Revenue metering for Mixed type of Renewables (ie: Solar/Wind)

[Sn00ze]

I have been seeing a lot of new independent power producers and i am seeing new requirements for different types of set ups. I have not seen any conversations around set-ups where different types of renewables are used together.

Specifically when a single 35kV bus taking 5 feeders and 2 of those are solar while 2 are from wind turbine.

Typically we'd take revenue metering at the point of interconnection (Line breaker in a simple bus arrangement).

My question is, for this type of set-up. would the solar feeders require a separate or different type of revenue metering at the feeders? or would the single point at the point of interconnection enough?

Alternatively, if anyone knows of documentation that would guide me in the right direction. It would be appreciated.

This would be for NERC/Canada part of the world.

Cheers.

 

[davidbeach]

It depends. If there’s different rates or different tax consequences then definitely need separate meters. But if not, if it’s just straight interchange, then one meter could be enough.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[waross]

The secondary impedance of a CT is so high relative to the impedance of a revenue meter that CTs may be used in parallel to give acceptable accuracy for revenue.
There are some circuits in my metering handbook that use this relationship to meter three phases with a two element meter.
If single meter metering is usable but physical constraints two or more feeders to pass through a single CT, then the CTs may be paralleled.
If I am able to find my old metering book, I will supply a reference. I have used the effect that CT secondary current will pass through the metering elements rather than trough the other CTs to meter several customers.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bacon4life]

If this is for a new installation, I would not use an aggregate meter. It may be worthwhile to have revenue grade metering installed both on the individual feeders and on the aggregate bus. For new revenue and interchange meters, using paralleling CTs seems like it would significantly complicate the testing/maintenance/documentation.

Utilities near me need lots of meter retrofits to in order to join the CAISO market, and it might be similar for your regional ISO. For hydro plants, CAISO typical wants individual units to have metering rather than aggregating at the plant level. Some details of CAISO's requirements are at

https://bpmcm.caiso.com/Pages/BPMDetails.aspx?BPM=Metering.

I am not sure exactly how CAISO's rules work for wind/solar plants, but I assume having two different types of generation mixed behind one meter would be highly problematic for participating in CAISO.

Another consideration for having separate meters is that the solar versus wind portions could easily be owned/operated by different entities at some point in the future. Having separate meters vastly simplifies any future split of ownership/operation. The two kinds of generation might even be owned by a single entity, but could operate under separate Balancing Authorities.

For regional modeling purposes, it is really nice when revenue and SCADA metering aligns with how generators are modeled in the based case. Having two kind of generation behind a single meter makes much more complicated to model the correct output from each unit during regional studies. Regional planners already struggle with modeling combined cycle natural gas plants that have combinations of gas turbines and steam turbines. Combining totally unrelated kinds of generation like wind and solar would be even more problematic than modeling combined cycle plants.

Specifically for NERC compliance, a few different places to check include:
-NERC MOD-032 requirements
-Regional modeling guidelines such as the WECC Data Preparation Manual. This document requires explicit transient stability models for anything over 10 MVA, so it applies to lots of non-BES generation.
-Any additional requirements from your specific NERC Planning Coordinator and Transmission Planner. The PC/TP may have additional rules that would discourage aggregation.

Regarding renewable energy credits (RECs), eventually there may be a switch from just counting all energy as equal to a much more detailed system that accounts for the specific hour that each MWh was produced. Separate revenue metering for each kind of generation might simplify/enhance calculation related to RECs.

 

[Sn00ze]

Thank you all for your responses.

This points me in the right direction and who to ask what. I really appreciate the insight.

After reading your responses I went ahead and contacted our Meter supplier who also program our meters and confirmed this would be driven by the user/utility's contract.
Usually this requires a meter on every 34.5kV feeder, and an additional high side 138kV or 240kV meter point.

In addition to metering on every feeder, a post-data collection bill splitting algorithm will be required to mathematically derive the Solar and Wind quantities.

So, at the very least I have a good idea of how to approach this now.

Thank you personally @bacon4life, @waross and @davidbeach. I've noticed you guys always give great advise to me and everyone on the forums.