Rooftop power plants

Massive blackouts and brownouts followed Japan's March 11 Tohoku earthquake. Businesspeople in the Tokyo and Osaka areas immediately turned for help to Ma Chen-chi, a professor of chemical engineering at Taiwan's National Tsing Hua University (NTHU). They were seeking easily installed and removed small-scale wind-driven turbines to provide urgently needed electrical power to disaster victims.

Transportation difficulties prevented any of Taiwan's small wind turbines from quickly getting to the disaster zone, but they attracted attention nonetheless.

Given the tightness of contemporary energy supplies and worries about the safety of nuclear power, will we see widespread use of small and medium-sized wind turbines? Will the industry take off?

Most people are familiar with the giant white turbines that tower over the Gao-mei Wetlands and the Hsin-chu-Harbor-area coastline. But they often overlook the many small and medium-sized wind turbines generating power that surround them in their everyday lives.

Such turbines really are everywhere. You'll find them on the quaint old streets of Danshui, along the Taoyuan stretch of National Highway 1, at elementary schools in Zhuwei and Danshui, and on the campus of National Taiwan Univer-sity of Science and Technology and NTHU.

For example, there's a streetlamp with its own hybrid wind and solar power system on the right side of the road as you enter the NTHU campus. The installation consists of three or four turbine blades spinning atop the lamp pole, a small solar panel, and an LED light fixture. Because the turbine is so much smaller and quieter than a large-scale windmill, it's easy to miss.

Images of windmills and idyllic scenes of the Netherlands tend to leap to mind at the mention of wind power.

The world's first wind-driven grain mill was built in the Netherlands in the 12th century. The Danes developed a wind-powered electrical generator in the 19th century. The Americans began to commercialize wind-generated electricity in the 20th century, but it was the French who developed the first small-scale (100-300 kilowatt) wind-driven turbine and kicked off the era of small wind.

The leading edge of small wind

Taiwan began developing small and medium-sized turbines five years ago, and NTHU's "Green Energy Development Team" has done stellar work in the field.

The team works on "three-in-one" hybrid power systems that combine wind and solar power with storage. The university formed the team around Yip Ming-chuen, a professor in the Department of Power Mechanical Engineering, Ma Chen-chi, a chaired professor in the Department of Chemical Engineering, and Pan Ching-tsai, a professor in the Department of Electrical Engineering. The team, which brings together expertise in the fields of nanomaterials, mechanics of materials, and electrical networks, has been working diligently to develop better small vertical-axis wind power systems.

It costs little to generate electricity from wind power. According to Ma, wind generates electricity at a cost of less than NT$2 per kilowatt-hour, versus roughly NT$3 per kWh for coal and NT$11 per kWh for diesel.

"But wind is variable, sometimes strong, sometimes weak," says Ma. "Currently, that's its biggest constraint." And not every location can be exploited for wind power.

Taiwan's prime wind sites-those that meet the internationally recognized economic viability standard of having winds of at least five meters per second for at least 2,500 hours per year-consist of only the stretch between Hsin-chu and Zhu-nan, Mai-liao Township in Yun-lin County, and the Zhongtun area of -Penghu.

Given the variability of the wind, the new trend in green energy has been to use wind and solar power in a complementary fashion.

Wind and solar

Typically, sunny days mean little wind, and windy days mean little sun. Neither sun nor wind is a perfect solution by itself, but they complement one another very well.

Take the wind-solar hybrid streetlamp on the NTHU campus, for example. NTHU may be located in the windy city, but the area's strong monsoonal winds blow only from October to April. There's hardly a breath of breeze to stir the turbine blades in the summer, leaving the lamp dependent on its solar panel for power. Even so, over the year as a whole, the lamp gets four times as much power from the wind as it does from the sun.

The main reason that wind generates more electricity than the sun has to do with the conversion ratio. The conversion ratio for wind energy to electrical energy is in the 30-40% range, while that for solar energy is just 10-20%. In the case of the 300-watt wind-solar streetlamp on the NTHU campus, one day's good wind can power the lamp for three to four days.

The hybrid generating system routes wind and solar power through a voltage regulator, then converts the DC current into AC, and stores the power in a storage system. This power can be used where generated or the system can be linked to the grid and the power used as part of a household's electrical supply. (Current is drawn from Taipower only after that generated by the system is exhausted.)

The rated power of a turbine is related to the turbine's swept area and the cube of wind speed. In other words, the bigger the blades and the taller the turbine's tower (wind speeds are higher at altitude), the more power produced. For example, a 1.65 megawatt wind turbine mounted atop a 78-meter tower has a blade diameter of 82 meters and generates about 4.3 megawatt-hours per year, enough to power about 970 homes.

But such large wind power generators may impact air safety, could damage their surroundings in an earthquake or typhoon, and are a noise hazard. Since no one can safely live within 200 meters of them, they must be built in remote locations or even offshore. In addition, wind power projects of this size are subject to environmental impact reviews. But small wind is more flexible in terms of its siting and doesn't require an environmental impact assessment. It can even be integrated into the built environment, cohabiting with buildings, parks, and farms.

But Ma points out that while small wind is less constrained by location, buildings and trees interfere with airflow. In urban areas, it is best suited to rooftops. Given that limitation, it might be more aptly called "rooftop power."

Small wind, big market

The Taiwan Small and Medium Wind Turbine Association (TSMWTA) currently has 39 members. According to Su Mei-hui, the group's deputy secretary-general, the high price of infrastructure such as power plants and power grids is encouraging many nations to install distributed generation systems in remote areas beyond the reach of their power grids.

Following the trail blazed by solar power, small wind has been a supplemental power option since 2009. Government subsidies vary from nation to nation, ranging from 30% in the US to 60% in Korea.

