There are two basic ways of connecting electrical components into a circuit, namely series and parallel. In general, most circuits are composed of a certain number of circuits in parallel and/or series.

① Series circuit

The path through which current flows from one potential to another is called a circuit. The current flows through all electrical components in sequence, which is a series circuit. As shown in Figure 1, the resistors R_{1} and R_{2} and the battery are connected in series.

There is only one path through which the current flows, so all the components in this circuit have the same current. The current will be blocked by all the individual electrical components in this path, so the total resistance R_{T} is

R_{T}=R_{1}+R_{2}

Assuming that the battery in Figure 1 is 12V, there are:

(1) If R_{1}=R_{2}, then the voltage on R_{1} and R2 is 6V each.

(2) If R_{1}=2R_{2}, then the voltage on R_{2} is 4V, and the voltage on R_{1} is 8V.

In order to explain more clearly, suppose R_{1}=4Ω and R_{2}=20, then the current I should be 12V/(4+2)Ω=2A. The voltage on R_{1} should be 12A×4Ω=8V, and the voltage on R_{2} should be 2A×2Ω=4V.

Figure 2 shows that two batteries are connected in series. In this example, the voltages of the batteries will be combined (added). If a single battery is 12V, then the potential difference on R is 24V. If R is a constant, the current flowing through R will increase (because I=U/R) when continuing to connect in series.

Photovoltaic modules are similar to batteries. In Figure 3, the standard voltage of photovoltaic modules PV_{1} and PV_{2} is 12V, and the current capacity is I_{1}=I_{2}=3.5A. Then the output voltage of these two modules applied to the resistor R is that of these two modules. The sum of voltages, namely

PV_{T}=12+12=24 (V)

And the current I_{T} is equal to the current on a component, namely

I_{T}=I_{1}=I_{2}=3.5A

When more components are connected in series, the current remains the same, but the voltage accumulates. A photovoltaic module can be regarded as a limited current source. When photovoltaics are connected in series, they are called strings.

Although the batteries in Figure 4 are connected in series, they are connected in opposite directions. Assuming that they have the same voltage, there will be no current flowing in the circuit, and the potential difference on R is zero.

Figure 5 is a schematic diagram of an open circuit of a series circuit. The open circuit may be caused by a switch disconnection or a fuse blown. There will be no current flowing in the circuit. The total voltage can be obtained by measuring the voltage across the open circuit point.

②Parallel circuit

When two or more components are connected across the two sides of the same power supply, they form a parallel circuit. Each component connected in parallel forms a separate “branch”. Although each branch has the same potential difference, there may still be different currents flowing through each branch.

In the circuit of Figure 6, the total current IT is equal to the sum of the currents of all parallel branches I_{1}+I_{2}, but the potential differences on all branches are equal. If we connect multiple power sources in parallel, such as photovoltaic modules, assuming that they are all the same, the potential difference will also be a constant, and the current will be equal to the sum of the currents of all branches. The calculation formula is

U_{T}=U_{1}=U_{2}

I=I_{1}+I_{2}

For example, the standard voltage of the photovoltaic module in Figure 7 is PV_{1}=PV_{2}=12V, and the current is I_{1}=I_{2}=3.5A, then the output current of the circuit is

PV_{T}=12V

I_{T}=3.5A+3.5A=7A

If you continue to connect the components in parallel, the voltage will remain constant, but the current in the entire battery array will continue to increase.

③Hybrid series/parallel circuit

Through the mixed connection of series and parallel circuits, photovoltaic modules (or batteries) can be configured to any desired voltage or current level. A sequence of photovoltaic modules connected in series and/or parallel is called an array.

Figure 8 shows the circuit of photovoltaic modules first in series and then paralleled. Assuming that the parameters of a single photovoltaic module are the same as the previous example, the output voltage and current of this photovoltaic array are

PV_{T}=12+12=24(V), I_{T}=3.5+3.5=7(A)

(Notice:

When photovoltaic modules are connected in series, the voltage is added and the current remains constant, and the current is equal to the minimum current provided by the photovoltaic module with the smallest power in the series circuit.

When photovoltaic modules are connected in parallel, the voltage is equal and equal to the average output of each module in the parallel circuit, and the current connected to the parallel module circuit is equal to the sum of the output currents of all parallel modules. )

**④Summary**When photovoltaic modules are connected in series, the voltage is added and the current remains constant, and the current is equal to the minimum current provided by the smallest photovoltaic module in the series circuit.

When photovoltaic modules are connected in parallel, the voltage is equal and equal to the average output of each photovoltaic module in the parallel circuit, and the current connected to the parallel photovoltaic module circuit is equal to the sum of the output currents of all parallel photovoltaic modules.