I’m wondering if this has something to do with my solar inverter setup.
My solar setup is Enphase microinverters. So instead of 1 x 240 volt AC inverter to monitor, I have 16 inverters feeding to the electricity meter.
Reading the Enphase micro inverter specification sheet I note that the AC voltage from the Micro inverts have a very broad voltage range. 211 - 264 volts.
I’ve not yet measured the voltage at the meter board to see what is coming down from the solar (not at home during the day).
I’m wondering if the under voltage (< 240 volts) and over voltage condition (> 240 volts) is causing the calculation of the Current Transformer observed solar watt generation to be mis calculated?
If you think this is a possible cause, maybe a solution is for me to buy another EmonTx and dedicate this to solar feed in measurements. They key being that the the 9v AC reference adaptor would be powered from the solar feed circuit (not the street utility feed) and would vary the apparent power calculation for the solar automatically?
i.e: as the Solar AC voltage fluctuates over time, the solar connected 9V AC adaptor would see the change in the reference 11 volts, and adjust the formula for calculating solar watts ( ? )
on further review (and reading excellent Community posts!) I have got to the bottom the exporting more than I’m generating.
I learned that solar generation must be added to grid power to get the “use” power.
I still have a question regarding the broad power range of my micro inverters and the influence this has on measuring solar generation with the Current Transformer, and no reference voltage.
I’m wondering if the under voltage (< 240 volts) and over voltage condition (> 240 volts) is causing the calculation of the Current Transformer observed solar watt generation to be mis calculated?
I have the same set-up (Enphase M250 micro inverters) and as long as you are measuring the voltage on your emonPi / emonTX all the other numbers will be correct. I have never seen the voltage go much outside the 240-250 range over two years.
The inverters are designed to match grid voltage and frequency (they have to)
Acceptable UK Grid UK voltage is 230V +10% - 6%
So a G83 compliant inverter (which they have to be certified to to be allowed to be installed in the UK) has to be able to match from 254V to 217V at the same time they must also disconnect themselves from the grid if it is outside this range, so if you are getting overvoltages, then they’ll disconnect and try again in 3 minutes. (Regulations)
i.e Solar Voltage and Grid Voltage will be the same so long as the inverters aren’t on a 40m long cable connection and the cable is adequately sized.
A normal distribution circuit is allowed a 3% voltage drop from the grid point, a Solar PV circuit is only allowed to be 1%, hence the larger cable requirement.
So long as you are reading the grid voltage, your results should therefore be within 1% plus other inaccuracies in CT’s, voltage reference methodology etc.
So yes to properly measure the Solar PV power (kW) and energy (kWh) you do need to have the reference voltage.
As all the PV micro-generators kick in on a sunny day, and the wind turbines on a windy day, the grid voltage will rise.
