EVSE Charging with solar and night rate energy

I have a local emonpi, emontx3 and Open EVSE and Solar PV.
I would like to change the way OpenEVSE works with my PV as I have recently signed up to Octopus
Energy, who make 4 hours available at night at 5p/KWh (nr) and their day rate is 14p/KWh (dr).
I am looking at changing my EVSE charging algorithm method to charge my car at the cheapest rate per KWh.
Once the Grid Export has reached the point where the day rate is less than 5p/KWh for a minimum 6A charge.
ie. (1-(nr/dr))*(230V x 6A) = 887W or say 1KW the EVSE will charge.
To stop the EVSE contactor clanking in and out I will need some hysteresis and think that the stop charge point should be about 500W of minimum grid export. (I respect the present idea of leaving charging on till finished to reduce wear etc.).
To ensure the car is fully charged ready for the next day, once the night rate is applicable turn on full charge (32A) for the duration.
So how to go about doing this… Should I go down the MQTT route or look at the present EVSE code.
Any thoughts would be welcome

Hello @paulbernardr we are hoping to do similar but are some way off everything you are after there. There’s a longer discussion of our intentions here: OpenEnergyMonitor Demand Side Response Development and info on demand shaper module which has an octopus forecast input for their agile tariff Emoncms Demand Shaper module.

I imagine however that it will be easier for you to achieve what you are after, at least in the meantime, with MQTT, NodeRed? @glyn.hudson might have some more ideas.

Hi @paulbernardr,

Nice setup! I have similar myself. This is something we are working towards being able to handle better. Have you considered using the OpenEVSE timer function to charge during the low cost 4hr period? Outside of this period if you have Eco mode enabled the OpenEVSE will charge from solarPV.

If you want more control MQTT and NodeRED is the way to go. Here is an example NodeRED flow we used to test the solar PV divert algorithm before it was implemented in the OpenEVSE firmware:

Thanks Glyn,
I have written some basic Perl code that runs on another pi and reads data from emonpi via mqtt and writes to openevse via rapi ‘okish’… (the openevse does not seem to like a mixture of rapi commands and web interface settings).
Early days yet and once refined I will make available for all.
I will also have a look at Node-Red and have installed on my emonpi.

Got a simple perl prototype up and running without the night rate mode at this stage…
PVEVSE.txt (4.3 KB)

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