Good morning gents.
I am considering adding monitoring to an off-grid installation. Initially probably just an emonpi for two feeds but possibly expanding this further in future.The set-up is a single phase Sunny Island created standalone grid with wind, solar and generator, all AC coupled. I can’t see why this would not work but thought I should check a couple of points in case I have missed something fundamental:
The grid frequency is varied (by the Sunny Island) 50 - 52 hz (approx.). Ostensibly to limit the wind and solar GTIs but in reality this is used to control diversion loads. Does this frequency variation have any implications for the emon install?
The network is not operational 24hrs for power saving reasons (this is after all off-grid). How does this affect remote logging?
My technical knowledge is limited with regard to the emon set-up so please be gentle. I would hope to be become more proficient with time.
Good morning gents.
No. It might mean that the acceptable frequency limits for the PLL sketches would need adjusting as the standard tolerance is ±1%, but that is not relevant for the standard software used in the emonTx and emonPi.
If you run your emonPi from batteries instead of a mains-USB ‘phone charger’-type adapter (both via the USB power connector), then it will record zero power when the network is down. If it is mains powered and you have an internet feed of time, then it should get the time when it restarts and I think it will show a straight line between the last point recorded before the outage and the first point after. If it cannot get the internet time, I suspect you have a big problem because as far as I know, the Raspberry Pi does not have a battery-backed clock. I’m not absolutely certain of all this, those who know more about emoncms will no doubt correct me.
Correct. RTCs are an aftermarket option.
Thanks for those responses - seems I did miss some fundamentals!
Not really a problem though provided;
a) I stay with standard software or am prepared to amend sketches. Important to know where I may be going from the outset though.
b) Don’t shutdown the network - not really an issue as the power saving benefit is limited in the grand scheme of things anyway.
To keep consumption to a minimum, I wonder if a Pi Zero, with an EmonPi card only, powered through an RPi UPS LiPo battery setup would work. Need to know if the UPS card GPIO pins would interfere with the EmonPi card. It is a shame the UPS card is not just a UPS but includes a load of other stuff.
A USB based 3G dongle would sort remote logging (assuming not so off grid there is no 3G signal). There are some cheap low cost low data plans out there.
Don’t really know enough about the EmonPi card to be sure if this is a goer or not.