Southern California Edison is Leading California's Charge to meet the nation's most ambitious renewable portfolio standard (RPS) targets: 20% by 2010 and even higher in years ahead. To satisfy these aggressive targets, Southern California Edison (SCE; Rosemead, California, U.S.) has taken the initiative to add a planned 250 MW of new photovoltaic (PV) resources to its system.

While PV is a recognized and well-understood renewable resource, its development and deployment on a massive scale is an emerging and evolving practice. Another challenge is the cost of PV. Through SCE's PV program, costs could be driven down to reach US$3.50/W.

The first 2.44-MW installation of the initiative has been built and is currently providing virtually greenhouse-gas-free power to the grid. The experience and knowledge gained from this installation will help accelerate the commercial viability of PV, a critical component to the green goals of SCE, the state of California and the U.S.


SCE's completed 2.44-MW Fontana rooftop project is the first of many 1-MW to 2-MW systems that, in aggregate, will comprise SCE's proposed Solar Photovoltaic Program (SPVP). SCE is seeking approval from the California Public Utilities Commission (CPUC) to build and own 250 MW of PV, installed in the sunny eastern area of SCE's service territory, primarily in 1-MW to 2-MW systems, on top of huge warehouse rooftops. If the opportunity were to arise, SCE would consider constructing PV on rooftops that could accommodate systems larger than 2 MW, or even on a few ground-mounted systems.

The renewable-resource generating units in SCE's SPVP will be close to customer load centers and connected directly to the utility's distribution grid, thereby avoiding the extra cost (capital facilities and electrical losses) of delivering remote green power to load centers. The Fontana site is one of three pilot projects SCE is building in advance of the CPUC's final decision on the full program.

In selecting sites, SCE looks for roofs that are less than five years old and greater than 300,000 sq ft (27,871 sq m) on buildings that have little on-site load and are owned by a company or real estate trust, preferably with a portfolio of candidate buildings.

From a grid standpoint, the location must be served by a primary distribution circuit with the electrical characteristics to receive the PV-generated power.

The Fontana project site fit these criteria. The host building's rooftop is 600,000 sq ft (55,742 sq m), has little on-site load and is owned by ProLogis, one of the world's largest owners and developers of warehouse and industrial space. ProLogis served as general contractor during the construction of the Fontana PV unit on this building.

The PV array was designed and engineered by First Solar Inc. (Tempe, Arizona, U.S.). The array uses First Solar's FS 272 modules — cadmium telluride (cad-tel) thin-film products. The equipment used to convert the PV array's DC output to AC for delivery to the grid was designed and built by Satcon Technology Corp. (Boston, Massachusetts, U.S.). The project used four of Satcon's 500-kW Generation II inverters. The aggregate 2-MW (AC) output is stepped up to 12.4-kV primary distribution voltage through SCE's standard distribution switchgear and transformer.

ProLogis applied for construction permits with the local permitting authority. However, no permitting fees were required for the Fontana site, because the permitting authority had zoned this area to encourage construction of renewable green power. Approval by the local fire authorities was a bit more challenging, as PV is a relatively new technology to them, and PV safety coordination procedures with the utility and PV labeling standards had not been definitively specified. In the end, satisfactory solutions were negotiated with the permitting and fire authorities.

Gregg Electric Inc. (Ontario, California) performed the construction under a participating labor agreement with the International Brotherhood of Electrical Workers Local 47. Construction of the 2.44-MW unit took 60 days to complete.

The facility was commissioned on Dec. 1, 2008, by California Gov. Arnold Schwarzenegger and Ted Craver, chairman and CEO of SCE's parent company, Edison International.


To date, SCE has learned valuable lessons in the key areas pertaining to efficient project execution: building structure, permitting, and PV panel racking and wind loading issues.

Building selection is a critical issue that can derail an installation plan. For example, SCE found that buildings can appear to be excellent candidates and comply with previous building codes, but are not amenable to the utility's rooftop PV arrays. This type of problem was discovered when SCE and First Solar were in the panel-layout stage for another site in the pilot project.

