On water the array has to move several metres vertically between dry season and monsoon while staying exactly where you put it. Anchoring, haor seasonality, cable management and the maintenance access that eats the cooling gain.
On land, the foundation's job is to resist wind. On water, the array has to rise and fall by several metres between the dry season and the monsoon while staying exactly where you put it horizontally, under wind, under wave and under the pull of its own cables. A mooring that holds laterally and releases vertically is the central problem of a floating plant, and it is what separates one that is still generating in year ten from one that ends up piled against the embankment after a single bad night.
Bangladesh faces a fundamental constraint for large-scale solar deployment: land scarcity. With one of the world's highest population densities, every hectare of agricultural land is precious. Yet Bangladesh has an extraordinary alternative resource: approximately 7 million hectares of water bodies, including haors (seasonal wetlands), baors (oxbow lakes), fish ponds, and irrigation reservoirs. Floating solar (also called floatovoltaics or FPV) deploys solar panels on pontoons or floats on these water surfaces, generating electricity without consuming agricultural land.
Floating solar systems typically generate 5–15% more electricity than equivalent land-mounted systems in the same location. The reason is the cooling effect of the water beneath the panels. Solar panels lose efficiency as they heat up, and the evaporative cooling from the water surface keeps panel temperatures lower. In Bangladesh's hot and humid climate, this performance advantage is particularly significant during the April to June peak heat period.
Two qualifications belong next to that figure. The gain depends on the array sitting close to water that is deep enough and moving enough to behave as a heat sink; a shallow, still, weed-covered pond in April is a good deal warmer than people assume, and a design that lifts the modules well clear of the surface gives away part of the benefit it was built for. Second, the gain has to be set against floats, mooring, marine-grade cabling and a maintenance regime that all cost more than their land equivalents. Floating solar earns its place because the land is unavailable or the water body is already yours, not because of the yield uplift on its own.
There are three broad approaches and the choice is set by how far the water level travels and what the bed is made of. Bank moorings run lines to piles or dead-weights on shore and suit small ponds with modest level change. Bottom moorings use anchors on the bed with catenary or elastic lines that take up slack as the level rises and falls. Pile-guided systems let the float slide vertically on a guide pile, which handles large level swings cleanly but needs a bed that will accept piles and a budget that will accept them too.
The failure modes are all seasonal. A line sized for monsoon level goes slack at low water and lets the array wander; a line sized for low water goes taut as the level rises and either lifts the anchor or tears out the float fitting. Bangladeshi beds are frequently soft silt with very little holding power, so a dead-weight anchor that would be adequate on a rocky bed simply ploughs. And a floating array has almost no structural damping: wind gusts and wind-driven waves put dynamic, cyclic loads into the mooring rather than the steady load a ground-mount frame sees.
| Water body type | Suitable for floating solar? | Typical application | Capacity range |
|---|---|---|---|
| Fish ponds (private) | Yes, excellent | Farm power + fish production | 10 kWp – 2 MWp |
| Irrigation reservoirs | Yes, excellent | Pump power + grid supply | 100 kWp – 10 MWp |
| Haors (seasonal) | Seasonal only (dry season) | Seasonal generation | 1 MWp – 50 MWp |
| Baors (oxbow lakes) | Yes, good | Community power | 50 kWp – 5 MWp |
| Industrial ponds | Yes, good | Factory power | 50 kWp – 5 MWp |
A haor is not a lake. In the monsoon it becomes an open sheet of water with kilometres of fetch and a wave regime that a pond design would not survive, and in the dry season it drains back to cultivated land. An array floating in Bhadra may be sitting on a dry field by Falgun. Anything built there has to either ground out safely and be re-floated on a known schedule, or be confined to the perennial beels that hold water all year. Add to that the fact that the same water is a fishery, a Boro cropping area after it drains, and a navigation route for the people who live around it. A haor project is a land and water use negotiation with local stakeholders first and an engineering exercise second.
Every cable on a floating plant crosses a joint that moves, forever, in sunlight and water. That is a completely different service condition from a rooftop tray, and it is the commonest source of long-term trouble on FPV.
A soiled string on a factory roof is a ladder and an hour. The same string on a floating array is a boat, two people and a working method. Bird fouling is heavier over water than over a roof, splash and algae mark the lower module edges, and the whole plant may be effectively unreachable for days during a monsoon blow. Walkways between rows add cost and add area, and on any plant that is expected to be maintained properly they earn it back. Decide the access strategy while the layout is still on paper, because retrofitting a walkway into a completed float array is close to impossible.
One of the most promising applications of floating solar in Bangladesh is agri-aqua solar, combining fish farming with solar power generation on the same water body. The solar panels provide shade that reduces water temperature and algae growth, improving fish yields. The electricity generated powers aerators, water pumps, and processing facilities. Studies in China and India have shown that agri-aqua solar systems can increase fish yields by 10–20% while generating significant electricity revenue.
The variable that controls all of this is the coverage ratio, the share of the water surface under panels. Shade suppresses algae and lowers water temperature, which is why the fish benefit, but light also drives the primary productivity and the dissolved oxygen that the pond depends on. Cover too much and you have created a problem that the aerators are then paying to solve. Coverage is a fisheries decision taken jointly with the electrical design, not an output of it, and it should be agreed with whoever actually manages the pond. On an irrigation reservoir the same shading gives a different benefit, reduced evaporation from stored water, which in the dry season is worth something on its own account.
SREDA (Sustainable and Renewable Energy Development Authority) has identified floating solar as a priority technology for Bangladesh's renewable energy expansion. The Bangladesh Power Development Board (BPDB) has issued tenders for floating solar projects on government-owned reservoirs. Private sector investors can develop floating solar under the net-metering framework for systems up to 100% of sanctioned load (80% of transformer capacity for MV consumers), or under the Independent Power Producer (IPP) framework for larger utility-scale projects.
For a private pond or reservoir owner, the binding constraints are the same ones that bind a rooftop project. What is your sanctioned load, what is your transformer capacity, and which distribution utility area are you in, because BPDB, DPDC, DESCO, NESCO and BREB do not all handle an application the same way. Then the question that is particular to water: who owns it. A leased khas water body, a fisheries lease, a shared irrigation reservoir or a water body inside a factory boundary are four very different legal starting points, and the tenure has to be settled before a mooring is designed, not after.