Solar Panel Connection II – SS1 Solar Photovoltaic Installation & Maintenance Lesson Note (Second Term)

A parallel connection joins all the positive (+) wires of solar panels together and all the negative (-) wires together, so the voltage stays the same and the current adds up.

Behavioural objectives

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

1. Explain how solar panels are joined in a parallel connection.
2. State the effect of a parallel connection on current and voltage.
3. Calculate the total current of panels connected in parallel.
4. Explain why shade on one panel affects a parallel connection less than a series connection.
5. State when parallel connections are used and why thicker wires are needed.
6. Compare series and parallel connections.

What is a parallel connection?

A parallel connection is a way of joining solar panels in which all positive terminals meet at one point and all negative terminals meet at another.

• The rule: positive to positive, negative to negative.
• The result: one big “super-positive” junction and one big “super-negative” junction.
• The idea: think of it as a “team” setup, not a chain like a series connection.
• Use in Nigeria: it is used to “fatten” the power, so batteries charge faster and heavier loads run during the day.

How do we connect solar panels in parallel?

Panels are connected in parallel in four steps.

1. Check that all the panels have the same voltage rating.
2. Join all the positive (+) wires to one positive junction.
3. Join all the negative (-) wires to one negative junction.
4. Run thick cables from the two junctions to the charge controller.

How does a parallel connection affect current and voltage?

In a parallel connection, the current of the panels adds up and the voltage stays the same.

What is the current effect (the “flow” rule)?

• Rule: total current = current of panel 1 + panel 2 + panel 3 and so on.
• Two panels of 8 A each: 8 A + 8 A = 16 A.
• Three panels of 8 A each: 8 A + 8 A + 8 A = 24 A.

What happens to the voltage (pressure)?

• Rule: total voltage = voltage of one panel.
• Example: if each panel is 18 V, the whole group is still 18 V.
• Meaning: the “pressure” stays the same and only the “volume” of electricity in the wires increases.

Worked example: panels of 18 V and 8 A each

Why is a parallel connection better in shade?

A parallel connection copes better with shade because each panel works independently of the others.

• In series: if bird droppings cover one panel, the whole chain suffers.
• In parallel: a covered panel reduces only its own output, and the others keep working.
• The analogy: several people pump water into a tank through separate pipes. If one person rests (shade), the others still pump at full speed.
• In real life: where there are many trees or overhanging roofs, a shadow on one panel does not “kill” the production of the others.

When do we use parallel connections?

Parallel connections are used mostly in smaller systems and with certain types of equipment.

1. PWM charge controllers: basic PWM controllers cannot handle high voltage, so panels for a 12 V battery are joined in parallel to keep the voltage low.
2. Faster charging: a panel added in parallel raises the amps going into the battery, so it fills up faster.
3. Low voltage systems: 12 V DC bulbs or fans need a 12 V system, and parallel lets you add many panels (for example 10) while keeping 12 V.
4. Shaded sites: parallel is the better choice where shadows often fall on part of the array.

Why do parallel connections need thicker wires?

Parallel connections need thicker wires because the total current is high.

• The warning: you must use thicker wires for a parallel connection.
• The danger: thin wires carrying many amps get very hot and can cause a fire.
• The sign: a smell of burnt plastic from the cable insulation means the wire is overheating.

What are the advantages and disadvantages of a parallel connection?

Advantages

• Shade tolerance: shade on one panel does not stop the others.
• Low voltage: it suits PWM controllers and 12 V systems.
• Faster charging: more amps flow into the battery.

Disadvantages

• High current: it needs thicker and more costly wires.
• Fire risk: thin wires can overheat.

How do series and parallel connections compare?

A series connection joins panels in a chain, (+) to (-), so voltage adds up and current stays the same.

A parallel connection joins (+) to (+) and (-) to (-), so current adds up and voltage stays the same.

Evaluation

1. If you have two 12V, 5A panels and you connect them in parallel, what is the final voltage and current?
2. Why is it “safer” to have a tree shadow on a parallel system than on a series system?
3. Case study: Mr. Okon bought 4 panels for his shop. He used very thin wires to connect them in parallel. Why did he start smelling “burnt plastic” after two hours of bright sunlight?
4. Give two situations in which a parallel connection is the better choice.

Assignment

1. Draw three solar panels connected in parallel and label the positive and negative junctions. If each panel gives 18V and 8A, write the total voltage and current beside your drawing.