Al Gore recently claimed that the US can and should pursue 100% renewable power within 10 yrs.
i doubt there is a person in the world willing to disagree that this would be nice, if it were possible.
but, it is just so laughably impossible for so many reasons, technical, legal, economic, & political/environmental.
technical: there are too many technical problems to go into. technically, nothing is impossible. but there are a lot of hurdles. we'd need a new transmission system, new ways to monitor and control power flows, new ways to manage how much energy is consumed on a real-time basis, and all sorts of other incredibly complicated and expensive systems to take a collection of highly unpredictable power sources and transform them into the high quality power that customers are used to. to compare this to going to space is silly. they had one control room monitoring 2 men in a sealed capsule the size of a VW beetle for a few days. the energy system has thousands of control rooms spread over the country, monitoring tens of thousands of power sources exposed to the world and all of its randomness, being asked to perform flawlessly 24/7 for decades.
legal: again, too many issues to cover, but i'll mention one. the energy sector is still highly regulated in most of the country. generating companies go through a big expensive licensing process to get permission to build generation plants. as a return for their investment, they expect to be able to use these plants to produce power that they can sell to recover their investments. new coal plants are still being licensed for construction today. from the beginning of licensing to the completion of construction is often more than 10 years. after that, utilities expect to be able to run their plants for at least 30 years. telling utilities that they can't use their brand new plants is breaking a pledge. this isn't a free market. it is a heavily regulated one.
economic: everything about renewable power is expensive. the only way that anyone in the US can economically build wind power (by far the cheapest renewable power source today) is by using tax credits. even with the tax credits, most utilities can't economically justify wind power because of all of the extra costs that come along with unscheduleable and highly variable power supply. this is why renewable production mandates were created in many states - to force utilities to buy renewable power even though it isn't economical.
political/environmental: most energy projects face NIMBY problems. renewable energy projects face NIMBY problems on crack. anything involving water (wave, tidal, hydro, run of the river hydro) faces dozens of stakeholders, many of which are seeking to protect the environment and have veto rights unless it can be unequivocally proven that the project will produce exactly zero impact. wind is only slightly easier to find a location for. solar is easy to site, but all available solar technology to date uses huge amounts of nasty chemicals mined and refined in nasty ways.
i'm sure Al Gore is aware of these things. and i don't think he is actually insane. more likely, he is just trying to grab some attention and reframe the renewable energy debate. i think his hope is that he'll change the debate from "should we have 0, 5, 10, or 15% renewable power within a decade" to "should we have 100, 80, or 60% renewable power within a decade."