[strider3700]

I just checked the overnight charts on the hotwater heater and every 3 hours the tank ran for about 3 minutes to maintain it's temperature. So that works out to 24 minutes of operation per day. If it's using 5kw while running then it's using 2 kwh each day. or roughly 15 cents.

<Edit>

I did a bit of thinking on how to calculate total daily usage and came up with a pretty accurate in this case solution. I simply go to my spreadsheet and added a column with =if(wattage>100,1,0) so basically if the wattage being read is above 100 then it's on else it's off. The 100 is used to remove noise from the readings, I get spikes up to 50ish watts which is probably just random noise in the signal. The heater definitely uses more then that when turned on so I'm ignoring them. Anyways this gives me a minute by minute account of if the heater is on or off. From there I just sum the number of minutes it was on and applying the 5kw value calculate the total kwh used during the day.

So yesterday from 12:15 to midnight we used 9.5kwh to heat hotwater which cost roughly 76 cents. This sounds high but our major water usage came in the afternoon so the morning probably wouldn't be much more usage.

This works out to roughly $22.8/month for hotwater or $277/year for hotwater. Assuming I can achieve 70% solar heating which is the commonly thrown around number for my location then my in progress solar hotwater setup will save me $194/year giving me a roughly 5-6 year payback I think. THis is before utility increases and in a house with a baby and a toddler. Long term hotwater usage will go up and the utility has already applied to have a 10% a year increase in costs for the next 3 years.