SolarToolsHow This Tool Works
The Microgrid Sizing Calculator designs a complete solar + battery + generator microgrid for commercial facilities, community buildings, or off-grid operations. Microgrids combine multiple energy sources — solar PV, battery storage, and backup generation — to provide reliable power independent of or in parallel with the utility grid. This calculator sizes each component and estimates total cost and resilience.
Microgrids are increasingly popular for: critical facilities (hospitals, data centers, emergency shelters), remote operations (mining, telecommunications, agricultural), community resilience hubs, and commercial buildings seeking energy independence. Note: the federal ITC expired Dec 31, 2025 for residential. Commercial Section 48E credit may still apply through 2027 for third-party-owned systems.
The calculator's resilience score shows how well your microgrid handles grid outages. A score of 80+ means the system can ride through most outages automatically. Below 40 means the system provides basic backup but won't maintain full operations during extended outages.
- Daily energy load — facility's daily kWh consumption. From your utility bill or sub-metering.
- Peak load (kW) — maximum simultaneous demand. From your demand meter or electrical engineer.
- Peak sun hours — annual average for your location. Use worst-month for resilience design.
- Required autonomy — hours the battery must cover without solar or generator. 24 hours = 1 full day.
- Grid reliability — percentage of time the grid is up. 95% = 18 days/year down. 99% = 3.6 days/year.
- Generator cost — diesel/propane backup generator installed cost. Enter 0 if no generator.
- Diesel fuel price — local diesel price per gallon.
- Generator run hours/year — expected annual runtime for gaps solar/battery can't cover.
The solar fraction shows what percentage of annual energy comes from solar. Above 70% is excellent for a microgrid. The remainder comes from the grid (when available), battery, or generator.
When to Use This Calculator
Microgrid architecture
A microgrid typically has four components: (1) Solar PV — primary energy source, produces during daylight. (2) Battery storage — stores excess solar for nighttime and covers short outages instantly. (3) Backup generator — covers extended cloudy periods when battery is depleted. (4) Microgrid controller — manages all sources, automatically switches between grid/island mode, optimizes for cost and resilience.
Sizing philosophy: resilience vs cost
Microgrid sizing is a tradeoff between resilience and cost. More solar + battery = higher resilience but higher cost. The calculator uses a balanced approach: solar sized for daily load, battery sized for 24-hour autonomy (configurable), and generator for extended gaps. For critical facilities (hospitals), increase autonomy to 72+ hours. For cost-optimized systems, reduce to 4–8 hours and rely more on the generator.
The generator's role
In a well-designed microgrid, the generator runs rarely — only during extended cloudy periods (2+ days) when the battery is depleted. Annual runtime is typically 50–500 hours. The generator provides insurance: it's cheaper to run a $15,000 generator 200 hours/year than to size the battery for 5-day outages (which would cost $200,000+). The calculator estimates fuel costs based on expected runtime.
Grid-tied vs island mode
Grid-tied microgrids can export excess solar to the grid (revenue) and import when needed. Island mode (off-grid) requires larger battery and generator capacity. Most commercial microgrids are grid-tied with island capability — they normally operate grid-connected but disconnect and self-supply during outages. This provides the best economics and resilience.
Microgrid controller intelligence
The microgrid controller is the brain — it monitors all sources, predicts solar production, manages battery state of charge, and decides when to start the generator. Modern controllers use weather forecasting to pre-charge the battery before storms and load-shed non-critical loads during extended outages. Controller cost: $10,000–$50,000 for commercial systems.
Commercial ITC and MACRS
Commercial microgrids qualify for: (1) Note: the residential ITC expired Dec 31, 2025. Commercial Section 48E credit may apply through 2027 for third-party-owned systems. (2) MACRS accelerated depreciation (5-year) on the full system. Combined, these can reduce effective cost by 50–60%. A $200,000 microgrid might net-cost $90,000 after incentives.
Frequently Asked Questions
Typically $150,000-$500,000 for a small commercial facility (500 kWh/day load). Solar is $1.50-3.00/W, battery is $400-600/kWh, generator is $10,000-30,000, controller is $10,000-50,000. Note: the residential ITC expired Dec 31, 2025. Commercial Section 48E credit may apply through 2027 for third-party-owned systems. MACRS depreciation (5-year) still applies to commercial installations.
A microgrid adds a backup generator and intelligent controller, and can operate in 'island mode' (disconnected from the grid) during outages. A simple solar+battery system shuts down when the grid goes down (anti-islanding). Microgrids provide true energy independence and resilience.
For 24-hour autonomy on a 500 kWh/day load: ~650 kWh of battery (500 kWh usable at 80% DoD). For 72-hour autonomy: ~1,900 kWh. Battery cost at $500/kWh: $325,000 (24h) to $950,000 (72h). A generator ($15,000) covering extended outages is usually cheaper than 72-hour battery capacity.
Yes, but it's expensive. Off-grid requires larger solar (sized for worst-month production), larger battery (3+ days autonomy), and significant generator runtime. Most commercial microgrids stay grid-connected for economics but have island-mode capability for resilience. True off-grid is for remote locations where grid connection is unavailable or prohibitively expensive.
LFP batteries in commercial microgrid applications last 10-15 years or 4,000-6,000 cycles, whichever comes first. At one full cycle per day, that's 11-16 years. Battery replacement at year 12-15 costs $150-300/kWh (projected future prices). Note: the federal ITC expired Dec 31, 2025. Check if your state offers battery rebates.
Typically 7-12 years, depending on electricity rates, grid reliability, and incentives. A $200,000 microgrid (net $90,000 after ITC + MACRS) saving $15,000/year on energy + $10,000/year on demand charges + $20,000/year in outage cost avoidance pays back in ~2.5 years. Without outage avoidance value, payback is 6-8 years.
Further Reading
Deep-dive articles and guides related to this calculator.