Kinetic Solar Energy

Solar energy is the predominant driver of activity at Earth's surface and in its atmosphere. With few exceptions, the energy that:

is solar. Originally, animals only had access to to the solar energy in chemical form: energy was captured by photosynthesizing organisms and later eaten by animals. For all but a few, (E.G.: Portuguese man-o-war, right) that's as far as it gets. Human history has seen the successive exploitation of the other forms of solar energy as well, including: Human use of the wind as an energy source is the topic of this lecture.

Big Messages

We address two very different applications of wind power:

Nevertheless, they embody the same major principles. These are:

  1. Security: For a society to rely primarily on the wind (for locomotion or industrial power) it must be secure and very well ordered. If it isn't, wind power can only serve as an auxiliary source.
  2. Unpredictability: The limiting factor of wind use: Wind power is unpredictable and intermittent.
    • Sometimes there is not enough.
    • Sometimes there is too much.

Future shock: Through it all, we aim to emphasize a proverbial truth: Technological changes have unintended consequences. Examples are legion, E.G.:

The industrialists of the mid 20th century didn't envision that by selling labor-saving household devices (washing machines, vacuum-cleaners, dishwashers, etc.) they were setting the stage for the massive entry of women into the professional workforce.

Any time we contemplate technologic change, we have to consider its indirect consequences. The history of humanity's use of wind power is full of object lessons.

Wind powered locomotion

Humans have travelled across water on rafts or boats since near the emergence of the human mind roughly 50,000 years ago. In fact, the peopling of Australia (40,000 years ago) could not have occurred without them, and there is evidence that the New World might have been settled by people arriving in boats. For most of that time, propulsion was strictly by muscle power. The oldest depiction of a wind-powered vessel is from an ancient Egyptian pottery shard from ~3200 BCE. The Nile is a logical place for humans to hit upon sailing as a useful technology because while the river has a swift current, prevailing winds blow upstream. Thus:

Going straight downwind is the simplest kind of sailing to master, and doesn't require much in materials or skill. Any floating platform (boat or raft) with enough ballast not to tip over, and a piece of cloth hanging from a stick will do. (Indeed, 1200 years later (~300 BCE), the ancient Norse reinvented the technique by cutting tree branches and holding them upright in their rowboats.)

Sailboats are capable of much more than sailing straight downwind. Modern sailing vessels can sail at any angle to the wind greater than ~45 deg provided their hull has some sort of keel to prevent slipping to the side. Indeed:

Note: Many contemporary sailors are obsessed with sailboat racing. Races typically follow a triangular course so that at some point, the contestants must sail upwind. Thus, modern vessels tend to be optimized for sailing upwind fast, yielding boats with tall narrow high aspect-ratio sails. In the age of commercial sail, this was not such a great priority, so naval architects were happy to trade off fast upwind sailing for rigs with high overall speeds.

People didn't master these skills overnight, but by historical times, we see complex large vessels capable of transporting goods over long distances. Again, Egypt took the lead. Egypt was not blessed with good shipbuilding materials. Nevertheless, by 1500 BCE, the Egyptians had mastered the construction of ocean-going ships and sailing them to distant destinations in Eritrea, Yemen, and Somalia. Some of these are so well known both from ancient documentation and from a recently unearthed wreck, that an accurate reconstruction, the Min of the Desert, has been built and sailed (right). Soon, the Canaanites, Minoans, Phoenecians, and Greeks were crossing the Mediterranean in sailing vessels. Sailing was independently invented at least four times in:


Future shock I - 6th century BCE: Consider that the rise of shipping in the Mediterranean occurred at the end of the "bronze age," however bronze (an alloy of copper and tin) remained an important commodity. At this time, Celtic communities of northern Burgundy became prosperous as middle-men along the trade route between the Mediterranean (source of quality manufactured goods) and Cornwall (southwestern Britain - source of tin for making bronze.) These Celtic towns, situated at transshipment points between rivers flowing into the Mediterranean and the English Channel, cashed in on this trade until the Carthaginians discovered the direct sea route to Cornwall during the fifth century BCE. Thus, the rise of wind-powered shipping drastically altered traditional economies and benefitted societies like Carthage at the centers of shipping networks.

Reconstructions teach us the limits of ancient vessels. Merck's guilty secret: For a time in the 1980s he sailed with the Viking Longship Company, Ltd. aboard the Fyrdraca (right). The Fyrdraca can sail to windward (poorly - maybe 75 degrees from windward) and can tack, but does both slowly and clumsily. Moreover, it requires an absolute minimum crew of four (but really needs six or more for comfort). A similar sized modern boat could normally be sailed by two and can be kitted out for single-handing. Min of the Desert required a crew of 24.

