As owners of enormous amounts of warehouse space, electrical distributors may take special interest in last month's announcement that warehousing giant ProLogis, Denver, Colo., had signed new leases with Southern California Edison to let the electric utility install PV systems on 4.8 million square feet of its warehouse roof space.

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. Southern California Edison (SCE), the largest electric utility in California, is installing the PV panels 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 industrial buildings. SCE incurs the installation costs and leases rooftop space from building owners.

According to information on the company's website, in June the utility obtained approval to cover 65 million square feet (roughly 2.33 square miles) of unused Southern California commercial rooftops with 250MW of the latest photovoltaic technology — enough generating capacity to meet the needs of 160,000-plus homes.

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.

While California has taken the early lead in the utilization of vacant warehouse space for PV arrays and has a strong backer in Governor Arnold Schwarzenegger, 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 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 from NJRCEV that will lock in lower utility rates.