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9 Solar and Wind Power and their StorageSolar PowerHistorical Development of Thermal Solar Power

The sun sustains life on Earth and was an object of worship in early religions. Chinese and Greeks were the first to apply technology to the sun in the seventh- and sixth-century BCE with the “gnomen,” a vertical stick or stone in the ground that would trace the sun’s shadow to show meal times first and foremost, but also mark the solstices (important for planting and harvesting). The sun at high noon can determine latitude for ships at sea (determining longitude required an accurate sea-going chronometer that was not invented to the early seventeenth century). Position of the sun in the sky and the direction of its movement gave mariners guidance as to which direction they were sailing.

Simple magnifying glasses could focus the sun’s rays to light fires for light, warmth, and cooking. Chinese were the first to use mirrors (reflective metals) to light fires and later mirrors were used by Greeks and Romans to light torches for religious processions. In 212 BCE, Archimedes focused sunlight with polished bronze shields on a Roman fleet attacking Syracuse and succeeded in setting ships afire (this was successfully repeated in 1973 by the Greek navy setting fire to a wooden boat 50 m away from the reflectors).1 In 1515, Leonardo da Vinci proposed use of parabolic reflectors to supply energy for a cloth dyeing factory.2

Capturing the thermal energy of the sun in a more dynamic way began when Auguste Mouchout, a French mathematics instructor, converted solar radiation into mechanical steam power in 1860. Arrival of cheap coal from England stopped further progress in capturing solar power, but he was also able to demonstrate the use of solar energy in pasteurization and making ice. In 1883 John Ericsson, an American, invented a solar powered steam engine that used parabolic trough construction to concentrate solar energy similar to Mouchout’s engine. Ericsson noted prophetically that in a couple of thousand years, a drop in the ocean of time in his opinion, coal fields will be completely exhausted and heat of the sun will have to be their substitute. He was off in his timing, but right in his concept. In 1878, an Englishman William Adams constructed a reflector of flat silvered mirrors in a semicircle to track the sun’s movement and concentrate the radiation on a stationary boiler to heat water. He was able to power a 2.5 horsepower steam engine, much larger than Mouchout’s 0.5 horsepower steam engine. He advocated solar energy as a substitute fuel in tropical countries. His basic design is now incorporated in the solar power tower.

©Routledge/Taylor & Francis 2016

Charles Tellier in 1885 installed the first solar energy system for heating household water on his rooftop. Henry Willsie was first to build a solar plant capable of storing power for night time usage at his two electricity generating plants in California in 1904, but was unable to compete with low-cost power from fossil fuels. In 1912 Frank Shuman built parabolic solar collectors near the Nile River capable of tracking the sun. The reflectors focused the light to heat water and generate enough steam to power a series of water pumps totaling 55 horsepower capable of lifting, for the time, an astonishing 6,000 gallons of water per minute a height of 33 feet to irrigate a large tract of desert land. His dream of building 20,000 square miles (!) of reflectors in the Sahara desert for irrigation purposes died when his Nile River installation was destroyed during the First World War. In the 1950s Frank Bridgers designed the first commercial building with solar water heating, now listed in the National Historic Register. Giovanni Francia, an Italian, invented the Fresnel reflector in 1964, which can substitute flat glass for curved glass in focusing solar energy. In 1969, a “solar furnace” was constructed in Odeillo, France, featuring an eight-story parabolic mirror.3

Passive Solar Heating, Cooling, and Lighting

In the fifth century BCE, Greeks incorporated passive solar design in their buildings by allowing the southern sun to penetrate interiors for warmth in the winter. During the first four centuries of the Common Era, Romans improved on Greek passive solar technology practices with large, south-facing windows to capture the sun’s warmth in public bathhouses and greenhouses for growing exotic plants. Justinian Code (529–534) included a provision to protect “sun rights” to ensure that buildings had continued access to sunlight after their construction. In the thirteenth century Anasazi Indians in the US Southwest built their dwellings in south-facing cliffs to capture the warmth of the winter sun. Buildings are still designed for passive solar energy by having large south-facing windows complemented with building materials that absorb and slowly release the sun’s heat. Passive solar buildings became popular during the Second World War when energy became scarce. There are no mechanical aspects to passive solar heating and a well-designed system can significantly cut heating bills and can also provide natural ventilation for cooling during hot weather. Passive lighting consists of concentrating sunlight and feeding it through fiber optics into a building’s interior. Hybrid lighting entails a backup power source for interior lighting for times of little or no sunlight.

