STAT FAQs Part 1: Floating Solar

April 4, 2018 by Benjamin Mow

The Solar Technical Assistance Team (STAT) receives many interesting and broadly applicable questions from state and local governments. The STAT FAQs blog series will highlight pertinent information as it relates to questions STAT receives. The focus of Part 1 in the series is floating solar.

Background: Floating solar (the focus of multiple requests for STAT analytical support over the past two years) is a solar photovoltaic (PV) application in which PV panels are designed and installed to float on bodies of water. Floating solar has many reported benefits, including:

• PV system efficiency gains due to lower ambient temperatures
• High panel density for a given area
• Reduced rates of evaporation
• Lower land acquisition and site preparation costs

While the bulk of installed floating solar systems are located in Japan, localities in the United States are showing an increasing interest in installing this innovative solar technology. For example, several wineries in California are installing floating solar (in Sonoma County and Napa County for instance) and a 6 megawatt installation is proposed for Olivenhain Reservoir in San Diego County.

Figure 1: Floating solar array near Tokushima, Japan

Question: What is the average expected energy output of a 1 megawatt (MW) floating solar installation?

Answer: The energy output of a floating solar installation will depend on the solar radiation at the location where the PV system is installed. Sites with a higher solar resource potential will have an increased energy output for each installed watt. NREL has developed tools that use localized weather data, along with other default and user-defined inputs, to estimate energy output of solar technology. These tools include PVWatts, an online solar energy production and cost of energy calculator, and the System Advisor Model (SAM), a free tool available for download with increased functionality compared to PVWatts. To adapt the standard photovoltaic performance model in these tools to a floating solar specific model, the primary input change is to set the tilt to 11 degrees. NREL research has shown that this is the typical mounting angle for floating solar systems.[1] Performing this tilt angle alteration and proceeding to run the model with accurate location-dependent inputs will provide a reasonable estimate for average energy output for a floating solar installation.

As an example, a hypothetical 1 MW floating solar array located in Napa, California would generate approximately 1,492,560 kWh per year based on a high-level PVWatts analysis. Inputs into this PVWatts model are shown in the table below, using default assumption except for DC System Size and Tilt.

Table 1. Hypothetical PVWatts inputs for a 1MW floating solar array in Napa, California 

For information about solar technical assistance, or to ask a solar-related question, visit www.nrel.gov/state-local-tribal/states.html or email stat@nrel.gov.

[1] Rob Spencer, Jordan Macknick, Matt Reese, Alexandra Aznar, and Adam Warren. “Strategic Initiative on Floating PV.” (Unpublished manuscript, October 31, 2017.) Microsoft PowerPoint file.