Urban wind power systems aren’t new. Way back in the mid-70’s, the first rooftop windmill was installed on top of a NY City co-op building. The wind turbine generated enough electricity monthly - 200 kilowatt-hours - to power the building with enough electricity left over to deliver some to the Northeast power grid. So why didn’t urban wind generation catch on? For one thing, the technology was primitive compared to today’s. The early models were noisy and vibrated enough to be felt throughout the buildings. They looked like propellers on sticks to some people and weren’t aesthetically pleasing at all.

Things have certainly changed. When Chicago turned to Bil Becker, of Aerotecture International, http://www.aerotecture.com, he was able to provide the city with vertical-axis wind turbines that are almost beautiful. More like modern sculptures, these new rooftop turbines are able to generate electricity no matter the wind direction. Unlike horizontal-axis turbines, they can do that even when the wind is blowing with 100 mph gusts! Their price — under $4,000 and falling –make them accessible to the residential market also. Thanks to new design technology, vertical-axis turbines are almost no hazard to wildlife, they don’t vibrate at all and produce very little noise.

With very little fanfare, these rooftop arrays have multiplied at an increasing rate over the last decade, according to the American Wind Energy Association, and the industry is expanding exponentially. Phillipa Rogers, a spokesperson for Quiet Revolution, says, “We can’t make the turbines fast enough.” Company president, Phil Watkins, sees more than 40,000 turbines distributed by next fall. (http://www.plentymag.com/features/2007/09/a_mighty_wind.php)

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In 1970 at Odeillo, France, a solar furnace was built. Focusing the sun’s light, thousands of mirrors combine to produce temperatures up to 5,400 F. The furnace has applications in scientific research, can fire ceramics, and could even generate hydrogen. It was also in France, much earlier in 1949, that the first known modern solar furnace was built by Professor Felix Trombe. It was also built in the Pyrenees due to the almost 300 days of sunshine. Over fifty years old, it is back online and attracts 30,000 visitors annually. It is a dual reflection solar furnace with an array of 1,420 mirrors.Solar furnaces produce extremely high temperatures by using mirrors to parabolically reflect light onto a relatively small area of focus. This effect is similar, only on a larger scale, to the effect of focusing the sun’s rays through a magnifying glass to set fire to a piece of paper. (It’s also reputed to be the method that Archimedes used to burn Roman ships at the Siege of Syracuse.  (source: MIT)
While the heat of a solar furnace can melt steel, whether or not Archimedes’s Death Ray actually worked is unknown.

While some solar furnaces are used to refine metals, coat building materials, incinerate hazardous waste and fire ceramics, others are used for power generation. A type of solar furnace that generates electricity transfers the collected or focused energy of the sun and stores it in a substance for later use. Although water was originally used for a storage medium, liquid sodium is now used due to its higher capacity for heat retention. The stored energy can be used to boil water into steam to power turbines that generate electricity and can also be accessed even during darkness or cloudy days. Spain’s 15 MW Solar Tres Power Tower and 11 MW PS10 Solar Power Tower are based on this design. Other countries, including South Africa, have solar furnace based Solar Power Towers in the planning stages.

The PS10 tower is 40 stories high and is surrounded by an array of 600 heliostats or mirrors which are focused on water-filled plastic tubing at the top of the tower. Because of the reflected light, dust and water vapor in the air are illuminated into a pale fog which surrounds the tower. The tower is projected one day to provide enough power for the 600,000 inhabitants of the city of Seville, but is currently not up to that capacity at 11 Megawatts. Heliostats are being added and as they come online, capacity will increase. Abengoa, the company which owns the tower facility, and Solucar, the operator, report that the cost of generation is three times the cost of conventional power generation, but the tower produces no greenhouse gases, a fact that must be figured into the cost/benefit ratio. And as gas and oil prices rise and more solar furnace technology is adopted, construction and generating costs will no-doubt come more into line with conventional power plant costs. The subject of intense interest, PS10 is Europe’s first commercial Solar Power Tower operation. (http://news.bbc.co.uk/2/hi/science/nature/6616651.stm)

In the US, two Solar Power Tower projects were funded by the Department of Energy. Solar One and Solar Two, sited in the Mojave Desert in the Southwestern US, were limited successes and resulted in research which proved that liquid sodium is a much better medium for heat storage than water and that the Power Tower design was feasible. Spain’s Solar Tres was based on these projects and used Solar Two as a partial model for its tower design.

