Having just had a new solar pv installation, I've been looking for ways to monitor my import/export/generation/consumption.
Unfortunately it seems that my installer has made things as hard as possible.
- I have a type 2 installation.
- Furthermore, the cable from the inverter is a twin-core plus earth type instead of separate wires.
- Finally, the only place I could put a CT clamp for the import/export is nowhere near a socket. (Not keen on running the cable out through the cavity wall.)
This leaves me with many questions...
- Question1: If I use a transmitter (emonTx or emonPi) with an AC-AC adaptor to measure import/export, will it still work for that with only the CT clamp between the meter and the consumer-unit/fuse-box? (The inverter output would be measured directly by running an ethernet cable to it. There would be no CT clamp on the inverter cable.)
- Question 2: As I've said, there is no socket for the AC-AC adaptor nearby by. Could the current direction be determined by using the optical pulse sensor on the import meter (as it would pulse for import and not for export).
- Question 3: How do solar immersion devices like iBoost/Immersun work with only having one clamp? How do they determine current direction?
I'm not adverse to a bit of code hacking, but my electrical engineering knowledge is sadly lacking :(
Thanks :)
Re: Type 2 with one CT clamp? Pulse meter instead of AC-AC?
1. For a type 2, you want to know separately the PV generation and the nett grid import/export. How you measure them is immaterial, provided that you know the sense of (ideally) both but particularly the grid power. (I say 'ideally' because inverters tend to consume a small amount of standby power when it's dark, and people who don't know that and don't know the direction of the power flow wonder how they can generate 10 W or so at night!). Therefore, your ac adapter and CT will give you the nett import/export with the sign giving the direction, and separately in emonCMS you'll get the PV generated power from the inverter direct.
2. That's a very tricky one, the probable answer is not easily if at all. That's because different meters behave differently when exporting, and you need to distinguish between three states: import, export and anti-creep. Say your meter LED is on in anti-creep, off when exporting and flashing when importing, the hard part is knowing when an import just above anti-creep when the LED flashes are a long way apart is import and not export. I haven't seen a report of anyone doing that, but it may be possible.
How far is the nearest accessible socket (bearing in mind that you should have no problem extending either the ac adapter or the CT cable by 10 m or so. Would you be happier bringing the CT in through the cavity wall?)
3. I've never got my hands on one of those and tested it, so I can't comment.
Re: Type 2 with one CT clamp? Pulse meter instead of AC-AC?
Question 3: How do solar immersion devices like iBoost/Immersun work with only having one clamp? How do they determine current direction?
According to Immersun's website, their wireless sensor "uses the main supply voltage to calculate the power accurately unlike third-party monitoring devices using current only". So this should allow them to determine the direction of energy flow at all times, just as my own Mk2 PV Router design does.
On another page, we find that Immerson's wireless sensor has a "Response time 1 second", thereby ensuring "fast accurate performance".
Maybe I'm biased, but this appears to be a very poor element in their chain of control. When a kettle is turned on, any diversion of surplus power needs to be reduced or halted immediately, otherwise a penalty charge is likely to be imposed by the user's meter. Under such conditions, the Mk2 PV Router (including its RF-linked variant) will respond within 30 ms.