Quick thoughts on "alternative" energy costs

I have been doing some research on the issues of costs, scale,sustainability and short term feasibility. Some very quick thoughts, if anyone wants to look further there is plenty on the web. The "benchmark" electricity generation would be costs at an efficient fluidised bed coal fired power station, some where around 3-6 USc/KWh, depending on location, gas fired generally a bit higher (and up to double a year or two ago) but more flexible and suitable for peak power.

Hydro: drowns valleys but otherwise wonderful, cheap but available resources used up long ago.

Biomass: am I alone in thinking this a short term kludge? At best carbon neutral, good farmland will be in short supply in the global greenhouse, and will encourage deforestation. Utilising wastes like woodchips and straw will be more helpful, but this will not solve world energy problem except at the margin

Wind: not so much higher cost than fossil fuel when the wind blows at the right strength, and a rapid advance in turbine technology, but just so unreliable: even if the wind is too strong (over 25 metres/sec) blades have to feathered and power drops. Even in Denmark, a fairly windy place and the biggest per head investor in wind farms, special connections to Scandinavian hydro grid are in place for when the wind does not blow, and capacity utilisation is around 30%, no better than solar. Massacres birds.

Tidal power: limited sites and environmental issues (turbines in tidal estuaries rather than barrages can alleviate some of these). Needs a lot more research. Great potential for the UK, especially Severn estuary

Wave power: lots of potential, but too early to develop. Big inherent problems with storm damage

Solar photovoltaics. Horrible costs, even allowing for a normal halving on "experience curve" as technology matures, still far too high for mass power generation. Exotic cells use rare elements like gallium, those using more common materials (essentially crystalline or amorphous silicon)have an efficiency limit of 10-15% per cent.

Geothermal: limited sites in volcanic areas where underwater superheated reservoirs can be exploited, attractive costs where they are, but even then no truly renewable. Sites are "harvested" in a few decades, and prolonging life by water injection has problems e.g water disappears down fissures, or can even cause earthquakes. Not everyone can live in Iceland. The really interesting development is hot dry rocks. At certain locations (not sure how prevalent, there is test development in Australia and Germany)naturally mildly radioactive granites at up to 5km depth (the limit for commercial drilling technology) are overlain with impermeable rocks and have a temperature gradient of 40deg c/km instead of the normal 30. Inject water down under pressure to fracture the rock, and pump up again at temperatures of around 200 deg C to drive turbines. Far too experimental to be developed, so costs cannot even be estimated yet, but has the potential to be developed quite rapidly

Solar thermal: either a mass array of parabolic reflectors heating up water or another fluid, or hot air from a greenhouse array being conducted up a solar tower where it drives turbines. Works well in desert mid latitudes (20-40degrees of latitude, plenty of that around the world). Operating costs two to three times normal power costs, mainly because unit capital costs so high (plant only used at peak power for 30% of time) and power obviously intermittent. However there is interesting potential to bypass power generation entirely, with much greater efficiencies: temperatures generated are so high that it can be used to split water into hydrogen and oxygen thermochemically.

More about this in a subsequent post, and more about the obvious two medium term solutions, carbon capture at thermal power stations (sequestration) and nuclear