Types of Solar Energy System – SS1 Solar Photovoltaic Installation & Maintenance Lesson Note (First Term)

The three types of solar energy system are on-grid, off-grid and hybrid, and they differ in grid connection and battery use.

Behavioural objectives

By the end of the lesson, students should be able to:

1. name the three main types of solar energy system;
2. explain how on-grid, off-grid and hybrid systems work;
3. state one advantage and one limitation of each system;
4. suggest where each system is best used;
5. compare the three systems in terms of batteries, cost and independence.

What are the types of solar energy system?

There are three types of solar energy system: on-grid, off-grid and hybrid.

• On-grid system: connected to the main power lines of the national grid.
• Off-grid system: fully independent, running on solar panels and batteries only.
• Hybrid system: connected to the grid and also fitted with batteries.

• Deciding factor 1: whether the national grid (“NEPA”) reaches the area.
• Deciding factor 2: how much money is available for batteries.

What are the main parts of a solar energy system?

A solar energy system is made of parts that collect, store, convert and deliver electricity.

• Solar panels: change sunlight into direct current (DC) electricity.
• Inverter: changes DC electricity into alternating current (AC) for home appliances.
• Charge controller: protects the batteries from overcharging in systems that use batteries.
• Batteries: store electricity for use at night or on cloudy days.
• Mounting frame and cables: hold the panels in place and carry the current.

What is an on-grid system?

An on-grid (grid-tied) system is a solar system connected directly to the national electricity lines.

How an on-grid system works

1. The solar panels make power during the day.
2. The inverter changes the power to AC.
3. The building uses the power it needs.
4. Any extra power goes back to the national grid.
5. At night, the building draws power from the grid.

Features of an on-grid system

• Main advantage: it is the cheapest to install because it does not need expensive batteries.
• Main limitation: it shuts off automatically when the grid goes down (blackout).
• Reason for the shut-off: it stops power flowing into a line that a technician may be repairing.
• Best use: big businesses or homes in cities where the grid is stable and the aim is a lower monthly electricity bill.

What is an off-grid system?

An off-grid (stand-alone) system is a solar system completely disconnected from the national grid.

How an off-grid system works

1. The solar panels make power during the day.
2. The charge controller sends the power safely into a large bank of batteries.
3. The inverter changes the stored DC power to AC.
4. The batteries supply the building at night.

Features of an off-grid system

• Main advantage: total independence, with no worry about grid collapse or estimated bills.
• Main limitation: a large battery bank is compulsory, which makes the system costly.
• Care needed: heavy loads such as an air conditioner can drain the batteries on a cloudy day.
• Best use: rural villages, farmhouses and remote clinics that the national grid has not reached.

What is a hybrid system?

A hybrid system is a solar system connected to the grid that also has batteries.

How a hybrid system works

1. The system uses solar power first.
2. If the sun is not enough, it draws from the batteries.
3. If the batteries are low, it switches automatically to the national grid or a generator.

Features of a hybrid system

• Energy management: it picks the cheapest or most reliable source of power at any moment.
• Main advantage: power is available all day and night, because batteries act as backup when the grid fails.
• Main limitation: it costs more than an on-grid system because it needs batteries.
• Best use: homes and small businesses in Nigerian cities where the grid is unreliable and blackouts are frequent.

How do the three systems compare?

The table below compares on-grid, off-grid and hybrid systems on five features.

How do you choose the right solar energy system?

The right system depends on grid availability, grid reliability and budget.

Evaluation

1. Name the three types of solar energy system.
2. If you are building a hospital in a remote village in Adamawa where there are no electricity poles, which system would you install? Give a reason.
3. Why is an on-grid system often frustrating for a Nigerian home during a national grid collapse?
4. State one advantage and one limitation of a hybrid system.
5. Between initial cost (price to buy) and running cost (price to keep it going), which system is the most expensive over 10 years? Give a reason.

Assignment

Write short notes on the on-grid, off-grid and hybrid systems. For each one, state how it works, one advantage and one place where it is best used.