Another point about what slowed the introduction of PHEV's, I do not want to sound conspiratorial but the automotive industry paid homage to its biggest shareholder, the petroleum industry.
The vast majority of patents for batteries, solar PV and syn fuels are all owned by various petroleum conglomerates. Clearly it is in their interest to do so but it is also in their interest to ration the distribution of competing methodologies and limit the rate of developmental progress at times.
In the case of PHEV's, the battery tech was never an obstruction to the basic option because short distance and emergency usage of a switch to override the ICE and allowing for a plug in re-charge option is a minor change that has actually been around since the beginning of this technology.
BTW, the PHEV mod is not possible on the Honda hybrids because their ICE and the EM share a power shaft. The Prius uses the electric transmission to apportion power from both sources independently.
Back to the market issue; the oil companies saw the idea of the PHEV as a potentially dangerous shift in market share away from oil based *pump* tech they control to grid based power that they do not have as much return from for many reasons.
When thinking of a PHEV it is important to realize that it is an integration of grid based and pump based technologies AND markets. Grid based power comes largely from coal now (60%) but it is also hydroelectric, wind, solar, and nuclear and in a way a PHEV is an *atomic car*.
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However technically the *electric recharge* part of a PHEV can be considered to be mostly powered by coal and that coal is burned with an economy of scale that is vastly more efficient, cheaper per kilowatt and cleaner than most individualized technologies (liquefaction) are going to ever provide.
Grid based power means much more than just a shift of fuel source away from a centralized product and profit structure by global cartels, it means a shift into energy generation that is significantly more *regulated* than pump tech and actually more free market based with the potential for many more people to profit from but those profits would not be as controlled by big oil and that represents a significant loss of market share on a global scale. Grid sourced power is a way of integrating ALL available energy sources on a large scale and moving engine development away from the ICE.
BTW I have just finished increasing the size of my solar PV array to 180 watts and I am powering my electric bikes largely by solar but the most efficient use of the solar energy would be to apply a grid-tie technology to it that allows for a back charge meter reversal to the grid. Decentralized energy production is an important part of the solution that is still vehemently resisted by industry as it represents a large scale loss of market share through increased competition and the loss of control through distributed sourcing and regulatory demand.