Mismatch: an invisible issue affecting PV production

All photovoltaic systems are affected by mismatch to varying degrees. But what exactly does it mean?

What is module mismatch?

The performance of an entire module string can be influenced by the lowest-performing module. Since modules are connected in series, when one module operates below its potential, it can also limit the performance of the others.

Even an apparently negligible difference, such as a 1% loss on a single module, can have an amplified impact. In a string of 20 modules, for example, this imbalance can result in an overall production loss of up to 19%.

Mismatch can be caused by several factors commonly found in photovoltaic systems: partial shading from trees or obstacles, snow or leaf accumulation, dirt, natural module ageing and even standard manufacturing tolerances. Over time, all these factors can affect the system’s overall energy yield.

The intelligent response of Tigo TS4 optimisers

Tigo TS4 optimisers are designed to effectively address module mismatch.

Each optimiser continuously monitors multiple parameters of the module to which it is connected, operating at very high speed and adapting its behaviour to extract the maximum possible energy.

This allows each module within the string to contribute as effectively as possible to overall production, without being limited by — or limiting — the performance of other modules.

The result is a more balanced and efficient PV system, where the performance potential of individual modules can be maximised while the impact of mismatch is significantly reduced.

Reclaimed Energy: recovered energy measured and made visible

Tigo’s approach to optimisation is based on data transparency. The additional energy generated through the action of the optimisers can be viewed directly within the Tigo Energy Intelligence monitoring platform under the Reclaimed Energy metric.

This allows system owners to clearly understand how their PV installation is performing and how much additional energy is being generated through optimisation, while also providing useful data for calculating the return on investment.

What are the benefits of optimisation?

The benefits of optimisation are not merely theoretical but have been widely demonstrated in real-world installations. In an analysis of more than 18,000 systems equipped with Tigo optimisers, 25% of sites recorded average production increases of more than 10%, while 76% achieved an increase of between 3% and 15%.

PV optimisation in practice: one system, two strings, more energy

A practical example helps illustrate how module-level optimisation works. The residential PV system shown in the image is equipped with a three-phase inverter and two strings:

• String A consists of 16 modules
• String B consists of 13 modules

The entire system is equipped with Tigo TS4-A-O optimisers.

String A includes modules installed across three different roof pitches to maximise the available roof space and is affected by shading caused by an air vent and a satellite dish. In the example, the modules highlighted in green indicate the additional energy generated thanks to optimisation.

The use of TS4-A-O optimisers also prevents the modules installed on the less favourably oriented roof pitch from limiting the production of the other modules in the string.

String B, on the other hand, is affected by shading from surrounding trees and buildings. Here too, the optimisers help extend the system’s production cycle beyond the hours with the most favourable solar irradiation.

Without optimisation, the inverter would have to select a lower operating point for the entire string, limiting the contribution of the unshaded modules. With optimisers, the higher-performing modules can continue operating at the maximum power point set by the inverter, while the weaker modules are individually adjusted to achieve the best possible overall result.