If you have been following my posts in the OpenEV forum category, you will be aware that I have been working towards using OpenEVSE open-source electric car charging station to control EV charge rate based on excess solar PV production and improve OpenEVSE integration and control via MQTT.
Update: We (OpenEnergyMonitor) are proud to announce that we are now the UK / Europe reseller for OpenEVSE charging stations, see OpenEnergyMonitor Online Shop.
Solar PV diversion is now fully integrated into the OpenEVSE Wifi-gateway firmware
I have now implemented a working solar PV diversion prototype using NodeRED, the plan eventually is to build this functionality directly into the OpenEVSE ESP8266 Wifi module, my progress is in the feature/solarpv-divert branch of the openevse Wifi 2.0 repo. However, the nodeRED control is very functional and might well be the preferred choice for users who want functionality.
How it works
The NodeRED flow uses MQTT to interact with the emonPi (to get solar PV gen feed) and OpenEVSE (to get state and set charge rate). NodeRED is pre installed and configured on all emonPi’s, therefore it’s very easy to set up.
The actual charge rate is controlled by the car (my Nissan LEAF in this case), the OpenEVSE requests a particular charge rate by changing the pilot signal duty cycle, see my OpenEVSE blog post for more info. The OpenEVSE ESP8266 wifi module communicates with the OpenEVSE controller via serial. NodeRED communicates with the Esp8266 Wifi module (running firmware V2.0) via MQTT.
The NodeRED flow also supports communication with the OpenEVSE via HTTP, direct serial and Emoncms via GET API. However I recommend using MQTT.
More details and the NodeRED flow .json can be found in the repo:
I tested the implementation by simulating solar PV output, since March is not a good time for solar PV here in North Wales! See the ‘solar-pv-simulation’ folder in the repo for the data I used, and a nodeRED flow to post the .csv (exported from Emoncms) to MQTT.
There are two charging modes defined:
1: Normal Fast Charge (default)
- Charging at maximum rate irrespective of solar PV output
- Charging level is moderated to match solar PV production
- If use (on-site consumption feed) is provided it will be subtracted (excess solar diversion)
- Charging will not start until available power > min charge rate (default 6A)
- Once charging has started charge rate will modulate down to min charge rate (default 6A)
- Charging will not pause once started since it was decided stopping / starting charging causes excess wear on the EVSE and the car.