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North America / Island & remote community

Alcatraz Island Microgrid

Current status, energy mix, organizations, suppliers, equipment, controls, reported specifications, and project updates—with source-level citations.

CoverageDetailed public record
Named organizations6
System facts35
Sources reviewed11
Evidence reviewed2026-07-20

Alcatraz Island's National Park Service power system is an off-grid solar-battery-diesel microgrid commissioned in 2012 to replace diesel-only service. The as-built record identifies 305 kW of SunPower PV, a 1.9 MWh East Penn gel lead-acid battery, eight Princeton Power 100 kW bidirectional inverters, two 250 kW MTU diesel generators, and Princeton controls. DOE reports approximately 400,000 kWh of annual savings and a roughly 75% reduction in diesel delivered to the island after installation, while later NREL analysis found that generator-led battery charging was still curtailing PV and raising fuel and battery costs.

Research status
The microgrid remains an active NPS/NLR optimization project, but its lifecycle has included material failures. A federal procurement account says the battery system failed and was replaced in late 2018, and an October 2019 energy-management failure left the two diesel generators supplying all power until repairs. NLR's page, updated 23 April 2026, says NLR was working with NPS and Princeton Power to implement and measure a revised load-following strategy. Public sources reviewed do not establish when that implementation finished or disclose current component availability, so uninterrupted full-hybrid operation should not be assumed.
Historical classification
Island
Reported capacity
See component specifications
Coordinates
37.82698, -122.42296
Evidence note: “Every company” cannot be proven from public material alone. This page lists every organization found in the recovered record and reviewed sources, preserves unknown roles, and explicitly marks undisclosed controller or equipment details.
Report missing evidenceResearch methodology

Project delivery

Who was involved in Alcatraz Island Microgrid?

6 publicly identified organizations. Where a recovered source named a participant without explaining its work, the role remains explicitly unspecified.

Organization

Alcatraz Island Services

NPS concession contractor that maintained the island electrical system and, according to the federal repair justification, replaced the failed battery system in late 2018. [10][11]

Organization

Hal Hays Construction

Installation contractor; work began in October 2011. NLR also identifies Hal Hayes Construction as a project partner. [9][7]

Organization

National Laboratory of the Rockies (formerly National Renewable Energy Laboratory)

Analyzed microgrid dispatch with REopt and was working with NPS and Princeton Power on implementation and measurement of a load-following control strategy. [7]

Organization

National Park Service

Federal site owner and operator responsible for Alcatraz Island and its off-grid electrical service. [5][6][7]

Organization

Princeton Power Systems

Supplier of the eight power-conversion units and site energy-management/controller platform; later implementation partner for revised dispatch controls. [9][7][10]

Organization

U.S. Department of Energy Federal Energy Management Program

ARRA-era project funder/supporting federal program and publisher of the official capacity, cost, completion, and savings record. [5]

System evidence

Energy mix, capacity, and specifications

Values can describe different project phases, generation sources, storage systems, or other components. Source citations are attached to each figure so discrepancies remain visible.

KW Solar
400 [1]
Storage
1400/1900 kW/kWh [1]
Verified solar PV rating
305 kW [3]
PV module count
959 panels [4]
Typical island demand
Approximately 70–80 kW [4]
Reported annual electricity production
Approximately 400,000 kWh [3]
Reported diesel reduction
Approximately 75% [3][4]
As-built solar PV capacity
305 kW from 959 SunPower 318 W modules; an NREL O&M case study later rounded the system to 308 kW [5][6][9][8]
As-built battery rating
Approximately 1,900 kWh at 480 V, arranged as two parallel strings of 240 cells; NREL's later O&M case study reports 1,920 kWh [9][8]
Battery operating window in the as-built account
40%-80% state of charge [9]
Diesel generation
Two 250 kW generator sets [9]
Typical site load
Approximately 70-80 kW [6]
Project cost and completion
$8.5 million; completed in 2012, with the technical account recording first operation on 15 February 2012 [5][9]
DOE-reported annual benefit
Approximately 400,000 kWh saved and 337,000 kg of greenhouse-gas emissions avoided per year [5]
Energy mix outcome
PV, battery storage, and diesel; DOE says diesel volume transported to the island fell approximately 75% after the system was installed, but no verified current annual renewable-energy percentage is published [5][7]

Controls and hardware

Equipment and controller details

Manufacturer and model are shown only when a source names them. Generic descriptions are not converted into guessed product assignments.