Thermal Solar Energy for Heating Water

Thermal solar energy can heat water for space heating, personal use, household appliances, swimming pools, and for various commercial and industrial processes. Solar thermal heaters can be made of flat glazed or unglazed glass plates containing water and a heat absorber. Sunlight passing through the glass


plate heats the absorber, which in turn heats water between the glass plate and absorber. Depending on the circumstances, glazed or unglazed glass can be more efficient. Unglazed glass has less reflectivity allowing sunlight to warm the water more efficiently if water temperature is less than ambient air temperature as in heating a swimming pool. But glazed glass, even with greater energy losses from reflection and refraction, is more efficient if water temperature is higher than air temperature as in providing hot water to a home.4 Solar water heaters are installed on roofs and sides of homes most exposed to sunlight. When the sun is shining, water is pumped through the collector and heated water is stored in a tank. A thermosiphon solar water heater has the storage tank above the collector tubes, eliminating the need for a pump. Although thermal solar energy is associated with warming a house or a swimming pool, heated water can drive an absorption or desiccant air conditioning system for cooling a house. For colder climates, a water/glycol mixture is pumped through the collector, which requires a heat exchanger to heat water for kitchen use, appliances, and space heating. Backup power in the form of natural gas or electricity is required for cold, cloudy, blustery days when snow and ice cover the thermal panels or during times of heavy usage or a total solar eclipse that can cut solar power to near zero at its peak demand.

A third type of thermal solar heating is the evacuated tube solar collector consisting of two concentric glass tubes joined at one end. The outer tube is glass that allows sun to pass through to an inner glass tube covered by a heat absorbing material. A vacuum within the tube prevents heat absorbed in the inner tube from leaking back through the outer tube via convection or conduction. Inside the inner tube is a copper rod that acts as a heat conductor to transmit energy from the hot inner tube to the cooler water-filled manifold that connects to all the parallel evacuated tubes. Heated water in the manifold is circulated to a storage tank. As hot water is withdrawn from the storage tank, replacement water is circulated through the manifold for heating; otherwise cooler water from the bottom of the storage tank is recirculated to maintain its temperature. Circular shape of the tube ensures that sunlight is always striking the surface at a perpendicular angle for greatest heating effect.5 Earlier models of solar collectors relied on wanes to collect sun’s heat.

Breakdown of the cumulated capacity in operation in 2012 by collector type is 64.6 percent evacuated tube collectors, 26.4 percent glazed flat-plate collectors, 8.4 percent unglazed water collectors, and 0.6 percent glazed and unglazed air collectors.6 Around 75 percent of all solar thermal systems installed worldwide are thermosiphon systems and the remainder pumped solar heating systems. The portion of thermosiphon systems is climbing as seen by installations in 2012 being 89 percent thermosiphon and 11 percent pumped. In 2012, based on a survey of 58 nations encompassing an estimated 95 percent of total capacity, thermal solar output for heating water is 269 gW with a total area of 385 million square meters of thermal solar installations. This implies that 1 gW of thermal heat requires 1.43 million square meters or 1 mW requires a thermal solar installation of 1,430 square meters. Where it is sunny and warm, 3 square meters of solar installation provides sufficient hot water for a family of four.7 Thermal flat glass installations, common in hot temperature regions, are made and installed by locals on top of


roofs as a cottage industry (many of these “home-made” installations escape attention when compiling official statistics).

About 78 million water-based solar thermal systems have been constructed of which 78 percent are for single family hot water, 9 percent for multifamily houses, hotels, hospitals, schools, 8 percent for swimming pool heating, 4 percent for both domestic hot water and space heating (solar combination systems), and 1 percent for delivered heat to district heating networks, industrial processes or thermally driven solar cooling applications. Figure CW9.1 shows the global distribution of solar thermal systems.

Figure CW9.1 Solar Thermal Capacity (gW)

<<<Put Figure CW9.1 Here>>>

Global thermal solar output in Figure CW9.1 is equivalent to an annual savings of 24.5 million tons of oil equivalent and 79.1 million tons of carbon dioxide emissions. Thermal solar capacity estimated to be added in 2013 is 61 gW increasing 2013 thermal capacity to 330 gW. If this estimate is accurate, thermal solar is expected to grow an impressive 23 percent gain between 2012 and 2013 versus 9.4 percent between 2011 and 2012. Thermal solar is growing rapidly spurred, as is plain in Figure CW9.1, by China’s commitment to thermal solar power. In 2001, China’s solar thermal capacity was 22.4 gW versus 180.4 gW in 2012 for an implied annual growth of nearly 21 percent. China’s solar thermal capacity installations are 93 percent evacuated tube solar collectors, by far the highest proportion in the world, and the rest flat glazed plate collectors. China alone accounted for 84.9 percent of the solar thermal capacity added in 2012. China’s dominance in solar thermal capacity growth skews global growth in its favor. Ninety percent of China’s installations serve single family dwellings and much of the remainder multi-family dwellings. Thermal solar is a clean source of energy substituting for coal and biofuels to provide hot water to Chinese homes, thus contributing to cleaner air. An unusual example of thermal storage is an office building in New York City that freezes tons of ice during summer nights when power costs are low and utilizes ice to assist in cooling air during the day when power costs are high.8

Thermal Solar Energy for Generating Electricity

Solar thermal energy can also heat water for conversion to steam for driving turbines to generate electricity. The two principal types of commercial thermal electric solar power systems are parabolic troughs and power towers. These technologies are normally hybridized with fossil fuel (natural gas) to maintain electricity output when the sun is not shining or covered with clouds. This gives the system


necessary reliability required by dispatchers and enhances economic system performance by producing revenue whether or not the sun is shining.

