Sunrises on Rooftops

In the Doney Park area of Flagstaff, Arizona Public Service (APS) is transforming rooftops into what in essence will be an interconnected renewable power plant.

Unlike any other utility program, the APS Community Power Project is testing a high concentration of distributed solar power on a single distribution feeder (Sanvig 4) by installing photovoltaic (PV) systems on the rooftops of approximately 200 customers. Instead of supplementing the energy use of each home, the rooftop installations serve as mini-power plants by sending energy generated directly to the grid.

The pilot program is both a response to customer desire for access to solar energy and APS’s need to further understand the impact of a high concentration of solar power on the current distribution system. In addition to the 200 customer installations, the Community Power Project includes 500 kW of centralized solar and 400 kW of non-residential solar at an elementary school. When fully implemented, the project will deliver a total of 1.5 MW of power, with the Sandvig 4 feeder receiving more than 30 percent of its power from renewable energies.

Working with solar installers, APS developed a model that puts the up-front cost of solar installations on the utility. APS owns, operates and receives the energy from the solar panels. The customer grants a rooftop easement to APS and in return receives the Community Power rate, a fixed rate for 20 years. This creates stable electricity rates for the equivalent portion of their bill for participating customers. APS contracts with local solar installers to design implement and maintain the systems at no cost to the customer.

APS announced the Community Power Project in May 2009 and began taking applications from customers in July 2010. As of the print deadline, from a service area of just over 2,200 homes, 295 residential applications had been received, 90 customers were being reviewed and 52 systems (or 190 kW) had been installed. That is almost one-third of the project’s generation goal in just over six months. All systems will be installed by the end of the third quarter 2011. At that time, APS will begin to evaluate the system’s impact.

APS engineers will use the project as a real-world laboratory for a series of integrated studies. These studies will examine the effects of a high concentration of solar on the electric grid, energy storage opportunities, PV variability and intermittency, costs associated with the high penetration of solar power and the impact of solar water heating. It is the first fully integrated look at the impact that a high concentration of distributed solar generation will have on the reliability, operations and maintenance of utility energy production. APS additionally hopes to learn what the overall impact of this type of energy production could be and more about potential additive value for the utility distribution system.

Current distribution systems are traditionally designed for stable energy flow in one direction, from the utility to the customer. With a distributed energy (DE) model, energy travels in two directions, from the utility to customers and from customers back to the grid. In addition, there’s significant concern about how the intermittency of solar generation might impact system design and operations.

This study will provide real data and allow APS to expand on the findings of the 2009 Distributed Energy Valuation Study. In that work APS found that DE may provide some value to the utility: While DE cannot reduce the size of energy distribution infrastructure, it may be able shift or shave energy demand when used in dense amounts and in conjunction with energy storage.

The demand for the use of renewable energy sources from customers and regulators requires the utility industry to fully understand the impact that these forms of energy have on the electrical systems. It is understood that to be truly integrated into the current system a complex combination of technology, tools and creative business models must be developed to support the new energymodel. Through the Community Power Project, APS is taking a valuable step forward to advance the deployment of distributed renewable energy for an entire industry.

Pat Dinkel is Vice President, Power Marketing Resource Planning and Acquisition, Arizona Public Service.

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