Crystalline silicon wafers have many drawbacks. They’re expensive. They’re usually encased in glass, which makes them heavy and brittle. Their manufacture is dependent on fossil fuels and results in pollution and waste. In spite of this, they dominate the PV cell market. Because crystalline cells are connected in series, if one breaks, is shaded or isn’t connected properly, the array is dysfunctional. Although technically they are more efficient than other kinds of photovoltaic cells, they often don’t perform as well because of the high temperatures on rooftops which reduce their efficiency. Enter amorphous photovoltaic cells made by Energy Conversion Devices or ECD.

In the late 1990’s, a subsidiary of ECD — Uni-Solar — revealed a new class of PV cells. Triple Junction PV modules are named for the three layers of PV junctions that are stacked atop one another, with each layer attuned to a different wave length of light i.e blue, yellow/green and red. Compared to old-style glass type panels, Triple Junction PV modules are 30% more powerful and are much more effective in high temperature applications. Because they are coated with Dupont Tefzel glaze, they are able to withstand golf ball-sized hail and similar impacts. An installation funded by the Department of Energy in Hawaii in 1998 is still holding up and working well.

Perhaps the most surprising and promising facet of the Triple Junction line is that it can be used for roofing, just like normal shingles, and even looks like conventional shingles. Because, unlike glass encased PV panels, there is no need for an aluminum frame, it takes far less time to install Triple Junction PV modules. The flexible panels are laminated to metal roofing, on site, and in some instances are actually less expensive than composite shingles. According to Stan Ovshinsky, the inventor of amorphous PV cells and ECD’s founder and former CEO, “production costs are well below any other PV product. Our problem is keeping up with demand.” (http://www.renewable-energy-world.com) Because of these lower production costs, Triple Junction PV modules have the fastest energy payback — the time it takes to recover the costs of making them — of any PV cell.

When compared to fossil fuels or nuclear power, the ECD product is miles ahead in terms of efficiency and even cost, when factors like pollution, land area to return and transportation costs are taken into consideration. Coal for instance, involves mining land and the disposal of waste which covers vast areas in some places in the US and other countries. Nuclear power is dangerous, subject to terrorist threats and has an unsolved problem with waste disposal. Nuclear power also depends heavily on government subsidies, a hidden but real cost.

ECD is the biggest player in the amorphous film PV cell industry, as well as a key manufacturer of other renewable energy technology. The Ovshinskys, Stan and his late wife, Iris, his working partner for more than fifty years, concentrated their research in two areas: information and energy, which Stan called the “twin pillars of the global economy.” Their subsidiary, Ovonics Universal Memory, is involved in multi-level technology, phase-change research and innovative approaches to memory storage and artificial intelligence. In addition to amorphous PV cell modules and IT technology, ECD and its subsidiaries produce NiMH batteries, hydrogen-based vehicles, hydrogen storage systems and fuel cells.

The Ovshinskys have received many awards including the Popular Science Grand Award. They have been featured in two PBS documentaries and honored by the American Chemical Society for “significant and lasting contributions to global human welfare with their invention of environmentally sustainable energy generation and energy storage applications.” Their IT work funds their PV cell research, which gives them much more latitude in research than companies with a single-technology approach to PV cell manufacture. Add to that their many other lines of hydrogen-based technologies and it’s clear that amorphous PV cell research will be fully supported at ECD far into the future. In 2001, the Forum of Chalcogeniders established the Stanford Ovshinsky Award for Excellence in Non-Crystalline Chalcogenides to honor his pioneering work and recognize the contributions of scientists and technologists in this field. (http://www.ovonic.com)

Although a French physicist named Becquerel first reported the photovoltaic effect, the first solar cell was probably constructed by Charles Fritts in the early 1880’s. Fritts coated selenium with a very thin gold layer, but the efficiency of this first solar cell was abysmal. It wasn’t until 1941 when Russell Ohl patented the silicon solar cell that efficiency started to improve appreciably. Soon, other scientists had improved on Ohl’s silicon solar cell to achieve a 6 percent return on energy conversion in strong sunlight. Bell Laboratories produced the first crystalline silicon solar cell in 1954, but its efficiency was merely 4%.Because the first large-scale use for solar cells was space satellites, government funding began to power the research, which had a galvanizing effect on solar cell research. By the 1970’s, the USSR had created Gas heterostructure solar cells with a high efficiency, although production was very limited until equipment design caught up to design theory. By the 1980’s, the US had produced a cell with 20% efficiency for use in the space program. And by early in 2000, efficiency was up to 24%. As of 2007, solar cells with an efficiency of 28% are manufactured by the two companies that dominate world solar cell production, Spectrolab and Emcore Photovoltaics.

