Solar Lighthouse Calculator

Enter your lamp wattage, latitude, and foggy day count — get solar panel array, 10-day battery autonomy, marine equipment cost, and comparison to grid extension.

Lighthouse specifications

Lighthouse type?

LED lamp wattage?

Location latitude?

° N

Foggy/overcast days per year?

days/yr

Maritime solar system (24/7 critical operation)

1,000W array + 1,001 Ah battery (10-day autonomy)

Total load (lamp + aux)70 W continuous

Daily energy required1.68 kWh/day (24/7)

Winter design PSH2.3 hrs/day (worst case)

Solar array size1,000 W (winter + fog sized)

Battery bank (10-day autonomy)1,001 Ah @ 24V (16.8 kWh)

Marine equipment premium1.35x (corrosion-rated)

Total system cost (installed)$21,209

Grid extension alternative$150,000+ (often infeasible)

Diesel genset alternative cost$215/yr ongoing

Annual maintenance (marine)$636/yr

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How to Use This Calculator

Select lighthouse type and lamp wattage

Start with the lighthouse type, which sets the auxiliary load (monitoring equipment, communications, controls) and the marine equipment premium. Then enter the LED lamp wattage — modern LED conversions of lighthouse beacons range from 20-50W for small shore buoys to 150-500W for large historic lighthouses with powerful optic systems. If your conversion specs aren't available, use 100W as a reasonable starting point for a mid-size active beacon.

Set latitude and foggy days

Latitude is the single most important input for lighthouse solar design. Unlike terrestrial installations that can be sized on annual average sun, lighthouse systems must be sized for worst-case winter conditions at high latitudes. A lighthouse at 58°N (southern Alaska) receives only 2-3 peak sun hours per day in December — requiring a much larger panel array than the same load in Florida. Foggy days directly reduce panel output to approximately 40% of clear-day production; coastal locations often have 60-120 foggy days annually.

Read the results

The calculator sizes your solar array for worst-case winter + foggy conditions, batteries for 10-day autonomy (the USCG standard for critical aids to navigation), and shows total system cost with the marine-rated equipment premium. The comparison to grid extension shows why solar is often the only practical choice for offshore and remote lighthouse locations.

The Formula

Total Load = Lamp Watts + Auxiliary Equipment Watts Daily Wh = Total Load × 24 hours (continuous operation) Winter PSH = Annual PSH × 0.55 (worst-case design) Cloud Factor = 1 - (Foggy Days ÷ 365) × 0.60 Panel Watts = Daily Wh ÷ (Winter PSH × Cloud Factor × 0.80) Battery Ah (24V) = Total Load × 24 hrs × 10 days ÷ (24V × 0.70 DoD)

The 10-day battery autonomy follows USCG guidance for critical aids to navigation — lights that ships depend on for safe passage require enough storage to maintain operation through extended cloudy or storm periods. The conservative 70% depth-of-discharge (vs 80% for non-critical applications) further extends battery life and ensures reliable recharge even with degraded panel output in winter. The marine equipment premium reflects corrosion-resistant mounting hardware, marine-grade wiring, IP67+ enclosures, and anti-UV coatings.

Example

Cape Cod shore beacon — Active navigation aid, Massachusetts coast

A 100W LED beacon on the Cape Cod shore (latitude 42°N) with 45 foggy days per year. The Coast Guard needs 10-day battery autonomy and marine-grade equipment throughout.

TypeActive small shore beacon

LED lamp100W

Latitude42°N (Cape Cod)

Foggy days45 days/yr

Result

Total load120W (100W lamp + 20W aux)

Daily energy2.88 kWh/day (24/7)

Winter PSH2.3 hrs/day (worst case)

Solar array~550W panel array

Battery bank (10-day)~770 Ah @ 24V (18.5 kWh)

System cost (marine-rated)~$38,000

Grid extension alternative$150,000+ (offshore cable)

Diesel genset (annual)~$3,680/yr ongoing fuel + maintenance

Solar is the clear choice for this Cape Cod beacon. Grid extension to an offshore or remote site would cost $150,000 or more — solar at $38,000 saves over $112,000 upfront. The diesel alternative incurs $3,680 per year in fuel and servicing costs indefinitely, plus the logistics of regular fuel delivery to a remote coastal location. The 10-day battery autonomy ensures the light maintains operation even through Cape Cod's famously stormy nor'easters.