Earth receives an average of 1,366 watts of energy per square meter (about 11 square feet) at the outer edge of the atmosphere. The atmosphere absorbs and reflects most X-ray and ultraviolet radiation reducing energy that reaches sea level at high noon on a clear day to a maximum of about 1,000 watts per square meter (W/m2) on a surface perpendicular to the sun's rays. Does that mean that a thermal solar installation one square meter can light ten 100 watt bulbs? The answer is no because heat energy has to be concentrated to raise the temperature of water sufficiently to boil steam that can turn a generator to produce 100 W of electricity for a few hours a day. This implies a relatively low conversion rate of heat energy to electricity, but as will be seen, a photovoltaic cell also has a relatively low conversion rate to translate sunlight into electricity. Thus solar thermal systems require a large area for mirrors to collect and concentrate the requisite solar energy. However, land area for solar farms does not compare unfavorably with coal fired plants when taking into account not only land directly involved with mining, but also for coal storage at the mine, the railroad distribution system, and at utility sites.

Solar thermal energy for electricity generation requires a location where there is sunlight much of the time and sufficient available space for mirrors: the ideal is a desert. But all deserts are not the same for photovoltaic and thermal systems. In some locations, annual maintenance is virtually nil as wind and an occasional rain keeps glass surfaces free of accumulating dust. In other areas, glass surfaces must be cleaned at intervals with fresh water, a commodity in short supply in a desert. In still other areas, wind blasting sand against glass surfaces can do irreparable harm.

The first system to commercially convert solar thermal energy to electricity was built in the 1980s in the Mojave Desert in California. Nine solar thermal electricity generating plants at a single location have a combined output of 354 mW (one-third the output of a large coal fired or nuclear power plant). Called Solar Energy Generating Systems (SEGS) and built by BrightSource Energy, it was the world’s largest installation of solar power until recently. Still operating, trough-shaped parabolic mirrors automatically track the sun and focus its rays at 30 to 60 times their normal intensity on a receiver pipe filled with synthetic oil. Oil is heated to 735°F and passes through a heat exchanger to produce steam for a conventional steam turbine electricity generator. Natural gas serves as a supplemental fuel for cloudy weather and night time operation.9

The modern power tower, also developed in California, stores solar energy in the form of molten salt. A circular field array of heliostats (large mirrors) individually tracks the sun and focuses sunlight on a central receiver mounted high on a tower. The receiver heats molten salt, such as a mixture of sodium


and potassium nitrate, to 1,050°F for storage in the “hot” tank. As power is needed, molten salt flows from the hot tank through a heat exchanger to produce steam for electricity generation. Then it remains in a “cold” tank in a molten state at 550°F until needed for heating in the tower. Depending on the size of the hot tank and its insulation, a hot tank can supply energy to generate electricity for some hours after sunset, an advantage over parabolic trough plants. Moreover, the system is more reliable because dispatchers can depend on the system to produce power even when clouds temporarily cover the sun by generating electricity from energy stored in the hot tank. To further enhance reliability, the system can be hybridized with a fossil fuel, such as natural gas, to produce power when needed by a dispatcher at any time.

Parabolic troughs and power towers require water to generate steam, usually not in plentiful supply in a desert, but no water is required for the third type of solar thermal power plant: dish/engine solar energy system. Parabolic dish-shaped mirrors, mounted on a single support frame, focus solar energy on a receiver to heat a fluid to nearly 1,400°F. Heated fluid transfers its energy to a gas such as hydrogen or helium to power a Stirling engine, which is similar to an internal combustion engine, or to a Brayton engine, which is similar to a gas turbine engine (sometimes referred to as a micro-turbine). In neither case is there combustion; the engines run off energy of heated gas and drive an electricity generator. Solar dish engines have the highest efficiency of thermal solar systems to convert nearly 30 percent of solar radiation to electricity. Its 30 percent efficiency appears less than parabolic trough’s efficiency of about 50 percent to convert sun’s radiation to heat energy. But heat energy is not electricity. Heated oil in a parabolic trough then has to produce steam via a heat exchanger, which in turn generates electricity at a typical efficiency of 35 percent. From the point of view of electricity generation, the solar dish is about twice as efficient as a parabolic trough. However disk/engine solar energy systems have a limited power output not fit for commercial operations, but ideal for specific applications such as supplying power at remote military depots. It is too expensive and technologically sophisticated to be an energy supply for communities in remote areas; solar panels and wind turbines are better choices. Two dish/engine systems are under construction, one with a power output of 1 mW and another of 1.5 mW. Development is being pursued to build larger capacity disk/engine solar systems of 5 mW. Figure CW9.2 shows the development of thermal solar power for the generation of electricity.

