PV array

Do you know what photovoltaic cells, modules and arrays are?

Characteristics of photovoltaic cells
Each photovoltaic cell is unique and has unique characteristics. Since the battery characteristics of a module will affect the power output of the connected modules, it is very important to understand the battery characteristics when designing a photovoltaic array.

Graphical representation of photovoltaic cell performance

(I-V) curve

It is a very common way to graphically express the performance of photovoltaic cells with a current-voltage (I-V) curve. The I-V curve plots the trajectory of photovoltaic cell characteristics and highlights key features such as Voc, Isc, and Pmax. Photovoltaic cells will always work along this curve, that is, under a given voltage, the output current will always maintain the same value, and vice versa.
The power curve is used to find the maximum power point. The horizontal axis of the power curve is voltage and the vertical axis is power (current multiplied by voltage). When the power curve of a battery and the I-V curve are stacked, you can clearly see where the maximum power point is.
The I-V curve and power curve are very important, because the characteristics of each battery need to be known when designing components. Connecting cells with very different characteristics together has a great influence on the output power of the photovoltaic module (usually a negative influence).

Photovoltaic array seen from below
Photovoltaic modules 36 cells are arranged in a 4×9 grid

Connect photovoltaic cells into modules
Photovoltaic cells with the same characteristics will be joined together to form modules. In the series connection mode, the battery voltages add up while the current remains the same, that is, the component current is equal to the current of a single battery. Power loss occurs when a battery has poor performance. The battery may be damaged, and the more common situation is obstruction.
There is a free-of-charge data manual on the manufacturer’s website, which gives the battery characteristics. This data can be used to design photovoltaic arrays. The designer should always contact the manufacturer to ensure that the data manual provided on the website is up to date.
Specification Table
Purchasing photovoltaic modules from reputable manufacturers should provide a specification sheet (also called a data sheet). The data sheet includes important technical information required for the design and installation of photovoltaic arrays. When buyers compare different photovoltaic modules, the data sheet is also very useful, because the data sheet provides basic information such as efficiency, rated power and physical dimensions.

Sample data sheet

PV module string
A large number of photovoltaic modules are connected in series to form a module string. The electrical characteristics of photovoltaic modules connected in series into a module string are similar to that of photovoltaic cells connected in series: the output voltage of the module string is the sum of the output voltages of all modules, and the output current of the module string is the smallest output current among the modules.
Components can also be connected in parallel. In this case, the output currents of the components add up, not voltages. The output voltage is the voltage of a single component.

When three identical modules are connected in series to form a module string, the module voltages are added, and the total current is the current of a single module. The output power of the component string is P=IV
When different components are connected in series, the voltage is still added, but the current of the component string will be the lowest current in each component (4A in this example). The output power of the component string is P=IV
Three identical modules are connected in parallel, the total current is the sum of the currents of each single module, and the total voltage is the voltage of the single module. The output power is still P=IV
Note: The power is the same in series with three identical components.
When different components are connected in parallel, the currents add up, and the output voltage is equal to the lowest voltage in each component. The output power of the component string is P=IV
Note: Compared with three modules connected in series, the output power of this method is smaller.

Array formation
Designers can use a combination of series and parallel to connect photovoltaic modules into an array, and the output current and voltage are suitable for market applications. In a typical case, the components are first connected in series to form a string, and then connected in parallel to form an array.
The photovoltaic array outputs direct current, while the grid needs alternating current. Therefore, an inverter is required to convert photovoltaic direct current to alternating current, and the wiring of the photovoltaic array should make the maximum power point voltage of the array within the input voltage range of the grid-connected inverter

The process of forming a photovoltaic array: First, the cells are formed into modules, and then connected into a module string, and finally the modules are connected in series and parallel to form an array
In order to calculate the output power of the photovoltaic array, first calculate the output power of each application (as described above), and then process the module string according to the module method, and calculate the array output power by adding the power of the parallel modules