Sorry, your calculations are not off by 50%, without government subsidies and not including overly optimistic production assumptions not to mention maintenance expenses you are still off by well over 1300%.
Using the prices in Texas which has the cheapest systems in the county at $3.21 per installed peak wattage power production. A system that produced 100 k/W peak would cost $321,000 dollars to begin with for installation costs not $24,000 as in your assumption. That works out to 32.1 cents per kWh using your previous assumptions. Our friends who live off the grid spent $40,000 to have a 5 k/W residential system installed with storage batteries and a propane powered back up generator system. This comes up to $8.00 per installed peak wattage power production. This was a few years ago, but the actual prices people are paying for complete systems like theirs have not dropped all that much since. They also have had significant maintenance expenses not to mention their time. And during the winter their backup generator runs a good deal of the time, so their fuel expenses have been much more than they originally expected.
There are several other problems that you have not factored in... first is that to be autonomous the building would need to have an extremely expensive and very maintenance intensive storage system to provide power during times when the sun was not shining on the panels at full strength. Not to mention that the panels need to be cleaned frequently in dusty environments and the size you are speaking of would require a great deal of water and expensive man hours.
When customers decide to hook their systems into the power grid this requires additional expensive equipment also. The government has forced utilities in places like California to purchase excess power from people with solar panels. Unfortunately this mandate increases expenses for the utility because they still need to have the same amount of power production capacity available as they would without a bunch of privately owned solar panels hooked to their grid. This is why industrial users generally pay most of their power bill based not on consumption but on a demand metering system. It is the peak demand required for the infrastructure that costs utilities the most not the amount of money for required for fuel per kwh.
Where we live the power goes out frequently, so we have a backup generator that fortunately for us runs on natural gas which is far cheaper than propane gasoline or even diesel. So even though our generator is very inefficient as compared to a large power generation facility our cost per kwh produced while running the generator is barely more than what the utility charges us for electricity.
If we were to place the generator in the house in the winter with a secure exhaust system to utilize the excess heat coming from the generator, it would actually save us a significant amount of money during the winter. And this is where real gains in efficiency can be made. Utilizing waste heat from a generator to heat your house... some people already do it, but most of us just are too wimpy to risk dying from a Carbon Monoxide leak.
I was working backwards, trying to figure out the cost of the installation based upon the price per kWh stated in the article, while plugging in plausible values for the solar constant, an optimistic no. of hrs of sunshine per day, very high conversion efficiency, etc. So, to be able to produce electricity at a price of 2.4 cents per kWh, I arrived at a cost for the installation (which would have to have an area of approx. 800 sq. meters) of about $24,000. As I pointed out, that is a ridiculously low cost for a photovoltaic installation of that size. In that much, you and I are in agreement.
I intentionally did NOT consider such economic factors as amortization rates, variable power supply, etc.
I'm well aware of the other problems you mentioned.
Regards,