By Alexandra Mebane of Solarplaza
The PV world can expect changes and challenges ahead related to large-scale PV grid integration. Experts in the field from California in the United States can attest to the fact that control is effectively a brand new area of technology within the United States, and presents obstacles in two primary forms.
Tom Tansy is Chairman of SunSpec Alliance, which pursues information standards to enable “plug & play” system interoperability, discussed these challenges. “One of the hurdles is having the manufacturers bring this capability online and move it through regulatory approvals, while managing their supply chain as new technology comes on board,” he said. “The second comes in terms of policy: How will manufacturers and plant owners be compensated for the additional features they will be adding to the mix?”
Within California, there are 28 electrical utilities, including three investor owned utilities (PG&E, SCE, and SDG&E) that are directly governed by California Rule 21. This regulation describes interconnection standards for distributed energy resource systems and was revised on December 18, 2014. Because there is a large and diverse staff responsible for interconnecting new systems, there will inevitably be an uneven knowledge about Rule 21 and how it should be applied to generators connected to the distribution grid on the customer side of the meter. California Rule 21 will be one of the topics to be discussed at the conference Solar Asset Management North America, this coming April.
Limitations of today’s study process
Clyde Loutan, Senior Advisor Renewables Grid Integration of CaISO, discusses the limits that determine inverter characteristics and interconnection standards. “In North America, the need for reactive power support from asynchronous resources must be identified during the interconnection process,” he said. “However, the study process cannot anticipate all operating conditions such as what resources or transmission elements will be out of service at the time reactive power needs arise.” A system impact study may reflect that there is sufficient reactive power on the transmission system because of the capabilities of existing generators with reactive power capability and other reactive power devices.
However, once an asynchronous project is interconnected and is commercially operable, actual system conditions could be far different from the conditions that had been studied. Interconnection studies are also time consuming and iterative in nature. If the CaISO were to study all possible operating conditions and outage schedules for existing resources to assess the need for an asynchronous resource to provide reactive support, the system impact study process would become unduly burdensome.
“Prior to the December 2014 amendment to California Rule 21, grid operators had no ability to react to the impact of DER resources on the customer side of the meter,” Tansy explained. “The designers of the grid did not have in mind that individuals would have power plants at their houses, at least not to the extent that such systems have been deployed. A stable grid is dependent upon having reliable known frequency and voltage levels, so when these generators are unable to adapt other than by disconnecting, as was the case previously, it can cause the grid characteristics to drift and become unstable.”
Vladimir Chadliev, Director of Global Grid Integration with First Solar, offered an opposing view. He said with the high solar PV penetration levels being installed and planned in Western U.S., the need for grid operators and transmission planners to quickly assess the impacts of solar PV system stability has become critical. In the planning phase this assessment is normally done with analysis tools such as PSS/E or PSLF. The lack of proper models for the solar PV projects had been an obstacle in performing accurate interconnection analyses and planning analysis. The Western Electricity Coordinating Council (WECC) modeling working group recently completed work on a new improved model for the utility-scale station PV plants. The new model can represent characteristics of PV plants in a more realistic way. Therefore, assessment of the penetration level for PV into the electrical grid can be more precise.
Utility adjustment and the RPS program
Experts are split when it comes to the opinion of market development and its movement. On the one hand Loutan stated, “In California, utilities are adjusting to the 33% RPS (Renewables Portfolio Standard) and in most cases are on schedule to meeting this target.” Whereas Tansy believed that while the PV market is moving quickly, it is not moving fast enough. “RPS affects deployment of all solar, including resources that are not directly owned by utilities,” he said. “The utility business model is undergoing very dramatic change. There is an existential threat that is facing many utilities because of new players coming into the market whether its distributed generation or the so called “pro-sumer” movement. Are utilities moving fast enough? They are moving pretty quickly, though maybe not fast enough for many people’s appetites.”
There are some utilities in the Western Interconnection that are adapting somewhat quickly for a high level of penetration of solar PV. They are doing their homework, and conducted an integration analysis which helps them understand the impact of high level of solar PV on its system operation. These utilities already are gaining experience and can provide guidelines for the industry.
California leadership
California has proved itself to be the present solar leader within the continental United States. While Hawaii was an early testing ground, experiencing problems on the island grid first, California is now seen by manufacturers and producers as the forerunner since the national grids operate on the same frequency and can later follow suit if California’s plan of action is successful. “In dialogues with PV producers and manufacturers that are involved with the IEEE (Institute of Electrical and Electronics Engineers) process to define regulations for smart inverters, and the UL (Underwriters Laboratory) process to define the safety testing process for smart inverters, the general consensus is to allow California to continue doing its thing and figure out the effective settings as well as how to manage them,” said Tansy.
While the PV market in the United States is multi-regional, California still controls a lot of it, for many reasons not limited to the amount of sunshine, technological innovation of Silicon Valley, and booming energy needs. “California has a diverse generating resource mix, which is comprised of over 10,000 MW of non-dispatchable resources based on installed capacity,” Loutan said. “California also has aggressive energy and environmental policies changing both the supply and demand of electricity. Distributed rooftop solar PV is also increasing rapidly in the state and real–time production from these resources are not known by the transmission operator.
Role of PV over the next decade
The role of solar in California is only going to pick up over the next ten years. “Solar PV is expected to be over 50% of the variable renewable resources in the state [of California] by the end of the coming decade,” Loutan reported. This means that on some days the variable energy production could be over 50% of the overall resources on the system. With about half of the conventional resources being displaced, at times, PV resources would have to provide voltage control and also be able to provide some level of dispatchability.” The role of solar plus storage is going to be immense, and according to Tansy, will also become mainstream over the course of a decade. “Any new construction done will automatically come with solar,” he said. “Solar will become a new building feature as it’ll be available everywhere. Solar will also be coupled with batteries, so the advantage of solar will exist even when the sun isn’t shining.”
This article was contributed by Alexandra Mebane of Solarplaza, which organizes international conferences.
Topics such as the aforementioned, among others, will be discussed in further detail at the Solar Asset Management North America Conference, held April 1-2, 2015 in San Francisco. Join other key experts in the field to learn how to better manage PV assets and portfolios, and optimize solar power plant performance.
