Measuring and acting on solar export


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Davo99
Guru

Joined: 03/06/2019
Location: Australia
Posts: 1507
Posted: 02:45pm 07 Jan 2022      

Not exactly what you are asking for but I do the same thing slightly Differently.

I use a voltage monitoring Relay to switch on my water heater when the solar is producing.  IT have it set to measure the rise in the mains voltage and then switch the heater through another relay.

I also have a PWM controller on the heater so I can turn it down to say 1500W -2KW so it can heat using less power particularly in cloudy weather.

Voltage Relay

These can DO AC and DC so you could set it up on either side.
They have hysteresis and a timer function so you can set them so if the voltage drops say 3 V for 20 Sec, they kick out.  

I had Voltage rise problems initially and put one of these on so as to help pull the circuit voltage down to keep the inverter producing and it worked well.  Don't have the problem not but still use the setup as I took the HW off the off peak as my own power is of course Cheaper.

There is an over ride button which is handy if you get a lot of cloudy weather. I have 3-4 Days worth of reserve in my big tank so I have only had to kick it in manually a few times over the 2 years I have had this.

I also have some current sensitive switches I got. Haven't used them yet but could work a similar way.  They are adjustable and switch depending on the power running through the wire they surround.  You could put one on an inverter and tune it so it switches on the heater when there is sufficient power.

Current Switch

You would have to calculate your other loads and set wither one to a point you know the solar would cover the heater and the rest of the house loads.

I have seen meters that use CT clamps on all 3 phases to measure total production/ consumption but they were pricy  and didn't do switching.

The Voltage or Current relays are not perfect but probably a step up from a Timer.