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