But the big thing: These ancient vessels were always equipped with oar-ports, reflecting the fundamental limitation of wind power in any form:

Wind power is intermittent.

This was not a huge deal for the ancients:

Security: Although we often distinguish ancient commercial ships and warships, the ancient Mediterranean was crawling with vessels that were a little bit of both (E.G.: "Sea-People" aka Philistine ship, right). This was because any vessel venturing out of home waters was likely to have to defend itself against pirates.

Sailing commerce and security I: By the time of the Roman Empire, Mediterranean society was unified and organized, and greatly depended on large scale shipping not only to power its economy but to sustain its population. The annual arrival of the large (up to 1,200 tons displacement) grain ships (right) from Egypt (an agricultural exporter) was of crucial importance to Italian cities that could no longer feed themselves without imported staples. These ships were far too big to depend on auxiliary oar-power. They absolutely needed:


During the Middle Ages, Western and Chinese (right) maritime technologies slowly progressed, but the basic logistical constraints of wind-driven transport remained the same as they had been for the Romans. During the 15th century, the rulers of the Ming Dynasty "retired" China from major maritime commerce at the point at which Western sailing tech was about to make significant progress.

Future shock II - the fifteenth century and firearms: For warships, the combination of sail and muscle power worked well throughout the Middle Ages. During the 15th century, however, maritime technology met firearms. Canons were devastatingly effective but very heavy. Attempts were made to arm galleys with cannons but such ships were:

Navies traded maneuverability for fire-power, producing warships that were as dependent upon the wind as Roman grain ships had been, leading to the world's only navies of competent, purely sail-driven warships between the 15th and 19th centuries. During battle, rigging and sailors were terribly vulnerable (as in the combat of the Bonhomme Richard and Serapis, right). Were they effective? Apparently so. By 1800, the worlds oceans were as secure from piracy as the Mediterranean had been during the Roman Empire.

The tradeoff: Pure sailing was no longer a choice, and navies had to learn to cope with the vagueries of the wind. As a result, navies longed to reclaim the freedom that auxiliary oar-power had once given them. So, it was no surprise that, when steam engines became available as an auxiliary power source, navies scrambled to use them. By the time of the Civil War, a first rate warship like the CSS Alabama (right) would cruise under sail but fight, or maneuver in port under steam power that turned a propeller. For sea-going commercial vessels that could expect tug-boat service in port and didn't need to be weighed-down by a steam engine, pure sail remained the standard.

Future shock III - steam engines need fuel: In the mid-19th century, pure steamships were limited in range because of their need for fuel, and were used near the coast and on rivers. Still, the deployment of ironclad steam warships during the Civil War got navies thinking about the desirability of ocean-going steam ironclads.

The problem: Steam warships consumed prodigious amounts of coal and needed frequent resupply. The first ocean-going ironclad crossed the Atlantic in 1864, but such a ship could do little upon arrival until refueled. Alas, as armor and guns became more powerful, warships with sailing rigging were increasingly vulnerable, but switching navies over to steam power would require nations to develop global networks of well defended fueling stations. The HMS Captain 1869 (right) represents the last serious attempt by any navy to build a fully modern sailing warship. Its innovative design separated the gun turrets and rigging on separate decks. Unfortunately its design and construction had been poorly supervised and it was heavier and had a higher center of gravity than planned. It capsized and sank in heavy weather during its first year of operation. This event did for the image of sailing warships what the crash of the Hindenburg did for that of airships. The global powers took the steam plunge, with cascading effects. Global imperialism went from being an economic convenience to a military necessity.

Power warships and the price of strength: By the 20th century, naval ships (E.G., the HMS Dreadnought - right) were powerful steam-powered steel-hulled monsters. But there was a price for this modernity. Consider: In WWII, the Bismark, one of the most powerful battleships ever built, on its first combat mission, was severely limited in its operational scope and ultimately trapped and destroyed because of its need to reach a friendly port for refueling. Compare that to the CSS Shenandoah, which was operating in the north Pacific when its crew learned of the end of the Civil War, then sailed non-stop and undetected by U.S. authorities to surrender to the British in Liverpool.

Sailing commerce and security II: The switch to steam-powered warships didn't effect sailing commerce. Indeed, the Thomas W Lawson (right), the largest pure sailing vessel in history, was launched in 1902. As in the ancient Mediterranean, however, sail-propelled commerce required security. The breakdown of global security in World War I put an end to such vessels, which were very easy visible targets for steam warships and submarines. In response, freighters became steam or petroleum powered, for rapid passages and in WWII, to keep up with convoys.

To review: Wind powered commercial ships had to deal with the following limitations:

Sailing commerce was doomed during the early 20th century by the availability of non-intermittant energy alternatives and the insecurities of two world wars. We will see that the wind as a source of electrical power suffers from analogous limitations.

