That is the sad truth about alternative energy. They all have their limitation. Currnetly at best with the national grid system (despite it's current condition), alternative energy systems only supplement the grid. It helps but does not fix the proplem. Solar does work on cloudy days but not as good on a sunny day.
I agree completely. Though I disagree with your calculations. Though "in theory" each person might not need much, westerners use a disproportionately large amount of energy. In the north, demand goes up in the winter right when solar flux is dropping and solar panel efficiency is dropping from thermal derating and snow cover. So, unless you can pump that energy up from the southern hemisphere, you'd need something like 12,000 square feet per person. (That's just a stab; I worked it out once a while back, but don't recall the numbers offhand.)
Not to mention night
You still have the problem of "night" with the solar plant. In the winter that is a significant part of the 24 hour cycle and also when there is considerable demand. The wind might be blowing or it might not. That means you need some traditional capacity to handle the load but that will be sitting idle when it is not needed. It is hard to amortize that investment if it is idle most of the time (the goal).
The idea that you are going to supplement this with home generators is simply ridiculous, from an economic or pollution standpoint. The most expensive power anyone has ever used came from a small genset. These small engines are also massive polluters. I know people who lived off their generators for extended periods after hurricanes and they call it "feeding the monster". A generator might be handy for a short (day or two) outage once or twice a year but if you are using it much more than that fuel costs and maintenance will easily double or triple your energy bill. Honda and Generac can never compete with FPL.
Energy demand is still much higher in the day than at night, hence why energy is so much cheaper at night. Solar fits the bill very well with this respect, as it's peak production coincides with peak demand, and as it's only constituting a small % of the total power generation compared to normal day/night fluctuations in demand, its loss at night is not presently missed.
And I was not suggesting we use portable generators to supplement solar in any practical way. But if we use 20% solar and wind, it will frequently drop to maybe 10%, in which case a few gas-fired plants may be economicical, even if they're only running 25% of the time. But the chances of this 20% dropping to 2% or 0% are so small and so seldom, that pocos would rather see rolling blackouts than build those plants.
So, what I meant was that while amoritization of idle plants makes them impossible, we do have a huge number of stand-by plants sitting around. I'm not talking 3500W gas burners in a garage, I'm talking 3MW or 500kW energy efficienct diesels sitting in industrial parks. Amortization is irrelevant; they're required anyhow. These big gens pick up the slack, and joe homeowner is still fat dumb and happy on the remaining 80% of utility power. Fuel cost is about twice that of coal for a diesel gen, but cheaper than building a new power plant. CO2 emissions are slightly less than coal. Efficiency is somewhat lower than that of more massive plants, but it's not all THAT much lower, it's on the order of single digit percentages. And would only be running in that 0.0001% (or whatever) chance we simultanously lose all solar and wind power across north america.
Now, jack that 20% up to 80% like some environmentalists think is feasible and throw all this out the window!
FYI, fuel costs for a 500kW diesel generator run about $0.21/kWh (at $3/gallon) and all the other costs (including maintenance) are already a wash because they'd be required anyhow. You might see a small bit of increased maint if it runs a lot, but 24 hours per year for something like this would be insignificant to a typical stand-by generator.