The building chosen was slightly older than the target age of five years or younger. It met the construction regulations for the time it was built, but construction regulations had changed since then. The building did not include as large of a roof-weight safety factor as more current codes require. By the time it was discovered the roof could not hold the weight of the PV array, in addition to withstanding wind and earthquake loading, much time had been spent negotiating lease terms and developing the system design. In response, SCE now has a pre-screening process in place to filter out buildings that look like good candidates but are not strong enough for a PV facility.

Permitting on the Fontana site, initiated by ProLogis, had gone smoothly until the end of construction. The local fire department was concerned about first-responder safety in the event of an emergency at the site. At the time, there were no comprehensive standards for labeling conduit, combiner boxes and inverters. The California State Fire Marshall's office published a draft PV installation guideline on the Internet.

SCE found that the guideline provided some suggestions for residential and small commercial PV installations; however, very large facilities, such as the Fontana site, were not fully addressed. SCE came to an agreement with the local fire department regarding the signage the department wanted to have on the PV hardware. Once the type and number of signs needed were negotiated, SCE had the signs made and installed. After that, SCE and ProLogis were able to get the sign-off on the construction permit and commission the unit.

From this experience, SCE learned to identify the localities that encourage green power construction and the importance of working with them early on in the permitting process.

Transforming the PV Market

SCE's objective in requesting approval from the CPUC for this program is to transform the PV market by initiating a program that is large enough to lower the costs of PV component parts and installation. SCE also plans to develop a larger-trained PV installation workforce in Southern California. Both of these objectives will benefit not only SCE customers but also the people of California. SCE will have more green-collar jobs for people who will install PV generators of fossil-fuel-free renewable power.

SCE sees these very large warehouses with little on-site load as an under-utilized resource for PV installations. The California Solar Initiative, also known as the Million Solar Roofs program, provides rebates to customers who install less than 1-MW PV arrays on the roofs of their homes or businesses. The generation from these residential or small commercial PV facilities serves the electrical load of the host building, with any extra generation going to the utility grid.

SPVP proposes to build primarily 1-MW to 2-MW PV generating units on rooftops of huge warehouses that do not use enough electricity to justify installing a PV array. The warehouse owner will lease the rooftop space to SCE, gaining a revenue source previously unavailable.

SCE has identified large commercial warehouses in Southern California's Inland Empire with maximum rated wind speeds in the range of 80 mph to 105 mph (129 kmph to 169 kmph). SCE's first installation used First Solar's nonpenetrating racking system. No penetrations were made in the roof; instead, ballast (brick pavers) was used to weigh the system down, thereby reducing the potential for any roof leaks. SCE is evaluating both penetrating and nonpenetrating systems for future installations. As SCE considers buildings in the higher wind zones, penetrations may be needed to make sure the PV array does not overload the roof. When needed, these penetrations need to be designed to be reliable, leak-proof and accessible for inspection.

Next Steps to a Greener Grid

SCE's SPVP will contribute 0.5% to its RPS goals by 2014, if and when all 250 MW have been built. PV is currently and projected to be a relatively small contributor to RPS goals nationwide because of the high capital cost. In order for PV to make a more significant impact on RPS goals, the PV industry needs to become more cost competitive with other types of renewable generation. SCE's SPVP will help drive PV costs down, thereby helping to accelerate the commercial viability of PV and enable many more individuals and business to install their own PV generating units.

SCE is currently the only California Independent System Operator (CAISO) participant scheduling rooftop solar PV resources into the CAISO electric grid. SCE is very aware of the challenge solar-generated electricity creates. Solar PV resources of more than 1 MW must schedule power with the CAISO and will likely participate in the CAISO's Participating Intermittent Resource Program (PIRP).

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.


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.

Deanne Nelsen ( 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 ( 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 ( 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 ( 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.