Wind Turbine Gearbox Reliability:

The impact of rotor support by Jordi Puigcorbe and Alexis de-Beaumont Published: June 3, 2010 London As a key failure point, gearbox reliability continues to dog the wind industry and as turbines become larger the push to improve performance becomes paramount. Alstom believes it has addressed the issue by ensuring that torque transmission is performed independently of rotor support. This improves the reliability of turbine drive train components, in particular the gearbox, which is better protected and subjected to lower loads. Jordi Puigcorbe and Alexis de-Beaumont explain. One of the biggest concerns remaining in the wind industry is the reliability of the gearbox. 'With our current wind turbine fleet currently going out of warranty period, we estimate that we are carrying a potential risk on gearboxes of about US$300 million. Failures are still relatively rare these days because our fleet is recent, but we expect this will change dramatically as our wind turbines approach their 5–7 years of operation. Our concern is such that we are even considering acquiring a company with gearbox servicing capabilities.' This statement from a large US wind farm operator is far from being an isolated case in an industry that will see over 8000 MW of wind farm capacity go out of the warranty period every year in the US alone in the next few years. Recently, Sandy Butterfield, a former chief wind turbine engineer at the National Renewable Energy Laboratory (NREL) in Colorado, was quoted as stating that the wind industry expects today's gearboxes to last 7–11 years. This markedly contrasts with the 20-year design lifetime of the wind turbines. And the implications for the industry are huge, since changing a gearbox is typically a lengthy and extremely costly exercise. The gearbox's reputation for a high failure rate is linked to the extreme engineering challenge that gearbox technology faces in wind applications, and the difficulty in properly assessing the loads – and in particular the non-torsional loads that pass through the gearbox – and how these affect bearings and gears. Some manufacturers have chosen to move to direct drive to reduce the number of moving parts in the wind turbine more exposed to wear. But this has led to wind turbine specific generator designs that are usually more expensive and often come together with a long-term maintenance contract with the Original Equipment Manufacturer (OEM), which does not necessarily meet the operations and maintenance (O&M) concept of flexibility expected by customers. Of course, much has been done in the last decade to design and manufacture gearboxes ensuring a high quality, often with associated with over-engineering and increased cost. Many efforts are also being put in to performing proper monitoring and maintenance to detect and prevent any avoidable damage. These efforts have limited gearbox breakdowns in infancy, and sometimes allowed some maintenance activities to be initiated earlier than before, but they have not helped resolving a key cause of the problem: the rotor support concept, and how it distributes loads among the wind turbine structure and the gearbox. Loads affecting the gearbox are often underestimated because state of the art aero-elastic models do not consider complex non-linear phenomena produced during transients in the drive train like inner gearbox component dynamics coupled with bearings and support parts, and the flexibility influence of the rotor support on the gearbox that causes additional loads. Failure in Conventional Rotor Support Concepts Traditional rotor support concepts typically feature either one or two bearings as shown below. In a one bearing configuration, shown in the left hand image, the rotor shaft is supported by one main bearing and by the proper gearbox that is attached by two torque arms to the bedplate. Generally, the single main bearing does not absorb bending moments which result from the blades acting on the rotor shaft and, as a consequence, the planet carrier bearings transmit loads to the gearbox housing that are absorbed by the torque arms. Using this design principle, a gearbox absorbs additional loads introduced by the rotor shaft bending moment and also, to a lesser extent, those due to deflections of the bedplate and main bearing. The single bearing concept is basically a three point suspension for the hub, one point is the front bearing and the other two are the gearbox torque arm supports. All forces produced by the wind on the rotor are going through the gearbox to the structure, and therefore the gearbox itself becomes part of this structure. Conventional gearbox design techniques used in other industries have simply been proven insufficient to deliver designs that can bear such highly variable loads in all directions over 20 years of operation. In the two-bearing