Conexiones en serie y paralelo
Todos los circuitos se construyen a partir de dos tipos de conexiones eléctricas que determinan las características del circuito: serie y paralelo. Cualquier dispositivo que tenga más de una batería, como una radio o una linterna, utiliza una conexión en serie o en paralelo para lograr el voltaje deseado o la cantidad deseada de energía disponible. Todas las baterías tienen un electrodo positivo y uno negativo que son los puntos donde se hacen las conexiones eléctricas. Cuando el electrodo positivo de una batería está conectado al negativo de otra batería, esto se llama conexión en serie. Una conexión así en serie aumentará la tensión del circuito. Cuando el electrodo positivo de una batería está conectado al electrodo positivo de otra batería y el electrodo negativo está conectado al electrodo negativo de la misma batería, esto se llama conexión en paralelo. Una conexión así en paralelo mantendrá el voltaje del circuito igual, pero aumentará la corriente disponible para el circuito.
En los sistemas fotovoltaicos, las conexiones en serie se vuelven importantes ya que permiten variar las características de voltaje y corriente de un sistema, lo que ofrece importantes ventajas. Baterías y módulos FV se pueden conectar utilizando cualquiera de estos tipos de conexión o ambos. All baterías, módulos, controladores de carga y inversores están clasificados para funcionar dentro de un rango de voltaje y corriente dado, por lo que estos tipos de conexión se utilizan para garantizar que el sistema pueda funcionar en conjunto correctamente.
Es importante tener en cuenta que circuitos dentro de hogares y edificios para aparatos o iluminación solo usan conexiones en paralelo.
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Conexiones en paralelo
Una conexión en paralelo es una conexión que conecta circuitos que podrían funcionar por separado, por lo que hay dos o más caminos separados que la corriente puede seguir. En el caso de módulos fotovoltaicos y baterías, esto se hace creando una conexión entre todas las conexiones positivas de los circuitos y una conexión separada entre todas las conexiones negativas de un circuito. Las conexiones en paralelo afectan el funcionamiento de un circuito de las siguientes formas:
- Si las fuentes de energía, como módulos fotovoltaicos o baterías, del mismo tamaño se conectan juntas en paralelo, el voltaje del circuito permanece igual, pero la corriente que el circuito puede proporcionar se convierte en la suma de sus corrientes.
- Si cargas, como luces, del mismo tamaño se conectan juntas en paralelo, el voltaje del circuito seguirá siendo el mismo, pero la corriente del circuito se dividirá entre los diferentes circuitos en paralelo.
2 x 12V baterías de acido-plomo conectadas con una conexion paralela.
2 x PV módulos connectados con una conexion en paralelo en una caja de combinación.
Ejemplo 1: Se conectan en paralelo 2 baterías de 12V 100Ah (con una tasa de descarga de C/20). ¿Cuál es el voltaje del circuito y los Ah de corriente disponible a la tasa C/20?
- V = 12 V as the voltage stays the same.
- Ah = 200 Ah as the Ah of available current doubles in this case.
Example 2: Three PV modules with an open circuit voltage (Voc) of 40 V and a short circuit current (Isc) of 10 A are connected in parallel. What is the voltage and available current of the circuit?
- V = 40 V as the voltage stays the same.
- Ah = 30 A as the current tripes in this case.
Example 3: Two 12 W lightbulbs (12 V, 1 A) 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 = 12 V
- I = 1 A
- Circuit total
- V = 12 V
- I = 1 A + 1 A = 2 A
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: Two 12V 100Ah batteries are connected in series. What is the voltage of the circuit and the Ah of available current?
- V = 24 V as the voltage doubles in this case.
- Ah = 100 Ah 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 = 120 V as the voltage triples in this case.
- Ah = 10 A as the current tripes in this case.
Example 3: Two 12 W lightbulbs (12 V, 1 A) 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 = 12 V ÷ 2 = 6 V
- I = 1 A
- Circuit total
- V = 12 V
- I = 1 A (same 1A passes through each lightbulb)
Series vs. parallel
Series and parallel connections only change the characteristics of the circuit, but there is no power/energy gained or lost in the process. The correct choice of connection depends upon various factors.
Power with different connection types
Example 1: Three PV modules with an open circuit voltage (Voc) of 40 V and a short circuit current (Isc) of 10 A are connected in parallel. What is the voltage and available current of the circuit?
- (3 × 10 A) × 40V = 1200W
Example 2: Three PV modules with an open circuit voltage (Voc) of 40 V and a short circuit current (Isc) of 10 A are connected in series. What is the voltage and available current of the circuit?
- 10 A × (3 x 40 V) = 1200 W
When to use series and parallel
The type of connection is ideal for a circuit depends upon the components that will be used with the circuit. All components used in an electrical system have specific maximum current and maximum voltage ratings, but PV specific components like charge controllers and inverters also have minimum voltage requirements to function properly. The other important factor in determining the connection type is that increases in current require larger conductors to avoid electrical fires, yet voltage does not suffer from the same challenges. Increasing the voltage of a circuit can be used to increase the amount of power that a circuit is capable of carrying without the necessity of increasing the size of the conductor. This means that a higher voltage, as long as it is within the maximum voltage limits of all of the components in the system, is typically preferrable as it reduces the size of conductors needed for a PV system. Using a higher voltage is an important strategy to keep voltage drop to a minimum as well.
It is typical for an off-grid PV system to use a combination of parallel and series connections to be able to be able to match the design requirements of the system with the available equipment. Equipment for use with off-grid PV systems is only available in a few specific nominal voltage ratings (12V, 24V, 48V), specific maximum voltage ratings, and specific maximum current ratings. A combination of these different connection types allow system designs to choose the voltage and combination of components that will offer the best performance at the lowest price. See Special:MyLanguage/DC system voltage for more information about choosing the ideal voltage for a particular system.
