I did the figures not too long ago, but have forgotten the precise details. There are quite a few variables. Electric cars in themselves are much more efficient than internal combustion engines. But then you have to ask where the electricity is coming from. If it is from burning fossil fuels such as natural gas there is the generation efficiency to consider, plus transmission losses, plus battery charging losses. The "well-to-wheels" efficiency for fossil fuels turns out not to be enormously different whether you burn them in an ICE or burn them to generate electricity for an EV. Once you have a comparison of ICE and EV efficiency, with assumptions about the source of electricity, you can look up today's usage of electricity and fossil fuels for transport. A good starting point is this [broken link removed], which handily gives you energy use by sector in various comparable units such as toe (ton of oil equivalent).
Other sources ([broken link removed], ) say that Ireland uses 14.6 million toe in primary energy, of which all but 1.9 mtoe is imported. 47% of that is actual oil, and 70% of the oil is used for transport. That is 4.8 mtoe, which equates to 56 TWh. Our total current electricity generation is 27 TWh.
Being pessimistic, that means we would have to triple current electricity production to cater for EVs. Various points are debatable. We already have one of the highest penetrations of renewable energy in the world at about 25%, mostly from wind. It might be difficult to do any better than that as intermittent renewables start to destabilise the grid beyond a certain penetration level. But then, a smart charging infrastructure for a large number of EVs might make it possible to use higher wind penetration.
Solar power has been growing at exponential rates around the world. But there are limits to solar in our part of the world. There is simply not enough sunlight in winter to power the domestic car fleet in the British Isles. This highlights one of the drawbacks and current unknowns about future solar -- will we ever be able to store electricity on long time scales of weeks or months? There is also the question of the rate of growth of solar in mature markets. Technology optimists say that continued exponential growth will make solar the number one source of power worldwide in just a few short years. But in Europe it is showing signs of following a sigmoid curve -- slow early adoption, followed by a period of exponential growth, then a gradual plateau. Shortening the exponential growth phase by just a couple of years means that solar becomes a significant part of the energy mix but not the magic bullet that some claim.
A pragmatic point is that right now in Ireland we manage to increase the electricity generation capacity by 20% every decade. And that is just enough to satisfy ordinary electricity demand increases. If EVs require an additional 100% or more capacity increase, you are realistically talking about a transition period of many decades. The current electricity infrastructure in developed countries has taken a hundred years to build. Big energy projects work on those sorts of time scales. Anyone telling you that the electrification of the entire car fleet is just around the corner has not thought it through. (Also get ready for the reversal of tax incentives for buying EVs, plus electricity taxes to replace the huge revenues that currently come from fossil fuel taxes). The national grid company in the UK has said that beyond a few percent of EV penetration the electricity grid infrastructure would be creaking under the strain, unless capacity planning is undertaken now.
Needless to say, all predictions about the future must be taken with a grain of salt, as there are many uncertainties.