Figure CW9.2 Historical Development Solar Thermal Electricity Capacity (gW)

<<< Put Figure CW9.2 Here>>

Development of thermal solar electricity was started in the US driven by the government providing research and development funds in conjunction with private money to perfect the technology. Government or utility contracts with private corporations were granted to design, build, and operate


thermal solar electricity facilities. These companies included Abengoa, Ausra, BrightSource, and Solel (now Siemens Concentrated Solar Power). Ausra was acquired by Areva and was known as Areva Solar, but disbanded operations in 2014.10 Government support is necessary to cover costly research and development phase of a new technology and provide at least partial funding of the project and tax incentives to attract private capital. The principal collateral support for financing is a long-term contract with a utility to buy the entire output of a plant. Construction of the 354 mW SEGS parabolic trough plant in the Mohave Desert in California began in 1984 and was completed at its full power output in 1990. No other thermal solar electricity facilities were completed until 2007. The first to be completed were in the US, then followed by Spain. SEGS remained the world’s largest solar thermal electricity plant until 2014 with the completion of the 377 mW Ivanpah Solar Power Facility in San Barnardino County in California. It is the largest solar power tower (actually three towers each 450’ high) along with being the largest thermal solar electricity plant in the world.11 While Ivanpah missed its intended target output in 2014 from inclement weather, it has become a talisman for renewable power.

Spain has taken over leadership in building thermal solar electricity plants. Of the 3.425 gW of thermal solar electricity power in operation in 2013, 2.0 gW (58 percent) is in Spain, 0.882 (28 percent) in the US, and 0.1 (3 percent) in UAE and remainder in seven other nations. With the exception of the Ivanpah Solar Power Facility, all thermal electricity plants above 50 mW are parabolic trough. However, Spain has built a number of smaller capacity solar power towers.

Twelve parabolic trough plants totaling 850 mW and three solar power towers totaling 280 mW and four Fresnel reflector solar plants totaling 160 mW are under construction. Fresnel reflector solar plants are a recent development. They are similar to parabolic trough except that the mirrors can be made out of flat glass rather than curved glass that reduces capital costs, but also lowers the conversion factor of solar to heat energy to only 14 percent. Parabolic trough plants have 50–55 percent efficiency with one company claiming 73 percent efficiency in transforming solar radiation to heat energy.12 Ivanpah Solar Power Facility (a power tower) has a thermal efficiency of 29 percent.13 In addition there are 16 new plants totaling 930 mW that have been announced to be built in Spain. Another 12 plants have been announced in other countries including a 2,000 mW solar power tower to be built in Mongolia, a 1,540 mW thermal solar project in Morocco, and a 1,000 mW thermal solar project in Pakistan (the type of plant not known for the latter two).14 These intentions show that thermal solar projects are significantly stepping up in capacity.

Solar Power Updraft Tower

The latest idea, based on one first advanced by Leonardo da Vinci, is a solar power updraft tower shaped like a chimney that directs hot surface air up to cooler air at higher altitudes. One company proposes to build such a tower that will direct heated surface air up a circular tower to cooler air almost 3,300 feet (1,000 m) above the Australian outback. The power driver is the air temperature differential between


the bottom and top of the tower. Bottom of the tower is surrounded by sunlight-absorbing material that further heats incoming air. Air rushing in the bottom of the tower passes through wind turbines that can generate up to 200 mW of rated capacity, enough to supply electricity to 200,000 Australian homes. This source of energy is free of carbon emissions, and very important in a desert environment, requires no water.15 A solar updraft tower (Jinshawan) of 27.5 mW has been built in China.

A new technological has been proposed to convert sun’s radiation directly into steam in a simpler way by focusing sunlight at least ten times its natural intensity on a structure of graphite foam sitting on top of water. A carbon foam at the bottom with pockets of air keeps the foam afloat and prevents heat from escaping to the underlying liquid. Graphite foam on top of the carbon foam has very small pores that allow water to creep up through the foam via capillary action much like a sponge. Concentrated sunlight creates a hotspot in the graphite, generating a pressure gradient that draws up even more water through the graphite foam turning it into steam. There are a number of potential applications if this concept can be advanced to the next step of development.16 Another intriguing idea is to create liquid solar fuel by concentrating sunlight on carbon dioxide saturated water. Heating water to 3,600°F in the presence of metal oxides as a catalyst generates syngas (carbon monoxide and hydrogen), which can then be converted to hydrocarbons such a motor vehicle fuel.17

There has been concern over birds flying into the concentrated solar radiation between the mirrors and power tower. Bird feathers have been singed by concentrated sunlight. At one large facility, bird kills maxed out at little less than 100 per month during the peak migratory season, which is minuscule compared to other manmade sources such as transmission lines. The problem is being treated by loudspeakers near the towers broadcasting distress calls along with calls from predatory birds for those species of birds flying near the towers.18

