MPPT is a recent development in the world of solar power technology. MPPT gets upto 30 % more power from existing solar panels. Although MPPT was first applied in large grid solar power systems, the technology now finds it way into consumer market. Here’s a real example of MPPT in the Machine.
 

MPPT solar power battery charging

Already familiar with MPPT? Yes, take to MPPT solar battery charging in action.

MPPT stands for Maximum Power Point Tracking – a technology designed into a new generation of solar power battery chargers. In simple terms the technology ‘tracks’ or ‘follows’ the maximum power point for a solar panel. MPPT is not a mechanical tracking device to position the solar panel perpendicular to the sun – it’s about the electronics / firmware in a solar battery charger.

Just as maximum HP peaks at specific amount of rpm’s for car engines, the same applies for solar panels – but that’s how far the analogy goes. The maximum power point (MPP) for solar panels shifts by the amount of sunshine captured by the solar panel.

Conventional (PWM) solar power battery chargers manage the state of charge of the battery regardless of the maximum power point of the solar panel. Consequently, the battery ‘pulls’ the solar panel output away from it’s optimum. This is especially true when a battery is discharged. Basic measurements with a simple solar cell phone charger also showed this effect. (link).

In analogy with a car engine, a MPPT solar battery charger acts like an automatic gear box. Keeping the engine running at the optimum RPM it delivers maximum output. Now for a solar panel the sun is the fuel – captured energy varies with the time of day, clouds and solar panel temperature – requiring constant adjustment for optimum performance.

Had enough about MPPT? Take me to MPPT solar battery charging observations or read on.
 

MPPT solar battery charging in action

The machine is equipped with a IVT MPPT Solar Battery Charger charging a 24 Volt 230 Ah (5.5 Kwh) AGM type battery bank. It’s produced by Innovative VersorgungsTechnik GMBH in Hirschau Germany.
 

	The IVT MPPT solar battery charger

The MPPT charger logs it’s operating parameters to a 2 Gb SDCARD.
 

The IVT MPPT solar charger remote control panel

Below the MPPT voltage trend on an average sunny / cloudy day in winter time in southern Europe
 

MPPT Solar battery charging graph created from logged IVT data

Solar panel output voltage runs freely and peaks at 37 Volt while battery voltage averages just around 26 volt. The current from the solar panel is just below the battery charge current which peaks at 5.2 Amps. Round 2pm in the afternoon the AC mains battery charger was connected causing a jump to 28 volts. 15 minutes later the MPPT solar battery charger shuts down because of high battery float voltage.

The graph data comes from the 2GB SDCARD in the following raw format;
 

	The data format from the SDCARD logged by the IVT solar battery charger

The maximum logging rate is 1 measurement / 10 seconds and drops to a lower rate when there’s no change to report. Measurement (sampling) accuracy isn’t mentioned in the manual but values seem to roughly match.

The IVT MPPT solar battery charger, replaced a STECA PR2020 – a classic PWM multi-stage solar battery charger. The IVT MPPT charger allows solar panel voltage to run more freely, regardless of battery voltage.
 

MPPT battery charging observations

Most striking for MPPT solar charging are voltage levels at high and low solar panel output.

1)    When output is high, solar panel voltage moves towards battery voltage.
2)    When output is low(er), solar panel voltage can move up more freely.

Specially 2) shows the advantage of MPPT– in less ideal conditions there’s more power compared to classic solar battery charging.

In case of 1) the ideal situation would be a loss-less connection between Solar panel and battery – meaning battery voltage would be equal to solar panel voltage. However a small voltage drop can be expected, specially at high charge currents.

Peak solar panel power on 4 January 2010 was 156 Watt of which 137 Watt was converted to charge the batteries. The conversion efficiency at that moment was 156 / 137 = 88 % which is an average score. Consequently the IVT consumed about 19 Watts.

Accuracy of the digital measurement samples yet has to be confirmed by a future measurement with an external voltage trendmeter like the Fluke Scopemeter 123.
 

MPPT solar battery charging backgrounds

MPPT performs better in conditions when it’s needed the most;

-    When the battery is discharged
-    During cloudy, dusty or smoggy days
-    During partial shading of the panels

Conditions where solar panels perform worse:

-    When panel temperature is high
-    When solar panel is partial shaded
-    When solar panel angulations towards the sun is off

A good explanation of MPPT with backgrounds can be found in this MPPT article posting at the Solar Freaks forum.