Zero entropy energy, ZEE
Physical sustainability criteria
The qualification 'sustainable' has different connotations: economic, physical, cultural. From a physical viewpoint a sustainable energy supply system should comply with three conditions:
• lasting for indefinite periods of time,
• without contributing to the entropy of the biosphere,
• capacity potentially sufficient to meet the world energy demand.
Constant flow and constant quality
From the Second Law follows that a sustainable energy supply is not possible if based on mineral energy resources from within the biosphere, for reason of the finite size of the biosphere as system and consequently the declining thermodynamic quality of mineral energy resources as more of these resources have been consumed [more i41]. As a consequence the energy consumption of the extraction per unit useful energy rises with time at an increasing rate. Even if the final energy consuption would remain constant, the total energy consumption including extraction energy and losses, would rise exponentially.
A constant flow and constant quality of high-quality energy which can be converted into useful energy with low losses has to be based on a stable energy source outside of the biosphere. Fortunately man has such an energy source at his disposal: a reliable nuclear fusion reactor at a distance of 150 million kilometers and operating for free for the next several billions of years. With a solar-based system human society will mimic the biosphere itself: life on Earth proved to be sustainable for hundreds of millions of years, without energy sources from within the biosphere. On the contrary, fossil fuels are fixed solar energy from eons ago.
No contribution to the entropy of the biosphere
This condition is inextricably connected with the first condition of constant flow and constant quality. Prerequisite for an energy supply which can be sustained for indefinite periods of time is that the useful energy generation does not contribute to the entropy increase of the biosphere, to prevent devastation of too many and too large ecosystem services of the biosphere [more i40]. Serious damage to ecosystem services might turn vast areas into inhabitable regions.
From the Second Law follows that any sustainable energy supply complying with the second condition is possible only if based on an energy source outside of the biosphere, i.c. the sun. The entropy coupled to the generation of solar radiation remains in space, so the biosphere receives high-quality energy just about entropy-free: zero-entropy energy, ZEE. Basically the entropy generation associated with conversion of solar energy into useful energy is a fraction of the entropy reduction possible with the generated useful energy. Implementation of a ZEE system might result in a net entropy reduction of the human evironment and consequently an increase of usefulness of it. A ZEE system is a conditio sine qua non for a sustainable economic system, although it is not the only condition.
A ZEE supply system for the world economic system must be based on technologies harvesting solar energy, directly or indirectly, e.g. by wind turbines, photovoltaic (PV) panels and concentrated solar power (CSP) systems. With a ZEE system human society will be able to mimic life on earth: the creation of ordered materials out of randomly dispersed substances for free.
The joint capacity of renewable energy sources (e.g. wind, photovoltaics, concentrated solar power, biomass), though not infinite, is amply sufficient to meet the world energy demand. Evidently unrestrained growth of the economic system, implying unrestrained growth of the consumption of useful energy and raw materials, is impossible because of the finite size of the biosphere. This observation sets also limits to the world population.
Large areas are involved in harvesting solar energy, due to the low energy density of solar energy. To meet the final energy demand of the year 2010. A few figures may illustrate the potential of a ZEE system. Each of the following scenarios, based on currently proved and operational technology, would be able to meet the world’s final energy demand of 2010.
• Offshore wind parks of 5.25 million turbines of 5 MW each, spread over an area of 2.6 million square kliometers, surface footprint some 525 km2.
• Onshore wind parks of 6.66 million turbines of 5 MW each, spread over an area of 3.3 million square kliometers, surface footprint some 13300 km2.
• Photovoltaic parks in desert regions, occupied area around 450 000 km2.
• Photovoltaic parks in temperate regions (comparable to UK, Germany), occupied area around 950 000 km2. A substantial part of this area (one half?) could be roof-mounted. World built-on area is some 2 million km2.
A mix of these techniques is obvious, combined with other techniques, such as concentrated solar power, hydro power and biomass. Energy efficiency improvements might reduce the demand by 10-40%, without compomizing comfort. Biomass could be used most efficiently as chemical feedstock, rather than as fuel. A major part of the electricity generated in above scenarios is assumed to be converted into hydrogen, for energy storage, as chemical feedstock (e.g. steel production) and as fuel for transport.
Figure 44-1 Energy services
Symbolic representation of the main groups of the energy services needed to run the world economic system: heat (space heating, industrial process heat), ordered materials from raw materials (e.g. steel from iron ore) and power (e.g. electricity for lighting, transport, computers, and mechanical energy).
Figure 44-2 Mineral energy supply
Symbolic ourline of our present economic system, based on mineral energy resources. The economic system is a partial system of the biosphere. All materials and energy resources are extracted from the accessible part of the earth's crust and will return into the biosphere sooner or later. The entropy associated with the generation of useful energy from the mineral energy resources stays within the biosphere and becomes manifest as deterioration of ecosystem services (increasing mess and uselessness). The net result of the economic activities is an increase of the entropy of the biosphere, because the entropy reduction acchievable with the generated useful energy is much smaller than the entropy increase,
Figure 44-3 sustainable energy supply
Outline of the economic system based on zero-entropy energy supply (ZEE). The entropy generation associated with the generation of the high-quality energy (solar radiation) reaching the biosphere stays outside of the biosphere. The economic system can perform as a (nearly) zero-entropy economic system (ZEES) in the respect that the entropy reduction can by larger than the entropy generation by the economic system, depending on the way the zero-entropy energy is being utilized.