One Hour of Sunshine

Solar power advocates are inclined to say things like:

In just one hour the amount of energy that the earth receives from the sun exceeds the energy consumed by all of mankind in one year.
This is presumably intended to reassure us that solar power is plentiful, and that we should easily be able to harness enough of it.
They are wrong.
To put it kindly, it is imprecise, and misleading. It requires something like "all of human technology". In fact, it can be shown that the radiation the Earth receives from the Sun in one hour exceeds the figure collected for the entire planet's industry by the statistics of the USA's Energy Information Agency for the year 2004.

But the cause of global warming is the fact that the Earth has to get rid of the same amount of energy every hour, or it gets warmer.
It leaves out our consumption of food.
It certainly does not include the huge energy cost of the fresh water that is supplied to us by evaporation from the oceans. Worse yet, the aquifers that human industrial and agricultural thirst is depleting represent an energy demand that exceeds that supply of immediate solar fresh water.


Human food is ultimately provided by plant photosynthesis, which delivers a quite small fraction of the solar energy received by the plant.
The photosynthetic production of the coal which supplied the "alternative energy" of the Industrial Revolution took 64 million years to lay down the coal seams that we are consuming at thousands of times the rate at which they were created. Every coal seam represents the catastrophic drowning of a forest.

The Cooling Problem

The global warming problem is that the solar energy penetrating the earth's atmosphere has to be re-radiated, and global warming is the direct consequence of the fact that the Earth's surface (in particular the oceans) now has to be warmer than it used to be, to radiate the energy out again.

In fact, the actual heat generated by industrial processes is unimportant! A drop of one part in 8000 of the Earth's ability to radiate all the solar energy back into space, is enough to make a bigger difference. Carbon dioxide, and worse still methane leaks from fossil carbon mining (e.g. "Natural gas" fracking) are the problem.

One very significant mechanism for re-radiating the energy out into space must be the evaporation of water from the planet's surface, and its condensation as clouds high in the atmosphere. For every litre of water so transported, 2250 kilojoules of energy are released at high altitude. Some of that radiates out into space.

Solar Power is Dilute

Plants capture energy by photosynthesis. They convert quite a small proportion of what falls upon the leaves, to carbohydrate chemical energy. Coppiced willow, with a good water supply, is recommended as a renewable crop that supplies wood on a continual basis. Unlike sugar cane and maize, its fertilizer demand is modest. By my calculations, it takes about a square mile of coppiced willow to supply wood for a heat value of one megawatt-year per year. If you want to replace the coal demand of a base load 1000 MW generator, you'll need a thousand square miles or more. There is no way that any conversion of wood or other vegetable matter to ethanol or "bio diesel" can produce more energy than the heat value of the vegetable matter. Al Gore now knows that ethanol from 'corn' is a mistake, but even converting the cellulose of the leaves, stalks, and corn-cobs to ethanol, if you can bio-engineer the necessary organisms, can't supply more energy than just burning them.

Humans don't do much better with their machines. The biggest and most powerful of these, hydroelectric turbines, like the old watermills, use the gravitational energy of rainfall that has fallen high up in the hills of a watershed, to drive the machinery. The energy that evaporated the water was about 2250 kiloJoules per kilogram of water. If you have a turbine with a head of 100 metres, you get one kiloJoule out of each kilogram of water flowing. That's an energy conversion efficiency of about 0.05 percent. Hurricanes do much better, because the height of the "engine" is stratospheric. On the Columbia river, there are several hydro dams, so you get more energy from each kg. of water.

Direct Solar

The big advantage of solar power, compared with wind, is that although it cannot be "dispatched" like a hydro turbine, in sunny places it is usually available when the electrical load is at its peak.
Photovoltaics have efficiencies of a few percent. They're still expensive, and their lifetime is not well established. In 24 hours, a fixed array of photovoltaic panels with a peak capacity of 100 kW will deliver not more than 33x24 kWh of energy. That's simple trigonometry. Stirling engines powered with direct solar heat from steerable parabolic mirrors get perhaps 50% efficiency when there is no cloud cover. The deserts of Southern California are suitable locations. SCE are an example of (mostly) good solar renewable practice. But the acreages necessary, and the capital expense involved, to provide energy enough, on demand, to replace fossil carbon energy production, are prodigious.

Note that "14.5 billion kilowatt-hours" needs to be divided by a million times the number of hours in a year, to compare it with the annual output of one base-load 1000 MW (one Gigawatt) nuclear or coal burning plant.
It comes to just over 1.65 GW-yr, and half of it is geothermal.

Unfortunately, the wind turbine production includes the Altamont Pass wind farm, which is perhaps the worst known wind turbine killer of birds, at a rate of thousands per year, soome of which are rare and endangered species. An eagle or a hawk does not expect to have to pay attention to menaces descending upon it at the speed of a 100 metre turbine blade.

The capacity factors which you can compute for SCE's wind and solar components are 23.6% and 27.8%, whereas geothermal (if you can get it) gives 92.5%.

How is Our Consumption Measured?

Solar radiation is already being used by other organisms, and even ourselves. I do not know entirely how the energy consumed by humans is measured by energy agencies.

We do know that human agriculture has endeavored to harness the energy from the sun to feed people. It turns out that the efficiency available is such that very large areas of land are required, far more than if we could fuel our bodies directly with sunlight. It takes even more, if we want to eat other animals.
It is probable that, without artificially produced nitrate fertilisers, the Earth's present human population of 7,000 million could not be fed. The Inca civilization was one of the earliest to use nitrate enhancements on their soil. They got it from fairly old bird and bat dung accumulations. It's called guano. There's not much left.

Remember that a large proportion of the earth's surface is the sea, where it's pretty difficult to collect solar energy. Worse still, that's where hurricanes are born.
A hurricane is an instance of what phyicists call a heat engine. It acquires energy from the warm water of the ocean, and transfers it to the stratosphere, where it can be radiated into outer space. A typical one of these engines is vaster than anything humans have ever devised. It is as big as any two eastern US states, and several miles high. Its mechanical output is a large pattern of winds many times too strong to harness. We have trouble enough even trying to predict where hurricanes will go. Even the most enthusiastic "renewable energy" folk don't suggest "hurricane power".

A great deal of the energy is already being used to sustain the lives of non-humans. Actually, if you eat swordfish, how much energy do you consume? Is it the caloric value of the flesh you eat? Or that of the whole fish? Shouldn't it be that of the fish the swordfish ate? Plus that of the smaller fish and plankton that the prey of the swordfish ate.

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