Side Solar Analysis for the Triangular Seastead

Summary

The side solar would not produce much direct power when the sun is directly overhead, especially in the tropics. However, it would produce useful power during morning, afternoon, winter, and higher-latitude operation. It also receives diffuse sky light and some reflected light from the ocean.

Geometry and Available Area

Given:

• Equilateral triangle side length: 41.3 ft
• Wall height: 7 ft
• Three vertical wall sections

The side walls actually have slightly more gross area than the triangular roof:

Side wall gross area = 3 × 41.3 × 7 = 867 ft² = 80.6 m²

In practice, not all of this area will be usable because of doors, hatches, windows, corner structure, handholds, tracks, maintenance access, deck connections, and collision-prone zones. For the estimate below, I assume 75% usable side coverage.

Expected Extra Energy from Side Solar

For a first-order estimate:

Daily energy ≈ PV rating × horizontal sun hours × vertical-surface factor × performance ratio

Assumptions used:

• PV module efficiency: 22%
• Electrical performance ratio after temperature, wiring, MPPT, salt/soiling, inverter/charging losses: 0.75 to 0.85, using 0.80 as the central value
• Average good-ocean solar resource: 4.5 to 5.8 kWh/m²/day horizontal irradiance
• Vertical side solar receives roughly 45% to 70% of horizontal-plane energy depending on latitude, season, cloudiness, and heading

Central Estimate

Using a central case of:

• 75% side coverage: 13.3 kWp
• Horizontal sun: 5.0 kWh/m²/day
• Vertical-side factor: 0.55
• Performance ratio: 0.80

Side solar energy ≈ 13.3 kWp × 5.0 × 0.55 × 0.80 = 29 kWh/day

That equals:

29 kWh/day ÷ 24 h/day = 1.2 kW average continuous power

Range by Coverage

Comparison to Roof Solar

The roof is an equilateral triangle with area about 68.6 m². If around 85% of the roof can be covered with panels, that gives:

Roof PV area ≈ 68.6 × 0.85 = 58.3 m²

Roof PV rating ≈ 58.3 × 0.22 × 1000 = 12.8 kWp

In a good solar location, flat roof solar of this size might produce approximately:

12.8 kWp × 5.0 to 5.8 sun-hours × 0.80 ≈ 51 to 59 kWh/day

So side solar with 75% wall coverage could add roughly:

• 25 to 35 kWh/day extra energy
• About 45% to 70% additional energy compared with the roof-only case
• About 1.0 to 1.5 kW more average continuous power

Effect of Ocean Reflection

The ocean does reflect some light onto the vertical side panels. For ordinary dark water, the average albedo is usually only around 0.05 to 0.10. Whitecaps, sun glint, low sun angle, and bright haze can increase this temporarily, but it is not reliable enough to count as a major energy source.

For a vertical panel, a simple diffuse-reflection approximation is:

Reflected irradiance on vertical panel ≈ 0.5 × ocean albedo × horizontal irradiance

If ocean albedo is 0.06 to 0.10:

Reflected contribution ≈ 3% to 5% of horizontal irradiance

For the 75% side coverage case, this might contribute roughly:

So ocean reflection helps, but it should be treated as a small bonus. The main value of side solar comes from low-angle direct sun plus diffuse sky light.

Weight Estimate

For 75% side coverage, the added PV area is about 60 m² and the added PV rating is about 13.3 kWp.

Compared with the 45 ft high-cube container maximum payload of 62,000 lb, even the heavier rigid-panel option is not enormous. However, on the vessel itself, weight location matters. Side panels are above the waterline, so lightweight panels are preferable for stability and motion.

Cost Estimate

For approximately 13.3 kWp of side solar:

These figures do not include the main battery bank, but they should include reasonable allowance for extra MPPT controllers, wiring, disconnects, fusing, corrosion-resistant connectors, and mounting/adhesive hardware.

Electrical Architecture Recommendation

Because only one or two sides will be strongly illuminated at once, the three sides should not be placed on one shared MPPT string. The side solar should be divided electrically by face.

• Use at least one MPPT input per side.
• Preferably use two or more MPPT strings per side if panels may be shaded by railings, decks, dinghy supports, kite hardware, antennas, or people.
• Keep each leg's power system independent as planned, but allow controlled power sharing if desired.
• Use marine-rated DC disconnects, fuses, and arc-fault-aware design.
• Use tinned marine cable and sealed connectors.

Operational Pros and Cons

Advantages

• Adds a large amount of energy without increasing vessel footprint.
• Improves morning and afternoon production.
• Useful in winter and higher latitudes where the sun is lower.
• Vertical panels shed rain well and may accumulate less standing dirt than flat panels.
• Can reduce dependence on kite power, generator backup, or propulsion battery reserve.
• May shade and protect the living-area walls, reducing cooling load.

Disadvantages / Design Issues

• Higher salt spray exposure than roof panels; requires washdown and corrosion-resistant materials.
• Possible impact damage from docks, floating debris, dinghy operations, lines, and maintenance activity.
• Panels reduce available wall area for windows, hatches, handholds, emergency exits, and exterior attachments.
• Requires multiple MPPT inputs because side illumination is uneven.
• Flexible panels can have shorter lifetime if they run hot or are repeatedly flexed.
• Rigid glass panels are heavier and more fragile, especially on vertical exterior walls.

Recommendation

The best implementation is probably lightweight or semi-flexible marine PV integrated into the exterior wall panels, not ordinary glass panels simply bolted to the outside. Use tougher sacrificial rub rails or non-PV impact zones near corners, deck connection points, dinghy handling zones, and anywhere lines may rub.

If budget is tight, the highest-value side panels are likely:

1. The two side faces most often exposed during normal operating headings, and
2. Upper wall areas less likely to be hit by waves, dinghy hardware, or docking contact.

If the vessel will spend most of its time in the tropics, side solar is still useful, but less productive at solar noon. If it will spend substantial time above about 25 to 30 degrees latitude, side solar becomes even more attractive because the lower sun angle favors vertical surfaces.

Bottom Line