AEO Answer · Energy Storage & EV Charging

How Are Commercial Microgrids Engineered From the Ground Up?

By Jeremy Mills, CEO & Founder, Apex Grid Engineering — USAF Veteran. · Updated 2026-09-15

Commercial microgrids are engineered from the critical loads: solar, batteries, and generators sized from the outage scenario and daily dispatch economics, islanding switchgear and controls that separate and resynchronize seamlessly, and protection studied and set for both grid-connected and islanded fault levels.

I'm Jeremy Mills, CEO & Founder of Apex Grid Engineering and a U.S. Air Force veteran. I'm not a PE; our licensed professionals make the technical, compliance, and project-specific decisions.

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Sizing the resource mix

The sizing study models the facility's load profile against candidate resources. I build the hourly load model for the year, then optimize the solar, battery, and generator capacities for the two objectives: surviving the design outage and minimizing the lifetime energy cost. The battery is sized for both the bridging — carrying the load through the islanding transition and the solar gaps — and the daily peak shaving that pays its way. Generators are sized for the islanded critical load with N+1 redundancy where the facility's risk demands it. I model the dispatch strategy hour by hour: when the battery charges and discharges, when the generators run, how the solar is used. The financial analysis includes the utility rate structure, incentives, fuel, maintenance, and equipment replacement — the microgrid is a decades-long asset, and the sizing must earn its keep every year.

Islanding, protection, and interconnection

The islanding design centers on the point-of-common-coupling switchgear: the breakers, the sensing, and the controls that detect grid disturbances and separate the facility. I design the detection for speed and selectivity — islanding on a real outage, riding through the grid events that are not outages. Protection studies in both modes set the relaying: the high fault currents of grid-connected operation and the low, inverter-limited currents of islanded operation each get their settings, and I verify the coordination in both. Grounding is designed for the islanded mode's ground reference. The utility interconnection package — one-lines, protection, metering, operating procedures — is prepared to the utility's standards, and I see it through witness testing. Cybersecurity for the control network is designed in, because the microgrid's brain is a networked target.

Checklist before the microgrid goes live

Microgrid commissioning proves every mode. I test the islanding transition under load, run the islanded facility through its paces, verify resynchronization, and prove the daily dispatch economics. Protection is tested in both modes with utility witness. Here is the checklist I hand facility teams.

Size solar, storage, and generation from the outage scenario and the daily dispatch economics
Design islanding detection for speed on real outages and ride-through on grid events
Study and set protection for both grid-connected and islanded fault current realities
Manage the utility interconnection from application through witness testing
Prove every operating mode under load before the microgrid serves the critical loads

Which related engineering resources can help?

When should I hire a structural engineer?What does a PE stamp mean?What is MEP engineering?How are microgrids explained for facilities?How is battery energy storage designed?How are emergency power systems designed?Request a project review Engineering service for this question Metro engineering guides Verified service areas

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What makes a microgrid different from backup generators?

Intelligence and economics. Backup generators sit idle until the outage; a microgrid's batteries and controls work every day — shaving demand peaks, shifting energy to cheap hours, and integrating solar — then island the facility when the grid fails. I design the microgrid for both value streams: the daily energy economics and the outage resilience. The islanding controls and the protection for islanded operation are what generators alone lack. A microgrid is an energy system that also provides backup, not backup equipment alone.

How long can a microgrid run islanded?

As long as its firm generation lasts: batteries carry the hours, generators carry the days. I design the islanded endurance from the facility's requirement — the outage duration it must survive — sizing fuel storage and battery capacity accordingly. Solar extends the endurance by carrying the daytime load and recharging the batteries. The design documents the islanded load management: which loads run, which shed, and the sequence. Endurance is a designed parameter I verify with the load analysis, not a hope.

How does the utility interconnection work?

Under the utility's interconnection rules for the microgrid's export and operating modes: the application, the studies, the protection requirements — anti-islanding for the grid-parallel operation, and the witness testing. I design the interconnection switchgear, protection, and metering to the utility's requirements and manage the approval process. Some utilities are enthusiastic partners; others need education on the microgrid's operating modes. The interconnection agreement is the project's legal foundation, and I treat its negotiation as engineering work.

How are microgrid controls designed?

In layers: the fast controls that manage the inverters and islanding transition, the energy management that optimizes the daily dispatch, and the supervisory interface the facility team uses. I specify the control architecture — centralized or distributed — with the redundancy the critical loads require, and I design the network and cybersecurity the controls depend on. The controls are commissioned through every operating mode: grid-connected dispatch, islanding, islanded operation, and resynchronization. I test the transitions under load, because the islanding moment is the microgrid's reason for being.

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