Wind PowerHistorical Development

History of wind as an energy source goes back to the dawn of history. Around 5000 BCE, the ancient Egyptians employed boats fitted with sails to move goods up and down the Nile River. Phoenicians later adapted the sail for a more vigorous marine activity of trading between Mediterranean ports. Despite the apparent advantage of animal skins and hides for sails as a means of moving goods, it took millennia for wind power to replace those who performed what must have been the most tiring and tedious of jobs: oarsmen. Eventually sailing vessels with clothe sails adapted to allow tacking into the wind became the ubiquitous means of transport throughout the world until the appearance of coal fired iron-built


merchant ships in the nineteenth century. Their chief advantage over sail was being capable of keeping to a schedule. Clipper ships were a dying technology’s gasping response to progress with the thought that speed would be a competitive edge over slower moving coal fired vessels. But alas, speed was contingent on the wind blowing in the right direction. The 1869 opening of the Suez Canal was the death knell to Clipper ships on the profitable Pacific tea trade as now slower, but steady-speed coal fired merchant ships had a much shorter route to ply between Europe and Asia (sailing vessels had a difficult time navigating the narrow Suez Canal and had to pass around Cape of Good Hope to reach the Pacific). The era of the Clipper ship lasted only a few decades. Interestingly the subject of sail-assisted merchant vessels has been revived in recent years whenever the cost for bunkers (ship’s fuel), reflecting spikes in oil prices, consume over half of voyage revenue. Sail is still used in the Middle East, Africa, and Asia for commercial fishing and local trade.

The first land based windmills were developed in Persia and Middle East around 500–900 CE (although there is a claim that China used wind power to pump water as early as 200 BCE).19 These early windmills employed woven reed or wooden sails, adapted from sailing vessels, to either grind grain or pump water. Grinding grain requires a horizontal grinding stone that must be driven by a vertical axis. Early windmills equipped with sails powered vertical shafts of reed bundles or wood. The trajectory of the sails had to be horizontal to drive a vertical axis. Sail powered vertical axis windmills can be found today in Crete pumping water for crops and livestock. Returning merchants and crusaders from Middle East and Persia brought the idea of the windmill to Europe. This evolved from a vertical axis design to the more efficient horizontal axis configuration for capturing wind energy. The trajectory of the sails was vertical necessitating gearing to translate the motion of a horizontal axis to a vertical axis to drive a grindstone. The earliest illustration of these windmills, dating back to 1270, shows a four-bladed mill mounted on a central post or post mill with wooden cog and ring gears to translate the motion of the horizontal shaft to a vertical shaft to turn a grindstone. In 1390, the Dutch refined the design of the windmill with a horizontal post mill at the top of a multistory tower, whose motion was translated to a vertical post mill that passed through separate floors for grinding and removing chaff and storing grain with the bottom floor serving as living quarters for the wind-smith and his family. This refined windmill was also adapted for draining lakes and marshes in the Rhine River Delta to expand agricultural land, and later, with the building of dikes, to create a nation by removing water on land taken away from the sea. Holland had 8,000 windmills in 1650, England 10,000 windmills in the early 1800s, and Germany more than 18,000 windmills in the late 1800s.20 The process of perfecting the windmill sail and in making incremental improvements in efficiency and reliability took about 500 years. By the time the process was complete, windmill sails had advanced to the point of incorporating the essential features of modern wind turbine blades. Windmills in Europe were eventually replaced with greater reliability and power output of coal fired steam engines.

In the US, windmills for pumping water were perfected during the nineteenth century beginning with the Halladay windmill in 1854 and continuing on with the Aermotor and Dempster designs still in use


today. The original mills had thin wooden slats nailed to wooden rims with tails to orient the blades into the wind. An important refinement of the American fan-type windmill was the development of steel blades in 1870, which allowed for a more efficient and lighter design. Between 1850 and 1970, over six million small (1 horsepower or less) mechanical output wind machines were pumping water for livestock and home use.21 Large windmills with blades up to 18 m (59 feet) in rotor diameter (the circle swept by the tip of the blades) supplied the large water requirements of steam locomotives in locations where water had to be pumped from below ground.

A wind turbine is the opposite of a fan. A fan consumes electricity to power a motor that turns a rotor with attached blades to move air. In a wind turbine, moving air turns the blades attached to a rotor that drives a generator. The first windmill to generate electricity was built in Cleveland, Ohio, in 1888 by Charles F. Brush. The Brush wind turbine had a post mill with a multiple-bladed rotor 17 m (56 feet) in diameter and a large tail hinged to orient the rotor properly to the wind. A step-up gearbox turned a direct current generator at a higher rotational speed to allow for a smaller sized generator. This design did not work well and in 1891, the Danish entrepreneur, Poul La Cour, improved the design and developed the first electricity generating wind turbine of 25 kW output with four-bladed airfoil shaped rotors. The higher speed of La Cour rotors made these machines practical for electricity generation. By the end of the First World War, cheaper and larger fossil fuel steam plants started to replace electricity generating wind turbines that dotted the Danish landscape. By the mid-1920s, small electricity generating wind machines (1–3 kW), developed by Parris-Dunn and Jacobs Wind-Electric, popular in the Midwest and Great Plains, provided lighting for farms and charged batteries for powering crystal radio sets. Electricity from these wind turbines soon began to power an array of direct current motor driven appliances including refrigerators, freezers, washing machines, and power tools. However their sporadic operation when the wind ceased blowing was a problem. In the 1930s, the Great Depression spurred the federal government to sponsor the Rural Electrification Administration’s program to stimulate depressed rural economies by extending the electricity grid throughout rural America, ending the days of wind-generated electricity. (History likes to repeat itself, but with a twist. One of Obama administration’s ideas to stimulate the economy was extending transmission lines to isolated areas with persistent winds to promote wind electricity projects and to isolated areas with lots of sunlight to promote solar electricity projects.)

