The current PIRP does not include solar resources, but in general will facilitate participants of new desirable clean resources that introduce a new set of challenges. SCE is working with the CAISO to formulate protocols and data-acquisition system requirements, and to forecast methods for solar PV resources, just as SCE has done with the wind PIRP. The end goal — the Solar PV Program — will provide SCE with operational control of a utility-owned solar-generating resource, integrated and delivering clean power to the CAISO-operated grid.

SCE's distribution engineers will help the program study four key areas:

• Dependability and availability of generation from the SPVP

• Effects of increased amounts of solar PV on distribution circuits

• Reaction of SPVP generating facilities to grid disturbances

• Reaction of the grid to SPVP generating facilities' disturbances.

With this information, SCE and all system owners and/or operators interested in maximizing the participation and contribution of PV power can leverage SCE's findings and optimize the value and, ultimately, the success of this key emerging resource.

At the time of this writing, one critical SPVP element remained: SCE is expecting a final decision by the CPUC on its SPVP application in June or July 2009. If the CPUC's proposed decision is an indicator of key elements in the final decision, then one possible outcome would be approval of 160 MW of utility-owned PV generation and the remaining 90 MW installed and operated by independent power producers.

Acknowledgements

The authors wish to extend their appreciation to First Solar, ProLogis, Satcon and Gregg Electric for their contributions to meeting SCE's accelerated timeline constructing Site 1 in Fontana.

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Deanne Nelsen (Deanne.Nelsen@sce.com) is a project manager in SCE's generation business unit. Her work encompasses consideration and development support for new clean and green resource technologies. Most recently, she was a member of the first Solar Photovoltaic Program team. Nelsen's utility industry experience includes participating in the start-up of the California Independent System Operator and resource planning positions at Nevada Power Co. (Las Vegas, Nevada, U.S.). Nelsen has a BSME degree from the University of Utah and an MBA from California State Polytechnic University (Pomona, California, U.S.). She is a certified project management professional.

Rudy Perez (Rudy.Perez@sce.com) is the program manager for SCE's Solar Photovoltaic Program. Previously, he was distributed generation development manager for SCE, responsible for small generation integration into the grid. He also has been heavily involved in implementing innovative power-generation efficiency and reliability improvement projects. Perez holds MBA and BSCE degrees from the University of Notre Dame (Notre Dame, Indiana, U.S.). He has co-authored several papers related to power plant engineering.

Darell Holmes (Darell.Holmes@sce.com) has 19 years experience as a utility engineer developing generation, transmission and distribution infrastructure. His experience includes working in transmission planning, resource planning and generation planning departments. Currently, he is responsible for the electrical design and interconnection contracts for SCE's Solar Photovoltaic Program and developing other renewable generation projects. Holmes has degrees in electrical engineering, specializing in power engineering and law.

Mark Nelson (Mark.Nelson@sce.com) is director of generation planning and strategy for SCE, with management responsibilities for the project development division. He has held a variety of positions at SCE and other Edison International subsidiaries, ranging from planning engineer to director of retail energy operations. Prior to joining Edison International, Nelson was in management at MidAmerican Energy (Des Moines, Iowa, U.S.) and then a consultant to Midwest Solar Inc. Nelson has a bachelor's degree in economics with a chemical engineering emphasis and a master's degree in econometrics with an electricity demand analysis emphasis, both from Iowa State University (Ames, Iowa). He is an author of energy-related books.

SPVP Integration with SCE's Distribution Grid

Southern California Edison (SCE; Rosemead, California, U.S.) expects two basic interconnection designs will accommodate most all interconnection scenarios for its Solar Photovoltaic Program's (SPVP's) interconnection with the distribution grid.

The first design uses the existing 277/480-V system as the connection point. The single-line diagram illustrates this approach. Using the existing transformer located on the customer's property is the simplest interconnection. Interconnection facilities include a new line from the existing transformer to a new utility panel housing a meter and a disconnect switch. The utility panel also functions as an interconnection point to connect the output wire lead from the solar PV generation facilities into a utility electrical panel. SCE's preferred interconnection includes a visible disconnect switch, so utility workers can readily identify where to manually isolate solar PV generation from the rest of the electrical grid.

Some customer locations may lack a suitable transformer for low-voltage connection. In these instances, a medium-voltage connection to the distribution system circuit will be used. This slightly more complex interconnection uses a new transformer and padmounted switch. The interconnection facilities consist of wiring from the existing transformer to a new padmounted electrical switch. From there, a cable connects the padmounted switch to the new transformer. The remaining facilities are similar to the simpler interconnection.

The two figures illustrate the range of interconnection options SCE expects to use in the SPVP. All SPVP plants will be interconnected as wholesale facilities, which are not net metered (with building load).

SCE expects SPVP generation to easily integrate into the distribution grid by using built-in inverter protection schemes. Existing inverters offer sufficient protection schemes for most anticipated interconnections. These schemes include overvoltage and undervoltage, and frequency safeguards, as well as an anti-island protection scheme to prevent the inverter from feeding power to the grid in the event of a utility outage.

At some point, SCE may face new grid complications if generation stations become aggregated into a small distribution area. If this occurs, SCE expects that additional protection schema may be required to facilitate grid operations, which will be designed on a case-by-case basis.