An MPPT tracker controls the electrical operating point of a PV generator so that it delivers as much power as possible under the current irradiance and temperature conditions. MPPT stands for “Maximum Power Point Tracking”, meaning the continuous search for the point of maximum power on the current-voltage curve. The tracker is usually a control function implemented in the inverter or a DC/DC converter rather than a separate physical device.

MPPT Trackers at a Glance

• An MPPT tracker continuously adjusts the electrical operating point of the PV generator to achieve the highest possible power output.
• Multiple trackers enable independent operation of module groups with different electrical characteristics or installation conditions.
• An MPPT tracker does not necessarily correspond to a single string input. Multiple inputs may be connected to the same tracker.
• MPPT voltage, MPPT current and DC power provide important information for monitoring and troubleshooting a PV system.

How Does Maximum Power Point Tracking Work?

The electrical power of a PV generator is calculated by multiplying voltage by current. Both values depend on factors such as solar irradiance, module temperature, shading and the electrical characteristics of the connected modules. The optimum operating point therefore changes continuously throughout the day.

Through its power electronics, the inverter influences the DC voltage and consequently the current of the connected PV strings. Depending on the MPPT method used, the algorithm changes or evaluates the operating point and uses voltage, current and their variations to determine the direction in which higher power can be expected. Common methods include “Perturb and Observe” and “Incremental Conductance”.

The control function attempts to identify the Maximum Power Point (MPP) on the current power curve and track it as operating conditions change. Under largely uniform irradiance and with electrically homogeneous module groups, the power curve usually has a clearly identifiable global maximum. Partial shading, however, can produce several local maxima and make it more difficult to identify the global maximum.

Multiple DC inputs do not automatically mean that an inverter has the same number of independent MPPT trackers. If several strings are connected to the same tracker, they operate at a common MPPT voltage. Their number of modules, orientation and electrical characteristics should therefore be compatible.

Typical Applications of Multiple MPPT Trackers

Multiple independent MPPT trackers are particularly relevant for PV systems with differently configured sub-arrays:

• On east-west roofs, the two roof sections can operate independently because they reach their highest irradiance levels at different times of the day.
• Module arrays with different tilt angles or shading patterns can be assigned to separate trackers so that unfavourable operating conditions in one group have as little effect as possible on the other groups.
• In larger systems, different roof areas or sub-arrays can be monitored separately, provided that the inverter supplies the required measurement data.

Benefits, Limitations and Technical Requirements

Maximum Power Point Tracking improves energy yield because the PV generator does not operate permanently at a fixed operating point. Multiple trackers provide greater flexibility in system design and can limit losses caused by different operating conditions.

Its effectiveness depends on the design of the PV strings and the permissible voltage and current ranges of the inverter. During operation, the string voltage must remain within the specified MPPT voltage range. The start-up voltage stated in the datasheet, by contrast, indicates the voltage at which the inverter can begin operating. It is not necessarily identical to the lower limit of the MPPT operating range. If the permitted input current or voltage is exceeded, the inverter cannot operate the PV generator correctly.

MPPT voltage, MPPT current and DC power are particularly relevant for monitoring. Deviations between comparable trackers may indicate shading, soiling, string failures, wiring faults or module problems. However, raw power values can only be compared directly if the connected sub-arrays have a similar installed capacity and operate under comparable conditions. Otherwise, normalised indicators or expected-value-based comparisons are required.

MPPT Monitoring with EcoPhi

EcoPhi can collect, visualise and historically evaluate MPPT and string data made available through the inverter interface. Comparing technically similar trackers can reveal unusual performance differences and trigger alarms based on defined thresholds. For sub-arrays with different installed capacities, normalised indicators or expected-value-based comparisons are required.

The available measurements and their time resolution depend on the inverter, its internal measurement technology, register mapping and the specific communication interface implemented. If the device only provides aggregated DC values, individual trackers or strings cannot be evaluated separately.

MPPT Trackers in Summary

An MPPT tracker continuously adapts the electrical operating point of a PV generator to current operating conditions. Multiple independent trackers facilitate the operation of differently configured module groups. Available MPPT and string measurements can also provide an important basis for fault detection in PV monitoring.

Frequently Asked Questions About MPPT Trackers

Is an MPPT tracker the same as a string input?

No. An inverter may have multiple string inputs assigned to the same MPPT tracker. These strings then operate at a common MPPT voltage.

Why do inverters have multiple MPPT trackers?

Multiple trackers allow PV module groups with different electrical characteristics or installation conditions to be controlled independently. This enables different roof sections, for example, to operate at a suitable operating point.

How can a faulty PV string be identified?

A faulty PV string can be identified through unusual deviations in current or power compared with technically comparable strings, provided that string-level measurements are available. If several strings are only measured collectively through one MPPT tracker, the tracker values may reveal a deviation but cannot clearly identify the affected string. Differences in orientation, shading, installed capacity and operating conditions must be considered during the evaluation.

Is an MPPT tracker comparable to a power optimiser?

Not directly. An inverter’s MPPT tracker controls the operating point of a connected PV sub-array. Power optimisers may also use their own operating-point control, but they implement it locally at module or sub-module level.