Summary: Marine renewables, geothermal and algae supply. Some nuclear and CCS.
Mark Brinkley is the author of the Housebuilder's Bible.
Adding the cost information to the model introduces a whole new level of complexity which doesn't supply the easy answers you might expect. The most telling chart is Costs Compared: what stands out from this is that, on a 40 yr view, there is very little cost differential between the various options. The most cost efficient model costs £4750 per person per year, the most expensive (FoE) is around 20% more, but tellingly, doing nothing to mitigate CO2 emissions at all (i.e. leaving everything at Level 1) also seems to cost around £4750, almost exactly the same outcome as the most cost effective solution. That's a potentially explosive conclusion, and one which I am still trying to get my head around.
It's worth bearing in mind that the "Doing Nothing" scenario is not quite that at all. It is really more a case of "Do Little." It still involves many assumptions about the future, including having CCS power stations, 30,000 large wind turbines and 450,000 micro wind turbines (does anybody now really think this is likely?), and a fair amount of bioenergy. It might be more instructive to construct a future based on no renewables, and lots of new gas fired power stations, using Lancashire fracked gas as a power source, but this doesn't appear to be an option.
The big nuclear question turns out to be something of a score draw. The "let's build as many nukes as we can" option appears to be mid-range in the list of cost outcomes, cheaper than FoE's all renewables and demand reduction, but only by around 10% which is probably not significant on an exercise of this nature. My own stab at a solution (I haven't changed my original version) is one of the more expensive ones, largely because I ramped up tidal power which seems to be very expensive. I hadn't realised this. But then it's such a complex model, with so much information needed to drive it, that it's hard to build a coherent cost effective solution.
I think this calculator has great potential as a teaching aid, maybe at A level or even GCSE. Brilliant way to introduce the issues to the generation who will have to solve the problems we are leaving them with. At the moment, we are still scratching the surface, but the2050 Pathway does provide some sort of roadmap at last.