Taiwan began purchasing green power last year at a rate of NT$11 per kWh of solar power and NT$7 per kWh of small wind.

Su says that Taiwan's small (400 W to 150 kW) wind turbine industry is beginning to grow rapidly. The last three years have seen companies leaping into the business, and shipments have soared from over 4,000 units in 2009 to a projected 47,000 units in 2011. The industry's production value has also skyrocketed from something over NT$100 million in 2009 to a projected NT$1.7 billion this year.

"There's a huge market for small wind," says Su, explaining that people keep coming up with new applications for small and medium-sized turbines. In addition to providing power to remote areas, for household use, and for traffic signals and lights, such turbines are now also being deployed on yachts and fishing boats, particularly on the lakes of mainland China and Vietnam, where small wind is reducing diesel expenses.

Taiwan's vertical-axis advantage

Moreover, since the key technologies for large wind power systems are controlled by American and European firms, Taiwan must import most of the components of such systems. But Taiwan can go it alone on small wind systems. We have a solid foundation in all the technologies related to its production, from the manufacture of composite blades to that of the electrical control systems and the bases. Taiwanese small wind is well positioned to grow and create its own niches. Given that these efforts are being supported by outstanding R&D teams, the future looks bright.

Take the small wind system developed by NTHU, which utilizes composite blades and a vertical-axis design.

Vertical-axis turbines differ from horizontal-axis systems in the direction of the axis of rotation of the turbine's blades.

Horizontal-axis systems are very loud. (The noise created by the blade tips is in direct relation to the fifth power of the speed at which the turbine rotates.) They also kill birds and won't spin unless they are facing into the wind. As a result, some 22 US states bar the installation of horizontal-axis small wind turbines in urban and residential areas.

Vertical-axis systems, on the other hand, are quiet, safe, easy to install, and turn no matter what the direction of the wind.

Crucial to a system's longevity is the material from which its blades are made.

Manufacturers in Taiwan and abroad used to use stainless steel or aluminum for the blades. But the blades, which had relatively small cross sections, corroded badly in three years of testing in the icy, sandy conditions of Inner Mongolia.

NTHU developed a turbine blade made from a polymer composite consisting of glass or carbon fibers and corrosion-resistant polyvinyl resin. The blades are safe and easy to install virtually anywhere, providing portable power whether sited atop a commercial highrise, in an amusement park, neighborhood or park, or on a farm or school campus.

Blades made from the composite material are only about one-fifth the weight of those made from older materials, and are more easily turned by the wind. Typical small wind systems need only light winds (3.4-5.4 meters per second) to generate power, but the NTHU vertical system works in as little as two meters per second.

Even more amazing is that the strength and design of the blades gives them a functional life of 15-17 years.

Small wind systems currently utilize recyclable lithium iron phosphate batteries to store power, but NTHU and Bei-jing's Tsing-hua University are now working together on the development of third- and fourth-generation environmentally friendly all-vanadium redox flow batteries.

Outlook for exports

Small wind has numerous strengths, but most of the systems presently manufactured in Taiwan are destined for export. According to the TSMWTA, Taiwan exported some 79% of the small wind systems it produced in 2010, with 64% going to mainland China.

Ma says that the mainland is making an aggressive move into wind and solar power and that wind turbines from around the world dot the broad Hoh-hot Plains of Inner Mongolia, hybrid wind-solar systems from Taiwan among them. Nowadays, the shepherds of Inner Mongolia don't ride horses, they ride electric motorcycles. They are also installing solar panels on the outside of their families' yurts. Nowadays, even convenience stores are selling solar systems.

Why don't we see small wind systems and solar panels on every rooftop in Hsin-chu? The main reason is that power in Taiwan is cheap and small wind systems aren't. There's simply no incentive for people to buy them.

NTHU vice president Yip Ming-chuen, the force behind the school's "low-carbon, green-energy campus" program, says it takes at least a decade to earn back a hybrid wind-solar streetlamp's nearly NT$200,000 cost through energy savings. Such high costs have prevented large-scale installation of the devices. As a result, the school has just six that it is using for research purposes.

NTHU and the Hsin-chu City Government have now created the "Small and Medium-sized Wind Power System Demonstration and Testing Platform" to promote the lamps. Under the program, a row of the hybrid street lamps will be set up along the shore of Qing-cao Lake and alongside the Taiwan Pavilion (relocated from the Shang-hai World Expo, and due to open in Hsin-chu at the end of the year).

But demonstration projects are only worth so much. If we hope to deploy the technology on campuses, in communities, and around ordinary homes, discounts are going to be crucial.

Right now, a 300 W small wind system costs NT$100-120,000. The kind of system necessary to provide the 3 kW a typical home uses or the 5 kW consumed by a farm runs NT$400-500,000. Consequently, there's just no incentive to buy small wind.

Going green

Will our built landscape someday incorporate small wind systems turning atop every home? Su argues that electricity is just too cheap right now. Most homes use less than 330 kWh per month at a cost of only NT$2.68 per kWh. Moreover, wind conditions vary greatly across the island, making it unlikely that small wind will be implemented islandwide. At the present time, its use is generally lim-ited to outdoor facilities and public spaces, such as streetlamps and fishponds, on farms and schools, and in parks.

Ma, on the other hand, is very positive on the market's outlook, arguing that prices will fall if production capacity grows. He forecasts that in three to five years the price of a 300 W system will fall below NT$100,000 and that of a 3 kW system will drop to NT$200-300,000. At those prices, buyers would earn back their costs in about 10 years. He believes that if we simplify the process for having Taipower purchase green energy from producers, rooftop power generation could have a very bright future in Taiwan.