Let's look at some astounding history. We need only go back ten years to find a time at which solar was vastly more expensive than coal and natural gas. If you were concerned about climate change it was worrying because replacing fossil fuels would have meant switching to nuclear which would have cause the price of electricity to rise and along with opposition to nuclear plants a switch to nuclear would have been difficult to sell. But then the price of solar simply plunged.
The reason? Look back further to see how expensive solar panels were. In 1977 solar cost $76.67/watt. By the time the solar line appears in the first graph solar panels had dropped to around $8/watt. 10% of what they had cost 30 years earlier. And they kept dropping in price. This graph cuts off at 2013 with the cost at $0.74/watt. That's 1/100th of the 1977 cost and 1/10th the 2007 cost. Last week solar panel prices averaged $0.32/watt.
76.67 / .32 = 240. A 240x price drop from 1977 to 2017.
Solar panels now cost 0.4% of what they did in 1977.
How low will things go? Here's a graph of the record lowest price for installed solar for each year from 2013 through this year when we've just seen a contract for solar in Mexico at $0.0177/watt. Under two cents per kWh.
And what really astounds me about this graph is the fact that the curve shows no signs of flattening. Year to year drop remains roughly constant and steep. At some point the curve has to flatten and any further drops would be small as little tweeks make small reductions. But we haven't arrived there yet. Maybe next year. Maybe later.
I checked solar insolation for a couple of sunny places in Mexico. Not much different than Arizona. Land and labor costs might be higher in the US but even so land and labor are not major cost factors for solar. It looks to me that the US will have no problem generating electricity with solar for less than $0.03/kWh in sunny parts which would mean about $0.05 in less sunny parts.
Along with onshore wind now under $0.03/kwh in places with good wind resources we're looking at being able to eliminate fossil fuels from our grids and at the same time making electricity cheaper.