18/07/2026
☀️ SUNHARVEST TRAINING INSTITUTE
ADVANCED CERTIFICATE IN SOLAR PV SYSTEM DESIGN, INSTALLATION & MAINTENANCE
WEEK 2 – DAY 4 (FINAL LESSON)
ELECTRICAL POWER, ELECTRICAL ENERGY, POWER FACTOR, SINGLE-PHASE & THREE-PHASE POWER SYSTEMS
Duration: 2½–3 Hours
Teaching Methods: Lecture, Demonstration, Calculations, Practical Exercises, Group Discussion
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Learning Outcomes
By the end of this lesson, students should be able to:
- Define electrical power and electrical energy.
- Calculate electrical power and energy consumption.
- Explain the difference between power and energy.
- Define power factor and explain its importance.
- Differentiate between single-phase and three-phase power systems.
- Identify applications of single-phase and three-phase systems.
- Apply these concepts when designing solar PV systems.
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1. Introduction
Every electrical appliance consumes electrical power, while electricity bills are based on the amount of electrical energy used over time. A solar PV technician must understand how much power a load requires and how much energy it consumes in a day. These calculations are essential when selecting solar panels, batteries, inverters, and charge controllers.
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2. Electrical Power
Electrical power is the rate at which electrical energy is converted or used.
Formula
P = V × I
Where:
- P = Power (Watts)
- V = Voltage (Volts)
- I = Current (Amperes)
Example 1
A solar panel produces:
- Voltage = 40 V
- Current = 10 A
Power = 40 × 10 = 400 W
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3. Electrical Energy
Electrical energy is the total amount of power used over a period of time.
Formula
Energy = Power × Time
E = P × t
Units:
- Watt-hour (Wh)
- Kilowatt-hour (kWh)
Example
A 100 W television operates for 6 hours.
Energy = 100 × 6 = 600 Wh = 0.6 kWh
This is the energy consumed during one day.
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4. Difference Between Power and Energy
Electrical Power| Electrical Energy
Rate of using electricity| Total electricity used over time
Measured in Watts (W)| Measured in Wh or kWh
Instantaneous value| Depends on operating time
A common mistake is confusing a 1 kW appliance with 1 kWh of energy. A 1 kW appliance only uses 1 kWh if it operates continuously for one hour.
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5. Load Calculation
A load calculation determines how much electricity a customer uses each day.
Example
Appliance| Quantity| Power| Hours/Day| Daily Energy
LED Lights| 8| 10 W| 6| 480 Wh
Television| 1| 100 W| 5| 500 Wh
Refrigerator| 1| 180 W| 10| 1,800 Wh
Laptop| 2| 65 W| 5| 650 Wh
Total Daily Energy = 3,430 Wh (3.43 kWh/day)
This information is used to size:
- Solar panels
- Battery bank
- Inverter
- Charge controller
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6. Power Factor
Power factor is the ratio between real power (useful power) and apparent power (total supplied power).
Formula
Power Factor = Real Power ÷ Apparent Power
Power factor ranges from 0 to 1.
A power factor close to 1 means electrical equipment is operating efficiently.
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7. Importance of Power Factor
A good power factor:
- Improves system efficiency.
- Reduces energy losses.
- Reduces current in cables.
- Minimises voltage drop.
- Improves equipment performance.
- Reduces electricity costs in many commercial and industrial installations.
Poor power factor can:
- Overload cables.
- Increase energy losses.
- Reduce system efficiency.
- Cause overheating.
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8. Single-Phase Power System
A single-phase system consists of:
- Live conductor
- Neutral conductor
- Earth conductor
Typical supply in Zimbabwe:
- 230 V AC
- 50 Hz
Applications
- Houses
- Small offices
- Shops
- Small solar installations
Most domestic appliances are designed for single-phase supply.
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9. Three-Phase Power System
A three-phase system consists of:
- Phase L1
- Phase L2
- Phase L3
- Neutral
- Earth
Typical voltage:
- 400 V AC (between phases)
- 230 V AC (phase to neutral)
Three-phase systems deliver power more efficiently for large loads.
Applications
- Factories
- Hospitals
- Shopping centres
- Large farms
- Mines
- Industrial solar installations
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10. Single-Phase vs Three-Phase
Single-Phase| Three-Phase
One live conductor| Three live conductors
Lower power capacity| Higher power capacity
Mainly residential| Mainly industrial and commercial
Simpler installation| More complex installation
Lower installation cost| Higher installation cost
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11. Importance in Solar PV Design
Understanding power and energy calculations enables technicians to:
- Correctly size solar panels.
- Select the correct inverter.
- Design battery storage.
- Choose appropriate cable sizes.
- Prevent system overloading.
- Estimate customer energy requirements.
For example, if a customer's daily energy demand is 5 kWh, the solar PV system must be designed to produce at least this amount, with additional allowance for system losses and weather conditions.
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12. Practical Exercise
Students should:
1. Read the power rating from five household appliances.
2. Calculate the daily energy consumption of each appliance.
3. Calculate the total daily energy requirement.
4. Identify whether each appliance is suitable for a single-phase or three-phase supply.
5. Discuss how these calculations influence solar system sizing.
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Summary
Today's lesson covered:
- Electrical power.
- Electrical energy.
- Power calculations.
- Energy calculations.
- Load assessment.
- Power factor.
- Single-phase systems.
- Three-phase systems.
- Their importance in solar PV system design.
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Assignment
1. Define electrical power.
2. Define electrical energy.
3. Explain the difference between power and energy.
4. A water pump operates at 750 W for 4 hours per day. Calculate its daily energy consumption.
5. Explain the importance of power factor.
6. Compare single-phase and three-phase systems.
7. List five appliances commonly found in homes and estimate their daily energy consumption.
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End-of-Day Quiz (20 Marks)
Section A
1. Define electrical power. (2)
2. Define electrical energy. (2)
3. State the formula for electrical power. (2)
4. State the formula for electrical energy. (2)
Section B
5. A 200 W television operates for 5 hours. Calculate the daily energy consumption. (4)
6. A solar inverter supplies 230 V and 8 A. Calculate the output power. (4)
Section C
7. Explain the difference between:
- Power and energy.
- Single-phase and three-phase power systems. (4)
Total: 20 Marks
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WEEK 2 COMPLETE
Day 1
- Introduction to Electricity
- Atomic Structure
- Conductors, Insulators and Semiconductors
- Voltage, Current, Resistance and Power
Day 2
- Ohm's Law
- Kirchhoff's Current Law (KCL)
- Kirchhoff's Voltage Law (KVL)
- Series and Parallel Circuits
Day 3
- Electrical Measuring Instruments
- Digital Multimeter
- Clamp Meter
- Measuring Voltage, Current and Resistance
- Continuity Testing
- Testing Solar Panels and Batteries
- Electrical Fault Detection
Day 4
- Electrical Power
- Electrical Energy
- Load Calculations
- Power Factor
- Single-Phase Systems
- Three-Phase Systems
Day 5 – Weekly Revision & Assessment
Students will:
- Revise all Week 2 topics.
- Solve electrical calculation exercises.
- Measure voltage, current and resistance using a multimeter.
- Connect simple series and parallel circuits.
- Demonstrate safe use of electrical measuring instruments.
- Write a 40-mark weekly test covering all Week 2 lessons.
- Receive feedback and prepare for Week 3: Basic House Wiring.
End of Week 2
