Series and Parallel Circuits in Power Sources

Photovoltaic modules and batteries are a system's building blocks. While each module or battery has a rated voltage or amperage, they can also be wired together to obtain a desired system voltage.

1. Series Circuits

Series wiring connections are made at the positive (+) end of one module to the negative (-) end of another module. When loads or power sources are connected in series, the voltage increases. Series wiring does not increase the amperage produced. The image at right shows two modules wired in series resulting in 24V and 3A.

Series circuits can also be illustrated with flashlight batteries. Flashlight batteries are often connected in series to increase the voltage and power a higher voltage lamp than one battery only could power alone.

Question: When four 1.5V DC batteries are connected in series, what is the resulting voltage?

Answer: 6 volts

2. Parallel Circuits

Parallel wiring connections are made from the positive (+) to positive (+) terminals and negative (-) to negative (-) terminals between modules. When loads or sources are wired in parallel, currents are additive and voltage is equal through all parts of the circuit. To increase the amperage of a system, the voltage sources must be wired in parallel. The image at right shows PV modules wired in parallel to get a 12V, 6-amp system. Notice that parallel wiring increases the current produced and does not increase voltage.

Batteries are also often connected in parallel to increase the total amp-hours, which increases the storage capacity and prolongs the operating time.s

3. Series and Parallel Circuits

Systems may use a mix of series and parallel wiring to obtain required voltages and amperages. The image at right shows four 3-amp, 12 VDC modules wired in series and parallel. Strings of two modules are wired in series, increasing the voltage to 24V. Each of these strings is wired in parallel to the circuit, increasing the amperage to 6 amps. The result is a 6-amp, 24 VDC system.

4. Batteries in Series and Parallel

The advantages of a parallel circuit can be illustrated by observing how long a flashlight will operate before the batteries fully discharge. To make the flashlight last twice as long, battery storage would have to be doubled.

In the picture to the left, a series string of four batteries has been added in parallel to another string of four batteries to increase storage (amp-hours). The new string of batteries is wired in parallel, which increases the available amp-hours, thereby adding additional storage capacity and increasing the usage time. The second string could not be added in series because the total voltage would be 12 volts, which is not compatible with the 6-volt lamp.

5. High Voltage PV Arrays

So far in this chapter, we have only discussed input voltages up to 24V nominal. Today, most battery-less grid-tied inverters on the market require a high voltage DC input. This input window is generally in the range of 350 to 550 VDC. Because of the inverter's high voltage input requirements, PV modules must be wired together in series in order to sufficiently increase the voltage.

6. Series and Parallel Wiring Examples & Instructions

1. Connect the photovoltaic modules (array) either in series or parallel to get the desired system voltage.

2. Calculate total module output for volts and amps.

3. Connect the array to a charge controller.

4. Connect batteries either in series or parallel to get the desired system voltage.

5. Calculate total battery bank voltage and amp-hour capacity.

6. Connect the battery bank to the charge controller.

Source: “PHOTOVOLTAICS - Design and Installation Manual” by Solar Energy International.

Solar Certification Training from Professional Solar Installers

With 18 IREC-ISPQ Certified Solar Photovoltaic Trainers and 24 NABCEP Certified Solar PV Installers — more than any other solar training organization — Solar Energy International's experienced team is on the forefront of renewable energy education. If you are seeking online solar training or in-person lab training for the NABCEP Entry Level Exam or NABCEP Installer Certification, why not receive your education from a team of the most experienced solar installer professionals in the industry? Many SEI trainers have participated in the most notable solar installations within their communities stateside, and in the developing world.

To start your solar training path today with Solar Energy International, click here.