough.
• Flexibility: You can sell extra power back to the grid (if your local laws allow it).

The “Brain” – The Hybrid Inverter

In a standard system, the inverter just turns DC (battery/panel power) into AC (house power). In a hybrid system, the inverter is much smarter. It acts like a traffic warden.

The Hybrid Inverter decides:

1. “Is there enough sun? Use solar to power the house.”
2. “Is the battery full? Send the extra solar energy to the grid.”
3. “Is it raining and the battery is low? Pull power from the grid to help out.”

Understanding Grid-Tied Calculations

Before we install panels, we have to do the math. We need to know how much energy the house uses versus how much the sun provides.

Key Term: Peak Sun Hours (PSH) The sun isn’t at its strongest all day. We use “Peak Sun Hours” to represent the equivalent number of hours the sun shines at maximum strength (usually around 4 to 5 hours a day in most parts of West Africa).

The Basic Formula: To find out how many panels you need, use this logic:

Total Wattage Needed÷(Panel Wattage×PSH)=Number of Panels

Example: If a house needs 5,000Wh (5kWh) per day and you use 500W panels in an area with 5 Peak Sun Hours:

5000÷(500×5)=2 Panels

Sizing the Battery Bank

In a hybrid system, we don’t usually try to power the whole house on batteries for three days (that’s too expensive!). Instead, we size the battery for “Essential Loads” (lights, fans, fridge) during the night.

Important Rule: Depth of Discharge (DoD) You should never drain a battery to 0%.

• Lead-Acid/Gel: Only use 50%.
• Lithium-ion: Can usually go up to 80-90%.

Calculation Step:

Energy Needed (Wh)÷(Battery Voltage×DoD)=Amp−Hours (Ah) Needed

Efficiency and Safety

No system is 100% efficient. Energy is lost as heat in the wires and inside the inverter.

Loss Factors to remember:

• Inverter Efficiency: Usually around 90-95%.
• Dirt on Panels: Can reduce output by 5-10%.
• Wire Resistance: Long wires “steal” power.

Safety First:

• Circuit Breakers: Always place a breaker between the panels and the inverter, and between the battery and the inverter.
• Earthing: Essential to protect the system from lightning strikes.

Summary Checklist for Design

1. Audit: List every appliance and how many hours it runs.
2. Solar Array: Calculate panels based on Peak Sun Hours.
3. Inverter: Ensure the inverter can handle the “surge” (like when a fridge starts up).

Battery: Choose Lithium if the budget allows for longer life.