configuration B, shown above right, the rotor shaft is supported by two main bearings. With this arrangement the residual bending loads transmitted by the rotor shaft to the gearbox depend essentially on the stiffness of the double main bearing configuration and on bedplate stiffness. The conventional double bearing concept diverts most forces to the structure, and it would actually succeed in delivering pure torque to the gearbox if the shaft, bedplate and bearings were absolutely rigid and the system perfectly aligned. Unfortunately this is never the case, and it therefore creates potentially very high internal loads. Moreover, much of the certified software for wind turbine load assessment does not take this effect into account, leading to a significant underestimation of non-torsional loads, and to premature gearbox failure. Except in a few cases of major turbine concept issues or gearbox defects, modern wind turbines gearboxes usually do not fail in the first few years of operation. Turbines in the 1.5–3 MW class have been built on the experience of smaller machines where gearbox failure was a chronic issue, and wind turbine and gearbox designs have been improved, allowing gearboxes to work properly in the first years of operation. However, inspections after 3–5 years performed on gearboxes of these large wind turbines usually show that major gearbox overhauls or replacements will be required in the next few years. With one or two gearbox replacements expected over the 20-year lifetime of the turbine, even more in very windy sites, many customers are required by their lenders to include risk provision for extra material breakdown in the gearbox in their project business plan. This of course has a serious impact on project profitability. Indeed, gearbox failures are regarded as one of the most serious breakdown causes in a wind turbine for two reasons. Firstly, because of the high cost of repairing or replacing the gearbox and, secondly, because of the resulting downtime. Replacing a wind turbine gearbox involves primarily the gearbox cost itself, which typically represents around 10% of the total wind turbine cost. On top of this expense, must be added its transportation to site, crane rental and mobilisation cost, and the man-hours spent on the replacement. It means that the value can quickly reach about €200,000 – €500,000, depending on the turbine size and the wind farm's location. A gearbox failure typically causes two to three times more downtime than any other component failure. In general, a gearbox replacement takes about a week, assuming that the required spare gearbox is available. Customers may have invested in a few spare gearboxes to handle isolated failure cases, but mobilizing the cash to keep spares in inventories for a complete fleet of wind turbines approaching the critical '7 – 11 year' milestone will be a challenge of a different magnitude for wind farm owners. This uncertainty therefore adds to the gearbox replacement cost a significant unavailability risk that is difficult to assess and include in wind farm business plans. Improving Reliability with Novel Support Concept As previously mentioned, the main problem of conventional rotor support structures is that the gearbox is performing structural and mechanical functions at the same time, which makes it challenging to simulate loads properly at the design stage. This is especially critical in a component as complex as a gearbox, which is basically designed to withstand mechanical loads. This challenge is illustrated by the recent debate in the US about whether gearbox failures are due to the gearbox ability to withstand the specified loads, or to the fact that real loads experienced by the gearbox are higher than those specified by the wind turbine manufacturers. An efficient way to solve this problem is to use a rotor support concept that separates structural behaviour from mechanical behaviour. This allows designers to simplify the way the loads are transmitted in the drive train, and therefore specify the drive train components with figures that are much closer to the real loads. The company's trademarked Alstom Pure Torque system is a unique rotor support concept protecting the gearbox and other drive train components from deflection loads. It was introduced by Alstom's wind business, formerly Ecotecnia, back in 1984, and has since been installed in more than 1600 wind turbines. As shown in figure 2, above, the rotor, supported directly by a cast frame on two main bearings, is not supported by the gearbox, which is fully separated from the supporting structure. The two bearings divert weight and other loads to the main frame. The key feature of this arrangement is that torque transmission is performed independently of rotor support. The shaft and gearbox are thus protected from potentially damaging bending loads. The concept decouples