Advocating for Floating Solar
Advocating for Floating SolarAdvocating for Floating SolarAdvocating for Floating Solar
In the Colorado River Basin and beyond.
Mission
Water Wise Solar Solutions was formed to study the application of Utility Scale Floating Photovoltaic Solar Arrays as an effective mitigation strategy for evaporative water loss within the Colorado River Basin.
Colorado River Basin (CRB) Water Supply
Saving Water with Floating Solar
FPV Size and Business Case
May 5, 2025
The following sizing estimates and capital cost assumptions are based on publicly available data, satellite imagery, and generalized planning parameters. No formal engineering or utility interconnection studies have been conducted to date. As such, all figures presented here should be treated as preliminary feasibility guidance, subject to change pending detailed technical evaluation, utility feedback, and stakeholder engagement.
In particular, maximum array sizes are estimated based on the theoretical capacity of nearby transmission lines and substations. Actual usable capacity may be lower due to existing loads, grid constraints, or line congestion—factors that can only be confirmed through direct coordination with the serving utility.
General Sizing, Cost & Revenue Assumptions
As a rule of thumb, a floating solar array rated at 20 megawatts (MW) will require approximately 35–40 acres of open water surface, depending on design efficiency. This is based on observed density metrics from existing U.S. FPV installations, which range from 1.6 to 2.25 acres per MW, with a conservative planning average of ~2.0 acres/MW. A 20 MW array at this density equates to 40 acres, though highly efficient layouts (like Healdsburg, CA) may achieve closer to 32 acres for the same capacity.
This 20 MW scale represents a practical threshold for many utility-scale buyers considering Power Purchase Agreements (PPAs) or direct ownership and serves as a foundational planning unit.
Capital Cost Estimate:
- Estimated total installed cost: ~$40 million for 20 MW
- Cost per MW installed: ~$2.0 million
To estimate realistic capital expenditures for floating solar (FPV) development, it is useful to reference publicly available cost data from existing U.S.-based installations. Several wastewater treatment plant projects—typically among the simplest FPV environments due to flat water surfaces, limited recreation conflicts, and existing grid connections—have reported installation costs between $1.6 million and $1.9 million per megawatt (MW). These include notable systems in Healdsburg, California; Sayreville, New Jersey; and Cohoes, New York, each ranging from 3 MW to 5 MW in capacity.
Utah’s Park City FPV system, the state’s first of its kind, also falls within this range when accounting for construction savings tied to its location on a municipal treatment pond with minimal anchoring or permitting complexity. However, these projects represent ideal conditions and do not reflect the challenges posed by larger reservoirs, public access requirements, or more difficult site access in the West's varied topography.
Given those realities—and the added inflationary pressures on solar hardware, labor, and civil construction—a more conservative planning estimate of $2 million per MW installed is recommended for budgeting purposes. This figure allows for greater site complexity, phased deployment, advanced anchoring systems, and higher permitting and stakeholder engagement costs expected in multi-use water bodies. While actual costs may vary by reservoir and project size, this benchmark provides a sound basis for preliminary feasibility and long-term financial modeling.
Annual Energy Production Benchmark:
In New Mexico, a well-sited floating array can produce approximately 1.75 million kWh per installed MW per year, or 35 GWh annually for a 20 MW array, assuming fixed tilt, no tracking, and the added performance benefit of evaporative cooling from the water surface. This estimate is based on NREL-modeled output and is consistent with high-performance examples such as Healdsburg (7.18 GWh/year from 4.78 MW, or ~1.5 GWh/MW/year at a slightly lower irradiance site).
These assumptions reflect typical values for moderate-to-high elevation FPV systems and include allowances for mooring, anchoring, access, and interconnection infrastructure. Larger arrays typically offer improved capital efficiency, provided the site’s grid connection, bathymetry, and surface availability can support the capacity. Utah's expected production for a single MW of installation is 1.6 million kWh's and Arizona's is 1.9 million kWh's.
