What scale are we talking about if we want to provide a large majority of the worlds energy with Solar Concentration?
Temp and size
In terms of scale, there are two: temperature and power. Focal temperature is proportional to the concentration factor, regardless of size, and power is proportional to area of the machine multiplied by efficiency.
Efficiency is determined by environmental factors, the reflectivity of the mirrors, the difference between focal and application temperature, and absorption, convection and conduction losses. Since high reflectivity mirror is fairly cheap, and at high focal temperatures losses become crushed factors, the dominant factor for efficiency is focal temperature and thus concentration factor.
Efficiency
End of story: a high concentration reflector will be about 60-70 % in converting surface area of reflector into usable power (for relatively low temp applications, such as 200C steam). There’s about 1000 watts per m^2, so this makes say 600 watts of power.
Energy per person
According to this source, average power consumed per person in the world in 2005 is 1778 kg-oil-equivalent per year.
600 watts per m^2 working on average 6 hours a day, works out to needing about 15 square meter of reflector per person (see below for calculation), say 4x4 meters.
Bottom Line
For Solar Fire, Tinytech is confident they can produce at about 100 USD per square meter, in batches of 10. So this would mean 1600 USD investment for each person, which seems feasible on a global level. However, my feeling is that in a few generations of the technology it will be possible to produce high temp concentrator for less than 30 USD per m^2, which would mean 480 USD per person, which would work out to about 3.36 trillion dollars.
Using local wood for most of the structure my feeling is the cost can be reduced to 10 USD per m^2, which would be 1.1 trillion dollars. Mirror in India can be bought for 2USD per square meter, so if the structure is essentially free such as from local bamboo or hardwood and using local labour I think 10USD per m^2 seems reasonable considering the advances that would be made if the idea is to build 100 billion m^2.
Also, we have to consider the fact that the energy from these machines would be very cheap and the main ingredient to making more is energy (aluminum and sand for glass are abundant materials but require a lot of energy to produce), so the process would be positive reinforced.
Conclusion
Now, obviously even with 100 billion m^2 of solar concentrator there would still be need for other sources of energy for niche uses (though we can note that solar made charcoal is a way of storing solar energy by making biomass burning much more efficient), but I think it stands to reason that a large enough portion could be covered by solar concentration to radically reduce pollution, carbon emissions and deforestation enough to start massive reforestation which would capture carbon dioxide.
Other affects of this plan would be to radically increase clean water access since with energy access it becomes affordable to boil water to disinfect it (some water is polluted chemically, in which case distillation is also required, but most water issues are from microbes and boiling is all that is needed).
Land use perspective
So a village of 1000 people would need 14 000 m^2 of concentrator, 1.4 hectares. Currently in the US about .5 hectars of farm land is used per person, elsewhere about 0.25, so with solar concentration land use would add up to 501.4 hectares or 251.4 hectares, meaning land used for solar concentration is essentially insignificant compared to that needed for food.
Even with 0.07 hectares that is considered a bare minimum of farm land to sustain a person, this means 70 hectares for a village of 1000, still 50 times more than what would be needed for solar concentration.
So even if we multiply our estimate of solar concentration area required, by 3, 4 or 5, it’s still largely insignificant compared to farm land required. What’s more, solar concentration (unlike biofuels) doesn’t compete with farmland, as we can put a solar concentrator on arid land.
Does this make sense?
Estimates for biomass based societies result in far larger area of land required. For instance, already the use of corn to fuel cars has had impact on food prices while displacing an insignificant amount of fossil fuels use. It’s estimated all the farm land in the world would be required just to fuel the cars in America on bio-fuels.
How can solar concentration be radically different?
Both biomass/fuels and solar concentration get their energy from the same place: the sun. However, photosynthesis of plants is at best 10 % efficient in optimum conditions. Those optimum conditions are relatively rare and so if it’s too hot, too cold, too wet, too dry, the plant does not grow. So total solar energy captured is very low. Much of this energy that is "produced" is used by the plant to grow. Plants are simply not suited to run machines or kilns: though they are ideal to maintain the ecosystem.
Finally, when we burn a plant we don’t do so 100% efficiently. When a bio-fuel scientist says bio-fuel can be produced from some plant, such as corn or algae, at 40% efficiency in the lab, this is only to convert the plant into the fuel, not to convert the original solar energy into the fuel. However, an honest scientist would provide the figure of converting the solar energy to the bio-fuel, in which case the efficiency is very low regardless of the technology used since plants don’t store much solar energy (that’s not their purpose).
True plant-burning efficiency changes from place to place depending on conditions, but probably in the best conditions the figure is at best about 1% captured by the plant and then at best 60 percent of this lost in the cultivating-processing-burning process, working out to 0.6% efficiency. So to burn plants a huge amount of land is required.
Since solar concentration converts solar energy directly into thermal energy, the kind of energy we use and depend on most (and radiation to heat is among the most efficient energy conversions around), efficiency is extremely high and so much less land is required.
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