bedplate deflexion from the main shaft by means of a front elastic coupling that allows a certain degree of misalignment required in the system. The gearbox is allowed to pivot freely when the bedplate deflects. This ensures that only pure torque is going into the gearbox, allowing higher gearbox reliability without overdesign of the gearbox or unnecessary preventive maintenance costs. Figure 3 Above: Deflection loads (red arrows) are transmitted directly to the tower whereas only torque (dark green arrows) is transmitted through the shaft to the gearbox A cast frame goes entirely through the hub to support it and drive all deflection loads (red arrows) to the tower, as figure 3, shown above, illustrates. The shaft, connected to the hub at the front of the turbine, transmits pure torque to the gearbox. Technical Validation The technical benefits of this rotor support concept have been exhaustively validated in the field by measuring strains and displacements at several points in the structure and drive train. This experimental information has been used to complete and correlate the global virtual design models based on Finite Element Method-ANSYS and Multibody-SAMCEF design tools. Figure 4, below shows the most relevant results of this technical analysis in which, in addition to the Alstom Pure Torque validation, the global behaviour of the entire rotor support and the drive train is compared with a standard rotor support concept when a bending load is applied to the hub-rotor. For this comparison a standard rotor support concept with two main bearings has been used. When considering the standard rotor support concept, results clearly indicate the development of strain/stress all along the drive train, mainly in the bearing-shaft contact corners, but also affecting internal parts of the gearbox. In comparison, using same nominal bending moment and colour scale, the Alstom Pure Torque concept distributes strain/stress in the structural parts, isolating the drive train from bending moments. Above Figure 4: FEM comparison between a standard two bearing rotor support concept (top) and Alstom Pure Torque rotor support and drive train (bottom) when a bending load is applied to the hub-rotor. Equivalent results have been obtained using multibody numerical analysis. Results indicate a clear reduction of the radial bearing load for any relevant number of cycles when Alstom Pure Torque is considered compared with the standard configuration. Establishing a Track Record Alstom's competitive availability figures are in part due to its rotor support concept, because less time is required for gearbox maintenance and repair. A study of more than 200 units of Alstom's 750 kW wind turbines has shown a gearbox failure rate below 5% cumulated over the first nine years of operation. This number is remarkably low, and this statistic has the advantage of providing real life operation of the Alstom Pure Torque concept for longer periods than the megawatt class wind turbines. Alstom also analysed the performance of its ECO80 platform, looking at the gearbox failure statistics of a representative sample of over 600 wind turbines of 1.67 MW in over 50 wind farms that have been operating for up to seven years, and performing endoscopic analysis of the wind turbines that accumulated the highest number of operating hours in the sample. Results proved comparably high reliability performance of the concept in the ECO80 platform. Based on these results, Alstom is confident that the majority of its wind turbines could operate with their original gearbox for their whole design lifetime. Pep Prats, vice president of Advanced Technology, Wind, at Alstom, who was also one of the founders of Ecotecnia back in 1981, comments: 'We have worked with this design for a long time; we actually introduced it already in our very first turbine, a 30 kW unit that we installed in 1984. We made a short attempt to use a more conventional design in the 150–225 kW turbines we sold in the 90s, but we then decided to come back to this original design with our 600–800 kW wind turbines in the late 90s, and have since then based all our wind turbines on this concept.' Prats continues: 'Another advantage of this concept is its scalability. Our new ECO 100 platform, with rotor swept areas of over 7800 m2, have to handle 20 years of very significant loads. This is being achieved by simply scaling up our rotor support concept, without major redesign of the shaft, support systems and the drive train to cope with the loads. It is a very unique design, with built-in reliability.' The industry usually considers gearboxes as 'consumables', since – as mentioned previously – it is anticipated to be changed at least once, if not twice during the lifetime of their wind turbine. The Alstom Pure Torque concept gets customers away from the idea that a gearbox is a consumable.

