The proliferation of renewable power generation presents the world with both opportunities and challenges. For example, in the best of times, surging energy demand is being met by renewable energy sources, while, in challenging times, the momentary imbalances commonly associated with these resources are a threat that may cause capacity shortages, frequency variations, and outages. Energy experts around the world are innovating new technologies to allow us to define how we can effectively generate and consume always-on power in a decentralized grid.

Today, the grid is the primary source of power for most businesses and is largely reliant on nonrenewable sources. Emerging microgrid solutions provide the ability to toggle seamlessly between primary power sources (the grid) and secondary or tertiary sources, including renewable sources of energy. A microgrid is a self-sufficient energy system that provides power to a specific site or building, often using one or more kinds of distributed energy, including solar panels, wind turbines, and generators.

An increased focus on reducing carbon to net zero has data center operators looking at all sources of carbon. One option that has become more appealing is adopting a microgrid as an always-on energy source that contributes to the day-to-day energy supply, such as fuel cells, solar power, and battery energy storage. When always-on assets are coordinated with traditional backup power generation, the combination can provide the necessary backup and optimize energy use.

Batteries are the best-known type of energy storage technology, but there are many different types of batteries with distinctive technical specifications suitable for various applications.

For mission critical microgrid applications, battery energy storage systems (BESS) using lithium-ion (Li-ion) batteries are well-suited for managing hybrid energy sources. This article explores how BESS can help enable always-on power solutions for a microgrid and allow mission critical facilities to have an independent power source.

The fundamentals of BESS and controls

A BESS is typically composed of battery cells arranged in modules and connected into strings to achieve the desired DC voltage. The collected DC outputs from those strings are routed to a bi-directional inverter known as a power conversion system (PCS). The PCS converts the power to AC and then routes it through transformers and switchgear, where it can be used by the grid. Although many types of energy storage are undergoing development to improve efficiency and reduce cost, batteries continue to experience the most significant decline in costs. Electric vehicles (EVs) utilize the same battery cells as stationary battery systems, and the proliferation of EVs is driving down the cost of those batteries. Cost reduction coupled with excessive demand charges in some regions creates an ideal environment to implement both standalone energy storage and BESS integration in a microgrid. Controls are another crucial component, as they decide where the energy is sourced from as well as when and how much energy is needed to ensure success

Microgrid BESS applications

In some case, incorporating a BESS into a microgrid provides benefits that can be combined for what is known as “value stacking.” This is possible when two or more strategies are leveraged at the same site. These applications are typically implemented by a microgrid controller. A few examples are outlined below.

  • Peak demand reduction — Utilities often have demand-reduction programs that incentivize facilities to reduce electricity consumption during peak periods. In critical power environments, it’s not practical nor possible to participate in these types of programs unless power can be supplemented from another source, such as through a microgrid. Peak demand periods typically last around four hours, which is well-suited to the capacity offered by a BESS. A BESS can be charged slowly during periods of low demand and low time of use (ToU) rates and then discharged during peak demand periods to provide all power to the facility, avoiding the use of grid power. When combined in the context of a microgrid, peak demand reduction can be done without using other fossil-fuel burning microgrid assets, such as diesel generators.
  • Renewable energy firming — One commonly understood application of BESS strategies involves coupling with a solar photovoltaic installation to smooth out the intermittent fluctuations of solar production. This application can help prevent the need for utility curtailment of solar production and allow harvesting of more solar generation that might otherwise be wasted during the ramp-up and ramp-down phases, which are caused by production fluctuations.
  • Spinning reserve — For microgrids that still rely on multiple generators to serve the load, that load will ultimately fluctuate, so the generators are typically sized in increments to serve various stages of load need. If the overall load is low, the first stage of generator capacity kicks in. When additional power is needed, the second stage of generator capacity will activate. One issue with this strategy is that gas generators have a preferred efficiency window to optimize efficiency and fuel consumption. This optimal window is usually around 40%, so if an additional generator is cycling on and off, it reduces efficiency, consumes more fuel, produces more emissions, and adds stress to the generator. By combining a BESS with the generator, it can serve the additional marginal load before activating another generator and ensures the generators are kept within their optimal efficiency windows. The BESS can also tighten up the soft response of a gas generator.

Always-on power is emerging as the future of power for mission critical facilities, and equipment providers are piloting microgrid hybrid systems. These consist of fuel cells that can generate energy, have grid-interactive capabilities, and utilize a BESS controller, which allows for real-time or on-site control.