One of renewable energy's weak points to overcome: land use

Recently, two scientists have pointed out an important limiting factor of renewable energy sources, their use of land area. Each scientist use his own calculation.

1) Power density (W/m²; watts per square meter)
It was Vaclav Smil who has been a proponent of "power density", his own index of land use by energy sources.
To make a table from one figure in his 2008 book (on page 312), power densities of energy sources are:

Power Density (W/m2)	Energy Conversion Facilities (Roughly in descending but overlapping order)
100-10000	Oil fields
	Coal fields
	Thermal power plants
10-100	Flat plate solar heat collectors
	Central solar towers
	Photovoltaics
	Hydro: upper-course (high heads, small-reservoirs)
	Geothermal
	Tidal
1-10	Wind
	Ocean heat
0.1-1	Hydro: lower-course (large reservoirs)
	Phytomass

Compared to fossil-fuel energy conversion facilities, renewable energy conversion technologies have very low power densities.
(By the way, I hope he would provide exact numbers for each energy sources in his upcoming book, Energy Transitions: History, Requirements, Prospects (coming in June)).
* (Update on May 18, 2010) I think Dr. Smil made public specific numbers for energy densities of power resources in his latest series of contributions to MasterResource blog at http://j.mp/Smil_Power_Density.

2) Land use intensity(km²/TWh/yr)
Robert I. McDonald and his colleagues published a controversial article that compared land use intensities of energy sources. As you have already noticed from its unit of measure, this index is somewhat an inverse of Smil's 'power density.'
Dr. McDonald's calculation is like this:

Here again, renewable energy sources are disappointing. And one reason this figure is controversial is nuclear power's great efficiency in land use.

Then what should we do?
If we want to make the catch-phrase of the Institute for Energy and Environmental Research "carbon-free and nuclear-free" come true, we need resolute policy measures and radical changes in people's mindset.

Sources:

Makhijani, A. (2007). Carbon-Free and Nuclear-Free: A Roadmap for U.S. Energy Policy. Takoma Park, MA: IEER Press. [Full-text at http://j.mp/CFreeUFree]

McDonald, R. I., Fargione, J., Kiesecker, J., Miller, W. M., & Powell, J. (2009). Energy Sprawl or Energy Efficiency: Climate Policy Impacts on Natural Habitat for the United States of America. PLoS ONE, 4(8), e6802. http://dx.doi.org/10.1371/journal.pone.0006802

Smil, V. (2008). Energy in Nature and Society: General Energetics of Complex Systems. Cambridge, MA: The MIT Press.

Smil, V. (2010). Energy Transitions: History, Requirements, Prospects. Westport, CT: Praeger Publishers.