01

Microgrid controller

Princeton Power Systems — PPS Site Controller

Coordinates solar, battery, and diesel resources and starts diesel generation when renewable energy and stored energy cannot meet load. [2][4]

02

Bidirectional inverters

Princeton Power Systems — GTIB-100

The archived manufacturer case study identifies eight 100 kW-class power-conversion units; the federal page does not restate the model count. [2]

03

Battery storage

Model not publicly disclosed

Lead-acid battery bank. The reviewed sources do not disclose a battery manufacturer or cell model. [1][4]

04

PV modules

SunPower — E19/318

959 modules totaling approximately 305 kW on the Cellhouse roof. [9][6]

05

PV mounting

SunLink

Roof-mounting system used for the Cellhouse array. [9]

06

Bidirectional inverters

Princeton Power Systems — GTIB 480-100 kW

Eight 100 kW units: four interfacing the PV array and four interfacing the battery. The modular arrangement allowed individual units to be taken offline while the system continued at reduced capacity. [9][10]

07

Original battery bank

East Penn Manufacturing — 2AVR125-33 IL Gel

480 gel VRLA lead-acid cells in two 240-cell strings, approximately 480 V and 1.9 MWh. The manufacturer/model of the late-2018 replacement was not disclosed in the sources reviewed. [9][10]

08

Diesel generator sets

MTU / Valley Power Systems

Two 250 kW generator sets supplied by Valley Power Systems using MTU equipment. [9]

09

Energy-management system

Princeton Power Systems

Site controller/EMOS coordinated PV, battery, and diesel dispatch. The federal repair account identifies the EMOS and battery-management system as repair and retuning scope after the 2019 failure. [9][10][7]

Technical record

Architecture, performance, and project updates

Concise technical facts, milestones, operating results, and later developments. Dated notes distinguish historical design claims from current evidence.

  • Storage

    Lead Acid Battery Bank [1]

  • Dispatch sequence

    The controller prioritizes photovoltaic production, then battery energy, and calls diesel generation when those resources cannot support island load. [4]

  • Source reconciliation

    DOE reports a verified 305 kW array, while the recovered directory listed 400 kW; both values are preserved with provenance instead of silently selecting one. [3][1]

  • Disclosure gap

    Public federal sources do not identify the PV-module, battery-cell, diesel-genset, switchgear, or communications-network model numbers. [3][4]

  • Dispatch architecture

    NPS describes PV serving the load first, batteries covering the next increment, and diesel starting last; excess PV and excess diesel generation can charge the batteries. The island has no mainland utility connection. [6]

  • Commissioning issues

    The 2012 technical account reports an August 2012 battery-string ground fault and an inverter component failure attributed to condensation. Firmware was being tuned roughly every six weeks during early commissioning. [9]

  • O&M planning

    After a March 2016 site tour, NREL estimated an ideal annual O&M budget of $90,000-$100,000, including monitoring, three battery-test visits, and two PV-cleaning visits. It recorded planning assumptions of eight years for battery replacement, ten years for inverters, and seven years for the battery-management system; these were planning intervals, not verified replacement dates. [8]

  • 2018-2019 lifecycle failures

    A federal sole-source repair justification, available through a procurement mirror, says the battery system failed and was replaced in late 2018. It also says an October 2019 failure required removing the system from EMOS control, leaving two generators to supply all island power while repairs were arranged. [10]

  • Dispatch optimization finding

    REopt found that cycle-charging the battery from diesel left too little capacity to absorb midday PV. A load-following strategy was projected to cut PV curtailment from about 30% to 4%, halve fuel consumption and cost by about 15,000 gallons per year, and save approximately $115,000 annually in diesel and battery wear; these are modeled opportunities, not measured realized savings. [7]

  • Contract-oversight update

    A 2023 DOI Inspector General evaluation found that NPS could not consistently support required biannual rooftop-array inspections or weekly PV production reports under its concession contracts. This is an oversight and documentation finding, not proof that those activities never occurred. [11]

  • Evidence gap

    No reviewed source discloses the 2018 replacement battery manufacturer, chemistry, model, or present energy capacity; the completion date and measured benefit of the control change described by NLR in April 2026 are also not yet public. [10][7]

Provenance

11 sources

Primary owner, government, university, supplier, and engineering sources are preferred. Archived references preserve claims whose original pages moved or disappeared.

  1. [1]
    Recovered Microgrid Projects record

    Internet Archive · Archived source · captured 2020-11-30

  2. [2]
    Read More

    princetonpower.com · Archived source · captured 2020-11-30

  3. [3]
    Alcatraz Island

    U.S. Department of Energy Federal Energy Management Program · Primary source

  4. [4]
    Sustainable Alcatraz

    National Park Service · Primary source

  5. [5]
    Alcatraz Island

    U.S. Department of Energy Federal Energy Management Program · Primary source

  6. [6]
    Sustainable Alcatraz

    National Park Service · Primary source

  7. [7]
  8. [8]
  9. [9]
    Under the Sun: The Alcatraz Microgrid

    PHOTON International · Secondary research

  10. [10]
    Repair Electrical System on Alcatraz Island — Justification and Approval

    GovTribe federal procurement mirror · Secondary research

  11. [11]

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