As we interact with a variety of different solar system installers, we have got this question repeatedly – does MPPT make sense in Indian conditions.
The implied question is – MPPT controllers cost more than the PWM counterparts – is it worth the while to add this cost to the installation.
First : The difference between MPPT and PWM chargers. There are ton’s of literature on this subject on the net- briefly PWM chargers essentially short the panels to the battery and the power from the panels is extracted at the battery voltage. i.e Power extracted is Vbatt X I – which is the current dictated by the PV panel’s characteristic I-V curve at Vbatt. This Voltage and therefore Current I, when different from its Maximum power point Voltage, the PWM charge controller ends up extracting lower energy from the Panel compared to the maximum possible. The panels are matched to the battery voltage and the Vmpp of the panels chosen is always higher than the highest battery voltage. That is why, for example for 12 Volt battery systems, the so called ‘12V panels’ have Vmpp of 17V.
In Indian conditions, the cells in the PV panels are operating under ambient temperature conditions that are much higher than the ideal name plate Wp conditions i.e 25 deg C. The maximum power point voltage shifts to a lower value – and hence closer to the battery voltage. The difference between the Vmpp and Vbatt is considerably reduced . Hence the extra power extracted using a MPPT charger is reduced.
Note that the MPPT charger is going to deliver extra energy – BUT the addition over PWM chargers is reduced because of typical India conditions (at say ambient of 36 deg C and NOCT – 47 deg – the difference is about 15% ) For a 100 Wp system – this is only about 10 Wp in typical conditions and based on today’s Solar PV prices, that allows only ~Rs500 extra for a MPPT charger. However as the Wattage increases – the head room for MPPT is better – for a 500 Wp install the extra cost afforded for a MPPT charger is ~Rs 2700/- and so on. That is to get the same performance of a MPPT charger with a PWM charger – the installer has to spend Rs 2700/- worth of PV panel extra in a 500 Wp installation.
However this calculation completely ignores the other benefits of using MPPT chargers. With MPPT chargers, the need to match the PV panel Voltage with the Battery Voltage is no more present. The system integrator can choose mass produced PV panels that cost lesser on a per Wp basis.
Further if the MPPT charger is designed well – the input range of acceptable voltages is high and this means that the input can be operating at higher voltage – thus reducing the wiring and connector costs.
In conclusion : MPPT chargers can have the effect of reducing the system costs and deliver more energy even in Indian conditions.