Retention ponds sit along high-speed roads across fast-growing modern urban areas.
They are designed to do only one thing. They collect rainstorm runoff from all the asphalt we drive on every day.
Most of us have seen them but rarely ever notice them as they go by.
But there’s one small retention pond in Orlando, located behind a busy highway exchange, that has done something entirely different. The water surface on this small retention pond now holds 3,032 floating solar panels.
A highway drainage ditch turned into a functioning 2 MW power station.
It took a lot of work to move all the solar panels from solid ground to the top of public stormwater drainage.
Unlocking highway easements for floating solar farms
Typically, utilities look for wide open space in the middle of nowhere when developing new renewable energy projects. They look for land close to urban areas too. However, it is usually very expensive and hard to get large contiguous tracts of land.
State DOTs own many hundreds of thousands of acres of unbuilt stormwater retention basins adjacent to highways.
The Florida Department of Transportation opened up those existing easements and right-of-way ponds to private developers. Developers can rent them out for floating photovoltaic systems.
This is done without impeding or limiting local government agencies.
They retain full ability to maintain, repair, or upgrade the roads and other infrastructure through the area.
Opening up these right-of-way parcels allows the commercial solar industry to circumvent land acquisition issues. These site-access obstacles normally hinder the rapid deployment of regional solar infrastructure.
D3Energy was selected by the Florida Department of Transportation to negotiate the first stormwater pond lease agreement.
The engineering team knew construction would depend entirely on building within an artificially created 10-foot-deep stormwater retention pond.
Anchoring 2,000 kilowatts on a fluctuating water surface
In a typical ground-mounted solar electric facility, the developer uses steel beam pilings installed in dry soil.
In contrast, a stormwater retention pond has no rigid structural foundation. Because of this, standard foundation pillar designs were not feasible here.
Engineers could not drive pilings into the pond bed without compromising either the drainage function or the synthetic liner. This synthetic liner separates the pond from the surrounding soils.
Because of these limits, a unique solution had to be engineered specifically for municipal civil design applications.
Instead of installing pilings into the pond bed, D3Energy employed a specialized bank-anchoring system to stabilize the 2,000 kWp PV array.
High-density polyethylene pontoon structures float the entire array above the waterline. Yet they still allow the structure to freely rise and fall with changing water elevations during heavy seasonal rainfall events.
Additionally, the advanced string inverters used in this project connect the electrical output of each string directly back to the local utility company’s distribution grid.
This is achieved without affecting the primary purpose of the pond as a flood control device.
Converting idle drainage ponds into clean energy platforms
This project represents a model example of what can occur when public entities collaborate with private companies.
On this ordinary retention pond, a partnership was formed between FDOT and D3Energy to create a clean energy source for Orlando ratepayers.
The project positions specialized power inverters at the water’s edge to convert direct current into usable grid power. These inverters are strategically located at each end of the floating array.
Maintenance personnel can travel to the array via boat. They use boats for marine inspections, cleaning of individual panels, and checking of inverter performance.
This installation demonstrates that even modest-sized urban water bodies may provide sufficient buoyancy for substantial commercial scale PV installations.
Transforming municipal drainage into clean energy proves that regional solar expansion no longer depends entirely on acquiring vacant land.
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