In short, the most viable option currently, in his opinion, is the thorium reactors. Current uranium reactors can be converted to work with thorium.
"The main point of using thorium, in addition to the proliferation issues with uranium, is that there is 10 fold amount of it available compared to Uranium. If you take into account also the fact that we only use uranium-235 in our nuclear reactors, and this consitutes only 0.7% of the total amount of uranium, the increase is 100 fold.
Thorium reactors also operate by burning uranium. This is created from thorium by bombarding it with neutrons. This forms uranium 232, which is highly radioactive and is hence hard to deal. This is why U232 can't be used for nuclear weapons, it's hard to handle."
Don't take this the wrong way, but when the scientists or the government set an ambitious goal like this, that are 4 decades away. It usually means that currently we have no clue how to go about solving it and hopefully our successors will figure it out.
As Bill Gates explains the current renewable technology is not viable. This is because of various reasons, such as low ratio of energy invested vs energy returned, instability (eg. what you do when the wind is not blowing?), requirements for a possible site, et cetera.. I fully agree that it should be the long term goal to switch over to renewable energy, but with current technology it is out of reach. Therefore we a need a stepping stone that the nuclear energy can provide us with.
All the questions you mention have been discussed for a full decade here. Numerous research institutes have been working on that for a decade. Several plans have been proposed and discussed. As a first step Germany has jump started its renewable energy industry a decade ago. We moved from 6 to 16% during that decade and now have several hundred thousand employees in that industry, numerous small and medium companies, numerous research institutes, ... we are already exporting a lot of that technology. It is expected that in a few years this industry will be larger than our automotive industry.
Our government actually does something for the tax payer money:
Renewables' contribution to energy supply in Germany continued to rise in 2010
17 percent share of electricity supply
370,000 employees in the sector
The share of renewable energies in Germany's electricity supply rose further in 2010. At 17 percent, the share was about half a percentage point higher than the previous year. These are the preliminary results calculated by the Working Group on Renewable Energy Statistics (AGEE-Stat) for the Federal Environment Ministry. This growth was achieved in spite of the sector being hampered by adverse weather conditions. As there was very little wind in 2010, the wind power yield of 36.5 billion kilowatt hours (KWh) was the lowest since 2006. Even so, wind energy remained the key pillar of renewables, with around a 6 percent share of the total electricity supply. Clear increases were recorded for electricity generation from biogas and the photovoltaic sector. Solar power almost doubled its contribution, covering around 2 percent of total electricity demand.
Current scenarios show that in just ten years, renewables can cover 40 percent of Germany's electricity supply. An increase of 12 terawatt hours (TWh) per year is considered realistic. (1 terawatt hour = 1 billion kWh).
The renewables' share in total final energy consumption for heat rose from 9.1 percent in 2009 to just under 10 percent in 2010. The renewables' share in fuel consumption rose slightly to an estimated 5.8 percent (2009: 5.5 percent).
Overall, in 2010 renewables covered around 11 percent of Germany's total final energy consumption for electricity, heat and fuels. This is significantly higher than the previous year (2009: 10.4 percent) and is remarkable because energy consumption was considerably higher than in 2009, due to both the economic recovery and the cold weather.
Renewables also increased their contribution to climate protection. In 2010, around 120 million tonnes of greenhouse gases were avoided through the use of renewable energies (2009: 111 million tonnes). Around 58 million tonnes of these savings can be attributed to the Renewable Energy Sources Act (EEG) alone.
The figures prove that renewable energies were able to keep pace with the economic recovery and continue their trend of a steadily growing share in our energy supply.
Alongside this, renewable energies also gained importance as an economic factor. Initial estimates for the BMU show that, at around 26 billion euros, investments in renewable energy installations were around one quarter higher than in 2009 (20.7 billion euros).
This development is reflected in the employment figures linked to the expansion of renewables. Last year, employment in renewables rose again and latest estimates show there are now around 370,000 jobs in the sector. This is an increase of around 8 percent compared to the previous year (around 339,500 jobs), and well over twice the number of jobs in 2004 (160,500).
These numbers show the point I'm trying to make here. The resources currently occupied in putting the current inefficient technology to use could be instead used in R&D to develop the next generation solutions faster. During this period of time nuclear reactors (or thorium reactors in the future) could provide a fairly clean and stable source of energy until viable renewable alternatives are found.
A relevant TED talk by Bill Gates (Bill Gates on energy: Innovating to zero): http://www.ted.com/talks/bill_gates.html
In short, the most viable option currently, in his opinion, is the thorium reactors. Current uranium reactors can be converted to work with thorium.
"The main point of using thorium, in addition to the proliferation issues with uranium, is that there is 10 fold amount of it available compared to Uranium. If you take into account also the fact that we only use uranium-235 in our nuclear reactors, and this consitutes only 0.7% of the total amount of uranium, the increase is 100 fold.
Thorium reactors also operate by burning uranium. This is created from thorium by bombarding it with neutrons. This forms uranium 232, which is highly radioactive and is hence hard to deal. This is why U232 can't be used for nuclear weapons, it's hard to handle."