Floating Solar vs. Pile-Mounted Solar: Which Suits Your Water Site

Pile-mounted solar is usually the first option worth checking on shallow working ponds where piling is practical and boats or aquaculture still need access below the array. Floating solar often makes more sense on deeper reservoirs, where fixed supports become long or difficult to install. The final choice should come from water depth, bottom conditions, water-level changes, wind and waves, usable area, construction access, and lifetime cost.

A 20-hectare fish pond with 2 m of water and boats moving across it every day is nothing like a 20-hectare reservoir that is 15 m deep and drops 5 m in the dry season. The surface area may be identical, but the foundations, access, cables, maintenance, and usable PV capacity can be completely different.

Here, pile-mounted solar means an elevated fixed PV structure supported by piles driven into the bed of the waterbody. Floating solar means modules supported on buoyant structures and held in place by anchors and mooring lines.

Floating or Pile-Mounted: Start With These Site Conditions

There is no simple rule such as “3 m means piles and 10 m means floats.” A 2 m pond with very weak sediment can be harder and more expensive to pile than a sheltered 8 m reservoir is to float.

For a Shallow Aquaculture Pond, Pile-Mounted Solar Often Makes More Sense

Think about a working fish pond with an average depth of 1.5–2.5 m. Feed boats cross it every day. Aerators need maintenance, harvesting equipment comes in several times a year, and the center of the pond must stay accessible.

If geotechnical testing shows that piling is practical, an elevated array can keep much of that operating space open. The modules sit above the fishery while boats, pumps, nets, aerators, and feeding operations continue below or between the structural rows.

This is already used at utility scale. Tongwei's Fishery & PV Integration business reports more than 56 fishery-PV power stations across more than 20 provinces and municipalities, with total grid-connected capacity above 5.1 GW.

The layout still has to follow the real farm. If a boat needs a 3 m wide operating route, a 2 m opening does not suddenly become acceptable because it gives the PV system a neater layout. Aerators, feeding lanes, harvesting zones, drainage, and maintenance access should all be marked before the pile grid is fixed.

For a Deep Reservoir, Floating Solar Usually Deserves the First Study

Water depth directly affects a pile-mounted system because every support has to cross the water and still reach suitable material below the bed.

Take a simplified reservoir with:

• 12 m water depth;
• 7 m required pile embedment;
• 2.5 m between normal water level and the structural connection.

The simple geometric support length is already:

12 + 7 + 2.5 = 21.5 m

And that is before connection details, bending, buckling, waves, currents, corrosion, construction equipment, and actual geotechnical design are considered.

Floating solar avoids putting a fixed support under every section of the array. Water depth still matters for anchors, mooring geometry, underwater work, inspection, and cables, but it affects the system in a different way.

A deep, sheltered reservoir with moderate water-level variation can therefore be a good FPV candidate. A similar reservoir with steep banks, big waves, weak anchor conditions, or a 6 m seasonal drawdown may be far more difficult.

A Mixed-Depth Site May Need More Than One Answer

A large water site does not have to use one mounting method everywhere.

Suppose a 40-hectare property contains 15 hectares of active fish ponds that are 1.5–2.5 m deep, plus a storage reservoir reaching 8–12 m.

The shallow ponds can be assessed for elevated pile-mounted PV so aquaculture continues underneath. The deeper reservoir can be studied separately for floating PV.

That avoids forcing very long supports into the deeper area just to keep the whole project structurally identical. It also avoids covering active fish-farming water with floats when elevated PV would leave better access.

The downside is more complexity. A mixed project has two structural systems, two construction methods, and possibly two maintenance approaches. Price that complexity against the cost of forcing one unsuitable design across the whole site.

Water Depth and Bottom Conditions Need to Be Evaluated Together

“Average depth: 5 m” is not enough to make a foundation decision.

A reservoir averaging 5 m may have a 2 m shelf near the shore, an 8 m submerged channel in the middle, and several meters of soft sediment before competent soil begins. Supports in those zones may need very different designs.

For a simple pile example, assume one area has:

• 2.0 m of water;
• 2.5 m of structural clearance;
• 6.0 m of required embedment;
• 0.5 m allowed for connection and detailing.

The approximate geometric pile length is:

2.0 + 2.5 + 6.0 + 0.5 = 11.0 m

If water depth alone increases from 2 m to 5 m:

5.0 + 2.5 + 6.0 + 0.5 = 14.0 m

That is roughly 27% more geometric length before you even change the pile section, structural loads, installation method, or penetration depth.

Bathymetry should therefore map depth contours across the whole proposed PV area, not just provide a few spot measurements.

The World Bank estimated that using only 1% of the surface area of the world's man-made reservoirs could represent around 400 GWp of floating-solar capacity under its conservative global assessment. That shows the scale of the opportunity, but every reservoir still needs its own bathymetric, environmental, structural, and operational study.^[1]

Water-Level Variation Changes Both Designs in Different Ways

Compare a pond that moves only 0.5 m through the year with a reservoir that changes by 5 m.

