Highly Absorbing, Flexible Solar Cells

Highly Absorbing, Flexible Solar Cells
Supplied by: Scotty,Scott's Contracting, Green Builder, St Louis Renewable Energy.

02/16/1002/17/10


Caltech Researchers Create Highly Absorbing, Flexible Solar Cells with Silicon Wire Arrays

PASADENA, Calif.—Using arrays of long, thin silicon wires embedded in a polymer substrate, a team of scientists from the California Institute of Technology (Caltech) has created a new type of flexible solar cell that enhances the absorption of sunlight and efficiently converts its photons into electrons. The solar cell does all this using only a fraction of the expensive semiconductor materials required by conventional solar cells.

"These solar cells have, for the first time, surpassed the conventional light-trapping limit for absorbing materials," says Harry Atwater, Howard Hughes Professor, professor of applied physics and materials science, and director of Caltech's Resnick Institute, which focuses on sustainability research.

This is a photomicrograph of a silicon wire array embedded within a transparent, flexible polymer film.

[Credit: Caltech/Michael Kelzenberg]The light-trapping limit of a material refers to how much sunlight it is able to absorb. The silicon-wire arrays absorb up to 96 percent of incident sunlight at a single wavelength and 85 percent of total collectible sunlight. "We've surpassed previous optical microstructures developed to trap light," he says.

Atwater and his colleagues—including Nathan Lewis, the George L. Argyros Professor and professor of chemistry at Caltech, and graduate student Michael Kelzenberg—assessed the performance of these arrays in a paper appearing in the February 14 advance online edition of the journal Nature Materials.

Atwater notes that the solar cells' enhanced absorption is "useful absorption."

"Many materials can absorb light quite well but not generate electricity—like, for instance, black paint," he explains. "What's most important in a solar cell is whether that absorption leads to the creation of charge carriers."

The silicon wire arrays created by Atwater and his colleagues are able to convert between 90 and 100 percent of the photons they absorb into electrons—in technical terms, the wires have a near-perfect internal quantum efficiency. "High absorption plus good conversion makes for a high-quality solar cell," says Atwater. "It's an important advance."

The key to the success of these solar cells is their silicon wires, each of which, says Atwater, "is independently a high-efficiency, high-quality solar cell." When brought together in an array, however, they're even more effective, because they interact to increase the cell's ability to absorb light.

"Light comes into each wire, and a portion is absorbed and another portion scatters. The collective scattering interactions between the wires make the array very absorbing," he says.

This is a schematic diagram of the light-trapping elements used to optimize absorption within a polymer-embedded silicon wire array.

[Credit: Caltech/Michael Kelzenberg]This effect occurs despite the sparseness of the wires in the array—they cover only between 2 and 10 percent of the cell's surface area.

"When we first considered silicon wire-array solar cells, we assumed that sunlight would be wasted on the space between wires," explains Kelzenberg. "So our initial plan was to grow the wires as close together as possible. But when we started quantifying their absorption, we realized that more light could be absorbed than predicted by the wire-packing fraction alone. By developing light-trapping techniques for relatively sparse wire arrays, not only did we achieve suitable absorption, we also demonstrated effective optical concentration—an exciting prospect for further enhancing the efficiency of silicon-wire-array solar cells."

Each wire measures between 30 and 100 microns in length and only 1 micron in diameter. “The entire thickness of the array is the length of the wire,” notes Atwater. “But in terms of area or volume, just 2 percent of it is silicon, and 98 percent is polymer.”

In other words, while these arrays have the thickness of a conventional crystalline solar cell, their volume is equivalent to that of a two-micron-thick film.

Since the silicon material is an expensive component of a conventional solar cell, a cell that requires just one-fiftieth of the amount of this semiconductor will be much cheaper to produce.

The composite nature of these solar cells, Atwater adds, means that they are also flexible. "Having these be complete flexible sheets of material ends up being important," he says, "because flexible thin films can be manufactured in a roll-to-roll process, an inherently lower-cost process than one that involves brittle wafers, like those used to make conventional solar cells."

Atwater, Lewis, and their colleagues had earlier demonstrated that it was possible to create these innovative solar cells. "They were visually striking," says Atwater. "But it wasn't until now that we could show that they are both highly efficient at carrier collection and highly absorbing."

The next steps, Atwater says, are to increase the operating voltage and the overall size of the solar cell. "The structures we've made are square centimeters in size," he explains. "We're now scaling up to make cells that will be hundreds of square centimeters—the size of a normal cell."

Atwater says that the team is already "on its way" to showing that large-area cells work just as well as these smaller versions.

In addition to Atwater, Lewis, and Kelzenberg, the all-Caltech coauthors on the Nature Materials paper, "Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications," are postdoctoral scholars Shannon Boettcher and Joshua Spurgeon; undergraduate student Jan Petykiewicz; and graduate students Daniel Turner-Evans, Morgan Putnam, Emily Warren, and Ryan Briggs.