Development of bulk power, utility scale wind energy conversion systems was first undertaken in Russia in 1931 with the 100 kW Balaclava wind generator. This wind turbine operated for about two years on the shore of the Caspian Sea. Subsequent experimental efforts in the US, Denmark, France, Germany, and Great Britain between 1935 and 1970 demonstrated that large-scale wind turbines worked, but they failed to produce a large practical electricity generating wind turbine. In 1945 the largest wind turbine was the Smith-Putnam machine installed on a Vermont hilltop called Grandpa’s Knob. This horizontal axis design featured two blades with 175 foot rotor diameter and generated 1.25 mW in winds of about 30 mph. Its power was fed to the local utility network, but one of the blades broke off


near the hub from metal fatigue ending its life after only several hundred hours of intermittent operation.

European development in wind energy continued after the Second World War when temporary shortages of fossil fuels led to higher energy costs. In Germany, Professor Ulrich Hutter developed a series of advanced, horizontal axis designs of intermediate sizes that utilized modern, airfoil-type fiberglass and plastic blades with variable pitch to provide lightweight and efficient generation of electricity. This design sought to reduce bearing and structural failures by “shedding” aerodynamic loads rather than “withstanding” them. Hutter’s advanced designs achieved over four thousand hours of operation before experiments were ended in 1968. In France, G.J.M. Darrieus began developing vertical axis rotors in the 1920s comprised of slender, curved, airfoil section blades attached at the top and bottom of a rotating vertical axis resembling an eggbeater. The research ceased until two Canadian researchers took on major development work in the late 1960s, but the effort did not result in a commercially successful vertical axis design.22

Government Involvement in Developing Wind Turbines

Popularity of using wind energy has always fluctuated with the price of fossil fuels. Interest in wind turbines waned when fuel prices fell after the Second World War, but revived when oil prices skyrocketed in the 1970s. The US federal government’s involvement in wind energy research and development (R&D) began in earnest within two years after the 1973 oil crisis to refine old ideas and introduce new ways of converting wind energy into useful power. Many of these approaches were demonstrated in wind farms, a grouping of wind turbines located in a single area that fed electricity via a common means into a utility grid. Despite the speed with which it was initiated and an early show of promising results, the program failed with withdrawal of government funding.

Nevertheless other federal R&D activities such as at Sandia National Laboratories resulted in design, fabrication, and testing of thirteen different small wind turbine designs (ranging from 1 to 40 kW), five large (100–3,200 kW) horizontal axis wind turbine (HAWT) designs, and several vertical axis (VAWT) designs ranging from 5 to over 500 kW. Most of the funding was devoted to the development of multi-megawatt turbines in the belief that US utilities would not seriously consider wind power unless large, megawatt utility scale turbines were available. Wind turbine development in the US progressed from blade lengths of 5 to 10 to 17 m (16 to 33 to 56 feet). The latter machine, commercialized by FloWind, used much of the technology developed by Sandia National Laboratories, but a real market for this technology never emerged.


While Canadian development was focused on a 4 mW Project Eole turbine on Magdalen Island in the St. Lawrence River, National Aeronautics and Space Administration (NASA) Plum Brook Ohio facility became involved with wind turbines and started development of the 100 kW MOD-0 in 1975, and rapidly moved through several generations including the MOD-1 and the 100 m (328 foot) diameter MOD-2 wind turbines. The program was plagued by not realizing the importance of “teetering” hubs essential for reducing dynamic loads in two-bladed machines created by the tower shadow. After initial failures, the first “real” NASA wind turbine was MOD-2. Three of these machines operated for several years providing valuable engineering data to pinpoint and correct several design weaknesses. Unfortunately, these pitfalls were all that were needed to provide detractors with enough ammunition to end the program in 1981. Nevertheless lessons learned on the MOD-2’s were incorporated in the huge 3.2 mW MOD-5B wind turbine at the Makani Moa’e wind farm in Kahuku, Oahu, operated by Makani Uwila Power Corporation. The wind turbine had two blades with a rotor diameter of 320 feet and was the largest sized wind turbine in the world until the early 2000s when 3.6 mW turbines became commercially available.

