cc128-kWh-calculation.rb

# Thanks Seth Darlington!

price_per_kwh = 0.1248 # dollars
  
query = RealtimeMessage.this_month

previous = query.first
usage = query[1..query.count].reduce(0) do |sum, message|
  elapsed_seconds = (message.created_at - previous.created_at)
  elapsed_hours   = elapsed_seconds/3600
  
  kW  = message.ch1_watts/1000.0
  kWh = elapsed_hours * kW

  previous = message

  sum + kWh
end

cost    = usage * price_per_kwh
elapsed = query.last.created_at - query.first.created_at

p "Usage: #{usage.round(4)} kWh @ $#{price_per_kwh} = $#{cost.round(2)}"
p "Accounting for #{(elapsed/86400).round(4)} days (#{(elapsed/3600).round(4)} hours) in #{Date::MONTHNAMES[Date.today.month]}"