Make storage_cost configurable

app/models/entsoe.rb

@@ -13,10 +13,10 @@ class Entsoe
   attr_accessor :no_grid_charge_months
   attr_reader :storage_cost
 
-  def initialize(api_key = "c2287e07-0c26-4950-b430-22b7f75a8f2e")
+  def initialize(storage_cost = 0.05, api_key = "c2287e07-0c26-4950-b430-22b7f75a8f2e")
     @api_key = api_key
     @kwh_prices = {}  
-    @storage_cost = 0.05 # how much does it cost to store 1 kwh in battery
+    @storage_cost = storage_cost # how much does it cost to store 1 kwh in battery
     @no_grid_charge_months = [5,6,7] # months where we assume there is enough surplus from sun power
   end