As use of renewable energy sources continues to escalate, we must take a realistic look at how generation from these energy sources impacts current transmission and distribution (T&D) systems.

Unlike traditional energy sources, which can be relied upon to meet the energy needs of customers 24 hours a day, seven days a week, some popular renewable energy resources — solar and wind, for example — are intermittent. Energy from the sun is obviously not available at night and may drop off quickly during cloud and storm movements. Wind fluctuates significantly with variable force and duration.

While we have a good understanding of the clean and climate-friendly aspects of these renewable energy sources, we still do not understand the impact of the volatility of these sources on T&D systems.

At Arizona Public Service (APS), we are quickly growing our renewable energy portfolio. In the next four years, the amount of renewable energy provided to customers will increase from 3% to 10%. By 2025, APS is required to produce 15% of its energy from renewables. As the use of these resources grows, so does our need to understand how renewable energy impacts the cost, reliability and quality of the energy we provide to our customers. In order to have wind and solar sources approach 10% of the overall generation mix, intermittency of energy generation must be addressed.

To this end, APS is implementing a set of strategic, targeted and integrated studies that focus on results that offer tangible and real-life benefits to customers. For example, a percentage of the renewable energy expansion taking place at APS includes a distributed energy (DE) model that locates solar panels and systems at or near the customer. Current distribution systems are designed for stable energy flowing in one direction, from the utility to the customer. With a DE model, energy travels in two directions, from the utility to customers and from customers back to the grid.

Impact of Green on Power Delivery

APS commissioned the R.W. Beck study “Distributed Renewable Energy Operating Impacts and Valuation,” which demonstrated that there is value in producing DE on the APS grid. The study also determined that DE presented an opportunity to the utility if it were able to achieve high penetration over a long term, implement smart grid technologies and develop energy-storage opportunities within the system.

From the study, APS found that DE provided different points of value. While DE could not reduce the size of T&D infrastructure, there were other benefits. For example, if large amounts of DE systems are located in close proximity to one another, and energy storage is also available nearby, APS may be able to shift or shave energy demand. In this scenario, APS also may be able to defer system upgrades or expansions.

To demonstrate the impact of renewable energy sources on the power network, APS launched the Community Power Project. This high-penetration DE demonstration project combines elements of energy storage as well as customer-side wind and solar generation. APS first announced the Community Power Project in May 2009 and began accepting online applications from customers in July 2010. Community support has been overwhelming. As of the press time, from a service area of just over 2,200 homes, more than 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. Looking at solar alone, when fully operational in 2012, APS will have approximately 200 homes with 2-kW to 4-kW solar systems producing power directly to the grid.

The Community Power Project will serve APS as a real-world laboratory where we can see the impact of a high-penetration DE on a single feeder line. The goal is to develop and evaluate ways to ensure the stable and safe operation of the grid when penetration levels of DE reach or exceed 30% of total load. The Community Power Project also includes an energy-storage demonstration project using Lithium-ion batteries. APS also will perform studies with government and university to evaluate the potential impacts of high-penetration solar deployments.

For renewable energies to be viable for utility-scale projects they need to be able to produce reliable and consistent energy. 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 traditional systems. As APS moves its portfolio to 15% of generation from renewable energy, we understand that in order 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 energy model. The work we are doing will go a long way toward this end.


Phil Smithers (Phil.Smithers@aps.com) is manager of renewable energy technical services at Arizona Public Service.