BP CEO Tony Hayward's testimony before the House Energy and Commerce

British press turns on Hayward, with plenty of anti-Obama rage thrown in for good measure AP – BP CEO Tony Hayward testifies during a House Oversight and Investigations subcommittee hearing on the … Play Video Video:BP CEO: No evidence of reckless behavior WWL-TV, Channel 4 New Orleans Play Video Video:BP: 'We Care About The Small People' ABC News More from The Newsroom: Gulf spill could swing Obama's power play on energy policy Intelligence analysts say newspaper decline hurts foreign operations Murder of Hispanic man in Phoenix classed as a hate crime Gallup poll shows country divided on prospect of Obama's re-election Utah official gives execution go-ahead, then tweets Dems soften, backpedal NRA exemption ahead of campaign finance vote Alabama ad uses BP funds for containing spill damage to say beaches not suffering spill damage Florida candidate Rubio seeks to stave off foreclosure More » Fri Jun 18, 6:23 pm ET Many in the British press have slammed the U.S. government lately for demonizing BP, instead of simply holding the company accountable for the Gulf oil spill. But that sentiment has shifted noticeably since BP CEO Tony Hayward's testimony before the House Energy and Commerce committee Thursday. Hayward's inability (or unwillingness) to answer a number of direct questions about the decision-making that preceded the spill cost him many of his job responsibilities today — together with a good deal of his erstwhile cheering section in the British press. The Times (of London) didn't go easy on the oil executive, summing up its analysis of his performance in Washington with the headline: "From Mr. Bean to Mr. Has-been for BP's Tony Hayward." The Times' Giles Whittell wrote that Hayward "had a chance to save his career and the good name of his company by giving forthright, detailed answers to highly specific questions submitted in advance by two of the most astute and enlightened men in Congress." Instead, Hayward, he wrote, "seemed to have prepared by taking beta blockers." Whittell argued that Hayward stonewalled congressional interrogators, despite the executive's claims to the contrary. The Guardian clearly agreed with that assessment in its own piece on the hearing:  "BP oil spill: Tony Hayward stonewalls Congress." Although Hayward was "carefully coached by legal and media teams and was testifying under oath," the Guardian noted, he "failed to satisfy." Also, according to the Guardian, Hayward delivered his answers "in flat, impassive tones." In the Telegraph, PR branding specialist Mark Borkowski wrote that  "Hayward's communication skills didn't rival those of a tax inspector." "The new age demands a front-and-centre spokesman who can make the audience feel like he is listening and actually gives a damn," Borkowski wrote. "But Tony Hayward doesn't seem to have learned a great deal about being inclusive, about engaging with the public." "Accused of stonewalling, he stonewalled," Borkowski continued. "He couldn't, or wouldn't, answer most of the questions. In fact, he looked like a tired undertaker who was rather bored with having to look mournful." [PHOTOS: Haunting images of the oil disaster] Still, other British commentators had plenty of rancor left for the United States and its political leaders. Rupert Cornwell, a columnist for the Independent, added to the criticism that others in the British press have leveled against the Obama administration and Congress — that they're unfairly piling on BP even as the company tries to clean up its mess. Cornwell wrote that "yesterday's grilling of Mr. Hayward ... is a 21st-century version of the medieval stocks, public disgrace for the public villain of the moment." While Cornwell harkened back to medieval times to describe Hayward's treatment on Capitol Hill, the Daily Mail went back even further for a historical comparison. The British paper reported that Hayward was "subjected to a grilling so savage yesterday it was more like ancient Rome than Capitol Hill." "Wave after wave of criticism flew the way of the hapless boss and his company," the Daily Mail continued, "confirming them both as Public Enemy No. 1 in the U.S." The Economist, more highbrow than the typical Fleet Street tabloid, came out swinging at the Obama administration in the issue on newsstands Friday. However, the Economist's ire isn't motivated by jingoism or knee-jerk America-bashing — it's far too genteel for such tabloid sport. Instead, backed by its faith in free markets and neo-liberal trade policies, the Economist  came out in support not just of a British company but of business itself, which it judged to be unfairly maligned in the spill fiasco.  "America's justifiable fury with BP is degenerating into a broader attack on business," the Economist's editors wrote in today's lead editorial. The Economist expressed concern that business leaders who are "already gloomy, depressed by the economy and nervous of their president's attitude towards them" will likely not be encouraged by the treatment of BP. Because Obama's now pushing "firms into doing his bidding" — the magazine's characterizaion of efforts to hold BP responsible for an environmental catastrophe of its own making — the Economist draws parallels between the president and Russia's strong-armed former president and current prime minister. Hence the editors' new nickname: "Vladimir Obama." So while Tony Hayward is now a tarnished British hero in the Tony Blair vein, national morale may well rebound with the prospect of a good old colonial trade war — or Cold War, as the case may be. — Michael Calderone is the media writer for Yahoo! News.

