Apophis 99942

Energy naturally flows from a high potential to a lower one. The Earth is a location in the universe that has naturally high potential. Energy flows out from Earth in the form of heat radiating to outer-space. Humans quicken the release of higher pools of energy at the Earth’s surface when we burn wood or ignite gasoline. Temperature changes in the atmosphere result when there’s a mismatch between the energy released and the energy radiated.

Yet other contributors influence the atmosphere. Form Earth, Volcanoes blast molten rock up onto the Earth’s surface and release great quantities of energy over a short time. Asteroids from outer-space slam into Earth to make their own acute contribution.

The asteroid Apophis 99942 had the distinction at one time of having a very high calculated probability of hitting Earth. It’s impact velocity of 12.4 km/sec and estimated mass of 2e10kg would have added 1.6e18 Joules of energy in a very short instant. This would have to dissipate through the atmosphere and into space, likely over a very long time. People’s activity have added about the same amount of energy to the atmosphere as evident by the rise in temperature over the last century. This is certain.

Current calculations indicate Apophis will unlikely hit the Earth. But, should an asteroid strike, the Earth’s atmosphere will react. The asteroid that hit near Chicxulub released nearly 4e24 Joules of energy. A wise civilization, bent on survival, would be able to work through these acute events.

Asteroid


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Photovoltaics

Photovoltaic power. The mere word makes some futurists smile. Limitless clean power from the Sun making all our worries go away. Reality tells a different story about this energy source.

First, let’s consider the idea of limitless clean power. There is a limit. The amount of sunlight reaching the Earth’s surface amounts to 2.68e16 watts(1). This equals 8.45e23 Joules/annum (J/a), a huge amount. Even considering a 30% efficiency, this amounts to 2.5e23 J/a which is much greater than our current power consumption of 4e20 J/a. The limit certainly seems high enough to not be a concern. Let’s assume so for now.

Now consider the cleanliness. First consider the direct detriments. To get all the power, we’d have to cover every square kilometre of land on Earth with photovoltaic cells. There’d be no room for plants, animals or people. On the plus side, skin cancer would be a thing of the past. On the negative side, the ecosystem would be destroyed and so would end our dominion. Let’s see how.

We’d subtract the land area needed for cropland and urban areas, about 15% (1). Though possible, it is not probable that we could cover the ice regions like Greenland and Antarctica. Thus reduce the value by another 39%. The remaining 46% consists of forests, grasslands and inhospitables like deserts. We cover these with solar panels and we’d push almost all other life to extinction. This is hardly a clean power supply.

Next for cleanliness is the consideration of logistics. Photovoltaics don’t use a chemical reaction to make power so in this they are clean. But, they need energy for fabricating the necessary components as well as a means for their delivery to the end user. Fabrication means silicon, steel and plastic get shaped into panels. And aside from the ancillary inverters and power metres, we need a storage capacity. Batteries! Today, off-grid homes need over 700 kg of lead and acid to store their captured energy(2). If all houses in the United States (3) were using photovoltaic they’d need 7.75e10 kg. True there’s likely enough lead and acid available. But it would need processing, transporting and recovery to and from each home. The same goes for the panels which need be fabricated, transported and recovered. Undertaking this process leads to heat and chemical waste. Hardly clean.

Another problem with photovoltaics is its inability to provide the energy when and where needed. Most of the habited world is in the temperate northern hemisphere. In their winter there’s little Sun for energy but a great need for heating. In a quick review of current off-grid houses in this region(3), none have photovoltaic as the primary heat source. Most use wood. A large percentage of humanity lives in this region and unless they move to warmer climates, they will have to look for their energy supplies from other than purely photovoltaic.

Yes, photovoltaics are a means to extend our technological ability. It can provide power for lights, refrigerators and non-essentials like computers and stereos. It’s woefully inadequate for interior air conditioning whether heating or cooling. It’s equally inadequate for massive energy needs such as aluminium smelting (4). It can’t replace the transportability and energy density of petroleum and natural gas. Photovoltaics aren’t the answer for tomorrow’s energy needs. Our worries shouldn’t go away just yet.

  1. My book
  2. Off-grid
  3. Housing
  4. Karahnjukar Power Station

PanelsStationsmelting

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First Estimate

Planning for the future means having an objective and then assigning resources so as to meet it. Without setting an objective we can still set the bounds by considering the limits to resources; in particular, energy.

Let’s assume that people are wise enough to choose not to imperile their future. In using the economist’s expression, we choose to live off the interest rather than the principle. For people needing energy, they would take energy for themselves but leave enough so that other life forms can survive. This enables all life forms to continue and should enable people to continue to utilize large quantities of energy. In short, this future ensures sustainability and human advancement.

