A group of German scientists based at the University of Kassel has carried out a pilot-study which suggests that nuclear and fossil-fuel based energy can be phased-out and substituted by renewables, without interrupting the output from the national grid. As they point-out, renewable energy has certain limitations: e.g. cloudy or windless days are no good for solar or wind-energy. However, their innovative "combined power plant" draws its energy from 36 different kinds of plant, including solar, wind, biogas and hydroelectric designs, in an effort to prove that such a mix of renewable energy can yield a consistent and reliable output of power, under a range of prevailing weather conditions and according to non-constant demand for electricity as is the reality.
This has indeed been achieved on a relatively small scale so far, enough to power 12,000 homes, or enough for a small town/village. The village of Caversham, where I live, has a population of around 9,000 inhabitants (maybe 4,000 homes), if you include the effectively accommodative developments, i.e. with no shops or other amenities, and hence are pretty much dependent on car ownership. One significant aspect of the German design is that excess energy is used to pump water uphill into a large reservoir, which can be used during times of peak demand to drive hydroelectric turbines as an additional source of energy. The ability to thus store energy is a vital component of the overall scheme to provide a constant supply.
If this approach can be scaled-up, it is calculated that a total of 448 TWh/year might be produced in Germany, which breaks down to: 37.5% from 10,000 onshore wind turbines, 26.8% from 5,000 offshore wind turbines, 13.4% from photovoltaics (covering 20% of roof surfaces)and 22.3% from biogas, involving 17% of agricultural land. It is suggested that 40% of Germany's electricity needs could be thus met by renewables by 2020 and 100% by 2050. I append a link to the full technical report below.
A very interesting approach. Of course there is around another 40% of total energy to be found for space-heating etc. and another 40% for transportation in the form of oil, assuming that the German break-down of energy use is similar to that in the UK. However, a relocalisation of German society, as will be the case across the entire world as oil supplies begin to fail our demand for them, substantially eliminates the latter component and Germany has substantial reserves of coal, which can underpin heating etc., even if its use can be avoided in electricity generation. The scheme will doubtless require a massive investment of money, energy and other resources to expand it to the future levels of electricity provision that are proposed, but such an integrated mix of supply sources may well be the best way forward, even at a local level.
Ultimately, in order to survive, all societies will have to be sustainable in terms of energy, food and all else they consume.