Microgrid Battery Dispatch Project

This project designs a battery dispatch policy for a small microgrid. The goal is to produce a defensible engineering deliverable: operating requirements, critical-load assumptions, state-of-charge limits, islanded dispatch calculation, recharge plan, control rules, and validation evidence.

The project is not a generic battery sizing exercise. It asks whether a battery can preserve a defined microgrid service during a grid outage while still allowing limited grid-connected operation. A good answer explains when the battery may discharge, when it must hold reserve, how it recovers after an event, and how operators prove that the dispatch worked.

Project Objective

Design a dispatch policy for a battery energy storage system serving a campus microgrid with onsite photovoltaic generation. The final report should answer:

1. Which loads are critical during islanded operation?
2. How much battery energy can be used without violating reserve?
3. What dispatch sequence preserves voltage, frequency, SOC margin, and recovery capability?
4. How much economic dispatch is allowed during normal grid-connected operation?
5. How long does recharge take after an outage event?
6. Which tests prove that the dispatch policy is valid?

The deliverable is a microgrid battery dispatch report, not a procurement specification. It should be detailed enough for a design review, controls review, or student project submission.

Baseline Scenario

Use the following baseline scenario or replace it with measured site data.

A campus microgrid includes:

• a 3.0\ \text{MW} battery inverter;
• a battery with 10.0\ \text{MWh} current usable DC energy capacity;
• onsite photovoltaic generation connected inside the microgrid boundary;
• critical building, control, communication, and process loads;
• switchgear and protection capable of intentional islanding;
• a microgrid controller that can curtail PV, shed noncritical load, and command the battery.

Battery assumptions:

Parameter	Value
Current usable DC capacity	10.0\ \text{MWh}
Initial SOC before forecast outage	90\%
Minimum SOC	15\%
Protected restart and black-start reserve	1.0\ \text{MWh}
Discharge-path efficiency	94\%
Charge-path efficiency	96\%
Inverter continuous rating	3.0\ \text{MW}
Grid recharge power limit	1.5\ \text{MW}

These values are simplified. A real project should use current state-of-health capacity, vendor limits, thermal derating, protection studies, grid-code constraints, and site-specific load profiles.

Step 1: Define Operating Modes

The dispatch policy must distinguish operating modes:

Mode	Battery role	Main constraint
Grid-connected normal	peak shaving, PV smoothing, demand response	preserve resilience reserve
Forecast outage watch	raise or hold SOC	prepare for islanding
Islanded operation	supply net critical load and stabilize the island	avoid reserve breach
Recovery	recharge and restore normal reserve	avoid creating a new peak or overload
Maintenance or degraded mode	reduce service commitments	reflect unavailable equipment

Do not let grid-connected economics consume energy required for resilience. A microgrid that is profitable during normal days but empty during the outage has failed its engineering objective.

Step 2: Define Critical-Load Blocks

For the baseline project, evaluate an 8\ \text{h} islanded event using three load blocks.

Block	Duration	Critical load	Expected PV inside island	Battery AC discharge
1	2\ \text{h}	1.10\ \text{MW}	0.10\ \text{MW}	1.00\ \text{MW}
2	3\ \text{h}	1.30\ \text{MW}	0.45\ \text{MW}	0.85\ \text{MW}
3	3\ \text{h}	1.00\ \text{MW}	0.65\ \text{MW}	0.35\ \text{MW}

The battery AC discharge is the critical load minus PV contribution. If PV output falls below forecast, the controller must either increase battery discharge, start another source, or shed load.

Step 3: Establish Protected Energy

Initial stored energy:

Minimum SOC energy:

Protected stored energy:

Stored energy available before protected reserve:

The dispatch calculation must consume less than 6.5\ \text{MWh} of stored energy if the restart reserve is to remain protected.

Step 4: Calculate Islanded Dispatch

For each block, delivered battery AC energy is:

Stored energy consumed is:

Block 1

Remaining stored energy:

Block 2

Remaining stored energy:

Block 3

Remaining stored energy:

Final reserve margin:

The baseline islanded dispatch is feasible with about 0.54\ \text{MWh} of stored-energy margin above the protected reserve.

Step 5: Check Power Rating

The maximum scheduled battery discharge is 1.00\ \text{MW} in Block 1. The continuous inverter rating is 3.0\ \text{MW}, so the steady active-power requirement is within rating.

This does not finish the power check. The project should also review:

• motor starting and transformer inrush;
• reactive power during voltage control;
• apparent power limit when active and reactive power are both required;
• inverter current limits during faults;
• low-SOC and high-temperature derating;
• grid-forming control stability during load steps.

If the microgrid requires 1.00\ \text{MW} active power and 0.60\ \text{MVAr} reactive support at the same time, apparent power is:

This is still below the 3.0\ \text{MW} class rating if the inverter has sufficient apparent-power capability, but the actual equipment rating must be checked in MVA, not only MW.

Step 6: Define the Dispatch Rule

A practical dispatch rule for this project is:

1. During normal grid-connected operation, do not discharge below the resilience floor.
2. During forecast outage watch, charge to at least 90\% SOC unless thermal or warranty limits prevent it.
3. During islanded operation, serve critical-load tiers in priority order.
4. Curtail PV before overcharging the battery or violating voltage limits.
5. Shed noncritical load before consuming protected restart reserve.
6. If SOC falls within 0.3\ \text{MWh} of protected reserve, enter emergency load-shed mode.
7. After grid return, recharge to the required resilience SOC before resuming economic dispatch.

