Any way you cut it high availability costs money. If you expect the grid to handle backup for you then you should expect to pay them to do so. TANSTAAFL
An alternative could be to avoid simultaneous usage of the major appliances (A/C, electric oven, vacuum, washer/dryer, tea kettle, etc.), of course. That would probably require a mixture of behavioral changes and changes to the A/C system. For example a house with multiple A/C units (window units or upstairs/downstairs) could have them wired so they don't kick on simultaneously.
We live in south western ohio and said person took their bill from $300-400/mo to $30/mo (at 13 cents per kWh) with $11k of solar panels. They have a payoff period of about 3 years not including the $4k rebate they got which reduces the payoff cost to a little under 2 years.
Keep in mind this is a place that doesn't get nearly as much sun as much more southern areas/Hawaii.
I do agree that batteries still have a payoff period that is too long to be economical. Here's rooting for Mr. Musk.
It's based mostly on a recent paper in nature that estimates "that EV batteries in 2014 cost between $310 and $400 per kwh", but anticipates "It’s now in the realm of possibility that we’ll see $100 / kwh lithium-ion batteries in electric vehicles by 2020, with some speculating that Tesla’s ‘gigafactory’ will push into sufficient scale to achieve that."
His numbers roughly agree with yours:
So we’d estimate that at the following battery prices we’d
get the following effective LCOEs (Levelized Cost of Electricity):
- $300 / kwh battery : 33 cent / kwh electricity storage
- $200 / kwh battery : 22 cent / kwh electricity storage
- $150 / kwh battery : 17 cent / kwh electricity storage
- $100 / kwh battery : 11 cent / kwh electricity storage
All of those battery costs, by the way, are functions of
what the ultimate buyer pays, including installation and maintenance.