Renewable energy certainly remains on the agenda at the annual U.S. PowerGen event. Electric vehicles, CSP, offshore wind and hybrid renewable/fossil were combos that remained in the spotlight.
And conference tracks included solar, wind and biomass. But while previous PowerGen events have featured miniature wind turbines at the booths of dozens of energy companies – as they sought to highlight their renewable credentials – few windmill displays remain.
And the show's renewable pavilion, introduced with a fanfare a few years back, seems to have diminished. While Vestas, Clipper and REpower were in evidence in the beginning, none of the major renewable players appeared to be in evidence. Could it be the wrong message to send out that wind and solar companies prefer their own annual extravaganzas to what is the power industry's marquee event?
On a sobering note, renewable energy resistance was voiced in several sessions – even in the beginning keynote; David Walsh, senior vice president, service & manufacturing, at Mitsubishi Power Systems, America, questioned the economic viability of wind and solar.
In his analysis of the market, he highlighted the fact that as much as 25 percent of the U.S. coal-fired fleet is in jeopardy due to environmental regulations. However, when the top five utilities in America are studied, he said they will continue to have coal as a significant (though declining part) of their portfolios. Where these utilities will see the most growth, he said, was in natural gas. The top five are expected to increase their renewable assets conservatively from 5% to 7%, he added. The reason? He believes rate payers will force the power industry to find the most cost effective solutions available:
“With the EPA moving forward steadily, it's going to mean a lot of gas,” said Walsh.
Electric vehicles in the spotlight
Donald Karner, president and ceo of electric vehicle (EV) vendor ECOtality North America followed Mitsubishi to the podium. He admitted that there are currently only a few thousand EVs in the U.S., but stressed that lessons had been learned from the previous attempt in the late nineties to roll out the technology:
“We had a regulatory push in the late nineties whereas the rise of EVs today is market driven,” said Karner.
While he touched upon some of the consumer benefits of this form of transportation, he matched the reality of his audience by stressing the power generation and consumption side: Every 10,000 miles driven in an EV equates to the amount of power needed by one home in the U.S. for a year; the EV charging load is highly dispatchable; and is an off-peak load as cars are typically charged late at night, being left overnight:
“While EVs are left charging overnight, they take about 1.9 hours to charge so there is a huge opportunity here as the load can be spread and controlled across a 10 hour window,” said Karner.
But it's not all roses. Utility rates, he said, remain an impediment i.e. there are no rates available to validate this almost exclusively off-peak charging pattern.
Another obstacle in the North American marketplace is the permitting process to erect chargers – a major bottleneck in Karner's view. He ended by stressing the importance of using the latest technologies for EV chargers, rather than the cheapest available.
“It's not a good idea to install dumb, non-networked terminals that can't be managed on load and costs,” said Karner. “Each utility in the U.S. should be assessing the EV market now.”
Flexible gas-fired generation
Speaker after speaker at PowerGen noted that legislative momentum made abundant wind and solar on the grid inevitable. That gave rise to regular refrain at the conference – the need for flexible gas-fired generation to ‘compensate’ for wind/solar variability.
Siemens Energy pushed the value of having plenty of combined cycle gas-fired turbines to ramp up and down as renewable resources ebbed and flowed during the day. It is one of many vendors touting the rapid ramp up and low emission credentials of its latest turbines. Its Flex Plant 30 design, for example, can maintain emissions rates below 5 parts per million while it is ramping down.
“In most areas, renewables have the right of way onto the grid,” said Bonnie Marini, director of product line marketing at Siemens. “Our biggest challenge is ramping down other power sources to deal with renewables coming onto the grid suddenly.”
Other turbine manufacturer and utility presenters drew attention to the fact that renewables had completely changed decades-long power patterns. In the past, baseload power was provided by coal and nuclear resources. With these types of plants under fire or being phased out, renewables were now beginning to be counted on for baseload power. That meant that baseload could no longer be counted on as a flat line, as it had been in the past. Gas turbines (GTs), therefore, are now the medium of choice to pick up the slack in the absence of large-scale affordable energy storage technology.
“Renewables are driving the market for flexible gas-fired generation,” said Steve Rose, vice president of conceptual engineering at U.S. utility NRG. “With 90 GW of renewables called for in existing state Renewable Portfolio Standards (RPS), it requires 45 GW of gas firming. Most of it will be rapid response combined cycle plants.”
Carlo Luzzatto, president of turbine part and repair vendor Chromalloy, briefed the gathering on yet another renewable effect – changing the operating pattern of gas turbines from relatively few starts per year to many. They are starting and stopping multiple times and running for only a short time, as opposed to all day or all week as has been the GT tradition, he explained:
“If you look at Spain, renewables supply most of the baseload power and the GT's there are running only 15% of the time, down from more than 50%,” said Luzzatto.
Biomass to displace coal?
To be fair to PowerGen, a couple of conference tracks were devoted to renewables, as has been the case for many years. One biomass session, for instance, included a presentation on how Ontario Power Generation (OPG) is exploring options to repower its coal-fired fleet using biomass. It's Thunder Bay Station, for instance, is looking at how to convert the boilers designed for lignite coal to fire wood pellet fuel at two 163 MW units.
Several utilities in Europe have successfully employed modified coal pulverisers to handle pure wood pellets. So far, OPG has enjoyed some success with testing this approach within its internal biomass development program. The company has been working with Alstom Power to evaluate the capability of the Rotating Pulveriser (RP) design to grind and deliver wood pellets fast enough to be able to displace coal (note: the Province of Ontario has mandated all coal to be phased out by 2014). The study demonstrated that wood pellets could be used effectively to generate power at the plant, provided certain equipment modifications were carried out.