Solar Efficiency Breakthrough

Home > News Releases > University of Minnesota researchers clear major hurdle in road to high-efficiency solar cells

News Release

U of M researchers have cleared a major hurdle in the drive to build solar cells with potential efficiencies up to twice as high as current levels.

University of Minnesota researchers clear major hurdle in road to high-efficiency solar cells

Contacts: Preston Smith, University News Service, smith@umn.edu, 612-625-0552

MINNEAPOLIS / ST. PAUL (06/17/2010) —A team of University of Minnesota-led researchers has cleared a major hurdle in the drive to build solar cells with potential efficiencies up to twice as high as current levels, which rarely exceed 30 percent.

By showing how energy that is now being lost from semiconductors in solar cells can be captured and transferred to electric circuits, the team has opened a new avenue for solar cell researchers seeking to build cheaper, more efficient solar energy devices. The work is published in this week's Science.

A system built on the research could also slash the cost of manufacturing solar cells by removing the need to process them at very high temperatures.

The achievement crowns six years of work begun at the university Institute of Technology (College of Science and Engineering) chemical engineering and materials science professors Eray Aydil and David Norris and chemistry professor Xiaoyang Zhu (now at the university of Texas-Austin) and spearheaded by U of M graduate student William Tisdale.

In most solar cells now in use, rays from the sun strike the uppermost layer of the cells, which is made of a crystalline semiconductor substance—usually silicon. The problem is that many electrons in the silicon absorb excess amounts of solar energy and radiate that energy away as heat before it can be harnessed.

An early step in harnessing that energy is to transfer these "hot" electrons out of the semiconductor and into a wire, or electric circuit, before they can cool off. But efforts to extract hot electrons from traditional silicon semiconductors have not succeeded.

However, when semiconductors are constructed in small pieces only a few nanometers wide -- "quantum dots" -- their properties change.

"Theory says that quantum dots should slow the loss of energy as heat," said Tisdale. "And a 2008 paper from the University of Chicago showed this to be true. The big question for us was whether we could also speed up the extraction and transfer of hot electrons enough to grab them before they cooled. "

In the current work, Tisdale and his colleagues demonstrated that quantum dots—made not of silicon but of another semiconductor called lead selenide -- could indeed be made to surrender their "hot" electrons before they cooled. The electrons were pulled away by titanium dioxide, another common inexpensive and abundant semiconductor material that behaves like a wire.

Tags: Institute of Technology

"This is a very promising result," said Tisdale. "We've shown that you can pull hot electrons out very quickly – before they lose their energy. This is exciting fundamental science."

The work shows that the potential for building solar cells with efficiencies approaching 66 percent exists, according to Aydil.

"This work is a necessary but not sufficient step for building very high-efficiency solar cells," he said. "It provides a motivation for researchers to work on quantum dots and solar cells based on quantum dots."

The next step is to construct solar cells with quantum dots and study them. But one big problem still remains: "Hot" electrons also lose their energy in titanium dioxide. New solar cell designs will be needed to eliminate this loss, the researchers said.

