Just a quick update as this thread is appropriate :

Here are some details from the next firmware build of Paladin (V7xx) that some may find interesting.   Don't get too excited though, it will be the end of the year at earliest, but will be fully compatible with V695 firmware and hardware.  None of this really applies to non-battery installations, so interest only for you folks. 

OK, so one of the most annoying problems I have identified, with my V695 build - and it applies to many, is that when on full battery support my inverter is only capable of 2.5kW of output.  If I draw any more than that then the balance comes from either solar, if there is sufficient, or the grid.  But my HW element is 3kW, so even without a house load I am always going to be hit with some grid input during a top up without some solar available.  Not the end of the world perhaps, but definitely annoying.  The obvious answer is to fit a smaller element, but how small? and what about transfers - they will then be restricted to element size.

So all that follows is about top ups only.  Either forced by minimum temperature or Legionnaire's, or manually by the top switch.  Transfer / Diversion is not affected.

So I wanted what is effectively a Virtual Element (VE) that could be set to any wattage up to the physical value of the physical element.  I also wanted to introduce a much slower and steadier ramp up (and down) of power to allow the inverter to keep up.  A sudden surge in power is never captured that well by any inverter I have experience of, so a slower ramp up would allow the inverter time to adjust in tandem if you will.

The code to do this was superficially quite long and CPU intensive in terms of limiting Paladin's grid measuring cadence, so a suitably elegant and speedy solution was a good while in creation.  As is often the case in these things, the answer came eventually and it is actually rather simple once you get the idea minimised to its' basics.

Anyway, Paladin now has a selectable VE that will maintain the selected wattage on a top up and ramp up in 30 secs to VE power.   The next item was what to do about excess solar during a top up.  If I stayed to that selected VE then excess solar would be exported, not at all ideal.  But that was solved as well using a second positive feedback loop comparing actual transfer with a meld of selected VE and exported watts.

Now what happened if there was an increase in house load during a top up and the sum of house load and VE exceeded inverter output.  A slight modification of the feedback loop solves that as well by pulling down the VE value until the house load reduces, allowing the inverter to carry the load without grid activity.  

The final hurdle was what would happen if you wanted to use full element wattage for a rapid top up regardless.  I have provisionally covered that by dumping the overnight boost on the LH switch poition and making that an 'emergency boost' at full wattage all the way to maximum temp, or until the switch is returned to the centre.  I say provisional because the jury is still out on whether that should be to maximum temp or just to selected minimum.  My gut feeling is that as this is essentially a manual over-ride, it might as well be to maximum temp as the user can turn it off as required.  This will also be useful for those with a free power period in their plan.

Finally, while all this was being crafted, I realised that this method allowed me to fully implement a feature that had been available, but somewhat clunky on the existing software, for forcing a fixed export wattage and allowing the remaining power to the HW element.  This was actually easy as it uses an almost identical method to the VE concept. 

I am presently modifying the serial port API to accommodate these changes so that those with a bent for HA and the like can hack these extra features as they feel the need.  Then I can get this version on my wall and try it all in real life.