While silicon wafer-based first-generation solar cells make up almost 90% of the solar cell market for terrestrial applications, second generation or thin-film solar cells make up the same percentage of the space applications. While nowhere near as efficient as their first generation relatives, these thin-film cells are much lighter and more pliable, prime considerations for space flight. Other cells are being developed at the present time including some that are dye sensitized, and thus able to respond to all light frequencies, unlike the silicon-based cells. There are even cells that are capable of using infrared frequencies, which would allow them to operate at night to some extent. Solar cell technology now in the research stage includes nanocrystal solar cells, photo electrochemical cells and polymer solar cells. One emerging leader in the solar cell technology race is Nanosolar at http://www.nanosolar.com, a company that is partially owned by the founders of Google, Sergey Brin and Larry Page.

There is very little to wear out on photovoltaic cells. It’s reasonable to expect a well-designed and properly installed system to have a lifetime of three decades or more. The most common failure in a photovoltaic system are the other components that are needed to convert electrons to AC current. The inverter, the batteries, the wiring — all are subject to corrosion, wear and aging. Batteries will need to be replaced at proper intervals, for instance. The cells themselves, however, should need no maintenance over the course of their lifetime unless they’re exposed to unusually harsh weather conditions.

Something that needs to be taken into consideration is the amount of sunlight that falls on the solar cells. This can significantly affect the electrical output. Mechanical devices to assist the cells in “tracking” the sun are often built into solar modules and arrays. Before installing photovoltaic cells, contractors often research the sun’s irradiance at the latitude of the installation. Irradiance can be determined by consulting the Department of Energy’s charts or at Advanced Energy Group’s website at http://www.solar4power.com.

Modules are groups of solar cells connected in a series and attached to a panel. Modules are constructed to deliver a range of output. Depending on the application, output is measured in watts or kilowatts and is calculated using a formula that takes into consideration peak power usage and average power output of each cell. Arrays are groups of modules and several thousand may be used in an electrical generating plant designed to power hundreds or even thousands of houses. Solar power is extremely adaptable to a wide range of applications, which puts it at the forefront of renewable energy sources.

The initial cost of a small wind turbine that will power an average home runs from $40,000 to $50,000, which is a significant investment. Why then do homeowners in 47 states have these windmills installed on towers on their property? For most of them, conventional electrical costs of over ten cents per kilowatt and plans to stay in their home long-term make it likely that they’ll more than pay for their windmill. They may very well save money over the monthly cost from their power company.Although there are drawbacks to home windmills, there are many benefits and the drawbacks can be overcome with some careful planning and research. The most important consideration, as you may imagine, is the average wind speed in your area. If there isn’t a steady source of wind, a windmill is not a good investment. Better to opt for solar or geothermal. If there is a steady wind, then the next consideration is probably the tall tower that you have to either erect yourself or have built for the wind turbine.

Some homeowners feel capable of doing this, especially if they purchase kits that allow you to build the tower in sections and then tilt it to put it up. Most, however, elect to hire qualified builders to put up the tower, and perhaps the turbine also. Proper installation will insure that your turbine is facing in the right direction and safely and securely fastened to the tower. At http://www.housingzone.com/probuilder/article/CA6406833.html there are recommendations for installing a home wind generator and links to wind power resources. And for further information, including plans, visit http://www.awea.org/smallwind.

But before you even unpack the turbine, you should make sure that its site is far enough from your dwelling to eliminate the noise issue. At least 160 feet is recommended. This is the one complaint that crops up again and again from homeowners who installed their unit on their garage roof or their home’s roof. Most small wind powered turbines are about as loud as the average clothes washer. If you take that into consideration when you are choosing a site for your generator, you’ll save yourself a lot of problems down the road.