U.S. utility Southern Company outlined its plans to add as much as 1000 MW of biomass over the next few years. It has already implemented co-milling, which involves the creation of a fuel mix of biomass with coal. In addition, Southern Company is involved in the development of higher efficiency technologies including torrefied wood – where the wood is heated in the absence of oxygen to create a dry, high BTU fuel.
To date, one utility scale test burn has been completed. Another approach being evaluated by the company is biomass gasification – where the biomass is turned into a gas which is then ignited in a turbine combustor.
Offshore versus onshore wind
Andy Wickless, associate director of renewable energy at Navigant Consulting presented on offshore wind. He made the point that offshore and onshore wind geographic markets have been markedly different. Those high in onshore market share in 2010, for example, are low in offshore and vice versa. Only Germany ranks high in both.
“Addressing offshore markets will require focus on specific geographies,” said Wickless. “Many manufacturers and developers are setting up operations in Northern Europe, especially in the UK, to better meet offshore demand.”
Navigant's expectation is that within ten years, 96% of the offshore wind sector will be in Europe and China. Within Europe, Germany and UK will account for the bulk of installations.
He raised the spectre of supply chain bottlenecks. Unlike the onshore sector, these typically involve balance of plant items such as vessels and cabling, as opposed to components such as gearboxes.
He contrasted offshore and onshore financing. In the former case, it generally comes down to utility money as opposed to individual project financing due to the magnitude and risks associated with offshore. Wickless called attention to another bottleneck – the necessary infrastructure to support offshore construction and production.
“Most sea ports were built without an offshore wind sector in mind,” said Wickless. “Ambitious offshore wind development plans will necessitate investment in port and grid infrastructure.”
As the audience was largely from the mainstream power sector, he educated them on the various offshore tower and foundation technologies, as well as how turbines were being designed to increase maintenance intervals.
“Remote condition monitoring and predictive maintenance are more critical offshore given increased access constraints,” said Wickless. “Repairs can only be made in periods of low wind and good weather.”
To date, he added, the Vestas 3MW turbine is the bestselling offshore model. While larger models are available, offshore economics demand the usage of only proven models. This will inhibit the deployment of newer, larger turbines until they have developed a track record of high reliability.
Parabolic trough versus tower versus CLFR
The solar track at PowerGen covered the basics. The U.S. National Renewable Energy Laboratory (NREL) showcased possible solar/gas hybrid designs. These focused on parabolic trough Concentrating Solar Power (CSP) plants.
While there is 450 MW of CSP operating in the U.S. (and 250 MW under construction at the Solana plant in Arizona), as well as 500 MW operating in Spain, NREL believes that hybrid designs can help reduce CSP's Cost of Energy (CoE), ease financing and provide it with a competitive advantage over Photovoltaics (PV). In addition, the pairing of gas and solar would lower risk for utilities, while increasing dispatchability.
One example cited was an Integrated Solar Combined Cycle Hybrid. Its advantages include the ability to share infrastructure between the solar and gas elements, and it is high efficiency. However, this concept tends to rely more on gas, with solar only providing a small percentage of the annual energy generation.
To make solar more than a cosmetic addition to traditional gas-fired generation, therefore, NREL is investigating various possibilities including the use of a parabolic trough using oil as a heat transfer fluid (with the gas turbine operating purely as a backup system to a solar field which supplies the majority of the power), as well as implementing aeroderivative gas turbines (AGTs) such as the GE LM6000 which provides 40 MW at 41% efficiency.
As the name implies, AGTs originated in the jet engine field. As a result, they are lighter and more flexible than the usual industrial gas turbines. NREL has been experimenting with oil HTF/AGF hybrids as well as salt trough/AGT setups. Early results indicate that these hybrids lower capital costs and overall COE.
Areva Solar touted Compact Linear Fresnel Reflector (CLFR) technology as a way forward. In this CSP method, reflectors focus the sun's heat onto an elevated receiver. Water runs through tubes in the receiver and the concentrated sunlight boils the water in order to generate superheated steam. Solar steam generators (SSGs) drive steam turbines and can also provide steam for other processes.
The company's senior vice president of engineering William Conlon contrasted the various approaches to CSP, to highlight why Areva preferred CLFR.
In Areva's configuration, each SSG contains one receiver with boiler tubes. Multiple reflector rows are independently aimed at the receivers. According to Conlon, these units continue to deliver steam for 18.5 minutes after light is removed. At the 750 MW Kogan Creek power station in Queensland, Australia, for example, CS Energy and AREVA Solar are adding 44 MW peak (23 MW average) in additional electrical output via CLFR.
Bechtel Corp. completed the solar presentations by covering the Ivanpah Solar Electric Generating Facility in California's Mojave Desert. This is the largest solar plant under construction in the world, and is comprised of three solar plants situated about 50 miles from Las Vegas.
When it goes online, Ivanpah will produce almost 400 MW using heliostats (targeted mirrors) to focus the sun onto solar receivers atop three towers. The project uses BrightSource Industries' Luz Power Tower LPT-550 and heliostat mirror technology to create steam to drive a turbine. Each heliostat consists of two flat mirrors and a tracking system to follow the sun across two axes.
As can be seen in table 3, over 170,000 heliostats will be required. To accommodate such a vast undertaking, Bechtel has been erecting a custom-made manufacturing facility at the site. This consists of three fabric covered buildings totalling 67,000 ft2 (6240 m2) with an automated heliostat assembly line inside.
Once heliostat production is wrapped up, it will be dismantled and moved to a future project site. As a result, pre-manufactured, reusable foundation and structural elements have been employed to facilitate rapid deployment and future reuse.
About: Drew Robb is a graduate of the University of Strathclyde in Glasgow. Currently living in Los Angeles, he is a freelance writer focusing on engineering and technology.