How to Wire Two or More Solar Panels in Parallel

How to Wire Solar Panels in Parallel

Welcome to this informative article.

In this page we will teach you how to wire two or more solar panels in parallel in order to increase the available current for our solar power system, keeping the rated voltage unchanged.

We will also explain the difference between a parallel connection of two or more identical solar panels and a parallel connection of two or more solar panels with different technical characteristics. Finally, we will provide you with valid and practical tips to get an efficient system that is fully protected against possible damage due to faults or short circuits that can occur on individual solar panels.

Well, now let's get started! The connection of multiple solar panels in parallel arises from the need to reach certain current values at the output, without changing the voltage. In fact, by wiring several solar panels in series we increase the voltage (keeping the same current), while wiring them in parallel we increase the current (keeping the same voltage).

Parallel connection of two identical solar panels

If we have two solar panels with same voltage and power, the connection will be very simple.

As clearly visible in the picture, it will be enough to wire the positive pole of one panel to the positive pole of the other one and then wire the negative pole of one panel to the negative pole of the other one. To make this type of connection we can use a pair of MC4 Y-branch solar connectors.

We have also added a blocking diode in series with each panel. Later we will find out the reason for these diodes.

This type of connection is really efficient if the following conditions are met:

•   Place the panels close to each other and oriented to the sun at the same angle
•   Check that the panels do not shade each other and that they are far from possible causes of shading
•   Choose an appropriate section of the electrical cable according to the distance of the panels
•   Use junction boxes to neatly wire the panel terminals together

What happens in case of shading?

First of all, it is good to know that the voltage that we find at the ends of a shaded solar panel does not depend on its irradiation condition, but rather on the load conditions to which it is subjected. In fact, a shaded panel is still perfectly able to receive the widespread share of solar energy and therefore can still offer a positive working voltage with a value almost identical to when it is fully irradiated (what decreases proportionally to the solar radiation it is the current). It is therefore clear that in a grid-connected PV system it is important to choose the right solar inverter which will have the task of seeking the maximum power point (MPP) of the panel string both in full irradiation and in shading conditions.

In an off-grid solar power system, on the other hand, this task is performed by the MPPT solar charge controller. So what is the blocking diode for? The blocking diode is used in large solar power systems to protect entire strings from possible reverse currents. With regard to reverse current in solar panels, it is useful to know that recent studies conducted by the prestigious Fraunhofer Institute for Solar Energy Systems ISE have shown that solar panels are able to withstand reverse current up to seven times higher than the short circuit current, without suffering any damage. It is also a good practice during the design, to choose those solar panels that are internally equipped with at least three bypass diodes, in order to avoid energy losses due to shading.

Choosing the correct diode

There are many types of diodes on the market. The best type of diode for solar applications is the Schottky diode. This type of diode has a very low threshold voltage (in the order of 0.35V against the 0.6V of common diodes), that ensures a less power dissipation. Please, pay attention also to the choice of the length and section of the electric wire since as the number of panels increases, the current also increases and therefore the energy dissipation in the wire itself. For high current, a cable with a suitable section is required.

Parallel connection of two solar panels with different power

If we have two solar panels with the same voltage but different wattage, there is no problem; they can be wired in parallel.

On the other hand, if our two solar panels have both different wattage and different voltage, then parallel connection is not possible, since the panel with the lowest voltage would behave like a load, and would begin to absorb current instead of producing it, with the relative consequences.

What if we have one 12V panel and two 6V panels? In this case, it is possible to wire the two 6V panels in series and then wire the resultant array in parallel to the 12V panel. However, the latter type of connection is at the expense of efficiency. It is therefore essential, before making a parallel connection, to carefully check the voltage of the solar panels. Here is a very clear picture of how to wire two mismatched solar panels in parallel.

Beware of current!

You can wire multiple solar panels with this method, but you must pay attention to the current. If your output value is greater than 70A, your panels and your system can be damaged and suffer problems related to the management of this high current. In order to avoid this, it is customary to wire panels in series and parallel, thus increasing both voltage and current simultaneously.

For example, if we were to wire six 10A panels in parallel, we would find a fairly high current at the output, that is 60A. To solve this problem and to optimize the energy performance of the entire system, it is advisable to wire two panels in series (obtaining a doubling of the voltage) and then wire in parallel the three pairs previously wired in series (so as to have doubled the voltage and tripled the current). Looking at the picture it is possible to understand the scheme of this connection. This type of connection is frequently used for high wattage systems. In an off-grid solar power system, the choice of the total wattage and of the battery bank voltage must be carefully evaluated at the design stage.