Japan transformed its entire country from nearly complete devastation during WWII into a tech leader in various manufacturing and industrial technologies, including automation and robotics. They also possess some of the world's best research and technology institutions (e.g. Tokyo University). So if it's "hand-wavy" to believe in their capability to build better future, based on a quite miraculous track record, you can call me "hand-wavy."
It is handwavy. Name the source of that energy that will allow providing that much electricity.
Back of the envelope calculations. Even that is somewhat handwavy.
For example, with solar power in Japan, you could get maybe 100% (EDIT: fixed the estimates! They're better but not better enough.) more than is currently grabbed - with massive subsidies and research already there! And it is one of the countries relying on a lot of it! Comparable with Germany in fact, but with better insolation.
It is not enough. Nowhere near. That expansion will provide about 25-30% of current power use in solar, total.
With hydro and tide power, just 10-15% more is available unless you want to destroy all the coastline (then maybe 25%), which you cannot if you want to feed people. Again not enough. Japan already uses a lot of available hydro capacity.
Wind is not really feasible either... About 10% more is available of mostly offshore wind. Everywhere feasible is already installed.
Biomass, maybe 25% more for total conversion - and it is not a clean fuel.
Fusion is too far away for now extrapolating the linear improvements in this technology.
Additionally, everything in Japan (production, services etc.) is already tweaked to be energy efficient...
As it is now, Japan is burning a lot of oil and coal. On the order of ~50% electricity is fueled by those sources. It has increased additionally since the disaster because no other source can cover it.
Serious solutions involve:
1) Clean and safe nuclear fission power. Again. I'm sure Japanese are able to figure that one out, even in their special circumstances which complicate matters.
2) Massive breakthrough in fusion. Good luck with that. There is already much increased investment. Given current trends, even if the linear factor on the development of fusion improves, we're looking at 50 years or so of development time for that to be viable.
3) Solving huge political issues to expand out-of-country solar capacity, import even more green electricity from other countries. We're talking world government scale here.
4) Another undisclosed physics discovery worth a few Nobel prizes.
Not the OP but I don't believe you are very familiar with modern Japanese history.
First, your point that they had a "miraculous track record" in the past means it's reasonable to be "hand-wavy" about the future is absurd. Are you familiar with the phrase "Past performance is no guarantee of future performance?" Would you say Germany or South Korea can implement any nationwide policy easily because they share a similar historical background as you've described?
Second, Japan's miraculous growth had a lot to do with direct US intervention and the Korean War. The US created a Supreme Command of Allied Powers program directed by MacArthur that made a wide set of economic and political reforms. [0] And the Korean War essentially made Japan the de facto supply depot for the UN, driving a lot of US investment money there. [0]
Third, Japan in the past had plenty of human capital and cheap labor. This is certainly not the case anymore. I'm not saying they're doomed, but their population pyramid is quiet different from post-WWII Japan. [1]
I'm quite familiar with the history of modern Japan and the US' role in establishing its prominence. It's what I studied as an undergrad, actually. And yes, the strength of their economies and technical standing, derived from this historical support, are precisely what put them in a good position to achieve this aim. It has allowed them to advance manufacturing technology to a far greater degree than the US, who let all of their expertise wither with offshoring (in part to assure alliances with client states). As such, Japan has a large, skilled manufacturing sector base that can tackle this undertaking. In addition, their resource constraints have created similar expertise in advancing energy efficiency and maintaining modern grid infrastructure, both key to making renewables successful.
Japan was largely shunted down the path of nuclear energy because of US intervention in their energy sector. Now that enthusiasm for nuclear energy has largely cooled in the US, both because of its expense and a renewed emphasis on fossil fuels, Japan has greater freedom than ever to transition to renewables. They don't have fossil fuels and nuclear energy is more widely unpopular than it has ever been in the wake of Fukushima.
As for the labor market, there a large issues with structural unemployment among young people which this transition could help address. And regardless, the Japanese government is more directly interventionist in their economy, such that were this change affected, big businesses would follow suit. The line between TEPCO and the Japanese government is already as blurry as blurry can be.
