Which would be the correct way to set this up?
Currently i have 1 emontx setup with firmware emontx123 measuring the solar output and 1 emontx setup with emontx-123-voltage connected to the grid feed with an ac ac adaptor. I have amended this http://openenergymonitor.org/emon/applications/solarpv/emoncms slightly to account for the separate emontx's and the calculation looks to be right.
This is giving me some slightly odd readings, solar output is reading a few watts when its dark?? and grid consumption is down around 150-200 watts its should be?
Re: Solar PV with 2 Emontx
The sketch emonTx123 calculates Irms and then multiplies this value by 240.0 V to obtain an estimate of power. Any noise in the signal from the CT will be squared and seen as real power. A background reading of a few Watts is therefore to be expected.
When a voltage sensor is available, the level of background noise in the V*I power calculation is greatly reduced. Although I don't use this actual source code, my Mk2 PV Router sketches perform similar calculations and the level of background energy flow is never more than around 0.5 Watts.
With a 10-bit ADC system that is correctly set up for measuring kW, there are fundamental difficulties when power levels are very small. There is an article about this topic in the Building Blocks section.