How to tell if a solar regulator is MPPT or PWM

Question

I have a solar cell charging a 12v battery via a maplin TPS 1230 solar charge regulator. By using some basic instrumentation and some simple maths (i.e. measuring the current and voltage on the input & output and multiplying to produce a figure for power) I determined that I wasn't getting as much power out of the system as I thought I should.

Having read-up on the subject, I believe this might be due to the solar charger being a PWM type - not very efficient. I've just ordered what claims to be a MPPT solar charge regulator (much more efficient). listing here

After placing the order I did a little more reading (yes, I know, I got this the wrong way round!) and discovered that apparently many cheap MPPT charge regulators from china aren't really MPPT after all - just PWM chargers with a different label.

When my order arrives, is there any way of telling if it really is MPPT or not?

Answer 1

Having read-up on the subject, I believe this might be due to the solar charger being a PWM type - not very efficient. I've just ordered what claims to be a MPPT solar charge regulator (much more efficient).

MPPT does not make the charger more efficient. It loads the solar panel in a way that draws the maximum power that the solar panel can provide for a given level of solar radiation. The only way to verify that the charger is doing that is to measure the solar power being received by the panel and comparing that with the power being delivered to the charger by the panel. Then determine from the panel's characteristic curves if the maximum power is being delivered for the measured level of solar radiation.

The efficiency of the DC to DC power conversion by the charger is another issue. The efficiency is likely to be highest when the input power is highest. When purchasing a charger, you can only really determine how efficient it will be if that is stated by the manufacturer. It efficiency is stated at all, it will likely be only the best efficiency that can be realized, not the efficiency for every operating condition.

You also must consider limits that might be put on the charger by the battery. If charging the battery too quickly will shorten the battery life, operating at the maximum power point of the solar panel might not be the best strategy.

Answer 2

What is your actual Voc/Isc=Zmpt and efficiency? MPT is when this impedance is matched on the PV array around 82% Voc in full sun and shifts down towards 70%Voc at half power. Step down SMPS conversion to battery might be max 90% efficiency.

What do you get? For all the above parameters:

Voc max min.
Isc max min.
Vout CC I out CC

use the above to compute what to expect.

Or \$P_{PV}= V_{mpt}*I_{mpt} = I_{in}^2 * (V_{oc}/I_{sc})= I_{in}^2 * Z_{mpt}\$

If I in = I mpt then it is a good MPT tracker.

PWM can only be an MPT track if it switches continuous current via an inductor with low ripple voltage around Vmpt at Impt, which reduces I faster than V as it is a quasi-current source with reducing solar input. Then TWO separate SMPS are needed for both input voltage tracking of MPT and CC/CV tracking of battery by sensing input/output V and current I with “some” algorithm. ( several for different PV ratings and several for different battery chemistry.)

Update

MPPT ONLY occurs when the current source effective (incremental) impedance matches the load impedance. This must be nearly constant for constant solar power input and raise the impedance as solar power declines. In order to regulate constant V/I , this is done like a buck converter with PWM and a series inductor to minimize the ripple. The switch losses are thus minimized rather than using a linear regulator to hunt and match impedance.