Not sure what my power costs off the top of my head. It is different for the house vs the greenhouse. Think it was around .10 for our house. I tried to be excessive on the estimate. Better to over estimate a bit than underestimate when considering costs! Some parts of the country are even a little higher than .15 but I figured that was a safe point to use.
Interesting if you plug in .10 vs .15 changes the total to $4.20/month