A floating array rises and falls with the water. Its mooring system has to work across the full range. Lines cannot become too tight at high water or allow uncontrolled movement at low water. Floating-to-fixed cable sections also need enough movement allowance.

A pile-mounted array stays at one elevation. If the lowest structural member sits 2 m above maximum operating water level and the reservoir later drops 4 m, that same member is now about 6 m above the water.

The structure may still be fine, but maintenance and operation have changed. Boat access, ladders, cable transitions, inspection points, and working height may all be different.

Historical water-level data should therefore include minimum, normal, maximum, flood, seasonal range, and any rapid drawdown that matters to the site.

Wind, Waves, and Open-Water Exposure Can Change the Preferred System

A floating array passes wind and wave forces through the connected platform, mooring lines, and anchors. The critical weak point may be nowhere near the module itself.

A pile-mounted array sends loads through the elevated frame and columns into fixed foundations. Open water offers little wind shelter, and tall structures can see substantial lateral and uplift loads.

Long open-water fetch can also allow bigger waves to build. Some sites have additional issues such as flood flow, debris, currents, or ice.

Design from local extreme conditions, not from how calm the reservoir looked during one site visit. Resolve wind speed, waves, current, flood behavior, and water-level extremes before comparing final structural quantities.

Aquaculture Projects Should Calculate Usable Water, Not Total Water

A 20-hectare fish pond rarely gives you all 20 hectares for PV.

Suppose the operator needs navigation lanes, aerator zones, harvesting areas, ecological buffers, and shore access. If only 35% remains usable:

20 ha × 35% = 7 ha usable area

If one early layout needs 1.4 ha of gross usable water per MW:

7 ha ÷ 1.4 ha/MW = 5 MW

A second layout keeps wider boat lanes and needs 1.75 ha/MW:

7 ha ÷ 1.75 ha/MW = 4 MW

Wider operating corridors reduce practical capacity from 5 MW to 4 MW, a 20% drop, even though total pond area is unchanged.

The 1.4 and 1.75 ha/MW values are only examples. Actual density depends on module dimensions, tilt, row layout, access, orientation, electrical blocks, shading, and water-use restrictions.

Do Not Give Floating Solar an Automatic Energy-Yield Bonus

Water can change module temperature, and some floating projects may run cooler than comparable land systems.

That does not mean every FPV project should automatically get a 5% or 10% production bonus in the model.

IEA PVPS notes that floating-PV performance depends strongly on system design, environmental conditions, thermal behavior, waves, soiling, degradation, and other site characteristics. The performance advantage cannot be generalized across all projects.^[2]

Pile-mounted modules above water can also have plenty of air movement underneath them. Model each concept using its actual tilt, temperature assumptions, shading, availability, electrical losses, and structural layout.

Suppose a 10 MWDC concept has a modeled specific yield of 1,500 kWh/kW per year:

10,000 kW × 1,500 kWh/kW = 15,000,000 kWh/year

or:

15 GWh/year

A one-percentage-point change in annual availability equals:

15 GWh × 1% = 150 MWh/year

At an illustrative electricity value of $60/MWh:

150 MWh × $60/MWh = $9,000/year

Across 25 years, that is $225,000 before discounting, degradation, inflation, financing, or changes in electricity prices.

This is why maintainability and energy yield belong in the same discussion as structural CAPEX.

Module Format Changes Module Count and Structural Layout

Choose the module early enough for it to influence the water-site structure.

Tongwei's current module portfolio includes several formats and power classes for utility-scale and other PV applications.

For a simple 10 MWDC comparison:

Using a 670 W module:

10,000,000 W ÷ 670 W ≈ 14,926 modules

Using a 750 W module:

10,000,000 W ÷ 750 W ≈ 13,334 modules

That is roughly:

14,926 − 13,334 = 1,592 fewer modules

Tongwei currently lists up to 670 W for the TWMNH-66QD and up to 750 W for the TWMNF-66HD.

Fewer modules do not automatically mean fewer piles, fewer floats, or a cheaper BOS. Module size, weight, support points, wind area, row geometry, electrical design, structural spans, handling equipment, and float compatibility all matter.

The real question is how the chosen module changes the full structural and electrical layout for the same MW target.

Construction Method Can Reverse the Early Cost Comparison

Consider two fish ponds that are both 2 m deep.

Pond A can be drained for eight weeks, letting construction equipment work from the exposed bed after suitable preparation.

Pond B has to stay full because fish production continues during construction.

The finished pile-supported arrays might look almost identical. But Pond B could need barges, temporary platforms, smaller piling equipment, staged work zones, water-traffic control, and more complicated worker-safety measures.

Floating PV has a different constraint. Large systems need suitable shoreline space for unloading floats, assembling sections, installing components, launching the array, and towing sections into place.

