diff --git a/R/define_inputs.R b/R/define_inputs.R
index bf5f39f..217a0d2 100644
--- a/R/define_inputs.R
+++ b/R/define_inputs.R
@@ -1,4 +1,4 @@
-#' make a list of bird parameters for input into CRM
+#' Make a list of bird parameters for input into CRM
 #'
 #' Makes a list of avian biological parameters for the bird(s) being modelled
 #' as a function directly in R. This function is designed for R-based workflows.
@@ -15,8 +15,7 @@
 #'  - a single number representing the average (preferably median) of the
 #'    variable
 #
-#' @returns list where items define the value or stochastic distribution f
-#'    or each parameter
+#' @returns list whose items define the value or stochastic distribution for each parameter
 #'
 #' @param species char; species identifier
 #' @param bird_length Length of archetype bird (metres), or distribution
@@ -82,9 +81,9 @@ define_bird <- function(
 
 #' define_turbine
 #' 
-#' make a list of turbine parameters for input into the default CRM
+#' Make a list of turbine parameters for input into the default CRM.
 #'
-#' Makes a list of parameters for the a given turbine
+#' Makes a list of parameters for the a given turbine.
 #'
 #' # Details
 #'
@@ -95,13 +94,17 @@ define_bird <- function(
 #' up stochastic inputs.
 #'  - a single number representing the average (preferably median) of the
 #' variable
+#' 
+#' If this object is being defined for multiple turbines of the same model
+#' `prop_operational` should be the average between all turbines. For example 
+#' if there are two turbines, and one is operational for 24 hours while the other 
+#' is operational for 18 hours each day, then `prop_operational = (0.75 + 1)/2 = 0.875`.
 #'
 #'
-#' @returns list where items define the value or stochastic distribution for
+#' @returns list whose items define the value or stochastic distribution for
 #' each parameter
 #'
-#' @param model_id character; Label for turbine model - allows the user to 
-#'define multiple turbine types on a site
+#' @param model_id character; Label for turbine model
 #' @param blade_length blade length (m)
 #' @param blade_thickness_narrow the thickness of the blade (side on) at its thinnest point (m)
 #' @param blade_thickness_wide the thickness of the blade (side on) at its widest point (m)
diff --git a/R/p_collision.R b/R/p_collision.R
index c735994..805ec5a 100644
--- a/R/p_collision.R
+++ b/R/p_collision.R
@@ -146,6 +146,9 @@ prob_collision_static <- function(
 #' @param bird_speed numeric; Average flight speed (m/sec)
 #' @param prop_at_height proportion of flights at rotor swept height
 #' @param prop_below_height proportion of flights below rotor swept height
+#' @param prop_operational  numeric; Proportion of a 24 hour day that turbines
+#' are operational. A single number or distribution information using 
+#' [set_random]. Default 1. See [define_turbine()] for more detail.
 #'
 #' @return numeric; probability of collision with leading edge of blade.
 #'         Range from 0 to 1
@@ -179,7 +182,8 @@ prob_collision_dynamic <- function(
   bird_length,
   bird_speed,
   prop_at_height,
-  prop_below_height
+  prop_below_height,
+  prop_operational = 1
 ) {
   
   stopifnot(
@@ -209,5 +213,5 @@ prob_collision_dynamic <- function(
   presented_area <- presented_area * prop_at_height /
     (prop_at_height+prop_below_height)
   
-  return(presented_area/turbine_plane_area)
+  return(presented_area/turbine_plane_area*prop_operational)
 }
\ No newline at end of file
diff --git a/man/define_bird.Rd b/man/define_bird.Rd
index 727f115..354d9ac 100644
--- a/man/define_bird.Rd
+++ b/man/define_bird.Rd
@@ -2,7 +2,7 @@
 % Please edit documentation in R/define_inputs.R
 \name{define_bird}
 \alias{define_bird}
-\title{make a list of bird parameters for input into CRM}
+\title{Make a list of bird parameters for input into CRM}
 \usage{
 define_bird(
   species,
@@ -33,8 +33,7 @@ the bird is active onsite}
 \item{avoidance_static}{avoidance rate relative to a static turbine}
 }
 \value{
-list where items define the value or stochastic distribution f
-or each parameter
+list whose items define the value or stochastic distribution for each parameter
 }
 \description{
 Makes a list of avian biological parameters for the bird(s) being modelled
diff --git a/man/define_turbine.Rd b/man/define_turbine.Rd
index 9df9f33..798e9de 100644
--- a/man/define_turbine.Rd
+++ b/man/define_turbine.Rd
@@ -25,8 +25,7 @@ define_turbine(
 )
 }
 \arguments{
-\item{model_id}{character; Label for turbine model - allows the user to
-define multiple turbine types on a site}
+\item{model_id}{character; Label for turbine model}
 
