So, I did a price comparison on water heaters since I may have to replace my electric water heater soon, and uh.. wow, the average energy usage difference in cost is pretty crazy. Prices are based on what I pay for natural gas/electric in my area in the states, usage is how many kilowatts/therms (1 therm is 99976.1 BTU) get used per hour. Daily usage is an estimate of how many hours each device uses per day.
The downside though is the hybrid electric (heat pump) water heater has a high up front cost. Easily 4x the cost of a standard electric heater. But the total energy usage and tax credits (if/when applicable) would more than make up for the difference in a few years, that's for sure!
Oh! Can't forget utility rebates either! For example, my electric supplier offers a $100 rebate bill credit on energy star hybrid electric water heaters!
Okay so it turns out the hybrid water heater does have 4.5kw elements inside of it, but I'm guessing that those are kind of like emergency backups to help keep up with unusually high demand. So while it is capable of pulling 4.5 kwh, it'll still use on average maybe a little over half a kilowatt.