A 100-hectare reservoir surrounded by steep banks can therefore have plenty of water but very little practical assembly space.

Construction cost should be based on a workable installation sequence for the real site, not just the quantities visible in the finished structure.

Maintenance Access Can Turn a Small Availability Difference Into Real Energy Loss

Suppose an inverter or electrical fault happens 180 m from shore during the wet season.

On a floating project, technicians may need a suitable boat, safe docking or platform access, acceptable wind and wave conditions, and enough working space to move replacement equipment.

FPV also adds inspections of floats, connections, mooring components, anchors, moving cable sections, and platform alignment.

Pile-mounted PV removes the floating platform and mooring system, but maintenance is not automatically easy. Badly placed structural members or missing walkways and boat lanes can make a fixed array awkward to inspect too.

IEA PVPS identifies FPV-specific reliability stressors and O&M requirements as important for long-term performance, and it notes continuing uncertainty around cost-efficient FPV maintenance strategies.^[3]

Tongwei's utility-scale PV project portfolio also shows why module choice, station design, and long-term operation have to be considered as one system rather than separate purchasing decisions.

Compare Lifetime Cost, Not Mounting Price

The cheapest float quote and the cheapest pile quote do not answer the real commercial question.

Use the same system boundary for both concepts:

A historical NREL bottom-up benchmark for a modeled 10 MWDC floating PV system found an installed-cost premium of about $0.26/WDC, or 25%, compared with conventional ground-mounted fixed-tilt PV under its Q1 2021 assumptions.^[4]

At 10 MWDC:

10,000,000 W × $0.26/W = $2.6 million

Do not treat that $2.6 million as the expected premium of floating solar over pile-mounted solar. The NREL study compared floating PV with conventional ground-mounted PV, not with an elevated pile system over water. It also used historical 2021 assumptions.

The benchmark is still useful because it shows that floats, anchors, mooring, and site-specific FPV work can materially change project cost. Pile-mounted water projects have their own cost sensitivity when pile length, steel, marine piling, or difficult access increases.

For the real decision, compare total installed cost and lifetime O&M against lifetime MWh using the same financial assumptions.

Water-Site Corrosion Affects Much More Than the Main Structure

Corrosion exposure is different below the waterline, through the wet-dry zone, and above the water.

On pile-mounted systems, it can affect piles, structural steel, bolts, connections, and electrical supports. Floating systems expose frames, connectors, fasteners, mooring hardware, electrical components, and other parts to humidity, splash, and direct water contact.

The U.S. Department of Energy recommends identifying corrosive agents in air, gas, soil, and water when assessing a PV site. It specifically mentions vulnerable parts such as module frames, fasteners, racking, inverter electronics, electrical panels, and connectors.^[5]

For coastal, brackish, or other salt-affected sites, IEC 61701:2020 provides salt-mist corrosion test sequences used to evaluate PV-module resistance in atmospheres containing dissolved salts.^[6]

Passing a module qualification test does not qualify the whole station. Fasteners, coatings, cable supports, enclosures, dissimilar-metal contacts, piles, and mooring hardware all need materials suited to their own exposure.

Electrical Design Must Account for Water and Movement

Floating-PV cables move with the array and with changing water levels. Bend radius, strain relief, abrasion points, connector positions, cable supports, and the transition between floating and fixed sections all need attention.

Pile-mounted systems avoid most platform movement, but electrical equipment can still face splash, condensation, flooding, and difficult access.

IEC 62548-1:2023+AMD1:2025 covers PV-array design requirements including DC wiring, electrical protection, switching, and earthing provisions.^[7]

On a water site, check inverters, combiners, isolators, connection points, and cable routes against maximum water and flood levels, not just the normal waterline.

Send the Same Water-Site Data Before Comparing Supplier Prices

A serious quotation needs more than a satellite image, total water area, and target MW.

If one supplier prices 2 m water and another prices an area that reaches 8 m, those foundation quotations are not comparable. The same problem appears when one contractor includes marine installation and another quotes only delivered structural material.

Compare Five Numbers Before Choosing the System

Installed DC capacity: Work out how much PV each design actually fits after navigation, maintenance, ecological, and operating exclusions.

Annual MWh: Build separate energy models using the real tilt, module format, shading, temperature, electrical losses, and availability of each option.

Total installed cost: Include the complete water-site structure, foundations or anchors, construction access, electrical work, development, and contingency.

Lifecycle O&M: Include inspection, water access, likely replacements, corrosion work, and structural maintenance.

Lifetime delivered energy: Use the same degradation and availability assumptions so both concepts are compared over the same project life.

Conclusion

For a shallow working pond with practical piling and active aquaculture, evaluate pile-mounted solar first. For deeper water where fixed supports become long or difficult, evaluate floating solar first. Make the final choice using the same usable area, annual MWh, installed cost, construction conditions, and lifetime O&M assumptions.