Their research was supported by BP and the Energy Frontier Research Center program of the Department of Energy, and made use of facilities supported by the Center for Science and Engineering of Materials, a National Science Foundation Materials Research Science and Engineering Center at Caltech. In addition, Boettcher received fellowship support from the Kavli Nanoscience Institute at Caltech.

Contact:
Lori Oliwenstein

Reduce U.S. Petroleum Consumption

Info Provided by Scotts Contracting, Green Builder St Louis Renewable Energy
March 10, 2010

Report Emphasizes Need to Reduce U.S. Consumption of Petroleum

The price of oil is currently hovering near $80 per barrel, but that doesn't include the potential economic costs to the United States that would be caused by disruptions in oil supply, according to a recent discussion paper by Resources for the Future (RFF), an independent research group. That report estimated the oil security premium for domestically produced oil at about $2.28 per barrel in 2008, rising to $4.45 by 2030, in constant 2007 dollars. In contrast, the oil security premium for imported oil starts at about $4.45 per barrel in 2008 and rises to $6.82 by 2030. While that analysis suggests that emphasizing domestic oil production over foreign imports has some advantages, the authors note that the security premium is minor compared to the current and future direct costs of oil, which the authors project to increase to more than $130 per barrel by 2030. Given that high price, the report concludes that the best policy would be to emphasize reductions in U.S. petroleum consumption, regardless of the source of oil. See the RFF summary and the full discussion paper (PDF 497 KB).

This is an excerpt from EERE Network News, a weekly electronic newsletter.

Plywood vs OSB pros and cons

Greening the Shell

How plywood and OSB stack up in the search for sustainable sheathing.

Supplied by: Scott's Contracting, Green Builder St Louis "Renewable Energy" Missouri By:Fernando Pages Ruiz

Back when I started framing houses, subfloor and sheathing choices were limited to solid, spaced sheathing and a still relatively new building product, plywood. The latter was gaining market share, but many old-timers resisted the thin, bendable, sometimes delaminating sheets of cross-grained veneer.


But eventually not a single floor, wall, or roof had anything but plywood over the joists, studs, and rafters, and today the same could be said for oriented strand board (OSB). Just as with plywood, some builders regarded OSB suspiciously before it became well established.

Today, a new generation of sheet materials is pushing this category toward new levels of performance, with products made from more durable raw materials and healthier resins, and panels that combine features that address moisture control, air infiltration, and energy performance in addition to their structural functions.

Before we explore these alternatives, let’s review the pros and cons of the old warhorses, plywood and OSB, as the former has made a comeback among quality-conscious builders, and concerns over deforestation and indoor air quality have muddled the question of sheathing with either plies or strands.

PLYWOOD VS. OSB

Plywood consists of an odd number of sheets of wood, glued together with the grain of each ply in a perpendicular direction, to create a structural panel with shear strength in all directions. Plywood’s cross-grain provides strength and greater holding power for screws and nails than solid-sawn wood.

Oriented strand board (OSB) uses a similar engineering principle, but instead of creating the multidirectional structure with large sheets of wood glued together, manufacturers of OSB arrange small strands of wood (2 to 3 inches in length) into a cross-grain pattern, and then bind them into a solid, structural panel using adhesives, pressure, and heat.

From an environmental perspective, the notable difference between the two panel products comes with the natural resources required to make them. The sheets of lumber used to make plywood are peeled in thin veneers off a log with a sophisticated lathe. The logs are older and larger, and from a more limited number of tree species, than those shredded for strands of OSB. Also, the plywood peeling process leaves a spindle of wood at the center, whereas manufacturers of OSB shred the entire log.

Green building certification agencies recognize the ecological advantage of engineered lumber products, principally OSB, which is used not only to make sheathing, but also joists, rafters, and substitutes for dimensional lumber.

Nevertheless, plywood has maintained its place and has seen some gains because of its greater resistance to moisture, especially around the edges, and slight advantage in nail- and screw-holding power. Many flooring and some roofing manufacturers prefer plywood under their products because of its greater stability versus OSB in humid conditions. Miami-Dade County, Fla., prohibits the use of OSB roof sheathing, given a comparatively high failure rate once wetted during historic storms.

With the exception of Miami-Dade, all national and international building codes regard plywood and OSB as equal, and use the generic phrase “wood structural panel” to clearly denote that the code recognizes these two materials on par. The leading green certification agencies, the USGBC and the NAHB, provide points for both products.

Both products carry similar performance-based certifications, primarily from APA-The Engineered Wood Association, and the U.S. Department of Commerce Voluntary standard for Wood Based Structural Panels (PS1 and PS2) that allow consumers and inspectors to know the exposure (outdoor, indoor, or marine), strength (structural capacity), span rating over framing members (adequate for 16, 24, 32 inches on-center), surface finish quality, and, more recently, compliance with air-quality standards.

