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A charge controller is required for most solar pv installations to prevent over-charging or over-draining the battery. A standard charge controller will manage this.

Curves for typical 225W PV module

However, all solar PV panels have an optimium working voltage, and this voltage changes depending on the amount of light available. This optimum voltage is known as the Maximum Power Point, and a charger which allows the panel to remain at this voltage is known as a Maximum Power Point Tracking (or MPPT) controller.

The chart (above) shows the typical characteristics of a panel. If you have, say, 1,000W/M2 of light, and you keep the panel at 24V because this is the battery voltage, your charging current will be about 7.9A, giving 189W of power. However, if you allow the panel to remain at its optimium voltage of 30V, it will deliver 7.5A, giving you 225W – 20% more power.

MPPT table for Turbotricity 235W module

The table shown here gives information on the Turbotricity range of Polycrystalline modules at various amounts of light level. It can be seen that the MPPT voltage for our 235W module varies between 29.82V and 26.99V depending on the light level.

A good MPPT controller will maintain the panel voltage as close as possible to this level, while delivering higher current at the battery voltage to optimise charging.

There are a number of MPPT controllers on the market, of various quality and performance. Some have absolutely no MPPT facility at all.

Test bed measuring current & voltage for two MPPT controllers

We are currently testing a number of MPPT charge controllers using a testbed which has two identical PV modules, two identical battery packs, and datalogging. This enables us to assess which MPPT controller provides optimum chage rates under various light conditions.

When we have clear results for all of the MPPT controllers under test, we will select products which we find are well made and perform best under various light conditions.

This may look like a spaghetti of wires, but we have used very accurate voltage sensing and current sensing transducers, and a micro-processor controlled datalogger to monitor performance over extended periods.

Qe measure solar voltage, solar current, battery voltage and battery current for each of two parallel systems. All readings are recorded once a second.

Turbotricity Ltd.

Moylagh, Oldcastle, Co. Meath, Ireland

info@turbotricity.com

Phone within Ireland Lo-Call 076 6152052

From overseas call +353 57 860 0054

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Delighted with my Turbotricity turbine. It works away effortlessly and quietly giving me plenty of clean free power Brendan Murphy
Bantry