So, tidal looks great. How much of the ~20 TW we use now, not to mention the increased usage as third world countries industrialize, can we get from that? (Serious question, please answer with a number and a citation) According to this:http://en.wikipedia.org/wiki/Cost_of_electricity_by_source
we can see that the costs of various methods of energy production vary dramatically with local conditions and regulatory frameworks. Hydro is generally the cheapest, but it has its own environmental impacts, and there are a limited number of sites to build on. Nuclear generally looks pretty comparable with other mainstream methods of production, and using breeder reactors probably wouldn’t make it cheaper, but it would increase the supply of fuel enormously and decrease the waste. I’m not sure where you got that bit about nuclear being expensive. (Unless you’re talking about the externalities, but those apply to a lot of things, particularly, as we are discussing, hydrocarbons.)
Nuclear, geothermal, and hydro are the only non-hydrocarbon methods that are suitable for base load, and, of the three, nuclear is the only one we can scale as much as we need to. (Tidal is also not a constant power source, though it is more predictable than wind or solar, so you could probably find a way to store some of the energy and jury rig it into base load. I don’t know how much it could scale, so it would be nice if you could find some numbers for that, but 20TW is a lot.)
Edit: I just found this website, extolling the virtues of tidal power: http://www.marineturbines.com/Tidal-Energy
From the website:While estimates of global potential may vary, it is widely agreed that tidal stream energy capacity could exceed 120GW globally.
Eg. Generally accepted estimates place the capacity of tidal energy at ~0.6% of current global energy use. Solar actually does scale, (If you consider covering ~1/4 of Arizona in solar panels to supply the US with its 5TW of power scaling) but storing the energy to use it as base load is an enormous engineering challenge.