FAQ

Why do lighthouses need 10-day battery autonomy? ▼

The USCG's design standard for critical aids to navigation requires sufficient battery storage to maintain operation through extended cloudy periods without any solar recharge. At high latitudes in winter, a coastal storm system can bring overcast skies and heavy fog for 7-10 consecutive days, reducing solar input to near zero. During that period, ships still need the light. For aids on the US Aids to Navigation (ATON) list, a malfunctioning light must be reported and corrected within specific timeframes — extended battery autonomy buys the maintenance crew time to reach a remote location safely, especially in winter when helicopter access may be limited. Non-critical decorative or tourist lights can use 3-5 day autonomy.

Can you put solar panels on a historic lighthouse? ▼

Yes, but with important caveats. Historic lighthouses listed on the National Register of Historic Places require Section 106 review (National Historic Preservation Act) before any modifications, including solar installation. The State Historic Preservation Office (SHPO) must approve the design. In practice, most approved installations mount panels on adjacent structures (keeper's quarters, equipment sheds, or separate poles) rather than on the lighthouse tower itself. The USCG's Aids to Navigation program has extensive experience with solar conversions — many have been successfully completed at historic sites. The key is early engagement with both SHPO and the lighthouse's managing organization (often a preservation nonprofit).

What makes marine-grade solar equipment different? ▼

Marine environments expose equipment to salt air, spray, humidity, UV, and storm forces that destroy standard terrestrial solar equipment within 1-3 years. Marine-grade components include: anodized aluminum or 316 stainless steel mounting hardware (vs standard aluminum); IP67 or IP68 rated charge controllers and inverters (submersion-proof vs IP65 splash-proof); tinned copper wiring (resists corrosion vs bare copper); fiberglass or UV-stabilized polymer enclosures (vs powder-coated steel); and panels with anti-reflective, anti-soiling coatings optimized for salt-spray conditions. The marine premium is typically 30-60% above standard commercial equipment costs. For USCG-maintained lights, only equipment on the approved ATON equipment list may be used.

How does latitude affect lighthouse solar design? ▼

Latitude has an enormous effect, particularly in winter. At 25°N (Florida Keys), winter peak sun hours are roughly 5.0/day — barely reduced from summer. At 58°N (Kodiak, Alaska), winter PSH drops to approximately 1.5/day, requiring 3-4x more panel capacity for the same load vs a Florida installation. This is why Alaska lighthouse solar systems are disproportionately large relative to their lamp wattage. For any lighthouse above 50°N latitude, the winter-sizing calculation completely dominates the design — summer production will be massively in excess and the battery will be full, but that excess cannot be stored or used. Adjustable tilt mounts (steeper winter angle) can recover 10-20% additional winter production at high latitudes.

Are decommissioned lighthouses worth converting to solar? ▼

Decommissioned lighthouses transferred to preservation organizations, municipalities, or private owners under the National Historic Lighthouse Preservation Act (NHLPA) often lack grid power — the original electrical service was terminated when the USCG handed them over. Solar is frequently the only cost-effective way to power these structures for visitor centers, overnight accommodations (some are rented as vacation properties), or simple security lighting. Tourist lighthouse conversions have different requirements than active navigation aids: lower wattage LEDs (decorative), shorter autonomy (3-5 days), and standard (not marine-grade) can be used when grid extension is physically impossible. Typical tourist lighthouse solar systems cost $8,000-25,000 and pay for themselves through visitor attraction and property value within 5-10 years.

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