The resilience floor for a forecast event should include the expected islanded dispatch requirement plus protected reserve. For the baseline event:

At a current capacity basis of 10.0\ \text{MWh}, this corresponds to:

Only energy above this floor should be available for routine economic dispatch when this outage scenario is active.

Step 7: Check Grid-Connected Economic Dispatch

If the battery starts a normal day at 90\% SOC and the outage watch floor is 84.6\%, then the stored energy available for economic dispatch is:

This is small. The result is intentional: when a severe outage forecast is active, resilience has priority over peak shaving or arbitrage.

If no outage watch is active, the project may define a lower grid-connected reserve floor. The report must state who has authority to switch reserve modes and how the system prevents accidental depletion before a known disturbance.

Step 8: Plan Recharge After the Event

After the islanded event, stored energy is 3.04\ \text{MWh}. To restore 90\% SOC:

With 1.5\ \text{MW} AC recharge power and 96\% charge-path efficiency:

Minimum recharge time:

The recharge plan should avoid creating a new demand peak, violating transformer limits, or charging during a period when another outage is likely. If PV is available after the event, the controller can reduce grid import while still restoring SOC.

Step 9: Evaluate Sensitivity

The final margin is only 0.54\ \text{MWh}, so sensitivity matters.

Useful stress cases include:

Stress case	Engineering concern
PV output 25 percent below forecast	Battery may consume additional reserve.
Critical load 10 percent higher	Load classification may be incomplete.
Battery capacity 8 percent below assumed value	State-of-health estimate may be optimistic.
Discharge efficiency 2 percentage points lower	Losses may erase reserve margin.
Block 2 lasts one extra hour	Outage duration may exceed design basis.
One inverter cooling path degraded	Power capability may be thermally limited.

For example, if Block 2 lasts one extra hour at 0.85\ \text{MW} battery discharge:

The reserve margin becomes:

The original dispatch would breach protected reserve. The project should therefore define a load-shed or source-start trigger before the margin is consumed.

Step 10: Define Control and Protection Checks

The project should not assume that energy balance alone proves microgrid readiness. Include checks for:

• point of common coupling opening and closing logic;
• grid-forming inverter mode;
• voltage and frequency regulation;
• relay and breaker settings in grid-connected and islanded modes;
• fault current behavior under inverter-limited operation;
• battery management alarms and shutdown states;
• emergency stop and fire response;
• communication loss between controller, inverter, meters, and switchgear;
• resynchronization permissives before reconnecting to the utility.

The dispatch policy should state what happens if the central controller fails. Local protection and safe shutdown should not depend on a single supervisory software channel.

Validation Test Plan

A practical validation plan should include:

Test	Acceptance evidence
Grid-connected dispatch limit	SOC does not fall below the active resilience floor.
Planned islanding	Microgrid separates without unacceptable voltage or frequency excursion.
Load-step response	Battery and PV stabilize the island after a critical-load change.
PV curtailment	Controller prevents overcharge and voltage violation under high PV output.
Reserve protection	Final SOC remains above protected reserve after the test profile.
Recharge recovery	Battery returns to required readiness within the specified time.
Communication loss	Local controls preserve a safe operating state.
Resynchronization	Reconnection occurs only when voltage, frequency, phase, and protection conditions are acceptable.

A paper dispatch table is not sufficient. The microgrid must prove the transition, control response, reserve policy, and recovery behavior with measured data.

Final Deliverable

The final project report should include:

1. one-line boundary and operating modes;
2. critical-load list and load-priority table;
3. PV or onsite-generation profile used in the dispatch;
4. battery current capacity basis and SOC limits;
5. protected reserve definition;
6. islanded dispatch table with stored-energy balance;
7. power and apparent-power checks;
8. economic-dispatch limit during grid-connected operation;
9. recharge plan after the event;
10. sensitivity cases and load-shed triggers;
11. validation test plan;
12. clear statement of whether the baseline design passes the defined objective.

For the baseline scenario, the design passes the 8\ \text{h} islanded energy check with limited margin. The project should therefore recommend conservative operating triggers: enter outage watch early, prevent routine discharge below 84.6\% SOC during the forecast scenario, validate PV assumptions, and define automatic load shedding before protected reserve is consumed.

Common Mistakes

A common mistake is treating the battery as spare energy that can be used for every objective. In a microgrid, the same stored energy may be claimed for peak shaving, demand response, backup, black start, and frequency support. The dispatch policy must decide which claim has priority.

Another mistake is checking average load instead of event sequence. Islanded operation fails at specific moments: a motor start, cloud transient, controller fault, protection trip, or unexpectedly long outage. The project should check the event that matters, not only daily energy.

A deeper mistake is not planning recovery. A battery that survives the first outage but cannot recharge before the next credible event may leave the site exposed. Resilience includes readiness, islanded operation, and restoration.

Microgrid battery dispatch is successful when the system can deliver the critical service, preserve reserve, operate within electrical and thermal limits, recover for the next event, and prove each of those claims with recorded evidence.