As owners of enormous amounts of warehouse space, electrical distributors may take special interest in the announcement earlier this year that warehousing giant ProLogis, Denver, Colo., had signed new leases with Southern California Edison (SCE) to let the electric utility install photovoltaic (PV) systems on 4.8 million square feet of rooftops at its warehouses.

The announcement highlighted the growing demand for rooftop space for solar projects in the Golden State and is the second phase of 100MW-worth of PV installations that SCE, the largest electric utility in California, is installing on ProLogis properties. The solar arrays are part of SCE's plans to develop the nation's largest installation of photovoltaic power generation modules to occupy unused rooftop space on commercial and industrial buildings. SCE incurs the installation costs and leases rooftop space from building owners. In June, the utility obtained approval to cover 65 million square feet (roughly 2.33 square miles) of unused Southern California commercial and industrial rooftops with 250MW of the latest photovoltaic technology — enough generating capacity to meet the needs of 160,000-plus homes. SCE's solar program is expected to create the equivalent of approximately 1,200 full time jobs per year.

ProLogis, a real estate investment trust (REIT) and one of the world's largest owners of warehouses, has more than 450 million square feet (approximately 16 square miles) of roof space worldwide available for photovoltaic installations and now has solar projects installed or under construction on 41 buildings throughout France, Germany, Japan, Spain and the United States, totaling 50 MW of generating capacity. The company leases its industrial facilities to more than 4,400 customers, including manufacturers, retailers, transportation companies, third-party logistics providers and other enterprises with large-scale distribution needs.

California has taken the early lead in the utilization of vacant warehouse rooftops for PV arrays and has a strong backer in Governor Arnold Schwarzenegger. He said in a speech at the SolarPower 2008 Conference held in San Diego that when he is flying by helicopter over the Golden State, he looks at all the unused rooftops of commercial and industrial buildings and sees enormous potential for the growth of the solar industry in his state.

USA Today recently reported that Arizona, New Jersey, New Mexico and North Carolina also offer financial incentives for these systems. Other notable rooftop arrays in the planning stages or currently installed on warehouses include an 870kW array on the 300,000-square-foot General Motors Service and Parts Operations facility in Fontana, Calif., that will provide about half of the electricity needed to run the facility and will feed enough extra electricity back to the grid to power over 300 California homes for a year; and an 8,500-panel installation that Porsche has installed at one of its facilities in Germany that's expected to produce approximately 2 million kilowatt hours a year — enough to power about 500 homes.

An 870kW New Jersey installation is also being developed by Uni-Solar, Rochester Hills, Mich., for New Jersey Resources Clean Energy Ventures (NJRCEV), Wall, N.J. This project is unique in because NJRCEV is leasing more than 300,000 square feet of roof space from Adler Partners, Edison, N.J., a commercial warehouse owner for 20 years. Building tenants will be offered a Power Purchase Agreement (PPA) from NJRCEV that will lock in lower utility rates.

Just last month, SCE announced that a solar power plant it has constructed on top of a 436,000-square-foot facility in Rialto, Calif., owned by an affiliate of AMB Property Corp. is now online and providing clean generation to Inland Empire customers. Power from the 16,300 advanced solar panels installed on the Rialto warehouse is connected directly to the utility's nearest neighborhood circuit and is fed to local customers.

“Completing this project with Southern California Edison has allowed us to maximize benefits and minimize exposure by working with an experienced utility that shares our commitment to renewable energy in one of AMB's core markets,” said Aaron Binkley, AMB's director of Sustainability, in an SCE press statement. “This project will become a model for future solar opportunities that allow AMB to benefit our shareholders and the environment.”

The utility completed similar installations in Fontana and Chino during the past two years. The three solar plants have a combined peak generating capacity of 4 million watts, or enough power to serve 2,600 average homes. Ten additional solar plants will be constructed in the Ontario, Calif., area and are expected online by the end of the year. These 13 Inland Empire solar installations are creating approximately 500 temporary construction jobs.

On a smaller scale, Duke Energy has several distributed generation projects underway in North Carolina utilizing the same concept. The company said it's producing electricity at numerous “micro-generating sites rather than at a large, centralized, traditional power plant,” and that by 2011, its distributed solar program will be generating up to 10MW of electricity annually. Its first installations use 19,288 solar panels to provide power to hundreds of homes throughout the state.

While some of the first rooftop “solar landlords” are REITs and office property owners, the concept would seem viable for many businesses, particularly those companies with hundreds of thousands of square feet of prime solar real estate on top of their warehouses — like electrical distributors.