Marlec HRDi controller v MPPT

[lw395]

Just recorded some bluesolar at work, great fun!
A buck converter puller the panel voltage down to 14v so unlikely to help a huge amount.

The basic cure is to set the buck converter to regulate its input voltage at an estimate of Vpp. Vpp can be estimated from the open circuit voltage, at least near enough to suit the number of panels in series.

 

[GHA]

The basic cure is to set the buck converter to regulate its input voltage at an estimate of Vpp. Vpp can be estimated from the open circuit voltage, at least near enough to suit the number of panels in series.

Never seen a buck converter which can do that - link to one?

How will it regulate the input voltage without altering the current it draws from the panel as conditions change?

 

[GHA]

And with watts , panel direct to the batteries at the end. With bluesolar - ~13.4W, direct- ~ 11.05W. So just over 20% power gain from the MPPT.

 

[noelex]

No it is not.
MPPT stands for 'maximum power point tracking'.
This means adjusting the current drawn from a solar panel to keep it at the optimum point on its V/I characteristic in whatever level on sunlight is hitting it at the time.

Yes an MPPT controller tracks the maximim power point and by adjusting the input voltage keeps the solar panel at the voltage where it can produce maximium power. It then converts this voltage to the battery voltage gaining some current in the process.

A non MPPT controller (sometimes called PWM) cannot do any of the above. This is why it is called a non MPPT controller.

 

[lw395]

Never seen a buck converter which can do that - link to one?

We're currently using the Texas bq24650 in some applications.
This can be made to track MPP by adding a microcontroller, but in its standalone form it basically current limits to avoid dragging the panel volts below a preset.

 

[lw395]

Yes an MPPT controller tracks the maximim power point and by adjusting the input voltage keeps the solar panel at the voltage where it can produce maximium power. It then converts this voltage to the battery voltage gaining some current in the process.

A non MPPT controller (sometimes called PWM) cannot do any of the above. This is why it is called a non MPPT controller.

No, genuinie MMP tracking actually adjusts the panel voltage to extract maximum power. You can tell when this is happening because the panel volts will take some time to settle.
Many simpler/older convertors simply aim for a fixed panel voltage.
The basic Victron and similar 'PWM' controllers only do any PWM when the available solar power is more than the battery requires. Otherwise they are not working as buck converters, just dumb switches that drag the panel right down to battery volts.

The acid test is when a panel is partially shaded, that changes its Vpp significantly. A true tracker will get more power then.

 

[GHA]

We're currently using the Texas bq24650 in some applications.
This can be made to track MPP by adding a microcontroller, but in its standalone form it basically current limits to avoid dragging the panel volts below a preset.

Ta, haven't seen those boards before.

But why not get a real one? Vpp changes with temperature, shading and probably other factors as well, so you'll guess at a voltage which will likely be wrong, looking at the victron graph it doesn't take much of an error to lose any current gain.

Edit, just tilted the panel to be closer to the sun, panel voltage went from 16.9v to 18.9v after stabilizing, suspect your power point guessing might actually be worse than direct a lot of the time. Nuther edit - very likely wrong to suspect that as long as you guess on the low side..even so, why bother with a guessing half way house when you can do it properly with all the other benefits like float & logging)

 

[noelex]

No, genuinie MMP tracking actually adjusts the panel voltage to extract maximum power. You can tell when this is happening because the panel volts will take some time to settle.
Many simpler/older convertors simply aim for a fixed panel voltage.
The basic Victron and similar 'PWM' controllers only do any PWM when the available solar power is more than the battery requires. Otherwise they are not working as buck converters, just dumb switches that drag the panel right down to battery volts.

The acid test is when a panel is partially shaded, that changes its Vpp significantly. A true tracker will get more power then.

This is all basically correct, but there are many controllers that cannot convert the panel voltage. These are called non MPPT (or sometimes PWM controllers/regulators).