 \item{blade_length}{blade length (m)}
 
@@ -63,14 +62,14 @@ are operational. A single number or distribution information using
 \link{set_random}. Default 1}
 }
 \value{
-list where items define the value or stochastic distribution for
+list whose items define the value or stochastic distribution for
 each parameter
 }
 \description{
-make a list of turbine parameters for input into the default CRM
+Make a list of turbine parameters for input into the default CRM.
 }
 \details{
-Makes a list of parameters for the a given turbine
+Makes a list of parameters for the a given turbine.
 }
 \section{Details}{
 Each input to this function must be either
@@ -81,6 +80,11 @@ up stochastic inputs.
 \item a single number representing the average (preferably median) of the
 variable
 }
+
+If this object is being defined for multiple turbines of the same model
+\code{prop_operational} should be the average between all turbines. For example
+if there are two turbines, and one is operational for 24 hours while the other
+is operational for 18 hours each day, then \code{prop_operational = (0.75 + 1)/2 = 0.875}.
 }
 
 \examples{
diff --git a/man/prob_collision_dynamic.Rd b/man/prob_collision_dynamic.Rd
index bd01c12..bcf27da 100644
--- a/man/prob_collision_dynamic.Rd
+++ b/man/prob_collision_dynamic.Rd
@@ -15,7 +15,8 @@ prob_collision_dynamic(
   bird_length,
   bird_speed,
   prop_at_height,
-  prop_below_height
+  prop_below_height,
+  prop_operational = 1
 )
 }
 \arguments{
@@ -40,6 +41,10 @@ prob_collision_dynamic(
 \item{prop_at_height}{proportion of flights at rotor swept height}
 
 \item{prop_below_height}{proportion of flights below rotor swept height}
+
+\item{prop_operational}{numeric; Proportion of a 24 hour day that turbines
+are operational. A single number or distribution information using
+\link{set_random}. Default 1. See \code{\link[=define_turbine]{define_turbine()}} for more detail.}
 }
 \value{
 numeric; probability of collision with leading edge of blade.
diff --git a/vignettes/deterministic-example.Rmd b/vignettes/deterministic-example.Rmd
index 5c6eff6..a05a72f 100644
--- a/vignettes/deterministic-example.Rmd
+++ b/vignettes/deterministic-example.Rmd
@@ -345,7 +345,8 @@ df_turbines$p_coll_dyn <- prob_collision_dynamic(
   bird_length = wte$bird_length,
   bird_speed = wte$bird_speed,
   prop_at_height = prop_at_height,
-  prop_below_height = prop_below_height
+  prop_below_height = prop_below_height,
+  prop_operational = v90_single$prop_operational
 )
 
 
diff --git a/vignettes/one-bird-one-turbine.Rmd b/vignettes/one-bird-one-turbine.Rmd
index ac3e36d..5fe7809 100644
--- a/vignettes/one-bird-one-turbine.Rmd
+++ b/vignettes/one-bird-one-turbine.Rmd
@@ -117,7 +117,8 @@ p_coll_dyn <- prob_collision_dynamic(
   bird_length = wte$bird_length,
   bird_speed = wte$bird_speed,
   prop_at_height = 0.75,
-  prop_below_height = 0.2
+  prop_below_height = 0.2,
+  prop_operational = v90_single$prop_operational
 )
 
 p_coll_dyn + p_coll_static
diff --git a/vignettes/simple-simulation-example.Rmd b/vignettes/simple-simulation-example.Rmd
index 537673c..e8f2558 100644
--- a/vignettes/simple-simulation-example.Rmd
+++ b/vignettes/simple-simulation-example.Rmd
@@ -490,7 +490,8 @@ lst_results <- lapply(1:iterations, function(i) {
     bird_length = bird_i$bird_length,
     bird_speed = bird_i$bird_speed,
     prop_at_height = prop_at_height1_i,
-    prop_below_height = prop_below_height1_i
+    prop_below_height = prop_below_height1_i,
+    prop_operational = turbines1_i$prop_operational
   )
   
   df_turbines_results[df_turbines_results$model == "Turbine 150",
@@ -505,7 +506,8 @@ lst_results <- lapply(1:iterations, function(i) {
     bird_length = bird_i$bird_length,
     bird_speed = bird_i$bird_speed,
     prop_at_height = prop_at_height2_i,
-    prop_below_height = prop_below_height2_i
+    prop_below_height = prop_below_height2_i,
+    prop_operational = turbines2_i$prop_operational
   )