I am not sure I understand? How would a proprietary PLC control even work with another vendors product?
They wouldn’t (hence the ‘proprietary’ part…).
The goal of standards like 1741 and Rule 21 are to have greater interoperability between products.
Absolutely. But they are not based on PLC.
1741 and Rule 21 built upon the standard ‘grid present’ specification for all grid-tie inverters but especially Microinverters.
Grid frequency must be within a standard min-max range and grid voltage must also be within a standard min-max range. If the grid signal seen by the grid-tied inverter is out of this range (for either frequency or voltage), the inverter must shut down.
This was for safety and this is the level of technology contained in my pre-1741, pre-Rule 21 Microinverters.
The 1741, Rule 21 standard built upon that by specifying that output power must reduce in steps from maximum output at maximum allowable frequency to no output (off) at minimum allowable frequency (and please don’t quote me, I may have it backwards, but it is one or the other).
And the same for voltage. I’m not sure whether compliant inverters must support both throttling methods or only one.
To make this work, there must be a hybrid inverter in between the grid and the inverter(s) to control/modify the grid frequency and/or voltage.
This is not Power Line Communication - this is updating a crude binary communication protocol (ON or OFF) to a continuous several-bits of greyscale protocol by requiring finer accuracy in both sensing and control of grid signal (frequency and/or voltage).
The ‘smart grid’ of the future will be based on this type of protocol - the grid itself will modify frequency when it wants less solar power to be exported (from all generators).
Power Line Communucation is a much more sophisticated protocol that involves sending packets of addressed digital information to individual receivers on the home’s power line.
PLC is used for power line Ethernet but each of those PLC Ethernet solutions is proprietary (they cannot be mixed-and-matched). Same for Microinverter monitoring gateways - they are based on PLC. My NEP gateway plugged into any 120V socket in the home is able to communicate with all of my 240VAC NEP Microinverters to download status and output data.
But each of those gateways is based on a proprietary PLC protocol. An NEP gateway will not work with Enphase Microinverters and Vica-versa.
Communication digitally using PLC is far, far more robust and reliable than communicating in analog using frequency or amplitude as the analog control variable.
While the 1741 / CA Rule 21 standards should allow interoperability, a year ago getting that interoperability to work correctly was proving to be much more problematic than expected.
Victron and AP Systems put out a press release to brag about being one of the first combos to prove interoperability:
https://emea.apsystems.com/wp-content/uploads/2018/03/APsystems_YC500_Victron-MultiPlus_2018_WP.pdf
When I spoke with Magnum regarding their PAE hybrid inverter supporting 1741 / CA Rule 21 one year ago, they essentially scared me away and told me that analog throttling of a DC coupled array using string voltage under control of an SCC was orders of magnitude more reliable than attempting to throttle AC-coupled Microinverters using frequency or amplitude shift.
I mean, think about it: every load in your house consuming energy monkeys with the grid signal (both frequency and voltage). Motors (ie: fridges and washing machines / dryers) are especially bad for this.
The new standard for Rapid Disconnect is a first effort to standardize PLC-like communication (digital heartbeat signal).
Building upon that, I suspect we will eventually see standardized PLC communication for Microinverter throttling, but that will take years, and until then, staying within a ‘walled garden’ which relies on proprietary PLC communication is likely to be much more effective than attempting to mix and match between vendors interoperating trough frequency and/or voltage shift.
At least that was the situation one year ago - perhaps everything is golden today.
The way my vendor, NEP, is solving this 1741 / CA Rule compatibility issue is that in addition to supporting frequency and voltage shift standards, they have instituted a proprietary PLC-based protocol to throttle-back microinverter output under the digital control of their gateway.
With the gateway as the master monitoring what level of power is needed and communicating reliably to the Microinverters using PLC, the possibility of ‘thrashing’ or analog throttling resulting in harsh ON/OFF control is greatly reduced.
I’m pretty certain Enphase has a solution based on exactly this. Whether it is the Enphase battery and/or an Enphase Hybrid Inverter, they communicate with the Enphase Microinverters using a proprietary Enphase PLC protocol to throttle output.
The inverters also need to support analog throttling through frequency and/or voltage shift to be 1741 / CA Rule 21 compliment - it is just that using the proprietary PLC protocol (when possible) will result in superior performance (and specifically lower likelihood of thrashing).