PV System Design Principle SS1 Solar Photovoltaic Installation & Maintenance Lesson Note

What is Load Assessment?

In solar talk, a “Load” is anything that uses electricity. Your fan is a load, your phone charger is a load, and your fridge is a very heavy load.

Load Assessment is simply making a list of everything you want to power with your solar system.

Think of it like planning a party. You wouldn’t buy food without knowing how many people are coming, right? In the same way, we don’t buy solar panels without knowing how many “appliances” are coming to eat the energy.

The Two Things We Need to Know:

1. Quantity: How many of each item? (e.g., 5 bulbs).
2. Power Rating (Watts): How much energy does each one “eat” at once? (e.g., 10 Watts per bulb).

Finding the “Secret Number” (Wattage)

Every electrical appliance in Nigeria has a “birth certificate”—usually a small sticker or a carved plate on the back or bottom. This is where you find the Watts (W).

• LED Bulbs: Usually 5W to 15W.
• Standing Fan: 50W to 70W.
• Plasma TV: 80W to 150W.
• Laptops: 45W to 90W.
• Electric Iron: 1,000W to 2,000W (This is why we say “Ironing and Solar are not best friends!”).

If you can’t find the Watts but you see Volts (V) and Amps (A), you can calculate it yourself:

Watts=Volts×Amps

Energy Demand (The “Hours” Matter)

Knowing the Watts is only half the story. We also need to know how long you will use them. This gives us the Energy Demand, measured in Watt-hours (Wh).

The Formula:

Watts×Hours=Watt−hours(Wh)

Example: If you have a 60W Fan and you run it for 10 hours at night:

60W×10 hours=600Wh

If you have 5 Bulbs (10W each) and you leave them on for 5 hours:

50W total×5 hours=250Wh

Creating a Load Table

To design a system, we put all this information into a table. This is the only way to be sure we aren’t forgetting anything.

Sample Load Table for a Small Room:

• 
  Total Watts (200W): This tells us how big the Inverter should be.
• Total Energy (1,300Wh): This tells us how many Batteries and Panels we need.

The “Efficiency Gap” (The 20% Rule)

One thing many people forget in Nigeria is that no system is perfect. As electricity travels through wires and through the inverter, some of it gets “lost” as heat. This is called System Loss.

In solar design, we always add a 20% to 30% safety margin.

If your calculation says you need 1,300Wh, you should actually design for about 1,600Wh. It’s like buying a little extra fuel for your car just in case there is a traffic jam. If you design “exactly” to your load, your batteries will die much faster because they are working too hard.

Class Activity: The “Home Audit”

1. Tonight, take a notebook and look at 3 appliances in your house. Find the Wattage sticker on each.
2. Estimate how many hours your family uses them in a day.
3. Calculate the Watt-hours for those 3 items.
4. Discussion: If your father wants to add an “Electric Kettle” (2,000W) to a small 1KVA solar system, what do you think will happen?