# POTOVOLTAIC SOLAR PANELS CONNECTION

The connection of solar panels is important must be made correctly so that the photovoltaic system fncioe correctmnte and deliver the highest performance.

We receive many questions of the type «how to connect the solar panels in series or parallel to get the maximum power», or «how to connect the solar panels to get the best performance».

## POTOVOLTAIC SOLAR PANELS CONNECTION

The answer is simple:  There is only one way to connect solar panels properly !

And of course, the power is the same regardless of whether they are connected in series, in parallel or in parallel series.

## The power does not change depending on the connection of the solar panels

The power is governed according to the formula  P = V x I ; where the power is constant. Therefore, if we increase the voltage (V) the current (I) will decrease and vice versa, but the power will be the same. Let’s see a real example:

12V and 150W solar panel with the following characteristics:

Power at the point of max. power  (Pmax) 150Wp
Open circuit voltage  (Voc) 22.6V
Voltage at maximum power  (Vmpp) 18.2V
Short circuit  current (Isc) 8.7A
Current at maximum power  (Impp) 8.25A

We can check that at maximum operating power: Vmpp: 18.2V x Impp: 8.25A = 150.15Wp

If we have 2 solar panels of 150Wp we have a total of 150wp x 2 =  300Wp  and as we will see below the power does not vary regardless of how we connect them.

If we connect them in series:  (we add the voltages and the current is maintained)

• Vmpp: 18.2V x 2 = 36.4V
• Impp: 8.25A
• Total power: Vmpp: 36.4V x Impp: 8.25A =  300.3Wp

Connection series solar panels

If we connect them in parallel:  (we add the currents and the voltage is maintained)

• Impp: 8.25A x 2 = 16.5A
• Vmpp: 18.2V
• Total power: Vmpp: 18.2V x Impp: 16.5A =  300.3Wp

Parallel connection solar panels

## How to connect solar panels well

With PWM controller

Calculation of the necessary PWM regulator

The PWM regulators are  simply responsible for controlling the charge voltages of the batteries. They are not able to modify the working voltage of the solar panels, therefore the solar panels will always work at the battery voltage.

If the battery of the solar installation is 12V:  The solar panels have to be 12V and very important 36 solar cells. The only way to connect the 12V solar panels with 12V batteries is by connecting the solar panels in  parallel . In this way the set of solar panels will work with a voltage as close as possible to the point of maximum power of this type of solar panels.

If the battery is 24V:  We can put groups of 2 12V solar cells and 36 cells connected in series to form 24V plates and 72 solar cells, or use 24V solar panels and 72 solar cells.

Again, each group of plates in series or solar panels of 24V and 72 solar cells can only be connected in parallel to work at the voltage closest to the point of maximum power of this type of solar panels.

Never exceed the maximum load current of the PWM controller.

Do not use 60-cell solar panels with PWM regulators.  24V solar panels that are not

With MPPT controller

The MPPT regulators  are capable of separating the working voltage of the solar panels or group of solar panels from the battery voltage. This feature makes it possible for the solar panels to always work at their maximum power point, regardless of the voltage of the battery.

There are 5 factors that we must take into account to know how to connect the solar panels to the MPPT controllers:

1.- Maximum load current.  The charging current is the current that will flow from the MPPT regulator to the battery. It is NOT the current that leaves the group of solar panels. To calculate it we will divide the power of the photovoltaic generator between the voltage of the battery.

For example: 3 solar panels of 250Wp are 750Wp, for a 24V battery the charging current will be: 750Wp / 24V = 31.25A. In this case, an MPPT solar regulator of 30A or higher can be used. In case we use a lower MPPT, it will limit the load current to the maximum supported by the solar regulator.

If the battery were 12V, we would have: 750Wp / 12V = 62.5A. In this case, an MPPT solar regulator of 60 amps would be necessary. Therefore, the higher the battery voltage the better because we will need smaller regulators.

2.- Maximum voltage Vmax. of the MPPT controller.  The most used are Vmax: 100V and Vmax: 150V

• With Vmax regulators: 100V we can connect up to 2 solar cells of 60 cells in series.
• With Vmax regulators: 150V we can connect up to 3 solar cells of 60 cells in series.

If you use solar cells of 36 cells or 72 solar cells.  Pay close attention to the Voc open circuit voltages of the plates. Exceeding the Vmax value of the MPPT solar controller will damage it.

Los reguladores solares MPPT fueron diseñados para ser utilizados con placas solares de 60 células, por lo tanto con estas placas son muy fáciles de configurar.

En cambio con placas solares de 36 o 72 células es más difícil de cuadrar la conexión para no superar la Vmax del regulador.

3.- Lo ideal es trabajar a la máxima tensión posible en el campo fotovoltaico.

Cuanto mayor sea la tensión del campo fotovoltaico menor será la corriente, (no confundir la corriente del campo fotovoltaico con la corriente de carga de la batería, ya que en los reguladores MPPT no es la misma).

La ventaja es que la sección de cables será menor y tendremos menos pérdidas en los cables por calentamiento. Además podremos situar las placas solares a mayores distancias del regulador solar.

Así pues, si el generador fotovoltaico trabaja a 60V la corriente será la mitad que si trabaja a 30V. Si el regulador solar lo permite será mejor trabajar a 90V.

4.- Las placas solares de una misma cadena deben ser iguales. Y las cadenas deben ser iguales.

Si una cadena está formada por 2 placas solares en serie, las demás cadenas deberán ser del mismo número de placas solares. Las placas solares en serie suman tensiones y las cadenas en paralelo suman corriente al campo fotovoltaico.

Por lo tanto solamente podremos formar conjuntos así:

• 2 placas solares: 2 placas conectadas en serie (Vmpp: 60V)
• 3 placas solares: 3 placas conectadas en serie  (Vmpp: 90V)
• 4 placas solares: 2 cadenas paralelo de 2 placas en serie (Vmpp: 60V)
• 6 placas solares: 2 cadenas paralelo de 3 placas solares en serie (Vmpp: 90V)
• 6 placas solares: 3 cadenas paralelo de 2 placas solares en serie (utilizar la anterior configuración si el regulador lo permite) (Vmpp: 60V)
• 8 placas solares: 4 cadenas paralelo de 2 placas solares en serie (Normalmente no se pueden poner más de 3 placas solares en serie) (Vmpp: 60V)

Nota: los inversores con MPPT son capaces de trabajar con 200V a 600V formados por conjuntos de 9 hasta 20 placas solares en serie. Los reguladores solares MPPT para instalaciones con baterías normalmente permiten 100V o 150V máximo.

5.- La tensión del campo fotovoltaico debe ser al menos 2,5V superior a la de la batería en todo momento.

We can not configure a photovoltaic field that works at 30V with a 24V battery, since the battery must reach 28.8V to charge at 100% and the photovoltaic field will have an insufficient working voltage for a perfect operation.

## CONCLUSION

Before buying the solar panels, you need to know if the solar kit will have an MPPT solar controller or a PWM, if the battery voltage will be 12V, 24V or 48V.