GRA wrote:Solar farms take up land, as do hydro and wind (although both of the latter allow concurrent uses), and so on.
I find it interesting that you exclude solar from concurrent uses - a statement which is simply wrong.
Let's list some of the concurrent uses along with photovoltaics:
- Vegetable farming
Permaculture News wrote:Japan requires about 2.5 million acres of land to supply the entire country’s electricity with PV . Under the solar-share scheme, it will take about 7 million acres of farmland to supply the same amount of electricity. Japan currently has more than 11.3 million acres of available farmland.
- Mushroom farming
- On rooftops - I suspect most of our electricity needs can be met this way.
- Over parking lots - another huge source of concurrent-use property for siting photovoltaics.
- Along the sides and in the medians of roadways.
At the end of the day, I doubt that photovoltaics need to take up ANY additional land which could have been used for food instead. Trying to compare photovoltaics with biofuels in this regard is extremely disingenuous.
PV on buildings is about the only energy source that doesn't take up any additional land. Large ground mount PV arrays do, although parking lots etc. won't be a problem. Biofuels take up much more space, and have much lower power densities as a result (actually, the lowest of all). I've recently got my hands on Vaclav Smil's 2015 book "Power Density", which details that for all energy sources, looking at not just the generating area, but also extraction, refining, transportation (and the energy/land needed for all those): https://www.amazon.com/Power-Density-Un ... 0262529734
PV has the highest power density (currently 10-15We/m^2) of all the renewable sources (barring solar water heating, which is around 100W/m^2), although wind, which is typically an order of magnitude lower than PV when looking at all the land area a wind farm takes up, improves some when looking at concurrent uses, as only the pad areas and access roads/transmission towers etc. preclude grazing and the like, although they may affect migration corridors.
Here's an extended quote:
The power densities of all energy production range over five orders of magnitude, from 10^-1 W/m^2 for liquid biofuels to 10^4 W/m^2 for the world's richest hydrocarbon deposits, but the final energy use of modern high energy societies fall mostly between 10^1 and 10^2 W/m^2 for homes, commercial buildings, industrial enterprises, and densely populated urban areas. This means that modern civilization extracts fuels and generates thermal electricity with power densities that are commonly at least one, usually two, and sometimes three orders of magnitude higher than the power densities of final energy uses in urban areas (where most people now live) and in individual buildings and commercial and industrial establishments.
Fossil fuels to supply urban areas are extracted and delivered with power densities that are higher than the power densities of large cities (10-30 W/m^2). Thermal electricity is typically generated with power densities that are one and often two orders of magnitude higher (300-3,000 We/m^2) than the power densities of electricity use in family homes (10-50 We/m^2). Liquid fuels for transportation are produced with power densities that are one to two orders of magnitude higher than the power densities of urban traffic. And even the very high power densities (300-1,000 W/m^2 for supermarkets, high-rises, factories, and downtowns) either overlap or are slightly surpassed by the power densities with which electricity and fuels are actually produced and delivered.
The modern energy system produces concentrated energy flows and then diffuses them through pipelines, railways and high-voltage transmission lines to final users. As a result, the space claimed by the extraction and conversion of fossil fuels is a small fraction of the ROWs [Guy note: Right of Ways] needed to distribute fuels and electricity. American extraction, processing, and conversion of coals and hydrocarbons take up less than 20% of the land that is required for pipeline, railway, and transmission ROWs and occupy less than 0.1% of the country's territory. In contrast, future societies powered solely or largely by renewable energies would rely on an opposite approach by concentrating diffuse energy flows captured with low power densities ranging mostly between 0.2 W/m^2 for liquid biofuels to 20 W/m^2 for [Guy note: future] solar PV-based energy. Renewable energy systems would have to bridge gaps of several orders of magnitude between the power densities of energy production and use.
As a result, tomorrow's societies, which will inherit today's housing, commercial, industrial and transportation infrastructures, will need at least two or three orders of magnitude more space to secure the same flux of useful energy if they are to rely on a mixture of biofuels and water, wind, and solar electricity than they would need with existing arrangements. This is primarily due to the fact that conversions of renewable energies harness recurrent natural energy flows with low power densities, while the production of fossil fuels, which deplete finite resources whose genesis goes back 10^6 - 10^8 years, proceeds with relatively high power densities. This power density gap between fossil and renewable energies leaves nuclear electricity as the only commercially proven nonfossil high-power-density alternative. That is why further advances in photovoltaic electricity generation, the renewable conversion with the highest power density, would be particularly welcome.
Several bold proposals would sever the link between renewable electricity generation and extensive land requirements. They include a variety of ocean energy conversions - exploiting the kinematic energy of waves and currents and the difference in thermal energy between surface and deep waters (Charlier and Finkel 2009; Cruz 2008) -- and wind generation by turbines placed within the jet stream (Roberts et al. 2007) None of these proposed alternatives is likely to evolve fast enough to supply a significant share of global energy demand (10% - 15% of 2013 use would mean 1.7 - 2.6 TW). Nor are there any realistic prospects for early, large-scale commercialization of landless PV conversions using giant buoyant PV panels in the stratosphere (StratoSolar 2014) or the Moon-based PV beamed to Earth by microwaves (Girlish and Aranya 2012).
Bolding is in the original. 255 pages of all the details for solar water heating, PV and CSP; wind; hydro including PHES; geothermal; biofuels; coal; oil; NG; and nukes, as well as calculations of land requirements use for various mixes of an all-renewable world, and that's quite enough typing for now.