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Both are exacerbated by the fact that all the easy-to-develop wind sites in the US have largely been developed. Enormous potential for more wind power capacity exists, but most of the sites that remain to be developed either lack adequate transmission lines to bring the power to market or face complications such as local opposition. Some must prove they do not interfere with military or commercial aviation radar systems.

Once believed to be largely resolved, radar in particular has re-emerged as a pressing issue. It first surfaced in a broadly public fashion in 2006 when as many as 2GW of proposed wind plants were issued notices of presumed hazard from the Federal Aviation Administration (FAA). Wind projects can sometimes disrupt radar, giving operators inaccurate air traffic readings or eliminating planes' radar signature altogether as they pass overhead. Most projects were eventually authorised after further review and political intervention.

"The issue has been coming up more and more," said Gary Seifert, programme manager at Idaho National Laboratory, and a specialist on the topic. It has meant projects take longer to get permits. "Last year 8,000MW were impacted by radar issues. We installed over 8GW last year so, for nearly every megawatt we put in the ground, we had another megawatt impacted in some form or another from the radar issue.

That's a serious number."

Radar concerns

William Van Houten is advisor to the deputy undersecretary at the unit of the Department of Defense (DOD) that ensures military infrastructure is environmentally sound. He said that the issue cuts across multiple departments. When the problem emerged in 2006 the DOD and FAA responded by creating a website enabling developers to see whether a proposed project would raise radar concerns, indicated by green, yellow and red zones. The system allowed developers to consult with the military on a project-by-project basis.

Yet developers often fail to check until the project is well under way, sometimes only months or weeks before construction is about to begin, said Houten. This was the case with the 845MW Shepherds Flat wind farm in Oregon, developed by Caithness Energy, which was halted just before the build began. Ultimately, the order was reversed but similar miscalculations are common.

Besides the colour-coded website, the military has offered few other solutions. An isolated example of DOD efforts to push wind power past the radar hurdle is the Travis Air Force base in California. It has recently worked with developers to measure the effects of wind projects on radar systems. The cooperation has enabled stalled wind projects in Solano County to move ahead. Projects by developers NextEra and EnXco are under construction, adding to the 622MW of wind already installed.

Houten acknowledged that the DOD has "probably not properly resourced" the radar issue and added that there may be a need for formal rules requiring notification to the DOD of wind projects 12-18 months before build begins.

Tricky technology

Even if the DOD approves a wind site, multiple projects built in the area may quickly reach a saturation point affecting radar. The DOD will then have to turn a previously approved area off limits to wind. There is also a "first in time, first in right" issue. At a site where the DOD allows 500MW, the first developers to build under that threshold will be clear, but developers that follow face closure. This adds risk to developers rushing towards a closing window.

Software can help radar systems to cope better with wind turbines but cost an exorbitant $7-14 million, and there is no clear agreement on who should pay. The DOD has pushed the wind industry to shoulder the burden.

But some wind experts say the sector should not pay when an ageing radar system needs to be upgraded regardless of regional wind development. Researchers have also studied equipping wind blades with radar-absorbing stealth technology, but the results have been inconclusive. "The only proven mitigation is to reposition turbines outside of radar line of sight," said Houten.

Mark Tholke, Southwest region director at EnXco, owned by France's EDF Group, said increasing certainty is the key goal. "As developers, what we hate the most is a surprise at the end. A surprise can get very expensive very quickly. We need to try and get our arms around it early," he said.

Houten said that more federal agencies are joining in an effort to produce a solution. "That might hit critical mass at the end of the year," he said. Legal proposals are also taking shape on Capitol Hill but it is too early for the DOD to comment, said Houten.

Plan, permit, pay

Transmission is another infrastructural challenge refusing to go away, according to delegates at the AWEA conference. The US wind industry's top priority is maintaining a robust wind market backed by long-term policies supportive of wind (page 47). But that cannot be accomplished without expanding transmission, said Rob Gramlich, senior vice-president of public policy for AWEA. Its transmission committee is focused on three key grid issues: planning, permitting and paying. The last one, paying for new wires, is the most challenging, said Gramlich.

Developers in some cases have resorted to building their own transmission lines to tie into the power grid. Kris Zadlo, vice-president at developer Invenergy drew an analogy with road infrastructure. "With transmission, we're in a pre-interstate highway system," he said, adding that the US lacks proper regulatory systems to nurture development of needed grid capacity. "As a developer, I've had to build over 200 miles of transmission lines. Imagine if a trucking company had to build over 200 miles of highway to run its business," Zadlo said.

He also called for regulatory reform and changes to financial incentives for building up the grid. The system currently regulates local utilities and local communities - a configuration that Zadlo described as archaic. "Now we're wheeling vast amounts of power across state lines and across the country, and yet we're regulating transmission in an ad hoc, fragmented way," he said.

Central control

Much of the US power grid and its regulatory structure is governed by separate Independent System Operators (ISOs). These large, often multi-state authorities operate power markets, ensure grid stability and regulate transmission and other aspects of the power system. Zadlo says there are mismatched priorities. "It's not efficient for utilities in a state and their staff to go down to an ISO and try and implement transmission expansions when each state and utility often has its own interests. We need one regulator for the entire grid," he said.

The Federal Energy Regulatory Commission (FERC) is a national regulator but its powers are limited by laws that tend to favour states and regional rights. At last year's AWEA conference, much hope was pinned on FERC's new chairman, Jon Wellinghoff, who made numerous statements championing wind power. But FERC has not yet put forward any new policies or rulings in the past year that are particularly helpful for the sector. In some cases it has even made rulings that will further hinder wind.

That was the case this winter when FERC supported a transmission cost-allocation decision by the Midwest Independent System Operator (MISO) that thrusts 90% of the cost of building new transmission on developers in the 13 state markets in America's windy heartland (“uåX˜äŠÊ˜·³Ç, December 2010). Experts at a transmission panel at the AWEA conference said the episode is seen as one of the biggest blows to wires for wind in the past year. MISO was forced to make its cost ruling because regional utilities unhappy with sharing transmission costs were threatening to leave the system operator. "The courageous thing for MISO to do," said Monty Humble, senior vice-president and general counsel at Mesa Power Group, "is ask FERC to allocate costs to all utilities in an ISO, whether companies stay or not. It would restore a balance of power."

Competing interests

Zadlo added that the financial incentives throughout the country are often at odds with building more wires for wind. The vast majority of wind and other renewables in the US is developed, owned and operated by independent power producers that sell to electric utilities. In the US, however, utilities get over 70% of their revenue from the generation base that they own - mostly carbon based sources like coal and gas, plus some nuclear and hydro.

"As renewables come online, we are displacing that generation and displacing those profits. So, what incentive do those utilities have to build the transmission that's necessary for us to displace them? It's business 101," said Zadlo. One solution moving forward is to expand more so-called unbundling market structures that disconnect utility profits from how much power they sell. Another solution is to allow utilities to pay up front for transmission needed for wind and then recoup the cost from the ratepayer. Success on this front has been seen in Texas, with its Competitive Renewable Energy Zone process, and in the Southwest Power Pool. "Those are the two bright spots," said Anna Giovinetto, vice-president of public affairs for developer RES Americas, who like other panellists called for a national transmission solution. "If not a national solution," she said, "then at least a top-down solution. Not a bottom-up solution like we mostly have today."