Community Resilience Hub Microgrid Sizing Calculator

Why Community Resilience Hubs Need Tailored Microgrid Planning

Public libraries, recreation centers, and congregational halls are increasingly tapped as resilience hubs—spaces where neighbors can charge devices, receive medical support, and shelter during heat waves or winter storms. Unlike typical commercial buildings, these facilities serve as lifelines when municipal services are stressed. They must power refrigeration for medication, provide Wi-Fi for emergency updates, run HVAC systems to maintain safe temperatures, and keep essential lighting and security equipment active. Traditional backup generator calculators ignore the interplay between solar, storage, and load shedding that makes community resilience hubs so effective. This calculator bridges that gap by combining critical load estimates with solar production, battery behavior, and fuel logistics.

The model is intentionally transparent. Rather than presenting a single yes-or-no answer, it highlights how each asset contributes to outage coverage and where gaps remain. Facility managers can adjust load flexibility assumptions, tinker with solar size, and see whether fuel deliveries must be staged for week-long outages. The tool also surfaces lifecycle costs, helping grant writers quantify the annualized expense of resilience relative to the value of service provided to the community.

How the Microgrid Coverage Model Operates

The simulation begins by converting the facility’s critical load into an outage energy requirement. Critical load in kilowatts multiplied by the target outage duration produces kilowatt-hours. Load shedding reduces the total by the percentage entered, representing thermostatic setbacks, reduced lighting, or relocating nonessential equipment. Mathematically, the outage energy demand is , where $P$ is the critical load in kilowatts, $t$ is target outage hours, and $f$ is the fraction of load that can be shed. For cross-checking, you can compare the result to your typical daily energy use; if daily critical energy exceeds the outage calculation, the calculator flags the larger value to avoid unrealistic optimism.

Solar contribution is derived from the array size, capacity factor, and usable sunlight hours. Capacity factor translates the DC nameplate into average hourly output, while sunlight hours represent the window during which solar power aligns with the building’s occupied schedule. The tool estimates total kilowatt-hours produced during the outage and caps the value at the critical load to avoid overstating midday surplus. Battery support comes next: the storage bank’s usable capacity multiplies by round-trip efficiency to determine net discharge energy. The calculator also checks whether the inverter and battery discharge ratings can cover the critical load; if not, it signals that power electronics upgrades are required.

Generators provide the final layer of defense. Fuel on hand divided by hourly burn rate yields run hours, which multiply by generator power to determine kilowatt-hours available. If the generator is oversized relative to load, the calculator still respects fuel limits. Any shortfall after solar, batteries, and generators is reported in both energy and hours so teams can decide whether to procure additional mobile batteries, secure fuel contracts, or lengthen outages they are willing to tolerate.

Worked Example: 72-Hour Heat Dome Response

Consider a resilience hub that must support 85 kW of diversified load for three days. Load shedding strategies—shifting laundry to daytime and consolidating cooling zones—trim 15% of demand, resulting in an effective 72.25 kW critical load. Over 72 hours, that equates to 5,202 kWh of energy. The hub already consumes about 1,900 kWh per day during normal operations, so planners know the outage calculation is in the right ballpark. A 150 kW solar canopy operating at an 18% capacity factor generates roughly 648 kWh per day, or 1,944 kWh over three days. Because much of that output aligns with a 4.8-hour daylight window, solar covers a significant portion of daytime load and trickle charges the battery.

The battery bank stores 600 kWh, of which 85% is usable. Applying 92% round-trip efficiency leaves 469 kWh of discharge energy. That covers 6.5 hours of critical load on its own. A 120 kW generator burning 8 gallons per hour with 600 gallons of diesel can run for 75 hours, delivering 9,000 kWh—well above the remaining need. Because the generator’s output exceeds the post-solar, post-battery shortfall, fuel reserves are more than adequate. The calculator reports total supported hours of 72.0, meaning the hub meets its coverage target with modest slack. It also reveals that extending coverage to 96 hours would require either another 270 kWh of batteries or an additional 320 gallons of diesel at the current load profile.

Scenario Comparison Table

The following table shows how different asset mixes impact outage coverage. Use it as inspiration for board presentations or grant proposals. The numbers are illustrative rather than tied to your inputs.

Scenario	Solar (kW)	Battery (kWh)	Generator Fuel (gallons)	Supported Hours
Minimal Generator Only	0	0	600	58
Balanced Hybrid	150	600	600	72
Extended Islanded Hub	240	1,200	800	104

The table underscores how batteries stretch fuel supplies and how solar reduces both generator runtime and indoor air quality concerns. By presenting multiple configurations, planners can align resiliency goals with community expectations and funding realities.

Cost Modeling and Limitations

Capital costs are estimated using the unit costs you provide. Solar cost per kilowatt and battery cost per kilowatt-hour combine with generator purchase and transfer switch expenses to create a baseline investment. The calculator applies a capital recovery factor to spread that cost over the analysis horizon, then divides by expected outage hours to produce a levelized resilience cost—essentially the dollars spent per kilowatt-hour delivered during emergencies. Fuel expenses are prorated by the ratio of expected outage hours to the modeled event. If your community expects one major outage per year, set expected outage hours equal to the target outage duration. If smaller outages are common, use the historical annual duration so the model scales fuel use appropriately.

Like any planning tool, this calculator simplifies reality. It assumes solar output remains consistent with historical capacity factors, even though storms often dim sunlight. To account for cloudy conditions, you can reduce the capacity factor or increase the target outage duration to introduce a buffer. Battery degradation and generator maintenance are not explicitly modeled; consider pairing this tool with the Battery Second-Life Capacity Calculator to account for aging packs, or explore failure risks using the Microgrid Islanding Failure Risk Calculator. The model also assumes fuel deliveries are unavailable during the outage. If you have guaranteed resupply agreements, you can lower the stored fuel input to reflect just-in-time logistics.

Using the Results in Community Planning

Present the output to stakeholders as a blend of technical readiness and budget impact. Sustainability coordinators can highlight avoided generator runtime thanks to solar and batteries, while emergency managers focus on supported hours and remaining gaps. Share the levelized resilience cost with finance committees to compare the investment against alternate strategies such as temporary mobile generators or mutual aid agreements. Integrating the results into grant applications demonstrates due diligence and helps justify funding for inclusive resilience hubs that serve frontline communities.

Finally, treat the calculator as a living document. Update inputs after energy audits, post-storm lessons learned, or changes in occupancy. Cross reference normal operations using the Grid-Interactive Building Demand Flex Savings Calculator and revisit demand flexibility strategies with the Residential Demand Charge Mitigation Calculator. With consistent updates, your community resilience hub will stay ready for whatever the grid throws its way.