DERs are energy supplies and power sources that tend to be smaller than the typical utility-scale sources and are usually positioned closer to demand centers, frequently co-located customer sites.

Description of DER technologies

The simplest description of DER technologies is distributed renewables, generation, and storage. Renewables such as rooftop solar panels (also known as photovoltaic or PV panels) and small scale wind turbines are principle DER technologies.

Site-based generators commonly associated with data centers also fall into this category. Many of the early generators installed in data centers were diesel fuel-based. Diesel would be hauled to the site and stored. Later implementations used natural gas which didn’t require any local storage capabilities and avoided the fuel quality issues associated with long-term storage. The most sophisticated implementations have multi-fuel capabilities—gasoline, natural gas, and diesel—giving the operator the ability to overcome any interruption in two of the three possible supply chains.

Energy storage is another DER technology that covers kinetic/mechanical storage (flywheel, compressed gas, or gravitational); chemical storage (primarily battery, including electric vehicles); and thermal storage (heating or cooling). Energy storage devices have the ability to absorb power from the grid and return it later. They have the unique property of appearing like an electrical load during the charging or storage phase, and a generation source when discharging.

DER’s role in outage prevention and service restoration

The key role of DER technologies in outage prevention is included in the word, “distributed.” Predominant reasons for a power outage are transformer failures and downed power lines, so it only makes sense that a distributed resource located closer to a customer demand center is less likely to be affected by a power line fault. Also, during demand response events such as when a utility is approaching a brownout condition, distributed energy resources can be engaged to effectively reduce the overall load profile in a service area and spare the consequences of crossing the brownout threshold. Distributed energy resources also tend to be very flexible, offering split-second response times in some cases to mere minutes in others, far faster than traditional generation facilities can respond.

Illustration

The Pecan Street project near Austin, Texas ( www.pecanstreet.org) is a 700- acre demonstration area built on the site of the former Robert Mueller Municipal Airport. Developed by a consortium that includes the City of Austin, the University of Texas, Austin Energy, and a variety of corporate partners, the project features the integration of a variety of DER technologies and, as described in a recent PBS NewsHour feature, the residents of Pecan Street have not experienced a power outage in more than four years.