In some cases, solar installations may be limited in export tariffs by an electricity provider due to high solar export concentrations in an area.
- What this might look like: You may have 10kW (41A at 240v) of peak generation capability through your solar panels, however your distributor may advise you that they will not pay for or accept export above 5kW (~20A) from your property. This effectively means that your solar PV generation above 5kWh is "lost".
- Aim: To utilize as much of the lost export for vehicle charging as possible, whilst exporting as much energy as possible within the exportable range.
- Considerations: We have the option to tune the charging to utilize flex power when charging starts. Rather than waiting for an entire 6A of generation above the intial 5kW to become available before we start charging, we can use flex to start charging just after we cross the 5kW threshold, which will dip into the exportable energy when we first start charging, but will give us a nice charge curve throughout the day.
- Outcome: We will set a static 5kW consumption value, which makes it appear to TWCManager that we are already consuming 5kW of the 10kW generation. Any household consumption will then be added on top of this value. This would leave a maximum of 5kWh (21A) for charging, which is higher than
minAmpsPerTWC = 6in our (EU) TWC example, and will allow us to start charging once 5kW is being generated - obviously you may change these values to suit your environment.- We will use flex charging to allow the charge to "dip" into up to 5kW of generation below the 5kW threshold to begin charging. The logic behind this is that once we have reached the threshold to start charging we can be relatively confident of remaining in positive generation throughout the day, however we may have short variances and a ramp-up period to get to peak generation. If we stop charging for every variance in output that puts us below 5kW, we're potentially then exporting up to 6.44kW of energy (5kW + 6A above export level), 1.44kWh of which is entirely wasted as it doesn't get counted toward export tariff, so dipping into up to 5A of exportable energy to keep from losing 6A of non-exportable energy is a reasonable balance to strike.
"minAmpsPerTWC": 6,
"greenEnergyFlexAmps": 5
- Via the web interface, set a Consumption Offset in watts of 5000W
This will have the following effect:
- Charging will not start until the generated energy is at least 20A (
minAmpsPerTWCbeing 6A and after the 5kW of consumption offset that we have configured). - Once charging has started,
greenEnergyFlexAmpscontrols how low the generation can go without charging stopping. AsgreenEnergyFlexAmpsis set to 5, this means that the generation can get as low as 16A without charging stopping (to account for cloud or conditions changing, or appliance loads). This ensures that we are always exporting at least 16A of the 20A exportable energy.
The below shows an illustration of how this configuration improves the effeciency of this setup, by starting charging after the orange band (which is 5kW of generation) and stopping it at the same point at the end of the day. This results in avoiding the loss of exports between the orange (5kW) and green (5kW + 6A minAmpsPerTWC) bands.
The following advice was contributed by @Saftwerk, and explains how to map a particular USB to Serial Device to a given device name to avoid issues with re-enumeration of devices:
List all USB devices:
ls -l /dev/*USB*
crw-rw---- 1 root dialout 188, 0 Jun 16 17:34 /dev/ttyUSB0
crw-rw---- 1 root dialout 188, 1 Jun 16 17:34 /dev/ttyUSB1
crw-rw---- 1 root dialout 188, 2 Jun 16 17:34 /dev/ttyUSB2
If you have only one entry, then you don't need this fix, but you can be prepared for future.
List infos about a device:
/sbin/udevadm info --query=all --name=/dev/ttyUSB2
P: /devices/platform/soc/3f980000.usb/usb1/1-1/1-1.4/1-1.4:1.0/ttyUSB2/tty/ttyUSB2
N: ttyUSB2
L: 0
S: serial/by-path/platform-3f980000.usb-usb-0:1.4:1.0-port0
S: serial/by-id/usb-1a86_USB2.0-Ser_-if00-port0
E: DEVPATH=/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.4/1-1.4:1.0/ttyUSB2/tty/ttyUSB2
E: DEVNAME=/dev/ttyUSB2
E: MAJOR=188
E: MINOR=2
E: SUBSYSTEM=tty
E: USEC_INITIALIZED=5776874
E: ID_VENDOR=1a86
E: ID_VENDOR_ENC=1a86
E: ID_VENDOR_ID=1a86
E: ID_MODEL=USB2.0-Ser_
E: ID_MODEL_ENC=USB2.0-Ser\x21
E: ID_MODEL_ID=7523
E: ID_REVISION=0254
E: ID_SERIAL=1a86_USB2.0-Ser_
E: ID_TYPE=generic
E: ID_BUS=usb
E: ID_USB_INTERFACES=:ff0102:
E: ID_USB_INTERFACE_NUM=00
E: ID_USB_DRIVER=ch341
E: ID_USB_CLASS_FROM_DATABASE=Vendor Specific Class
E: ID_VENDOR_FROM_DATABASE=QinHeng Electronics
E: ID_MODEL_FROM_DATABASE=HL-340 USB-Serial adapter
E: ID_PATH=platform-3f980000.usb-usb-0:1.4:1.0
E: ID_PATH_TAG=platform-3f980000_usb-usb-0_1_4_1_0
E: DEVLINKS=/dev/serial/by-path/platform-3f980000.usb-usb-0:1.4:1.0-port0 /dev/serial/by-id/usb-1a86_USB2.0-Ser_-if00-port0
E: TAGS=:systemd:
From the list choose a name like ID_SERIAL , wich would have a unique value from other USB devices.
Edit a rules file:
sudo nano /etc/udev/rules.d/99-com.rules
and append a new SUBSYSTEM line with your ID_SERIAL like my template which has now 3 lines:
....<truncared>....
elif cmp -s $ALIASES/uart1 $ALIASES/serial1; then \
echo 1; \
else \
exit 1; \
fi \
'", SYMLINK+="serial%c"
SUBSYSTEM=="tty", ENV{ID_SERIAL_SHORT}=="00F31F50", SYMLINK+="lesekopf0"
SUBSYSTEM=="tty", ENV{ID_SERIAL_SHORT}=="00F32228", SYMLINK+="lesekopf1"
SUBSYSTEM=="tty", ENV{ID_SERIAL}=="1a86_USB2.0-Ser_", SYMLINK+="USB_TWC"
Notes: Keep an empty line at the very end. If you replace the RS485 converter, then you have to edit this file again.
Now apply the changed rule:
sudo udevadm trigger
and verify the new entry:
ls -l /dev/*USB*
crw-rw---- 1 root dialout 188, 0 Jun 16 17:34 /dev/ttyUSB0
crw-rw---- 1 root dialout 188, 1 Jun 16 17:34 /dev/ttyUSB1
crw-rw---- 1 root dialout 188, 2 Jun 16 17:34 /dev/ttyUSB2
lrwxrwxrwx 1 root root 7 Jun 16 17:34 /dev/USBTWC -> ttyUSB2
Now you can use in config.json the new name "port": "/dev/USBTWC"