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Off-Grid Franklin Battery Systems, PE Stamp

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Hawaii.

Client

Confidential (Hawaii electrical contractor)

Industry

Residential/small-site solar plus battery storage (off-grid)

Location

Hawaii.

Dates

September 2025

Team Size

1

Services

  • Electrical review of three off-grid PV plus battery design sets

  • Review of cable and string sizing calculations

  • Off-grid operation and battery-depletion review

  • PE stamp on each set

Summary

A Hawaii contractor sent MHL three off-grid PV plus battery designs built around FranklinWH aPower batteries and aGate controllers. MHL reviewed each set and the supporting calculations, raised an off-grid recharge concern, and stamped all three after the contractor revised the drawings. The work ran from September 2 to 11, 2025.

Problem / Objective

The contractor needed a Hawaii PE review and stamp on three off-grid systems. One question was how the batteries would recharge after depletion, since the GoodWe inverters are not explicitly listed for off-grid use.

Process

  1. Received three sets: 15.66, 13.05 and 6.96 kW DC arrays with one, two and three-battery stacks (13.5 to 40.5 kWh usable); two use GoodWe inverters (11.4 and 9.6 kW AC) and one uses Enphase microinverters (5.856 kW AC), all single-phase 240V.

  2. Sent common review comments for all three sets and requested the cable and string sizing calculations.

  3. Raised the battery-depletion and black-start question and recommended considering a generator.

  4. Reviewed the contractor’s calculations and agreed to two drawing notes: one setting the scope boundary at the aGate, with the downstream 100A panel by others, and one describing grid-forming operation, minimum state of charge, and black-start.

  5. Reviewed the revised sets for all three systems.

  6. Stamped and returned all three sets.

Payoff / Results (Metrics)

  • Three sets stamped in about nine days.

  • Scope boundary written into the drawings: the contract ended at the aGate, with downstream loads by others under NEC Article 220.

  • Off-grid operation, minimum reserve, and black-start behavior documented on the sheets, with generator backup noted as optional.

  • Calculation errors the contractor found in two sets were corrected before the stamp.

When this applies

A Hawaii solar or electrical contractor designing off-grid or backup PV plus battery systems (FranklinWH aPower and aGate, GoodWe or Enphase inverters) and needing a PE review and stamp. It also helps if you need to address battery depletion, black start, or the line between your scope and downstream panels.

Testimonial

Assets

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