DIY Arduino based solar PV dump controller

I present here my ideas / design for my home built solar PV dump load controller, based around an Arduino microcontroller. It is not presented as a "design" but rather ideas for you to use or adapt as you see fit. This is my MK 2 design. For background, my Mk1 version was based on a design by Eric Ward in Jan 2011 which used a single current transformer, and sampled the ac waveform a number of times per cycle to determine if the measured current was being imported or exported. Thi

I am thinking of an addition to this. There are plenty of occasions when the excess PV exceeds what the immersion heater can soak up, so some power gets exported. I am considering dumping some of this "unusable" power to a small electric heater. In the summer that won't be needed, but now, in the shoulder seasons, a little extra free heat in the house would be useful and even now there is still sometimes some surplus around mid day., So I am thinking of makin