Most homeowners opt to have their generator tied into their local utility’s line so that they can sell their excess electricity. This can help offset the cost of the generator over the years. And since the power is being generated, why not profit from it rather than wasting it? Other homeowners, including those who live too far away from power lines, forego tying into the power grid and just power their house and outbuildings with their wind powered generator. There are many places all over the world, even in developed countries, where running a line from the nearest pole to a homeowner’s dwelling would be cost-prohibitive.

If you’re going to sell your excess electricity, it’s important that you meet with your power company’s representatives and arrange for them to be on site when the generator is connected to the grid. Of course, it’s important also that you’re aware of and follow all local ordinances. A trip to your town building inspector or the appropriate official is imperative. And because of the height of the tower, home windmill installations are more suited to rural locations where landowners have enough acreage to isolate their unit from neighbors’ views.

The last point to consider is maintenance. It’s really important to purchase a tower unit that can be laid down by crane in the event that the windmill needs repair or maintenance. Of course, when repairs are made or the unit undergoes maintenance, it’s very important that the electricity is disconnected. Industry insiders predict that smaller, more compact wind powered generators will supplant the tall towers and propeller-type windmills, and that probably will happen in the future. As of now though, throughout the world, the tall towers and whirly-bird generators still dot the landscape, powering lights and appliances for satisfied homeowners.

Wind turbines come in all sizes from small windmills designed to power fountains and garden lights to larger home wind turbines up to giant turbines whose blade area covers the space of 2 soccer fields. The largest turbines are usually grouped into wind farms and more and more often are used in offshore installations, especially in Europe where wind power generation is a larger part of total power generation than it is anywhere else in the world. Germany and Spain lead the world in percentage of wind power to conventional power but China, the US, Canada and France are experiencing very rapid growth which makes them major players in wind power also.The largest wind turbine in the world is currently the REPower 5M. According to RE Power’s web site at http://www.repower5m.com/index_flash_uk.htm the 5M has a rated output of 5 megawatts, a rotor diameter of 126 meters, and a hub height of around 90 meters at sea and 120 meters on land. This giant wind turbine is being used to power several wind farm projects including a demonstration project off the coast of Scotland.

To reduce weight, the three rotor blades are made from an innovative glass/carbon fiber hybrid fabric that is held together by synthetic resins. To further reduce weight, the 5M’s die cast rotor shaft is hollow.

Another innovation is a gearbox that may be repaired or removed without having to take apart the rotor. This could mean a significant saving in repair cost and downtime. To deal with one of the most persistent problems with any wind turbine system, wind turbulence, the nacelle, which also holds the inverter and transformer for the 5M, has 8 geared motors for tracking the wind. To keep the nacelle facing into the wind, the 5M is equipped with eight hydraulic brake calipers. As a backup, there are also electromagnetic disc brakes. This greatly minimizes problems with turbulence-related damage.

The 5M has many options: a helicopter platform for offshore sites and elevators to lift goods and workers to the top of the tower. The towers themselves may be made from tubular steel, concrete or a hybrid of both steel and concrete. Every tower is equipped with communication capacity and, of course, cables for energy transmission.

Safety is a priority with the 5M both for workers and the installation itself. Automatic high capacity fire extinguishers are programmed to operate when fire is detected and lightning protection - a must in the stormy offshore environment - is built in. All safety systems have backups built into the design. This means that the 5M has optimum power production with few offline instances.

No doubt, other giant wind turbines will come on line within the near future, especially since several companies, including Siemens and GE have announced wind power projects. At http://www.powergeneration.siemens.com/press/press-releases/search.htm Siemens has information about projects they’ve recently been awarded in Denmark and Spain.

As technology improves wind turbine design and technology, and more countries turn to wind to power their homes and factories, giant wind turbines will continue to play a big part in the wind power market. Siting them offshore ameliorates the problems of aesthetics, especially if they are out of sight of land.

Environmental concerns, while still a factor, are not as relevant. While the cables emit electromagnetic waves which are a problem for sharks and rays, technology has yielded designs that help to overcome this. The impact on the seabed is taken into consideration and every effort is made to make it as minimal as possible. Further innovations will emerge as designers find new ways to make the giant wind turbines as environmentally friendly as possible. When everything is taken into consideration, including how much pollution and environmental damage the wind farms prevent by replacing conventional power generating technologies such as coal and gas, it seems apparent that giant wind turbines are a reasonable alternative energy source.