Diy mppt?

[Xringer]

I've been looking into how I can get more PV watts into my 10 Ohm hot-water heater.

I've been looking at this pump controller.

Here: Build this simple Mini Maximiser

And thinking about the 'Knee' point (sweet spot) of a PV array.


This particular PV array seems to have a (1300w) sweet spot around 152 volts..
As you can see, the Open voltage (no load) is up around 200v.

Anyways, if you made a voltage divider similar to the Mini-Max (above),
fed the voltage to the comparator & FET, with your reference
pot pre-set to trigger the FET into conduction right at 152 volts (or higher)..

It seems like the load would only see 152v (or higher).
Once the RC time constant ran down a tad, the FET would turn off, and
the PV would take a little time to recharge the input cap, before the PV
voltage was high enough to trigger the FET again.

In weak sun, the off-on rate would slow down, as the PV struggled to keep up, charging up the input cap more slowly.

But, in bright sun, the off-on rate would zoom up and try to keep a continuous 152 volts on the load..

But, either way, while the FET was on, the load would see the highest voltage : power available from the PV.
Thus, making the fixed load, dissipate a maximum amount of watts.

Each time the FET turns on, it can hit the load with about 1300 watts.
If only for a short time.. But, the Flywheel Effect might help here.

By allowing only higher voltages to pass power on the feed lines,
allows for less line loss. (Especially with the small wire I'm using).


If I could use this type of circuit on my 10-Ohm hot-water heater,
zapping the load with full power hits, I'm sure it would put more heat into the water..


~~
Today, my 500w array shows 65.1v under load & 78.9v open (no load).
At the load, (after 75 feet of wire) the voltage is 63.3 (lost 1.8v ~ 11.4w).

63.3 volts (6.33 Amps) on the 10 ohm load dissipates about 401 watts.
With the line loss, 412 watts isn't too bad, but this is a peak reading.

The passing clouds allow the 10 ohm load to pull down the PV voltage,
making the line losses increase and the fixed load, seeing lower voltage,
can't draw as many amps.


I can't help but wonder if I could get closer to 500 watts, if the PV was
running at around 67-71 volts..?.

I have not worked with FETs for years, I hear they have some real good ones now.
What do you guys think? Good DIY, or start shopping for a pre-made?

Cheers,
Rich