From the article in the current edition (a few typos in it):
**Tank Water Heater **vs. Demand WH
Average Annual Traditional Tank Heater Costs

Annual hot water demand: 87 gallons / day

335 days / year = 29,145 gallons/ year (I guess we’re not home for 30 days/year)
Power to heat up 1 gallon of water from 57 to 110F according to the multihousing laundry association is 0.2 kWh. The annual power requirement of heating the water from 57 to 110F for an American household is: 29,145 gallons/ year x 0.2 kWh/ gallon = 5,900 kWh/ year
Annual cost of 5,900 kWh: 5,900 kWh/ year x $0.11/ kWh = $649
The cost to keep one gallon of water hot is $0.003. So, the cost to keep 21,145 gallons of water hot (standby): 21,945 gallons/ year x $0.003/ gallon = $87
**So the total annual cost of heating water using a traditional tank system is $649 + $85 or **$736
Average annual Tankless Water Heater Costs

Average energy to heat water to 110F is 6.2 kW

Average daily usage is 1.5 hours

Daily power needed to heat the water to 110F is: 1.5 hours x 6.2 kW = 9.3 kWh
Annual costs to heat water using a tankless water heater is: 9.5 kWh/ day x 335 days/ year x $0.11/kWh = $343
The total cost of heating water using a tankless water heater is $343 + $17 or $360.
MY ANALYSIS:
STORAGE TANK:
> 87 gal/day x 8.33 lb/gal** x** 1 btu/lbdeg x 57 deg temp rise = 41,308 btu’s/day
> divided by 3413 btu’s/kWh = 12.1 kWh/day used
> 12.1 kWh/day x 335 days/year x $0.11/kWh= $445.89 + $87 (yearly standby loss)= $532.89…a bit different than $736 in the article
TANKLESS:
The tankless instantaneous unit will still have to heat the same 87 gal/day of 57 degree water to 110 degrees and will use the same $445.89 electricity as the tank**. The only difference should be the** $87/per year standby losses.
SOOOO…Let’s come at it another way:

The tankless claims to use 9.3 kWh/day = 31,741 btu’s/day

8.33 lbs/gal X 1 btu/lbdeg X 57 deg temp rise = 474.8 btu’s/gal

Divide 1 by 2 = 66.9 gallons per day heated!!! A MISTAKE or A MISREPRESENTATION???
And they assumed that the tankless was 100% efficient but figures by better authors/orgs claim energy factors (EF) of from 0.82 to 0.94 for them. so add another 1015% onto the $445.89 comes to $490.48 to $512.77.
versus… $532.89 for a storage tank
Something’s amiss in the article!!!