The following is a partial list of key terminology (with acronyms, where applicable) related to VDE Americas’ hail risk advisory products and services.
Average annual loss
The estimated value of the expected financial loss that may occur in any given year based on severe hail events.
ArcGIS-based hail return interval maps
A set of contour maps delivered online via the ESRI platform showing return intervals for naturally occurring hail (NOH) categories across the Continental United States.
ArcGIS-based financial risk exposure maps
A set of contour maps delivered online via the ESRI platform showing probable maximum loss (PML) and average annual loss (AAL) estimates for a 100 MWdc PV power project over a range of tracker angles, facing into and out of the wind.
Co-probability of hail with wind
The co-occurrence probability of hail with wind, providing insights into combined risk factors for solar projects. Data outputs include co-occurring gust velocity with naturally occurring hail (NOH) size and the return interval NOH size with wind speed.
Continental United States (CONUS)
The 48 contiguous states between Canada and Mexico.
Cumulative distribution function
A probability distribution function that represents the probability that a selected random variable will be less than or equal to a specific value.
Freezer iceball (FIB)
A laboratory-manufactured hailstone proxy with standardized physical characteristics for conducting ballistic-impact testing to published engineering standards.
Hail monitoring and tracker stow protocol
Specifications for real-time monitoring and defensive stowing strategies to minimize potential damage during severe weather events.
Hail size category
A classification of naturally occurring hail sorted according to hailstone diameter above a minimum threshold.
Impact energy
The amount of kinetic energy of a falling hailstone, as determined by its mass and velocity, immediately prior to impact with the surface of a PV module or other object.
Naturally occurring hail (NOH)
Frozen objects of nature with widely varying shapes, sizes, and material properties. The kinetic energy of NOH varies from one event to another, resulting in differences in hailstorm damage potential.
National Oceanographic and Atmospheric Administration (NOAA)
A scientific and regulatory agency operating under the U.S. Department of Commerce that monitors oceanic and atmospheric conditions and forecasts weather.
Next-Generation Radar (NEXRAD)
A network of high-resolution S-band Doppler weather radar stations that detects precipitation and wind jointly operated by the National Weather Service, Federal Aviation Administration, and the U.S. Air Force.
Photovoltaic (PV)
Referring to the conversion of light into electricity.
Poisson distribution
A discrete probability distribution—named after French mathematician Siméon Denis Poisson—that is used in probability theory and statistics to show how many times an event is likely to occur over a specified period.
Probability distribution system (PDF)
A mathematical function used to specify the probability that a specific random variable will occur with some specified range of values.
Probable maximum loss (PML)
The estimated value of the largest financial loss likely to result from a hail event within a specific period of time, based on plant location and capacity, accounting for operating assumptions and excluding insurance considerations.
Pro-forma risk exposure for parametric (PREP) insurance evaluation
The estimated value of parametric insurance over a range of hail stone diameter attachment points based on estimated average annual financial loss resulting from severe hail events distributed over specified periods given certain operating assumptions (e.g., trackers tilted flat, 50, 52 and 60 degrees). The default assessment period is 10 years for tax equity providers and 40 years for owners. The resulting estimated values are provided in median (P50) and downside (P90 and P95) cases.
Return interval (RI)
The estimated amount of time between discrete events. Mathematically, it represents the value of a given quantity that is expected to be equaled or exceeded on average once every time interval (t) with an event probability in any given year of 1/t.
Severe Weather Data Inventory (SWDI)
NOAA’s integrated database of severe weather records for the United States.
Severe hail
As defined by NOAA, hail with a diameter greater than or equal to 25 mm (1in.). [Prior to 2010, NOAA defined severe hail as having a diameter greater or equal to 19 mm (0.75 in.).]
Storm Prediction Center (SPC)
An agency operating under NOAA, as part of the National Centers for Environmental Prediction, responsible for forecasting the risk of severe weather events including thunderstorms, hail, and tornados throughout the CONUS.