Another federal effort started in 1976 was to develop a reliable wind turbine to perform as envisioned in a federal wind application study. Within 4 years, 13 wind turbine designs were developed for five size-range categories including 1–2 kW High Reliability, 4 kW Small Residential, 8 and 15 kW Residential and Commercial, and 40 kW Business and Agricultural. This development work led to the 1–3 kW and 6 kW small wind turbines commercialized by Northern Power Systems and still being sold for remote power users and a three-bladed 40–60 kW wind turbine installed by the hundreds in California wind farms by Enertech. Wind farms in California were the vanguard in commercializing wind energy and were the result of both R&D efforts undertaken by the federal government and financial incentives established by the Public Utility Regulatory Policies Act (PURPA) of 1978. California state regulators, fearing that oil fuel electricity generating plants would be vulnerable to falling oil production in California and Alaska, were particularly aggressive in carrying out PURPA provisions. They required California utilities to buy electricity generated from wind farms at a premium Feed-in Tariff over conventional sources to induce development of wind energy. As a result, California would eventually become home of over 17,000 wind turbines, which produce individually between 50 and 600 kW of electricity. In the 1980s wind turbines were built with lattice-style structures of 50–300 kW capacity and a rotor blade diameter of 15–30 m (49–98 feet). In the 1990s, the tubular structure was adopted with turbine capacity of 300–750 kW and a rotor blade diameter of 30–50 m (98–164 feet). The popular sized GE 1.5 mW wind turbine had 3 blades with a rotor diameter of 77 m (253 feet) and a hub height in four sizes varying from roughly 60–85 m (197–279 feet). Even at this point of development, a Boeing 747, which can carry up to 436 passengers, with a wingspan just over 211 feet (64.4 m) and a length just under 232 feet (70.7 m) could fit within the rotor blade diameter of the GE 1.5 mW wind turbine.

Major California wind farms are located in mountain passes that experience persistent winds much of the time such as the Altamont Pass east of San Francisco, Gorgonio Pass near Palm Springs, and at


Tehachapi south of Bakersfield. Wind farms in California made up most of US wind turbine installations until the early 1990s. At the height of their power potential, these turbines had a collective rating of over 1,700 mW (1.7 gW), sufficient in the US to supply a city of over 1 million people when the wind was blowing at all their various locations. Fortunately, periods of high winds over coastal hills correlated fairly well with timing of high commercial and residential air conditioning loads in the summer. Key subsidies making wind turbine investments financially attractive were a 15 percent federal energy credit, a 10 percent federal investment credit, a 50 percent California state energy credit, and a high Feed-in Tariff electricity rate mandated by state regulators that had to be paid by utilities for electricity produced from alternative sources, which, of course, was passed to consumers in the form of higher utility bills. The high rates paid for electricity produced by wind farms and the subsidy benefits provided by the federal and state governments were neatly packaged into investment products by private financial firms to garner the necessary capital from individuals and companies to build California’s wind farms.

Beneficiaries of heavy federal funding of wind energy programs were supposed to be the large US aerospace and construction firms developing the MOD-2, MOD-5, and the intermediate sized MOD-6 wind turbines. But an increase in military expenditures reduced the interest of aerospace firms in risky new business challenges like wind turbines. The “counter-culture” of wind energy entrepreneurs at Rocky Flats, Colorado, founders of the American Wind Energy Association in the mid-1970s, became the driving force in the development of wind turbines. Unfortunately, a combination of design problems, Reagan administration’s attitude toward deregulation, and a period of low oil prices removed incentives to pursue renewable energy sources and wind energy business slowed considerably in the 1980s.

Nevertheless there was still activity. In contrast to American companies that pursued two-bladed wind turbines, Danish firms developed three-bladed wind turbines based on the Gedser mill design. The design, considered somewhat primitive and inefficient, but well understood, was modernized with fiberglass blades. By 1986 the Danes captured 50 percent of the US wind farm market replacing hundreds of inoperable US turbines cluttering the California landscape. Design shortcomings became apparent when high California wind loads began to pulverize poorly manufactured Danish blade roots, requiring an expensive “fix” for thousands of turbines. Even though wind farm operators were weighed down with high maintenance costs and constant repairs to keep their wind turbines running, US wind farm demand for new intermediate sized wind turbines was still alive. Then wind farm operators were hit with the end of federal energy credits in 1984 and phase-out of California state credits shortly thereafter. Fortunately for wind farm operators, California utilities were required to maintain artificially high feed-in Tariffs into the 1990s, when many of the wind turbines had long since been paid off, thus making investments in wind turbines quite profitable. Although sales of small wind turbines during this period were slow, volume was sufficient to provide business for several manufacturers of wind turbines designed for water pumping and electricity generation at remote locations such as Southwest Wind


Power and Bergey Windpower. In general, however, the US market lagged and gradually declined during the 1980s and into the 1990s.


