MPPT or PWM solar controller?

[p38arover]

I've wondered what was meant by MPPT and why they may, in some situations be better than the el cheapo PWM controllers supplied with portable solar panels.

This White Paper by Victron explains a lot: https://www.victronenergy.com/upload...WM-or-MPPT.pdf

Just changing to MPPT may not necessarily be better but it could be. I must get my infrared thermometer out and measure the panel cell temperatures this week when the ambient is in 40s C. I'll do that tomorrow and update this thread.

If I went MPPT, I could reconfigure my panels to be in series instead of parallel for better performance in (a) partially shaded conditions, (b) cloudy weather, or (c) high panel temperatures.

When I went camping a couple of weeks back I was struggling to keep my 2 x 45Ah AGM deep cycles charged with my 120w solar panels and I was only running the 29 litre Engel fridge. However, having said that, I had inadvertently isolated the connection between the main and aux batteries and only remembered 40km from my destination. The fridge had been running for a couple of hours at that point so my aux batteries were not fully charged to start. Then a couple of days of cloudy weather and the sun not getting into the valley until about 11am reduced the charging time. At peak, the panels were putting about 6-7 amps into the batteries. I did look at the power meter on the cable and was only getting about 30Ah into the battery on a good sunny day.

[DiscoMick]

I think you may need more solar and bigger batteries.
Another trick is to put the regulator close to the battery, rather than on the back of the panel. That way the full output of the panel can flow all the way down the cable, reducing voltage drop, and is only regulated just before reaching the battery.
From what I can figure as a non-expert, Maximum Power Point Tracking may give a slightly higher input than Pulse Width Modulation in some situations when the panel is performing at maximum output, but often there is little difference, despite the much higher price.
Here's another explanation :
MPPT vs PWM Solar Controllers - Enerdrive Pty Ltd

[DiscoMick]

Solar Regulators - Solar Charge Controller - MPPT Solar Charge Controller - 12v Solar Regulators

[p38arover]

I think you may need more solar and bigger batteries.
Another trick is to put the regulator close to the battery, rather than on the back of the panel. That way the full output of the panel can flow all the way down the cable, reducing voltage drop, and is only regulated just before reaching the battery.

2 x 45Ah are as much as I can fit in the space available under floor. I replaced the original cables with much heavier wire a few years back to reduce voltage drop. I'll check the voltage drop today, at 7A, I'm expecting less than 0.1V

[p38arover]

Ambient temp 39 deg C and the panel temp was 50 deg C after stabilising in full sun for an hour.

Voltage drop was a difficult to measure, it peaked at about 160mV in each cable leg at just over 5A - the current would rise and fall as the charge rate changed.

So I measured the cable resistance with a special ohmmeter (ESR Meter) that will measure very low resistance.

The measuring leads on the ESR meter measured 0.07 ohms and each solar panel cable measured 0.1 ohms (including the meter leads). So each cable leg has a resistance of (0.1 - 0.07) ohms = 0.03 ohms for a total cable resistance of 0.06 ohms.

At 7 amps that would be (7 x 0.03) volts, i.e., 0.21 volts or 210mV in each cable leg. That tallies with the measured 160mV at approx 5A mentioned above.

When it cools off in my electronics workshop, I'll put a power supply onto the cable and a load on the other end and measure voltage and current to check the measured resistance.

To be honest, I don't think it's an issue based on this sentence from the Victron White Paper:

Assuming a discharged battery the initial charge voltage will be around 13 V, and assuming a voltage loss of 0,5 V over the cabling plus controller, the panel will be at Vpwm = 13,5 V.

So the panel will make up for that voltage drop on the cable - the panels have an open circuit voltage of about 18V.

As an aside, what I did notice when camping was that angle of incidence to the sun made a marked difference in output. The legs on my panels put the panels at about 50 deg tilt (measured with an inclinometer). If I lifted the lower edge of the panels onto a camping step to reduce the angle to about 30 deg (I was camped at approx 34 deg south), the output rose nearly 15%. I will be modifying the supports to lower the angle. I believe that, in summer, they should be at the same angle as our latitude but in winter the angle should be about 15 deg more.

[austastar]

Hi,
March and September, panels at latitude, December tilt up 23 degrees, June tilt down 23 degrees.
Cheers

[p38arover]

Who do you believe? Some say 15 degrees up/down. Others say no change for summer, only for winter.

My house panels (33.75 deg latitude) are at 22.5 deg (the pitch of the roof).

[austastar]

Hi,
Ideally the panel should be fully facing the sun. Practicality however means as close at is possible without indulging in full xy tracking.
Cheers

[weeds]

For my portable panels I just face them to the north at 30 ish degrees...

at the end of the day I do face them east to catch the moon than the morning sun.

[p38arover]

Hi,
Ideally the panel should be fully facing the sun. Practicality however means as close at is possible without indulging in full xy tracking.
Cheers

I use the shadow cast by the panel to orientate the panel.