Sizing Considerations
- Transmission and Substation Capacity
The most immediate constraint on array sizing is often the available transmission infrastructure. Nearby substations or feeder lines may limit injection capacity due to transformer ratings, line amperage, or thermal constraints. Oversizing an array beyond available capacity introduces curtailment risk, which can erode financial viability and PPA competitiveness.
In nearly all cases, interconnection feasibility should be confirmed through a formal utility study to validate maximum injection limits, available line voltage, breaker capacity or any other equipment related bottlenecks. 2. Hydroelectric Integration
Several Western region reservoirs include existing hydroelectric generation. Where present, FPV systems should be designed to complement—not overwhelm—the operational dynamics of these facilities. Smart optimization between hydro and solar enables flexible dispatch, reduces grid congestion, and effectively turns the water body into an already existing hybrid energy + water storage system.
When co-sited with battery energy storage, these systems can help shift solar generation into peak evening hours while preserving water for drought resilience or emergency power generation. This author hopes to first focus on where these hybrid models are applicable first, for high benefit FPV installations. 3. Phased Deployment Strategy & Site-Specific Design Considerations
Most FPV installations will require phased implementation, driven by public engagement, regulatory approvals, and grid upgrade timelines. Phasing enables:
- Early-stage proof-of-concept deployment
- Gradual grid interconnection scaling
- Reduced visual and recreational disruption
- Iterative adjustment to stakeholder feedback
This strategy also lowers risk by allowing the technical and political viability of each site to be validated before full build-out.
Recreational Use and Public Access
Many New Mexico reservoirs serve dual purposes—water storage and recreation, though their stated purpose usually doesn’t include the recreation component. FPV development must respect existing public uses, particularly boating, fishing, and shoreline camping.
- Maintain open corridors for summer watercraft activity or install moving floating solar islands that can accommodate summer traffic patterns.
- Avoid placement near high-use shorelines, boat ramps, or scenic areas.
- Coordinate with municipalities and water conservancy districts to align with local planning goals.
On smaller reservoirs, this may significantly limit maximum surface area coverage. Stakeholder input is essential to balance community priorities with energy production goals.
Seasonal Variability and Topography
New Mexico reservoirs experience seasonal drawdowns and fluctuating surface levels. FPV arrays must be anchored to withstand changing water elevation and potential exposure of racking during low periods. Most systems are engineered to tolerate a dry slope of up to 15 degrees, beyond which structural stability may be compromised.
Steep embankments and irregular bathymetry increase installation costs and anchoring complexity. Reservoirs with broad, stable surface areas and gradual underwater slopes offer the most attractive conditions for cost-effective deployment.
Budget Neutral Simple Case Study
Assume a landowner agreement is secured and a single acre of floating photovoltaic (FPV) solar is installed at a capital cost of $2 million. That acre produces 1,750 MWh (or 1.75 GWh) of electricity annually — a reasonable benchmark for New Mexico based on NREL estimates and FPV system performance boosts.
The two main revenue streams are:
- Electricity sales at $0.10/kWh — slightly under the Windsor, CA PPA rate of $0.105/kWh
- Sale of solar renewable energy credits (sRECs) at $20 per MWh — a notch above PacifiCorp’s Blue Sky program ($19.50/MWh)
This results in:
- $175,000 in annual revenue from electricity (1,750,000 kWh × $0.10)
- $35,000 from sRECs (1,750 MWh × $20)
- Total annual revenue: $210,000
Assuming modest annual operations and maintenance (O&M) costs of $10,000, this leaves $200,000 available for principal, interest, and insurance (P&I&I).
Industry-standard FPV insurance costs range from 0.5%–1.25% of capital investment. Using a midpoint estimate of 1%, the annual insurance premium on $2 million is $20,000, leaving $180,000 per year for loan repayment. Using a 20-year amortization schedule, this level of debt service ($180K/year) supports a $2 million loan at an interest rate of approximately 6.4%, which aligns with conservative real-world financing expectations.
Building in profit would require either more revenue from the PPA, a lower interest rate, or reduced insurance or O&M costs per MW installed.
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