Todays Nature Journal (a top-tier science journal from the UK), has an excellent summary of the state of non-fossil fuel technologies, their capacities, and what it will take to meet power demand in the absence of burning fossil fuels. I think that most of the material is behind a subscription, so I thought it might be helpful to both point you to the article here, and to do a little summary below the flip.
There are several alternatives to carbon-based power generation. Electricity generation is about 40% of the global energy use today (all numbers here are sourced from the nature article, references within), which amounts to 18,000 terawatt-hours (18 times 10 to the 15th) annually, or 18 petawatt-hours for those peta fans out there. I recommend the article highly, just to keep all these potential energy sources in mind when considering a multi-source energy plan. For the purposes here, I'll stick mainly to the capacity question. These are also large scale technologies, to be plugged into a grid. The article doesn't focus on gains in efficiency, but mentions that usually efficiency doesn't necessarily lead to decreased power use, if people just find new ways to use power all the time.
Here are the main ones: (excerpted from Nature)
Hydropower
- there are now 45K dams in the world. It's estimated that they together provide 18 gigawatts. The europeans estimate that they are already at 75% of the capacity they could ever be at. The summary statement: A cheap and mature technology, but with substantial environmental costs; roughly a terawatt of capacity could be added.
Nuclear Fission:
- There are currently 439 reactors worldwide which generate 370 gigawatts. The most common fuel source (Uranium) is plentiful, especially if it is concentrated. Generally Uranium and Zinc are about equally common. The biggest hurdles are political, such as where to put the waste, although there appear to be technological solutions to these problems, given the political will. This technology is front-loaded in cost, and is vulnerable of attack, which is also true of hydropower (above). The summary statement: Reaching a capacity in the terawatt range is technically possible over the next few decades, but it may be difficult politically. A climate of opinion that came to accept nuclear power might well be highly vulnerable to adverse events such as another Chernobyl-scale accident or a terrorist attack.
Biomass:
- The oldest power supply. As of 2005, the World Energy Council estimates biomass generating capacity to be at least 40 gigawatts, larger than any renewable resource other than wind and hydropower. If all arable land not used for agriculture was 40% efficient, this might be increased to provide a maximum of 3 terawatts. The Intergovernmental Panel on Climate Change pegs the potential at roughly 120,000 terawatt-hours in 2050, which equates to slightly more than 5 terawatts on the basis of a larger estimate of available land. Summary: If a large increase in energy crops proves acceptable and sustainable, much of it may be used up in the fuel sector. However, small-scale systems may be desirable in an increasing number of settings, and the possibility of carbon-negative systems — which are plausible for electricity generation but not for biofuels — is a unique and attractive capability.
Wind:
- One of the largest potential power sources. The United States added 5.3 gigawatts of wind capacity in 2007 — 35% of the country's new generating capacity — and has another 225 gigawatts in the planning stages. With large deployments on the plains of the United States and China, and cheaper access to offshore, a wind-power capacity of a terawatt or more is plausible.
Geothermal:
- Only a couple of dozen countries produce geothermal electricity, and only five of those — Costa Rica, El Salvador, Iceland, Kenya and the Philippines — generate more than 15% of their electricity this way. The world's installed geothermal electricity capacity is about 10 gigawatts, and is growing only slowly — about 3% per year in the first half of this decade. Capacity might be increased by more than an order of magnitude. Without spectacular improvements, it is unlikely to outstrip hydro and wind and reach a terawatt.
Solar:
- a standard commercial solar photovoltaic panel can convert 12–18% of the energy of sunlight into useable electricity; high-end models come in above 20% efficiency. Increasing manufacturing capacity and decreasing costs have led to remarkable growth in the industry over the past five years: in 2002, 550 MW of cells were shipped worldwide; in 2007 the figure was six times that. In the middle to long run, the size of the resource and the potential for further technological development make it hard not to see solar power as the most promising carbon-free technology. But without significantly enhanced storage options it cannot solve the problem in its entirety.
Ocean Energy (tides and waves)
- There are a lot of projects planned for tidal current energy, but the largest one so far is a 1.2 megawatt turbine in Ireland that runs like a submerged windmill from the currents. The other kind of ocean energy comes from a "barrage" which is like a hydroelectric dam reservoir that gets refilled at high tide. The plant on the Rance estuary in Brittany, rated at 240 MW, remains the world's largest tidal-power plant more than 40 years after it came into use.
So there are lots of projects going on, and also quite a large delta between current use and non-carbon current non-carbon capacity. Sounds like a lot of new jobs to be created. Sorry for the briefness and lack of depth here, it's just really to let people know to go the article, which is really nice.