Residential Microgrid FAQ

A residential microgrid is a locally controlled electrical system that integrates on-site generation (solar PV, generators), energy storage (lithium battery banks), and intelligent power management hardware (microgrid controller, automatic transfer switch) to supply all loads at a property continuously — whether the utility grid is available or not. The defining characteristics are: coordinated multi-source control (not just co-located equipment), island mode capability (fully autonomous operation), and whole-home load coverage (every circuit in the main panel, not a critical sub-panel).

Island mode is the operating state in which the microgrid runs entirely from on-site resources — batteries, solar, generator — with no utility grid connection. The automatic transfer switch (ATS) opens the utility connection, isolating the property's electrical system. In this state, the microgrid controller manages all energy sources to sustain home loads. Transition to island mode takes <16ms in battery-first systems (sub-cycle speed — most electronics don't detect it). The system exits island mode automatically when the utility grid is restored.

A generator is a single power source: it runs on fuel, takes 10–30 seconds to reach operating speed (creating a gap in power), and operates continuously regardless of actual load. A microgrid uses batteries for instant-on backup — eliminating the startup gap — and activates the generator only when battery state of charge drops below a threshold. The generator in a microgrid runs on-demand rather than continuously, typically reducing fuel consumption by 60–80% versus generator-only operation during extended outages.

The Tesla Powerwall 3 is a 13.5 kWh, 11.5 kW consumer battery product designed to back up a critical load sub-panel — typically one refrigerator, select lights, and a few outlets. It has no generator integration, no dedicated microgrid controller, and cannot sustain a large home's full electrical load. A residential microgrid is custom-engineered to the property: battery capacity is sized to the full load profile (40–200+ kWh for estates), a dedicated controller manages multiple energy sources, and generator integration provides indefinite runtime.

Yes, when generator-backed. Battery capacity sets the pure-battery window (typically 3–8 hours for estates). When the battery reaches its minimum state of charge threshold, the microgrid controller activates the generator, which sustains all home loads and simultaneously recharges the battery. With adequate fuel storage (500–1,000 gallon propane tank typical), the system runs for weeks without manual intervention. Solar generation further reduces generator runtime during daylight hours.

Sizing starts with a load analysis: we measure or estimate peak demand (kW), average running load (kW), and daily energy consumption (kWh) for the property. Battery capacity is sized to (Average Load × Target Autonomy Hours) ÷ Depth of Discharge. Generator sizing must sustain average load AND recharge the battery simultaneously — typically 150–200% of average load. Solar is sized to meet target annual offset. The entire system is validated against seasonal load variation and worst-case weather scenarios for the property's location.

We specify Lithium Iron Phosphate (LFP) as our standard chemistry for residential estate applications. LFP offers 3,000–6,000+ cycle life (vs. 1,500–2,500 for NMC), significantly better thermal stability (critical for outdoor enclosures in coastal and high-temperature environments), and a 10–15+ year service life at rated capacity. The tradeoff is lower energy density — LFP requires more physical space per kWh than NMC. For properties where longevity and safety are non-negotiable (which describes most estates), LFP is the correct choice.

Day 1–3: Battery provides instant failover and buffers between solar charging cycles. Generator activates when SOC drops to threshold (typically 20–30%), runs 4–6 hours to recharge, shuts off. Solar provides daytime generation. Days 4–14: Same automated cycle continues without manual intervention. Remote monitoring shows system status in real time — owners who have evacuated can verify the property is operating. The only variable is fuel supply. A 1,000-gallon propane tank at the described duty cycle lasts 14–21 days. Fuel delivery can extend runtime indefinitely.

Yes, in most cases. A battery retrofit adds storage, a microgrid controller, and an automatic transfer switch around existing solar infrastructure. The integration method depends on the existing solar inverter: AC-coupling preserves the existing inverter by connecting the battery on the AC side; DC-coupling is more efficient but may require inverter replacement. Grid-tie-only inverters (which shut down during outages for anti-islanding compliance) require either a relay or inverter replacement to enable island mode. We evaluate existing equipment during the site assessment.

T+0: Utility voltage drops below ATS threshold (typically <80% nominal or frequency deviation). T+<16ms: ATS opens utility relay — the home is now on battery. T+<1 second: Inverter confirms island mode, all home loads sustained from battery bank. T+minutes–hours: If outage continues, battery SOC declines at the rate of (Load kW ÷ Battery kWh). Controller monitors SOC continuously. At threshold (20–30% SOC): auto-start signal sent to generator. T+10–30 seconds: Generator reaches operating speed, controller syncs generator to island microgrid, begins sustaining loads and recharging battery. Owner typically sees nothing — no flicker, no alarm, no interruption.

Prime Microgrid serves properties throughout the 48 contiguous United States. Alaska and Hawaii are not currently served. System requirements vary by climate, utility, jurisdiction, equipment, and property goals.

Grid-tied microgrid systems with solar can participate in utility net metering: excess solar generation is exported to the grid in exchange for bill credits. Eligibility and credit rates vary by utility and state. We manage the utility interconnection agreement and net metering application as part of the project.

N+1 redundancy means installing one more component than the minimum required — so any single failure does not cause a system outage. In microgrid terms: two generators where one would suffice, two battery strings where one covers the load, or dual inverter configurations. N+1 is standard practice in data center and hospital power infrastructure. For residential estates, it is appropriate for properties where continuous power is non-negotiable regardless of cost — remote estates with long service response times, properties with medical equipment, and owners with no acceptable downtime.