Please note that none of the discussions of near-term limits address the question of what physics, chemistry, and biology tell us about what is achievable in manipulating matter and energy. Instead, they look at what we have, and imagine minor improvements in technologies and changes in deployments of labour and capital to exploit them. Words and ideas I offer here may be used freely and without attribution.
And I wouldn't exclude human technology from biology. It's only a marginally more advanced example of tool use and resource extraction.
With respect to energy efficiency, answers vary depending on the process under consideration and the improvements range from small to an order of magnitude or more. As one important example, photovoltaic cells have already shown >40% efficient conversion of solar energy to usable free energy, electric power, but "The highest yielding crops convert solar energy into plant material with an efficiency of 1-2%".
The achievable efficiency of transforming matter from one form to another can be (at worst) comparable to that in biology, for comparable products, and the mass-efficiency of delivering useful functions (structural strength, motive force, information processing...) can in many instances be orders of magnitude higher, for achievable, very un-biological products (e.g., >40% efficient photovoltaic cells). Words and ideas I offer here may be used freely and without attribution.
40% efficiency of conversion of solar energy into electricity is not the same thing as 40% efficiency of conversion of solar energy into photovoltaic cells.
And those biological systems are self-repairing, self-assembling and fully biodegradable. Can the last politician to go out the revolving door please turn the lights off?
plus, many of them are edible and nutritious -- which is more than I can say for a milliamphour of solar power. The difference between theory and practise in practise ...
and that leads us to the next question: which is more important, eating, or having an internet connection / iPod / private auto / whatever ?
we are now faced with the question: which of these luxury lifestyle accessories is compatible with a decent diet for everyone? which of them is even compatible with a decent diet for the affluent elite nations? our appetite for toys and profit has now collided with our appetite for food... The difference between theory and practise in practise ...
Indeed, but 5% seems more than reasonable, calculating efficiency relative to the thermodynamic minimum for the required transformation of raw materials. This is good enough to be attractive: -----------
In the context of achievable systems, assume
"And those biological systems are self-repairing, self-assembling and fully biodegradable."
These are nice properties, but I'd settle for (other means of) low-cost production and maintenance, together with full recyclability.
One must also consider the environmental advantages of consuming no water and only 1/10 as much land area fore equivalent energy production. Replacing total human power consumption, ~ 14e12 W, would require only 0.03% of Earth's surface area. Picture sparse arrays in selected, scattered patches of desert. Words and ideas I offer here may be used freely and without attribution.