Still, "I'm comfortable saying that electricity from solar cells is going to be a large fraction of our energy supply in the future," Aydil noted.

The research was funded primarily by the U.S. Department of Energy and partially by the National Science Foundation. Other authors of the paper were Brooke Timp from the University of Minnesota and Kenrick Williams from UT-Austin.

tags: Institute of Technology, Wisconsin -- Scotts Contracting scottscontracting@gmail.com http://www.stlouisrenewableenergy.blogspot.com http://www.stlouisrenewableenergy.com scotty@stlouisrenewableenergy.com

Green Build Internet Special

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15 Ways to Stay Cool & Save

With summers trending hotter and budgets getting tighter, it's tough to stay cool. Here's how to reduce your summer energy bills without breaking the bank. Replace Your Windows According to the EPA, Energy Star-qualified windows can save the typical household $125-$450 per year in energy costs when replacing single-pane windows and $25-$110 per year when replacing double-pane clear-glass windows. What makes a window energy-efficient? -- Improved frame materials such as wood composites, vinyl, and fiberglass reduce heat transfer and improve insulation. -- Low-E glass with special coatings reflects infrared light, keeping out summer heat. -- Gases between the panes, such as argon or krypton, insulate better than regular air. -- Multiple panes of glass with air or gas in between insulate better than a single pane. -- Warm-edge spacers keep a window's panes the correct distance apart to reduce heat flow and prevent condensation. Parts 2-7 June 19,2010

The Solar Roadrunner

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Environmental Visionaries: The Solar Roadrunner

Highways basking in the hot sun are wasted energy. Scott Brusaw's solution? Make them out of solar panels

By John Bradley Posted 06.02.2010 at 3:19 pm 3 Comments

Scott Brusaw's Solar Roadways Kevin Hand

The road ahead is paved with photovoltaics. That's how Scott Brusaw sees it, anyway. His company, Solar Roadways, is embedding PV cells and LED lights into panels engineered to withstand the forces of traffic. The lights would allow for "smart" roadways and parking lots with changeable signage, while the cells would generate enough energy to power businesses, cities and, eventually, the entire country.

Each 12-by-12-foot Solar Roadway panel would produce about 7,600 watt-hours a day, based on an average of four hours of sunlight. At that rate, a one-mile stretch of four-lane highway could power about 500 homes. "If we could ever replace all the roads in the U.S., then, yeah, we would produce more electricity than we use as a nation," says Brusaw, an electrical engineer who completed his first prototype panel in February with funding from the U.S. Department of Transportation.

Brusaw's goal is to get the cost per panel under $10,000. That's roughly three times the cost of asphalt. But he wants to make panels that last three times longer than asphalt roads, which have to be resurfaced every 10 years in many places. "Then the cost is about the same," he says. "But that's just a break-even. We're also generating electricity."

The key to commercial viability will be the panels' glass. It must be textured for traction, embedded with heating elements for melting away ice and snow, and able to survive years of traffic. "The toughest is going to be that fast lane on the highway," Brusaw says, "where you've got a 40-ton truck, maybe with snow chains. It will have to be able to withstand all that." At the same time, it has to be self-cleaning if sunlight is to reach the PV cells; Brusaw points to experimental hydrophilic glass that uses sunlight to break down organic dirt, and rainwater to wash it away without streaking.

Next up for Solar Roadways will be qualifying for Phase II funding, a two-year, $750,000 deal to develop a commercial plan for the panels. At the end of those two years, Brusaw would like to be ready for testing in parking lots, which he sees as the perfect proving grounds for the lights and the power-generation system. Directional arrows and parking lines could be reconfigured to deal with busy times, and the electricity generated could feed adjacent businesses. "I talked to the guy in charge of power for Wal-Mart," Brusaw says. "Superstores are roughly 200,000 square feet, and parking lots are about four times that. I crunched the numbers for an 800,000-square-foot lot and told him how much power it could generate even if it was completely full of cars. It was 10 times the power they use."

