Deploying Solar-Plus-Storage Microgrids

Solar integrators will play an important role in the evolution of the 21st-century smart electric grid via the deployment of utility-interactive solar-plus-storage microgrids.

Technology is fundamentally changing the way electricity is produced, delivered and consumed. The electric grid of the future will inevitably be more decentralized, interconnected and resilient than it is today. Arguably, nothing represents this trend better than microgrids, which operate in parallel with the local utility grid and have the potential to benefit a wide cross section of stakeholders. Utility-interactive microgrids can benefit consumers and facility owners through lower bills, improved power quality and increased reliability. They can also serve as controllable grid resources for utility operators, which is a value proposition with broad societal benefits.

In this article, we briefly explore different microgrid definitions and applications. We then focus specifically on distributed grid-interactive solar-plus-storage microgrids, as these are most relevant to solar developers, engineers and integrators. We explore the pros and cons of different solar microgrid configurations. We consider some of the system integration challenges associated with designing and installing solar microgrids. Lastly, we provide practical insight about managing customer expectations with regard to system capabilities and economic performance.

What Is a Microgrid?

Microgrids are a key pillar of the 21st-century electric grid envisioned by the Smart Grid Research and Development (Smart Grid R&D) Program, which the Office of Electricity Delivery and Energy Reliability at the US Department of Energy (DOE) administers. According to the Smart Grid R&D Multi-Year Program Plan (2010–2014) (see Resources), the program’s short-term goals call for commercially viable microgrids by 2020, as well as a self-healing distribution grid with a high penetration of distributed energy resources, demand response and plug-in electric vehicles. In 2011, the Microgrid Exchange Group, an ad hoc group of subject matter experts within the Smart Grid R&D Program, put forward the closest thing to a consensus definition of a microgrid after much discussion and scrutiny.

As defined by the Microgrid Exchange Group, which comprises people researching and deploying microgrids: “A microgrid is a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid [and] can connect and disconnect from the grid to enable it to operate in both grid-connected or island mode.” This definition is generally consistent with one developed by a working group at the International Council on Large Electric Systems (CIGRE): “Microgrids are electricity distribution systems containing loads and distributed energy resources (such as distributed generators, storage devices or controllable loads) that can be operated in a controlled, coordinated way while connected to the main power network or while islanded.”

The similarities in these definitions belie the elasticity of microgrids in practice. Microgrids vary considerably in terms of scale, complexity and loads. They can incorporate many different types and combinations of power generation and energy storage technologies, including fossil fuel generators, microturbines, fuel cells, photovoltaics, wind, small hydro, biomass, batteries, flywheels, electric vehicles, energy management systems and controlled loads. While microgrid categories and reference architectures are fluid, the following are some examples of microgrid applications or types.

Campus microgrids. Military bases and university or corporate campuses deploy this type of microgrid. The customer or facility owner owns and maintains the microgrid assets as well as the dedicated distribution system behind the meter. Though interconnected to the local utility grid, campus microgrids typically support autonomous operation to some degree, either allowing the facility to operate independently during a utility outage or supporting critical loads. For example, Black & Veatch commissioned a microgrid at its corporate headquarters in April 2015 that incorporates combined heat and power (two natural gas microturbines), variable renewable energy (150 kW of rooftop solar), distributed energy storage (100 kWh lithium-ion battery) and controllable loads (45 electric vehicle charging stations).

Community microgrid. Community microgrids are integrated into utility networks rather than located behind a customer’s meter. Though community microgrids use the same technologies as campus microgrids, the utility controls the system and the distributed energy resources are subject to utility regulation. Customers often deploy community microgrids to improve grid resiliency or support essential community services in the event of an emergency that results in widespread power outages. The utilities that Hurricane Sandy impacted are among the early adopters of community microgrids.

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