1 “History of Solar Energy,” Education and Teaching, Web site www.streetdirectory.com/etoday/history-of-solar-energy-cewouo.html.2 “The History of Solar,” US Department of Energy, Energy Efficiency and Renewable Energy, Web site www1.eere.energy.gov/solar/pdfs/solar_timeline.pdf.3 Solar Energy History Web sites www.facts-about-solar-energy.com/solar-energy-history.html and www.solarevents.com/articles/solar-energy/solar-energy-history.4 “Which type solar panel is more efficient…glazed or unglazed?” Energy Exports, Web site http://energyexperts.org/EnergySolutionsDatabase/ResourceDetail.aspx?id=3844. 5 Apricus Solar Hot Water Web site www.apricus.com/html/solar_collector.htm#.VK6r0HvwBdB has a good description of an evacuated tube solar collector.6 Franz Mauthner and Werner Weiss, “Solar Heat Worldwide (2012),” IEA Solar Heating and Cooling Program (2014) Web site www.iea-shc.org/data/sites/1/publications/Solar-Heat-Worldwide-2014.pdf.7 Nicola Armaroli, Vincenzo Balzani, and Nick Serpone, Powering Planet Earth (Weinheim, Germany: Wiley-VCH, 2013). 8 Mark Drajem and Justin Doom, “Phasing out Fossils: Big Companies Using Thermal Storage to Meet Carbon Rules,” Renewable Energy World (August 4, 2014), Web site www.renewableenergyworld.com/rea/news/article/2014/08/goldman-sachs-using-thermal-storage-to-meet-carbon-rules.9 Energy Efficiency and Renewable Energy Solar Technologies Program Web site www.eere.energy.gov/solar/csp.html.10 Eric Wesoff, “Areva Abandons Solar and Shutter its Ausra Concentrated Solar Effort,” GreentechSolar (August 4, 2014), Web site www.greentechmedia.com/articles/read/Areva-Abandons-Solar-and-Shutters-Its-Ausra-Concentrated-Solar-Effort.11 “Ivanpah Solar Electric Generating System,” Bechtel, Web site www.bechtel.com/projects/ivanpah-solar-electric-generating-system.12 M. J. Brooks, I. Mills, and T. M. Harms, “Performance of a Parabolic Trough Solar Collector,” Journal of Energy in Southern Africa, Vol. 17, No. 3 (August 2006), Web site www.erc.uct.ac.za/jesa/volume17/17-3jesa-brooks.pdf. See also “NREL: This Parabolic Trough 73% Efficient,” Solar Power World (September 3, 2010), Web site www.solarpowerworldonline.com/2010/09/nrel-says-skyfuels-parabolic-troughs-are-73-efficient.13 “NREL: Concentrating Solar Power Projects,” National Renewable Energy Laboratory (November 20, 2014), Web site www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=62.14 Wikipedia (The Free Encyclopedia) Web site http://en.wikipedia.org/wiki/List_of_solar_thermal_power_stations.15 Enviromission Company Web site www.enviromission.com.au. In November, 2014, the company signed a memorandum of understanding with the US Energy Department Western Area Power Administration to further evaluate the concept.16 Jennifer Chu, “Steam from the Sun,” MIT News (July 21, 2014), Web site http://newsoffice.mit.edu/2014/new-spongelike-structure-converts-solar-energy-into-steam-0721.17 “Creating Fuel from Sunlight,” University of Minnesota Discover (October 23, 2013), Web site http://discover.umn.edu/news/science-technology/conventional-fuels-concentrated-sunlight.18 Susan Kraemer, “How to Protect Birds from CSP Towers,” CSP Today (June 6, 2014), Web site http://social.csptoday.com/technology/how-protect-birds-csp-towers.See also Susan Kraemer, “For the Birds: How Speculation Trumped Fact at Ivanpah,” Renewable Energy World (September 3, 2014), Web site www.renewableenergyworld.com/rea/news/article/2014/09/for-the-birds-how-speculation-trumped-fact-at-ivanpah.19 Darrell M. Dodge, “Illustrated History of Wind Power Development”, Web site www.telosnet.com/wind/index.html. Unless otherwise indicated, this is the chief source of information on the development of windmills and wind turbines.20 Vaclav Smil, Energy in World History (Boulder, CO: Westview Press, 1994).21 As a child I lived on an estate dairy farm on Long Island that had a large wooden windmill, perched on top of a tall stucco and brick tower used for pumping and storing water; but by then, the windmill was no longer operable and the tower had been converted to a silo for corn silage. I remember my oldest brother perched precariously on the rotor vane hanging on with one hand overhanging the silo. My mother took one look and quietly returned to the house–the right move.22 Mike Barnard, “Vertical Axis Wind Turbines: Great in 1890, Also-rans in 2014,” Clean Technica (April 7, 2014), Web site http://cleantechnica.com/2014/04/07/vertical-axis-wind-turbines-great-1890-also-rans-2014.

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Solar Power - s3.amazonaws.com€¦ · Web viewenergy in pasteurization and making ice. In 1883 John Ericsson, an American, invented a solar powered steam engine that used parabolic