Brusaw wants to start smaller, though—on the scale of, say, a fast-food restaurant. A McDonald's retrofitted with a solar parking lot could take itself largely or entirely off the grid or become a site for recharging electric vehicles (while the owners stopped inside for food, naturally). "Even the best electric cars have a range of about three hours," he explains. "But if all I have to do is find a McDonald's, I could drive from Idaho to the southern tip of Florida." Improbable? Yes. But "Billions of watts served" would be a cool new tagline.

The Lazy Environmentalist: No-Sweat Tips For Going Green

Get Paid to Save Money on Your Utility Bill
The My Emissions Exchange Web site challenges homeowners to conserve energy and calculates the equivalent amount of carbon emissions avoided. Reduce your electric bill by about $200, for instance, and you'll generate a carbon credit, which is equal to roughly one ton of carbon saved. My Emissions Exchange sells the credit on your behalf on the voluntary carbon market at a going rate of between $10 and $25, taking a 20 percent cut on all sales. The rest goes into your PayPal account.

Josh Dorfman is the author of The Lazy Environmentalist: Your Guide to Easy, Stly===ylish Green Living

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Best And Worst Home Improvements For The Buck

Boosting a home's value is easier--and cheaper--than you might think

By Stephane Fitch, Forbes.comJun 17th, 2010

If you plan to sell your home in the next year, you're probably keen on finding a few ways to gin up its value. For many people that means donning an old pair of overalls, pulling out the power tools and going to work on some ambitious renovation projects.

Here's a smarter idea: Leave the work duds in the closet, the tools in the garage and the renovation plans on hold. Instead, get out a large trash can and a dust rag.

20 Best And Worst Home Improvements For The Buck

"Just clean up your act," says Chicago real estate agent Zack Sudler. "Put your junk in a storage locker, neaten, fix the wobbly ceiling fan--and do it before you call your Realtor."

An important point that many home sellers fail to realize: Their first sales job involves hiring a top-notch agent. Many of the best professional home sellers will shy away from putting a lot of time into selling your home if it's a mess.

The only home improvement Sudler recommends is painting. Even there, he advises limiting the work to covering blemishes and repainting any rooms that have overly bright or outdated colors.

On the bigger pre-sale improvement projects, real estate pros tend to have a fairly uniform view: They're rarely worth the money and effort. For most, the value added is a mere fraction of the cost.

To be sure, home renovations can have enormous benefits--to residents rather than sellers. Air conditioning or a new kitchen might dramatically improve your lifestyle. But the incremental amount a buyer will pay for a home after such projects are completed is likely to be well below the seller's cost.

"We've seen homes where sellers have contractors still toiling away when the open houses start," says Patrick Lashinsky, chief executive of San Francisco-based realty agency ZipRealty. "It's a nightmare."

The National Association of Realtors conducts an annual survey of its members in 80 cities that is created by Remodeling magazine and used to estimate the return on investment for 33 home improvement projects. The 2009 report concluded that, on average, for every $1,000 homeowners spend on projects, they get back $638.

Even projects normally hyped as sure bets for adding value generate surprisingly weak gains, NAR reports. Converting an attic into a bedroom, for example, is typically regarded as garnering interest among potential buyers who might have otherwise disqualified the home from their search. An extra bedroom will indeed add value--just not for the majority of people who spend on the conversion. NAR figures homeowners recoup $831 on average for every $1,000 they invest.

Kitchens and bathrooms remain two of the most popular upgrades, and do have among the best returns on remodeling investments. But even for these rooms, mid-range jobs, which offer the highest returns, yield only about $720 and $710, respectively, on average, for each $1,000 invested.

The only investment that tends to get more out of buyers than sellers put into it is a heavy, insulated steel entry door, according to the NAR/Remodeling survey. Spend $1,000 on such an upgrade and you're likely to add $1,289 to your sale price.