A rough bounds for the amount of energy available from vegetation is 2.048 zettajoules (1). The following table gives an estimate of the number of people of various technological levels (2) who can live on the Earth given this energy limit. The number is the increase over our current population.

Technological Level Increase
primitive human 85.38
hunting human 34.28
subsistence agriculture 16.23
advanced agriculture 11.27
industrial human 4.24
technological human (US 1971) 0.92
Canada (2003) 1.09
world today 4.65
Future 0.17

Kardashev’s scale (3) presumes that future higher technological levels need more energy. The future civilization, to acheive the next technological step, will thus need an exponentially increasing amount of energy. Yet, the future population would have to number less than today’s population. For example, even if we tried to get everyone on Earth living at the same technological level as those of the United States of 1971, we’d need fewer people than today. This is shown in the table.

Let’s say an objective of our civilization today is to acheive a higher technolgoical level. This means that given Earth’s finite energy supply, the only way for us to achieve this is to reduce the number of people. This assumes we are wise enough to also choice a sustainable future.

This is a first estimate in energy calculations.

(1) Zetajoules

(2) Reference Book

(3) Kardashev

Example lifestyles for different technology levels;

Primitive Farming Adv Farm
Industrial Technical Advanced

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Zettajoules

The best source of energy is from the Sun(1). After 4.5 billion years, the best primary natural energy storage occurs with plants. These living organisms capture the Sun’s energy and store it within their bodies. Presumably their purpose is to ensure adequate energy for their survival and the propagation of their species. As long as they retain enough of the Sun’s energy, their future is assured.

We have made estimates of the amount of energy stored within all the plants and other living organisms of the Earth (2). As a means of estimating the energy availability, we can use these values and hypothesis our energy needs as in the following. First, consider the vegetation’s capture of solar energy as shown in the table below. In it, values of mass refer to dry matter.

Ecosystem type(3) Area Total NPP Mean energy of NPP Biomass Biomass Energy
x1012 sq.m. x1015 g/y x1018 J/y x1015 grams x1021 Joules
Tropical forest 24.5 49 873.8 1025 18.28
Temperate forest 12 15 267.5 385 6.86
Boreal forest 12 9.6 171.2 240 4.28
Woodland and shrubland 8.5 5.95 106.1 50 0.89
Savanna 15 13.5 240.7 60 1.07
Temperate grassland 9 5.4 96.3 14 0.25
Tundra and alpine 8 1.12 20.0 5 0.09
Desert and semidesert 42 1.68 30.0 13 0.23
Cultivated land 14 9.1 162.3 14 0.25
Swamp and marsh 2 4 71.3 30 0.53
Lake and stream 2 0.5 8.9 0.05 0.0
Total continental 149 114.85 2048.0 1836.05 32.74

From the above table, the total energy stored in biomass is about 32.74 zettajoules (x1021) while the amount of energy capture each year is 2.048 zettajoules. If we assume that all the cultivated land goes into food production, then there is 1.8857 zettajoules captured every year.

Total world primary energy consumption for 2005 was 10537.1 mtoe equivalent or about 0.44 zettajoules(4). We derive most (86%) of this energy from non-renewable fossil fuels. If our quantity of energy consumption remains at or above the 2005 level then after we completely consume all the fossil fuels, we will need 23% of all the energy captured annually by vegetation.

Presumably vegetation needs all its current NPP to maintain its own existence. If we were to allocate a quarter of the NPP for our own energy needs, can we expect the vegetation to survive?

Of interest, the proven petroelum and natural gas reserves is 13.67 zettajoules(3). From this, and knowing the rate of consumption of 0.44 zettajoules indicates a time of 31 years until their depletion if all our energy comes from them (rather than the true 60%).

(1)See Earth’s Energy Budget
(2)Global Carbon Cycle
(3)Whittaker, 1975.
(4)BPs Statistical Review

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Bounds to Energy

The Sun sends a finite supply of energy to Earth. Plants absorb this energy and store it. Animals eat the plants and absorb this energy for their own uses. If there are no plants available, the animals starve. If enough of the food supply disappears, a species becomes extinct. Once extinct, it will never return no matter how much energy comes from the Sun.

Many species have gone extinct from the Earth. Some, such as the Great Auk, directly fell because of the influence from people. By usurping food and area, human’s can lead to indirect extinction as with the Baiji Yangtze Dolphin. This path to extinction will be followed by many plants and animals unless people ensure they receive a share of energy.

As fossil fuel supplies diminish, we will replace their energy with energy directly from the Sun or second hand, via plants. The more energy we claim in this way means the less available for other life forms. This will further accelerate the rate of extinction. None of these life forms will ever return. As the rate of extinctions increase, the future of the world will include fewer and fewer life forms and all their real and/or potential benefits. We can save species for the future, are we ready to make the sacrifice for them?

The Sun Dolphin
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