Hi all,
I’m a newbie and apologise if this question has been asked/answered before. How feasible is it to divert excess solar to an immersion or specified sockets with a specified priority up to certain threshold but over that threshold a specified amount or all of the excess is used to charge an EV?
Many thanks,
Colm
It depends upon how much solar you have - most EV’s need at least 2KW (think about 8A) minimum to keep charging so you need a good sized solar array to even make it worthwhile - particularly in winter.
The immersion divert is easy enough, there are plenty of commercial units and this site has instructions on DIY solutions.
Just to clarify, the minimum EV charge current is 6A in J1772 (what you car will use, regardless of connector). The voltage is localised so you can, if you want, supply 6A at 110V (or less) but in the UK with the typical 240V this means you need 1440W minimum. More info SAE J1772 - Wikipedia - see the Signalling section.
In terms of the rest anything is possible - I use node-red to alter the advertised current to my EV - but you need to think about ensuring that whatever you turn on can stay on for some useful minimum period and not to thrash anything on/off too much. I use pairs of node-red triggers to wait for a minimum level for N minutes before triggering a relay to enable the EVSE and a similar pair to wait M minutes before turning it off again if the spare power falls below a chosen current.
Note: I am talking about my own emoncms/RPi implementation controlling an ABL Sursum EVCC, and not the OpenEVSE!
Two years later and I’m more or less looking at the same problem again but I can be more specific this time. Say I have loads - two hot water tanks that - I wish to divert excess power to. Is there a way that I could split the excess between them and/or prioritise one of them to heat the other?
Yes - and I did it for three tanks. It appeared to work on test, but was never installed because there was no need - the meter didn’t have a ratchet and was not replaced by the time the friend I built it for sold up and left! (It was a big 5-bedroom farmhouse B&B.)
It used an emonTx V2 (yes, that long ago) with a customised version of Robin’s sketch. One tank had priority, the other two were linked to each other by pipework but all had their own immersion heater and 'stat. The algorithm was: the priority tank turned on at a low “energy bucket” level in burst mode, when that failed to empty the energy bucket, it was followed by one of the other two chosen alternately (so as to share the heat). If that didn’t empty the bucket, it got exported. The main changes were just adding extra setpoints to turn the triacs on and off at carefully chosen levels - plus the logic to select the two linked tanks alternately. The power switch was a large cast metal box with three triacs bolted to it, using the box as the heat sink.
Robin has a sketch for multiple wired loads on his website - mk2pvrouter.co.uk