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

A solar panel connection is the way panels are wired together to supply more power. The two main types are series and parallel, and the two can be combined as series-parallel.

Behavioural objectives

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

1. Name the types of solar panel connection.
2. Connect solar panels in series by joining positive to negative.
3. Connect solar panels in parallel by joining positive to positive and negative to negative.
4. Calculate the total voltage and current of panels connected in series and in parallel.
5. State three reasons for using a series connection.
6. Explain why shade on one panel reduces the output of a whole series chain.

Why connect solar panels together?

Panels are connected together because one panel alone often cannot give the voltage or current a system needs.

• The problem: one small panel is like one person lifting a bag of cement. It may be too weak for the load.
• The answer: make the panels work as a team by wiring them together.
• Voltage: the “pressure” that pushes electricity through the wires, measured in volts (V).
• Current: the “flow” of electricity, measured in amperes (amps, A).

What are the types of solar panel connection?

There are three types of solar panel connection: series, parallel and series-parallel.

• Series connection: panels joined like a chain, positive to negative.
• Parallel connection: panels joined side by side, positive to positive and negative to negative.
• Series-parallel connection: groups of panels joined in series, then the groups joined in parallel.

How do you connect solar panels in series?

A series connection joins the positive (+) terminal of one panel to the negative (-) terminal of the next, like a chain.

1. Pick panels with the same rating.
2. Join the positive (+) terminal of panel 1 to the negative (-) terminal of panel 2.
3. Join the positive of panel 2 to the negative of panel 3, and so on.
4. Take the free negative wire at one end and the free positive wire at the other end to the charge controller.

• The rule: positive to negative.
• The flow: electricity passes through the first panel, then the second, then the third, like a baton in a relay race.

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How does a series connection affect voltage and current?

In a series connection, the voltages add up and the current stays the same.

The voltage effect

• Formula: total voltage = V1 + V2 + V3 + …
• Two 12V panels: 12V + 12V = 24V.
• Three 12V panels: 12V + 12V + 12V = 36V.

The current effect

• Rule: total current equals the current of one panel.
• Example: if each panel gives 5 amps, the whole chain still gives 5 amps.

How do you connect solar panels in parallel?

A parallel connection joins all positive terminals together and all negative terminals together, so the panels sit side by side.

1. Pick panels with the same rating.
2. Join the positive (+) terminals of all panels together.
3. Join the negative (-) terminals of all panels together.
4. Take one positive wire and one negative wire from the joined points to the charge controller.

The effect on voltage and current

• Voltage: stays the same as one panel.
• Current: adds up. Formula: total current = I1 + I2 + I3 + …
• Example: two 12V, 5A panels in parallel give 12V and 10A.

What is a series-parallel connection?

A series-parallel connection joins panels in series to make strings, then joins the strings in parallel.

• Use: large systems that need both higher voltage and higher current.
• Example: four 12V, 5A panels, arranged as two strings of two panels.
• Each string: 12V + 12V = 24V at 5A.
• Two strings in parallel: 24V at 5A + 5A = 10A.

What is the difference between series and parallel connection?

Series connection raises the voltage and keeps the current the same. Parallel connection raises the current and keeps the voltage the same.

When do we use series connections?

A series connection is used when the system needs higher voltage, for example with a long cable run or a higher-voltage battery bank.

1. To match the battery bank: the panel voltage must be higher than the battery voltage to charge it. Two 12V panels in series give 24V for a 24V battery bank.
2. To save money on wires: for the same power, higher voltage means lower current. Lower current lets you use thinner, cheaper cables over a long distance without overheating.
3. For MPPT controllers: an MPPT charge controller accepts a high input voltage and converts it into a higher charging current for the batteries.

Why is shade a danger in a series connection?

In a series chain, the whole system is only as strong as its weakest panel.

• The analogy: a small stone in a water pipe slows the water in the whole pipe.
• The reality: if a tree shades one of four panels in series, the power of the entire chain drops significantly.
• Prevention: keep tree branches, walls and other objects away from the array.

Evaluation

1. If you connect four 18V panels in series, what is the total voltage?
2. You have a 12V panel that produces 8 amps. State the voltage and current when two of them are connected (a) in series and (b) in parallel.
3. Why should you make sure no overhanging tree branches are near a series-connected solar array?
4. State how to join the terminals of panels in a parallel connection.
5. Give three reasons why a series connection is used.

Assignment

Three 18V panels, each giving 6 amps, are used in a solar system. State the total voltage and total current when they are connected (a) in series and (b) in parallel. Then explain, using the water pipe analogy, why one shaded panel lowers the power of a series chain.