Windmills: Industrial wind power

If the wind can move vehicles it can also power practical machinery. Ironically, the earliest known use of a windmill was as a novelty: The "windmill" of 1st century CE inventor-mathematician Heron of Alexandria powered a piston-pump supplying air to a pipe organ. The first widespread practical use was in 7th century Iran for milling grain. From there, windmills powered by sails either directly turning a vertical axis or turning a horizontal one that was geared to a vertical axis spread through the eastern Mediterranean to western Europe. In all cases, they were used:


But the wind is an intermittent resource. The industrial age provided alternative power sources to grain mills, but for tasks that didn't have to adhere to such exacting schedules, wind mills and wind turbines continued to predominate. The lightweight Aeromotor windmill was introduced in 1888 for pumping water, and is still in production in more or less its original form. Its use is favored, however, in places where electricity is not as readily available.

The wind as a source of electricity: 1888: Within a decade of the Edison's invention of a practical incandescent light bulb and well before widespread electrification, Charles Brush built the first electricity generating wind turbine in Cleveland, OH (right). By the 1930s (i.e. before widespread rural electrification but after electrical appliances were available) Aeromotor-type windmills were frequently used for electricity generation (5-25 kW) 1 kW=1.34 hp). These were largely discontinued when electrification connected farms to reliable power grids. Thus, in their earliest form, wind turbines were in competition with more reliable sources of electrical power.

The Smith-Putnam wind turbine, the first megawatt-sized turbine, was the first wind turbine to contribute to an electirc power grid, being connected to the Vermont grid in 1941.

Modern wind turbines appear in the 1980s: The petroleum supply shocks of the 1970s stimulated interest in alternative energy resources during the pivotal 1980s. Resulting in the development of new wind turbine concepts. While initially small (E.G. the Bonus 30 kW machine at right) these explored a variety of design concepts including upwind facing, downwind facing, and upright turbines. The 1980s saw the development of large modern machines like the Tvind 2 mW device. From this range of designs the modern industry has converged on a preference for upwind-facing three-bladed turbines.

Wind farms: The last two decades have seen the rise of wind farms - large arrays of wind turbines concentrated in regions of high wind energy potential. The earliest, on Crotched Mountain, NH was established in 1980. The largest in the US is currently the Alta Wind Energy Center of Kern Cty., CA (right). Wind farms are nice because they neither significantly degrade the land they occupy ecologically nor prevent its having other uses like agriculture. Many wind farms are offshore. A typical wand farm collects electricity generated by individual wind turbines and converts to high voltage current for the local grid.

The US Department of Energy reported that in 2012, wind turbines supplied 32% of US electrical power. As a percentage of installed electrical capacity, however, Denmark and northern Germany lead with wind supplying 25- 50% of power. China is currently investing heavily in wind farms and has the largest overall wind power capacity.

Issues with wind power: Basically similar to those of commercial sail, but with some twists.

Postscript: The future of future shock

The consequences of wind power: What will be the societal effects of the proliferation of wind power? We lack divine omniscience, but as wind power supplies increasing percentages of our needs, it will spark economic and political changes with unknown ramifications:

A return to sail? For land based power generation, the use of the wind and other "clean" alternatives is growing rapidly. Transportation, however remains dominated by fossil fuels. Can we ever use any alternative power source for moving vehicles and goods in a practical way? Maybe there is a future in high-tech sailing vessels. The problems really are more social than technological. Potential objections:

Cool toys for the fabulously rich, but are these actually useful? Indirectly, perhaps, as test-beds for potentially practical technologies, like Heron's windmill.

It's already been tried: During the 1970s there were times when petroleum really looked like becoming an intermittent resource, also. Along with the development of wind farms, there was serious consideration of commercial sail. The era's poster child: the Shin Aitoku Maru, a small (298 ft.) tanker equipped with computer controlled folding sails that could be used in favorable conditions. Comparisons with a power-only sister ship indicated 10 - 15% reduction in fuel consumption. Not bad. The Shin Aitoku Maru engaged in trials for three years before being retired. There have been no follow-on attempts at a high-tech sailing freighter. What was wrong?

Currently, shippers are experimenting with an improbable solution to the latter problem: Skysails such as those used by kitesurfers. These can be deployed from virtually any ship during favorable conditions and retrieved before maneuvering in harbors. Moreover this takes advantage of a basic fact: The wind blows faster at higher elevations.

Many more exotic proposals have been made for the refurbishing of sailing tech. The long and short is that wind power, for the foreseeable future, will be no more than a fuel-efficiency generating auxiliary source for vessels that are fundamentally petroleum powered for as long as:

Thus, for the most part, sailing remains the wind-power of the past and wind turbines the wind power of the future.