Most articles highlight the economic stupidity of Tesla's Powerwall. It only makes sense off-grid and requires heavy subsidies.
How You Get Suckered
Denninger's point is correct...as far as it goes.
But his numbers are a bit off. The
average cost of electricity
to residential customers in the U.S. was 12.3 cents/kwh in Feb. of this year, which is up from 11.9 a year earlier - it's only 10c per/kwh if you factor in commercial and industrial customers who can get quantity discounts. In half a dozen states, it's up around 20c per, and in Hawaii, 30c per:
http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a
Where his argument falls apart, is that he failed to take tiered rate plans into account, which are usually either tiered by how much is used per month:
http://www.pge.com/en/myhome/saveenergymoney/plans/tiers/index.page
Or, by time of day:
http://www.pge.com/en/myhome/saveenergymoney/plans/tou/index.page?
That PG&E plan goes from 15c at night, to 35c during peak hours (rounded off).
So....lemme see...just taking a WAG that say 1/3 of daily use is during that peak time. Average monthly use per residence is 909 kwh:
http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3
So that would be a savings of 20c/kwh x 303 kwh/month = $60.60 per month. Times 120 months = $7272.
Okay, so it's conceivable that used purely for a load-shifting strategy (no solar) it could at least pay for itself...in some areas...maybe...depending...
But If the price of the hardware comes down (which it might), or if the price of electricity keeps going up (which it will), then eventually, it might be smart to have it for load-shifting.
Add in the cost of solar and forget it - it'll probably never pay for itself.
But subsidizing might be worth doing if it enables large scale load-shifting - which averages the daily load on the grid and delays the cost of adding generating capacity to the grid.
But yea...like I said - screw the house, I want it for my camper.
