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CAISO Requirements for Solar PV Projects


The California Independent System Operator (CAISO) is responsible for maintaining the reliability and accessibility of one of the largest electrical grids in the world. CAISO maintains an exacting process to gain access to, and continue to participate in, California’s open energy market.


As solar PV plants grow in size and enter this open energy market, asset owners encounter the complex world of CAISO requirements. Let’s cover the basics of CAISO requirements, including the NRI process, CAISO RIGs and metering.


When and how did CAISO start? 

CAISO started in the late 1990s. Before then, energy was regulated at the state level. Local utilities provided generation, transmission and distribution services for specific areas. The Federal Energy Regulatory Commission (FERC) recognized these utilities as monopolies and decided to deregulate the grid. This created opportunities for Independent System Operators (ISOs) to form.


What are ISOs and how many are there across the U.S.? Do they all have the same or similar requirements?

ISOs coordinate, control and monitor the operation of the electrical power system, usually within a single U.S. state, but sometimes across multiple states. ISOs also act as a marketplace operator in wholesale power.




Not all states and regions have ISOs, and subsequently the utilities there don’t engage in wholesale power markets. These regions must still conform to open access as mandated by FERC, but the power exchanges between utilities are mostly facilitated through power purchase agreements (PPAs) and bilateral contracts.


There are currently only a handful of ISOs across the U.S. Each ISO has its own specific interconnection procedures, but CAISO’s are the most rigorous.


Do all solar projects need to comply with CAISO requirements, or only participating facilities? What criteria must be met in order to register with CAISO?

Any generator that participates in the California open energy market must comply with CAISO requirements. However, not all generators must participate.


Solar PV projects that are 1 megawatt or greater should participate. At 500 kilowatts and above, owners can choose to participate but don’t have to.


There are other potential criteria. An ancillary interconnection agreement and/or PPA may contain language that governs whether or not a generator needs to participate. This depends on the local utilities or balancing authorities.


What is the NRI process and what are the “buckets” everyone is always talking about?

The New Resource Implementation (NRI) process is the process by which a resource interconnects/syncs to the ISO grid. CAISO divides that process up into six individual steps, called “buckets.” Each bucket has its own set of deliverables and timelines. At the completion of the process, the resource achieves full energization and is set up for commercial operations. The ultimate requirement is to comply with the ISO tariff; going through the NRI process helps satisfy the tariff requirements.


How long does the NRI process take?

CAISO recently reduced the NRI timeline from 203 days to 84 days. That said, there’s a lot of time needed upfront for initial project registration and getting access to be able to submit documents. In our experience with the NRI process, it takes about 150 days, which leaves some extra room in the schedule to meet all critical deadlines.


Bucket 1: 84 Days Before Sync

To participate in California ISO or the state’s open energy market, the generator needs to submit documents necessary for full network model preparation.


Bucket 2: 84 Days Before Sync

At this stage, the generator needs to get the regulatory contracts started and submit the necessary information for ISO forecasting.


ISO metering information is also required in this bucket.


Bucket 3: 30 Days Before Sync


Deliverables for Bucket 3 include a letter of intent, generator resource data templates (GRDT), scheduling coordinator selection and acceptance letters, and metering, telemetry and RIG engineering requirements.


Required CAISO point to point testing is usually performed at this stage. It tests real-time and revenue data from the site to CAISO.


Bucket 4: 10 Days Before Sync


The generator needs to submit a request for trial operations, which includes a preliminary validation of meter data.


Bucket 5: 1 Day Before Sync


One day before the sync date, the site’s scheduling coordinator must contact the ISO outage management for subsequent testing and synchronization.


Bucket 6: Commercial Operation Date


Once the application is approved, the generator will receive a Certificate of Compliance. Then the generator can request a commercial operation date, to start distributing solar energy to homes and offices in California.


What is a RIG and what purpose does it serve in a CAISO project?

A Remote Intelligent Gateway (RIG) is a telemetry device that allows an ISO to collect data from the project site. You can think of a RIG as a sort of data aggregator. It collects data on a local basis—generation data from the meter, protection data, MET station data, etc.—concentrates it, and sends it off to CAISO. CAISO pulls this data every 4 seconds to keep track of generation in real time. Any generation facility that wants to interconnect at the transmission level must install and maintain a field RIG that meets CAISO’s requirements.


What are some of CAISO’s RIG requirements? What types of technology options are available to meet them?

There are various RIG options out there, and generators can use any of them so long as they satisfy CAISO’s requirements. CAISO’s RIG requirements include a specific DNP3 protocol which is used for communication between the project site and the ISO. There is a required security certificate that needs to be in place if the site uses a local ISP Internet connection or ECN connection. ECN stands for Energy Communication Network and is managed by AT&T. There is a third connection option, known as Dispersive Networks, which is a private network managed by Dispersive.


There are also specific approved meter lists that the project site must comply with.


What is a CAISO meter? How is it different from other solar project meters (owner meters, utility meters, etc.)?

A CAISO meter is a device that measures energy coming in and out of the project site. This ongoing direct measurement allows CAISO to manage and monitor power generation in real time, ensuring the stability of the grid.


CAISO meters are different from utility or owner meters in that they must conform to a certain set of programming and installation requirements. The meter must be inspected and certified by a third-party ISO inspector to make sure it complies with all of CAISO’s requirements. Accurate metering of electricity generated provides critical data to allow for power generation accuracy.


How many CAISO meters are needed for a solar project?

Typically, CAISO only requires one meter. However, there may be specific language in an interconnection agreement or PPA that requires the site to use a primary and backup meter. For larger projects, the industry standard is to have two meters onsite. In the event of meter failure, this allows for a seamless transition to the backup meter for settlement purposes.


What is AGC? What requirements must SCADA systems meet in order to support AGC requirements?

Automatic Generation Control (AGC) is an ancillary service that gives the ISO the ability to curtail the resource. Solar produces variability on the grid, and curtailment allows the ISO to mitigate this impact and maintain grid stability and reliability. This requires generator curtailment controls within the SCADA system that can ramp production up or down based on CAISO’s set point signal. The controls must follow specific ramp curves and/or hit specific output targets by a set specified timeframe.


What are the long term maintenance considerations for a CAISO project and associated equipment? (RIG re-certifications, CAISO  calibrations, etc.)

CAISO recommends meter testing every two years. Some asset owners prefer to test annually. Sometimes meters drift, and when they do, it’s never in favor of the project. Regular testing ensures that the meters fall within the acceptable accuracy tolerance.


There are also RIG re-certifications, which are done every three years for ISP or ECN-connective RIGs, along with general checks and/or firmware upgrades on the RIGs as needed.


What is the number one tip for asset owners looking to participate?

The biggest tip is to start early. Even though CAISO reduced the NRI window from 203 days to 84, it’s not realistic to get a plant online in three months. We recommend building enough time into the schedule to be able to hit all critical deadlines without causing any delays.


Can owners fulfill CAISO requirements in-house or should they look to hire outside support?

This process can be handled in-house, but it takes someone who not only has deep knowledge of ISO requirements, but has the capacity and wherewithal to tackle the NRI process on top of their day-to-day tasks. This doesn’t often happen. Third-party ISO consultants do this work every day and will be up-to-date with the ever-changing ISO market requirements.


Engineering Support for CAISO NRI, RIG & Metering Compliance

Nor-Cal Controls helps you comply with CAISO NRI, RIG, and metering guidelines. Through our CAISO support services, we’ll help prepare your solar facility for commercial operations, making sustainable energy easily accessible to more homes and businesses in California.


Schedule a call with us today.