Study delivers blow to urban microwind turbines

Small wind turbines attached to individual homes work fine unless you have lousy wind.

That's the upshot of a multi-site study called the Warwick Microwind Trial project, a year-long survey on the performance of roof-mounted turbines done in the U.K. done by Encraft, a low-carbon technology consulting firm.

The researchers picked 26 sites in the U.K where microturbines tied to the power grid were attached to people's homes to offset their electricity use. Many of the consumers clearly purchased the turbines to lower their fossil fuel energy use as some already had solar panels and ground-source heat pumps.

One of the building-mounted roof turbines tested in a year-long study of urban wind turbines in the U.K.

(Credit: Encraft)

But the Encraft study, which came out last month, found that many of the turbines didn't meet manufacturers claims for power generation. Some turbines needed to go offline at times because of technical problems or complaints over noise.

"The gap between average performance (or expectation) and reality is much larger than people could reasonably expect," Encraft managing director Matthew Rhodes said in a summary.

The survey doesn't conclude that small wind turbines, in general, are uneconomical or unsuitable for the U.K. Instead, the data points to the need for accurate wind measurements before installing microturbines, particularly in cities.

From the study: "Overall the trial has painted a picture of an industry and technology that is still at development stage and is likely to make a tangible contribution to energy and carbon saving only on the most exposed sites and tallest buildings. The combination of this reality, aggressive and over-optimistic marketing by some suppliers, and the enthusiasm and credulity of the market (and regulators) has potentially led to an unfortunate outcome where the wind industry as a whole is in danger of suffering from a setback in credibility."

In response to the report, the British Wind Energy Association noted that many of the urban sites chosen in the study have wind lower than 5 meters per second (or 11 miles per hour), considered the lower limit of commercial viability. It also said that the British government's online wind assessment tool overstated the available wind in cities.

"The overwhelming majority of small wind system installations are a success--when they are sited properly they save money and energy. The Warwick trials do not show that small wind is not viable. We know that it is, and the experience of thousands of UK users bears this out," said Alex Murley, BWEA Small Systems Manager, in a statement.

Poring over wind maps
In the U.S., urban wind turbines account for only one percent of installations but there is growing interest, according to the American Wind Energy Association (AWEA). In a report (click for PDF) on how municipalities should permit small wind turbines, the AWEA said understanding one location's particulars and how high a turbine is placed--which in general, means more wind--is crucial in urban locations.

"Siting becomes especially important for turbines in urban settings. Wind patterns behave very differently around buildings and in densely-built areas, so a turbine must be sited very precisely in order to gain access to wind of sufficient quality," according to a report by AWEA.

Small wind turbines overall are a fast-growing segment of the wind industry. Incentives to install small wind turbines improved last year, boosting the federal tax rebate to up to $4,000. Politicians, including New York City Mayor Michael Bloomberg, have called for placing turbines atop skyscrapers and public buildings.

To get a read on the suitability of a location, start-up 3Tier offers a free, Web-based wind and solar assessment tool, which gives people an idea at a high level how good wind is. There are state-level wind programs, and the Energy Information Association and National Renewable Energy Laboratories both publish national maps.

In isolated areas, a pitched roof causes wind to speed up. But the presence of nearby buildings in an urban setting can cause wind to slow down when it hits a roof, according to research from the U.K.'s Centre for Renewable Energy Systems Technology.

(Credit: S. Watson, Loughborough University)

Southwest Wind Power, which makes a small wind turbine that typically is mounted on a pole rather than a roof, offers guidance on minimum requirements, which include 10 mile-per-hour average wind and 20 feet clearance above obstructions.

Another manufacturer, Cascade Engineering, publishes specifications that assume a very good wind resource. The specifications for its roof-mountable small turbine indicate that it can turn out 1.5 kilowatts and the 2000 kilowatt-hours per year--or about one third or one quarter of a U.S. home's electricity. To meet that that threshold, however, a site needs 31 mile-per-hour wind, or 14 meters per second.

Some customers, meanwhile, don't do rigorous economic analysis beforehand. The Museum of Science in Boston, for instance, is now working on an educational project to put eight small wind turbines from different manufacturers on its roof

Harvard University, which plans to put some small turbines on an office complex and on a parking garage, told The New York Times that the installations are experiments and "outward symbols of our commitment to renewable energy and sustainability here on campus."

Aerovironment is targeting commercial customers for its small-wind turbines that are optimized for gusty wind coming off buildings.

(Credit: Aerovironment)

Small wind manufacturers say that the payback on small wind turbines--rooftop or pole-mounted--varies greatly based on how a machine is sited, which points to the importance of a good installer.

With good wind and high electricity rates, a homeowner could recoup the upfront investment of a small wind turbine in five or six years. But low electricity rates and marginal wind could mean 15 or 20 years, Andy Kruse, the CEO of Southwest Windpower, said last month.

Kruse is lobbying for government-sponsored work to make wind and solar maps that offer more specific information. "How do we create a new generation of maps so that we can understand resource, to make sure it works and stop guessing?" he said.

[ittesi259]

Wow...maybe its to early in the morning but where is Manhattan2 with his babble about Solar Transfer and how great it is but tells us nothing about it?

[The_happy_switcher]

"Small wind turbines attached to individual homes work fine unless you have lousy wind. " wow, I wonder how much money was spent on this study that concludes that windmills don't work very well without wind? What's next, lightbulbs don't work very well without electricity?

[Michichael]

Hardly! We need proof that water is wet first.

[rapier1]

Its sort of important to actually quantify these things. For example, if Company A says that Product B will produce 8 kilowatt/hours with a 5MPH wind its useful to know if it will actually do that. Especially if a lot of people are spending money on these things. In fact, if you read the article you'd pick up on why knowing how a small wind turbine would work in urban environments is important.

[sanenazok]

I completely agree with the Harvard rep. The turbines and panels are meant as an enviromessage ("outward symbols of our commitment to renewable energy and sustainability here on campus") to the local leftists that the university supports green causes. Next, there'll be a study that the only way to make these systems self-supporting is a giant government subsidy. Good thing government money falls from the sky like manna!

[-_o]

Anyone else feel like the article could have cut off "Poring Over Wind Maps?" That section has nothing to do with the study. Seemed like a combination of filler and subtle marketing.

[carlhage]

Interesting study. What matters is the cost/kWh/year. Because power is proportional to the cube of wind speed and wind speed rises dramatically with height, the tall turbines get much more power. Power is proportional to the square of the rotor diameter, so you'd need 10,000 1m turbines (on a 100m tower) to equal only 1 100m turbine, so it seems hard for urban wind generators to compete with the large turbines sited optimally. In this study, the average turbine generated <$10/year of electricity, and the best performing unit generated <$100/year. (They sell the data for each station for more money than was generated in electricity in a year! :-) Part of low performance was due to being broken or shut off, so the average would have been <$30/year if running all the time.

No mention was made of the cost/unit. The turbines look to be ~US$2-3,000, without the inverters.

It looks like UK government rebates are 30% of installed cost-- it would be better to have a production credit so the incentive is based on the kWh generated. That would move the subsidies to the most efficient installations.

It was interesting that the measured wind-speed vs power curves differed so much from manufacturer's data sheets.

[smithenergy]

A Crowd Sourcing map has already been started to map where renewable energy is being generated - go to www.buildbabybuild.net/blog/residentialmap/ to add new locations.