Solar Energy Terminologies SS1 Solar Photovoltaic Installation & Maintenance Lesson Note

Introduction to Solar Talk

When you want to buy a generator, you talk about “KVA” or “Horsepower.” When you want to talk about solar energy, there are special words we use to describe how much power we are getting from the sky.

If we don’t understand these words, we might buy the wrong equipment or wonder why our batteries aren’t charging. Today, we will look at the four most important terms: Irradiance, Insolation, Efficiency, and Peak Sun Hours.

Irradiance (The “Right Now” Power)

Irradiance is a measure of how much solar power is hitting a specific spot at this exact moment.

Think of it like rain. If it is pouring down very hard right now, the “intensity” is high. If it is just drizzling, the intensity is low.

• When is it highest? Usually at 12:00 noon when the sun is directly overhead.
• When is it lowest? Early in the morning or late in the evening when the sun is “weak.”
• Unit of measurement: It is measured in Watts per square meter (W/m2).

Insolation (The “Total” Power)

People often confuse this with Irradiance, but they are different. Insolation is the total amount of solar energy that has hit a spot over a period of time (usually a whole day).

To use the rain example again:

• Irradiance is how hard it is raining right now.
• Insolation is how much water is in the bucket after the rain has fallen all day.

In Nigeria, our “daily bucket” is usually very full because we have many hours of sun. This is why our country is so good for solar energy!

Efficiency (The “Honest” Result)

This is a very important word. Efficiency tells us how much of the sunlight hitting a panel actually gets turned into electricity.

No solar panel is 100% efficient. In fact, most panels we buy in the market are only about 15% to 20% efficient.

Why is it so low?

1. Heat: Ironically, if a solar panel gets too hot, it becomes less efficient.
2. Reflectance: Some light just bounces off the glass like a mirror instead of going inside.
3. Dust: If your panel is covered in dust from the Harmattan, the efficiency drops because the light can’t reach the cells.

Peak Sun Hours (The “Golden” Hours)

This is perhaps the most misunderstood term in solar energy.

A day might have 12 hours of daylight (from 6:30 AM to 6:30 PM), but the sun isn’t strong enough to charge big batteries all those hours. Peak Sun Hours are the hours during the day when the sun’s intensity is at its best (usually around 1,000W/m2).

• In most parts of Nigeria, we get about 4 to 6 Peak Sun Hours per day.
• Even though the sun is “out” for 12 hours, a solar engineer will only count those 5 “Golden Hours” when calculating if your system will work.

Summary Table for Revision