Series and parallel connections

All circuits are built out of two types of electrical connections that deteremine the characteristics of the circuit: series and parallel. In normal circuit wiring for homes or buildings - lights and outlets - only parallel connections are used. But in PV systems series connections become important as they enable the voltage and current characteristics of a system to be changed which carries important advantages. Batteries and PV modules can be connected using either of these connection types or both. All batteries, PV modules, charge controllers and inverters are rated to operate within a given voltage and current range, thus these connection types are used to sure that the system can function together properly.

Parallel connections

A parallel connection is a connection that brings together circuits the could operate seperately, thus there are two or more separate paths current can follow. In the case of PV modules and batteries this is done by creating a connection between all of the positive connections of the circuits and a separate connection between all of the negative connections of a circuit. Parallel connections affect the functioning of a circuit in the following ways:

• If power sources, like PV modules or batteries, of the same size are connected together in parallel, the voltage of the circuit remains the same, but the current that the circuit can provide becomes the sum of their currents.
• If loads, like a lights, of the same size are connected together in parallel, the voltage of the circuit will remain the same, but the current of the circuit will be divided between the different parallel circuits.

• 

  2 x 12V FLA batteries connected with a parallel connection.

• 

  2 x PV modules connected with a parallel connection in a combiner box.

Example 1: Two 12V 100Ah batteries are connected in parallel. What is the voltage of the circuit and the Ah of available current?

• V = 12V as the voltage stays the same.

Ah = 200Ah as the Ah of available current doubles in this case.

Example 2: Three PV modules with an open circuit voltage (Voc) of 40V and a short circuit current (Isc) of 10A are connected in parallel. What is the voltage and available current of the circuit?

• V = 40V as the voltage stays the same.

Ah = 30A as the current tripes in this case.

Example 3: Two 12W lightbulbs (12V, 1A) are connected in parallel to a battery. What is the voltage and current across each lightbulb and for the circuit in total?

• Each lightbulb

V = 12V

I = 1A

• Circuit total

V = 12V

I = 1A + 1A = 2A

Series connections

A series connection is a connection that brings together loads or power sources into one single circuit, thus there is only one path that the current can follow. In the case of PV modules and batteries this is done by creating a connection from the positive of one load/power source to the negative of another. Series circuits affect the functioning of a circuit in the following ways:

• If power sources, like PV modules or batteries, of the same size are connected together in series, the voltage of the circuit becomes the sum of their voltages, but the available current of the circuit remains the same.
• If two loads, like a lights, of the same size are connected together in series, the voltage of the circuit is divided between the different loads, but the current of the circuit remains the same.

• 

  2 x 12V FLA batteries connected with a series connection.

• 

  2 x PV modules connected with a series connection.

Example 1: 2 x 12V 100Ah batteries are connected in series. What is the voltage of the circuit and the Ah of available current?

• V = 24V as the voltage doubles in this case.

Ah = 100Ah as the available current remains the same.

Example 2: Three PV modules with an open circuit voltage (Voc) of 40V and a short circuit current (Isc) of 10A are connected in series. What is the voltage and available current of the circuit?

• V = 120V as the voltage triples in this case.

Ah = 10A as the current tripes in this case.

Example 3: Two 12W lightbulbs (12V, 1A) are connected in series to a 12V battery. What is the voltage and current across each lightbulb and for the circuit in total?

• Each lightbulb

V = 12V ÷ 2 = 6V

I = 1A

• Circuit total

V = 12V

I = 1A (same 1A passes through each lightbulb)