Injecting renewable energy into the distribution system

Jonathan Hawkins focused on PNM Resources’ work to integrate renewables generation with the distribution system (Sidebar 5). One motivator for this effort is New Mexico’s RPS, which requires that 1.5% of the company’s green electricity be produced by distributed generation facilities in 2011, rising to 3% by 2015.

PNM Resources currently gets most of its renewable energy from the 200-MW New Mexico Wind Energy Center, which has been operating since early 2003. The 136-turbine facility remains among the largest wind plants in the country.

New Mexico is said to have more than 300 “sunny” days a year, making PNM Resources the perfect partner for DOE in a Smart-Grid Demonstration Project that would incorporate a utility-scale battery (2 to 4 MWh) with a 500-kW solar (photovoltaic) installation.

Energy storage makes good sense, Hawkins said, because peak electric production from PV does not align with peak usage (Fig 24). Note that summertime peak demand occurs about two hours after the peak solar time. In winter, the separation between peak electric production and demand is greater. A battery allows electricity produced at the peak solar times to be used when customer demand peaks.

Based on work done thus far, Hawkins continued, simple arbitrage alone would not produce a large enough benefit stream. However, by monetizing other benefits—such as carbon reduction, deferred fuel, deferred T&D system build-out, enhanced reliability, etc—a battery might be justified financially. A battery also adds value by smoothing fluctuations in distribution voltage normally caused by intermittent sources such as PV.

Much work remains before the PV/battery system can be considered a firm, dispatchable renewable resource and achieve the stated goal of reducing peak demand by a minimum of 15%.

Areas of ongoing development work include these:

• Develop and test computer-based modeling tools capable of simulating the behavior of distributed generation and storage interconnected with the distribution system. The use of computer-based models can allow PNM to scale aspects of the project virtually to investigate other scenarios. As an example, the utility can look at the effects of larger PV installations or larger battery storage by scaling actual data.
• Optimize the intelligent control algorithms that will operate battery installations on utility grids.

Other project objectives are the following:

• Demonstrate mitigation of voltage fluctuations by the battery system.
• Quantify and refine associated performance requirements, operating practices, and cost/benefit.
• Reduce greenhouse-gas emissions through the expanded and more beneficial use of renewables.
• Extrapolate, where possible, the benefits of storage when coupled with renewables.

The DOE-funded demonstration project involves many organizations in addition to PNM Resources, including the following:

• Sandia National Laboratories: system integration and design support; testing and evaluation.
• University of New Mexico: system modeling and analysis; battery control algorithm development.
• Northern New Mexico College: data analysis.
• EPRI: Analysis and modeling using the research organization’s Intelligrid methodology. The PNM/DOE project benefits from the utility’s selection by EPRI as one of 11 worldwide hosts under its Smart Grid Demonstration Program. Under this program, PNM and EPRI are currently engineering the design and operation of commercial smart-grid systems.
• Industry vendors, such as manufacturers of batteries and PV systems.

Finally, Hawkins said that knowledge gained by PNM Resources’ personnel is being shared with the industry and the nation by participation in these programs.