Integrating renewable resources such as solar photovoltaic (PV) onto the grid can create challenges for system operators. Fortunately, energy storage technologies have been identified as a potential resource to help operators deal with their intermittent nature.

The Public Service of New Mexico (PNM) is addressing this issue as part of a smart grid demonstration project it is conducting with the Electric Power Research Institute (EPRI) and the U.S. Department of Energy’s (DOE’s) smart grid energy storage program with two related projects. First, PNM is demonstrating a system that uses energy stored in batteries to mitigate voltage fluctuations through battery smoothing and manage peak demand through battery shifting simultaneously. Second, PNM is collaborating on a demonstration of a commercial building micro-grid designed and built by the Japanese government’s New Energy and Industrial Technology Development Organization (NEDO).

Energy from solar PV systems can introduce challenges on the distribution system when a high level is integrated into the grid. Smoothing PV output is important because the ramp rates can be very fast. Ramp rates on PNM’s 500-kW PV installation have been recorded as fast as 135 kW/sec. This can cause unacceptable voltage variation on an associated feeder.

Also, because peak production from the PV system does not align with the times when energy is needed most on the system, energy storage can be used to shift PV energy to meet the system peak. This includes firming, which is the ability to guarantee constant power output to the electricity market during a certain period of time, and peak shaving, which is the ability to limit the load on a given feeder.

Major System Components

PNM draft graphic

Combined with the 500-kW PV installation, PNM’s energy storage system is comprised of Ecoult/East Penn Manufacturing Synergy advanced lead-acid batteries with an energy rating of 1 MWh for shifting and UltraBattery advanced lead-acid batteries with embedded ultracapacitors and a power rating of 500 kW for smoothing. The UltraBattery is built for quick response, operating at a high discharge and charge rate.

A data acquisition system had to be developed to record data and provide control signals for the project. The requirements included the capability of receiving and transmitting data from multiple sensors and control systems on site with sample rates of at least 1 second. Working with one of the project partners, Sandia National Laboratories, PNM installed phasor measurement units (PMUs) to obtain a very high sample rate of 30 samples/sec — granular data for characterizing the two components.

Cybersecurity also is addressed in a defense-in-depth approach, providing firewall, authentication, access management and auditing capabilities for access attempts to the site. Interoperability was facilitated by up-front use-case analysis using EPRI’s IntelliGrid methodology and adhering to standards identified through the Smart Grid Interoperability Panel (SGIP).

The commercial building micro-grid combines multiple customer-side generation technologies, storage technologies and an advanced energy management system (EMS) to create a self-optimizing building that can island for short periods of time. The generating resources include 50 kW of PV, a 240-kW natural gas generator and an 80-kW phosphoric-acid fuel cell. Energy storage resources include 150-kWh advanced lead-acid batteries, and thermal storage from heat recovery from the fuel cell and natural gas generator using water tanks. The water can be used to heat the building or used in conjunction with an absorption chiller to provide cooling. The building micro-EMS provides real-time control and optimization of building resources and provides schedule optimization.