Solar power plants on a house, cottage, boat or motorhome sometimes require modernization or repair, for example, after long-term use. There is also a situation when owners are faced with the need to replace a damaged solar panel or want to strengthen the system by adding a new panel.

Let’s consider a typical scenario using a motorhome as an example: two 100 W polycrystalline panels measuring 100×67 cm were installed on the motorhome and one of them is damaged. Years later, similar polycrystalline panels are no longer available on the market, and the closest size option is a monocrystalline panel. Owners often doubt whether it is possible to connect panels of different types, mono and poly, for fear of harming the system. In this article we will find out if this is so.

Poly- and monocrystal, what is the difference

Before discussing their interconnection, it is important to understand the main differences between polycrystalline and monocrystalline panels. Monocrystalline panels, recognizable by their uniformly dark cell color and cut edges, are made using a single, pure silicon crystal that is cut into cells. They are known for their high efficiency and elegant appearance.

On the other hand, polycrystalline panels, the cells of which have a characteristic “spotted” appearance with a blue tint, because they are made from several fused silicon crystals. They are slightly less efficient than monocrystals, but are cheaper. However, both poly- and monocrystalline panels have cells made of silicon, the process of generating electricity is based on the phenomenon of internal photoelectric effect. That’s why,

From the point of view of semiconductor physics, both types of panels, poly and mono, are identical and can be combined into a single system.

Problems of panel replacement and system expansion

We now know that when it comes to replacing or adding a new panel to an existing system, combining polycrystalline and monocrystalline panels is possible, but requires careful selection of parameters.

The key is to match the voltage and current of the panels to ensure compatibility and efficient operation.

Coordination of panel parameters

When replacing a damaged panel or adding a new one, it is important to consider parameters such as operating voltage and current, namely the current and voltage at the maximum power point, Imp And Ump, respectively. If a new monocrystalline panel has similar parameters to an existing polycrystalline panel, they can work effectively together, but if the difference is large, then losses need to be calculated.

Calculation of parameter matching using a real example

As described above, consider the case of two polycrystalline panels with a power of 90 W, let’s say one panel has failed and instead we want to install a monocrystalline panel with a power of 100 W. Below are photos of labels with technical characteristics of 90 and 100 W panels. Photo of Victron panel label courtesy of one of our customers.

To make it easier to compare the technical characteristics of the panels, we have compiled them into a single table below.

Parameter	Vostok 100M3	Victron SPP040901200
Type	Monocrystal	Polycrystal
Peak power	100 W	90 W
Ump	20.2 V	19.54 V
Imp	4.96 V	4.61 A
Uoc	24.7 V	23.44 V
Isc	5.24 A	4.98 A
Dimensions	770*670*30 mm	780*668*30 mm

Panels can be connected in different ways, so we will consider both connection options, parallel and serial.

Parallel connection of poly and mono

With a parallel connection, voltage is important to us, because the currents are summed up, and the voltage will tend to a lower value. For the Vostok panel, the voltage at the point of maximum power is 20.2V, and for Victron, the voltage is 19.54V, at the latter voltage the entire system will operate, respectively, the output power of the monocrystalline panel in this system will be 19.54V * 4.96V = 96.9W instead of 100W, those. we will lose ~3%. The total power from the two panels will be ~187 W.

Daisy chain poly and mono

When connecting mono- and polycrystalline panels in series, we look at the current at the point of maximum power (Imp), because with such a connection, the voltage will be summed, and the current in the circuit will be limited to the lowest value.

As can be seen from the table, the Victron Imp panel is 4.61A, and the Vostok panel is 4.96A, i.e. Victron will limit the current of the Vostok panel, the latter will produce 4.61A * 20.2V = 93W, i.e. Generation losses for a 100W panel will be ~7%, i.e. 7 W. The total generation from two panels will be 183 W.

Technical aspects and recommendations

You may be wondering if when connecting different types of panels you also need to take into account their different efficiencies? Monocrystalline panels are usually more efficient, which can cause some imbalance in the system. The answer is no, there is no need to take it into account, because… we have already taken it into account through the values ​​of Ump and Imp, because The efficiency of a solar panel directly affects the current produced.

Accounting for operating conditions

An important aspect when adding a new panel is taking into account the operating conditions. It is necessary to ensure that the new panel is installed taking into account the angle and orientation of the existing solar panel for maximum solar energy harvesting. Also avoid shading the new and existing panels.

Conclusion

So, connecting polycrystalline and monocrystalline solar panels in a solar power plant is a real, not prohibited and effective practice with the right approach. It allows not only to restore the functionality of the system after damage to the solar panel, but also to strengthen it, providing greater flexibility and efficiency in the use of solar energy.

Opportunities of REENERGO company

Don’t have time to figure out how to choose the right connection for solar panels? Contact REENERGO specialists who will help you choose the right equipment for your solar power plant.