If you're looking for examples of ways to waste money on renovations, there are lots of choices. Remodeling a home office yields just $481 for every $1,000 invested. Buying a backup power generator (perhaps from the likes of Honda or Briggs & Stratton) will add only $589 for each $1,000 invested.

All this is anathema to retailers like Home Depot, Lowe's, Bed, Bath & Beyond, Williams-Sonoma and Lumber Liquidators. They all benefit from the myth that pumping money into your house pays off later on the auction block. So do buildings materials firms like Chicago-based USG, maker of the popular Sheetrock brand of gypsum wallboard.

Lashinsky says that on occasion, buying a new appliance for your home can pay off--if the one being replaced is so horribly out of date that it unsettles potential bidders. The agent has a long list of bad ideas to avoid. Among them: Converting a bedroom into a home office and yanking out the closet to make the room look bigger.

"In quite a few states, you're not allowed to list that as a bedroom anymore," he says. Such renovations can be expensive and result in the loss of bidders who need the extra bedroom.

Lashinsky's choice for all-time worst renovation: A family that tore out a long wooden stairway leading up to their lovely hillside home and replaced it with a newly paved path. They made the change right before putting the home on the block in mid-winter, and the path kept icing over.

"People who wanted to see the house literally couldn't get up the path," says Lashinsky. "They kept sliding back down every time they got near the place."

10 Best And Worst Home Improvements For The Buck

Best Improvement: Clean Up
Cost: Negligible
Give your home a top-to-bottom cleaning or, better yet, hire a pro to do a deep clean. Do it even before you hiring a real estate agent. If you don't have a regular cleaner, hire one to keep the place tidy until your house is sold.

Good Improvement: Simple Repairs
Cost: Negligible
It is well worth the modest cost to fix broken outlets, tiles, light switches, door latches, folding doors and ceiling fans. Buyers view such flaws as signs of deeper problems--and may lower their bids accordingly.

Good Improvement: Store Your Clutter
Cost: $100 a month
A 10-foot-by-10-foot locker at Public Storage or one of its competitors is likely to cost you less than your phone and cable bills. Move out unneeded dishes, linens, personal items and furniture. Try to empty closets. Your house will appear bigger and more valuable.

Good Improvement: Paint Exterior and Interior
Cost: $100 to $1,000
If the paint on the front of your house is peeling, scrape it and repaint. Indoors, cover up any blemishes and repaint any rooms in loud colors that may be off-putting to others.

Good Improvement: Tidy the Yard
Cost: $100 to $300
No need to break the bank here. Mow the lawn, weed the flowerbeds and pull any dying bushes. Plant flowers in bare spots.

Good Improvement: Replace Hardware
Cost: $300
It's a mistake to replace the kitchen cabinets or closet doors. But you can convince buyers to pay a little more by installing new handles, knobs and drawer pulls where needed.

Good Improvement: Replace Ugly Appliance
Cost: $500 to $1000
A new stainless steel range will not prompt buyers to pay much more for your home. But a seriously bedraggled stove or refrigerator could scare them off. If you've got a junky-looking appliance, swap it out for a budget-minded replacement.

Good Improvement: Steel Entry Door
Cost: Around $1,170
A heavy entry door comes with an impressive return: You're likely to get back your investment plus a 29% gain, according to the National Association of Realtors remodeling 2009 report.

Good Improvement: Roofing Credit
Cost: $19,700
If your roof leaks, offer the buyer a discount. It's likely to cost you less than the difference between what it'll cost you to replace the roof before selling and the lesser amount you'll recoup afterward. Source: National Association of Realtors/Remodeling.

Bad Improvement: Family Room Addition
Cost: $82,800
If you're itching to add a family room, do it for your family. Do not do it to profit from selling your home; you're likely to be disappointed. Source: National Association of Realtors/Remodeling.

Click here to see the full list of the Best And Worst Home Improvements For The Buck

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Scott's Contracting
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