But OSB has become the clear leader in construction not so much for its ecological as economic advantages: OSB is generally several dollars per sheet cheaper.

News reports of formaldehyde concentrations in mobile homes provided to victims of Hurricane Katrina has made builders concerned about the softwood, exterior structural panels used to sheathe walls, floors, and roofs. But the moisture-resistant glues used to make exterior sheathing in the U.S. do not contain urea formaldehyde, the adhesive that has created indoor air quality concerns. According to Marilyn LeMoine, spokesperson for the APA, all of the exterior, structural panels manufactured in the U.S. today comply with or are exempt from the California Air Resources Board (CARB) Air Toxic Control Measure for Composite Wood Products, arguably one of the world’s most stringent standards regulating toxic off-gassing from building materials.

Most OSB and many plywood panels use the adhesive diphenylmethane diisocyanate (MDI) as a binder, which contains no formaldehyde and no ecological risks, says LeMoine. Some plywood and OSB contain binders made from phenol formaldehyde, which becomes stable during processing and results in such low emission levels in the finished material that these products remain exempt from all formaldehyde emission standards.

The statement “no added formaldehyde” in a wood product may sound like a hedge, but it is only because wood itself contains small measures of formaldehyde. It’s all around us, as natural as air and water. You just don’t want to breathe too much of it. How much is too much? No one knows, and hence the effort to avoid products that raise the concentrations of formaldehyde indoors beyond the background levels found naturally outside.

Some foreign-made, exterior-grade panels allegedly contain unsafe levels of formaldehyde; buying trademarked panels stamped with the U.S. Product Standard PS1 (plywood) or PS2 (OSB) ensures that you are not adding measurable risk. Panels with an APA stamp comply with the CARB standards.

GREEN CERTIFICATIONS

Beyond the structural stamps, plywood and OSB are available with certifications that confirm the product comes from a reputable source and sustainably managed forests. Although many forests are sustainably managed, the only way to provide credible proof is through independent, third-party auditing such as from FSC or SFI. Once the wood leaves the forest, a third-party, chain-of-custody certification monitors that the wood harvested is indeed the wood received by the end-user.

USGBC’s LEED program only gives points for FSC certification, but is currently considering including others; the ANSI National Green Building Standard and many other programs provide points for either.

VALUE ADDED

From a green building perspective, the most interesting developments in sheathing can be found in some new products that integrate structural features with other components, such as insulation or weather-resistive barriers.

Dow’s SIS panels, for example, combine structural lateral bracing, insulation, and a water-resistive barrier. Huber Engineered Woods’ ZIP System roof and wall sheathing offers structural panels with a proprietary coating that acts as a weather barrier.

Innovative products also are helping to stiffen floor systems and reduce squeaks. AdvanTech from Huber features advanced resins for greater water resistance than commodity OSB and plywood, according to the company, as well as greater design bending strength and stiffness.

Weyerhaeuser’s iLevel Edge and Edge Gold floor sheathing products offer similar higher performance in structural stiffness and moisture resistance.

And while roof sheathing with integral reflective radiant barriers isn’t that new, its use is growing in hot, sunny climates where solar heat absorption from roofs can really crank up cooling loads.

Various brands of fiberboard sheathing, once used as cheap filler between structural panels, now have rebranded themselves as ecological, energy-efficient, and mildly structural sheathing systems. Homasote 440, a product originally designed for sound attenuation, is being repurposed as a high-performance exterior sheathing panel made from nearly 100% post-consumer recycled cellulose fiber with a maximum shear strength of 309 pounds per square foot (compared to let-in bracing at 245 pounds).

Manufacturers are offering or exploring a number of resource-efficient sheathing alternatives, such as ERT4C’s Eco-sheet, a European plywood replacement made from a mix of recycled polymers and other recycled materials including waste electrical and electronic equipment.

And researchers at Canada’s Alberta Research Council are developing an oriented structural straw board (OSSB) product, but because of straw’s small, relatively weak fibers, this option has so far proven difficult and expensive to produce as a structural product. This group is planning to open an OSSB plant in partnership with a private manufacturer.

The sheathing category is clearly evolving quickly, driven by our expanded knowledge of building science and the technical innovations manufacturers are bringing to their products. There are some great new options for green builders these days, and I am sure we’ll see even more in the years to come.

Contact: Scott's Contracting for your Green Building Needs

Weatherization Assistance Program

Weatherization Assistance Program Announces Request for Information on Proposed Sustainable Energy Resources for Consumers Grants


March 09, 2010

The U.S. Department of Energy’s Office of Weatherization and Intergovernmental Program today announced a Request for Information (RFI) regarding the Department’s proposed Sustainable Energy Resources for Consumers (SERC) Grants for up to $109 million.

Under the Recovery Act, states and local service providers are accelerating the pace of weatherization to create jobs and increase the number of families who can benefit from the energy and cost savings available through the Weatherization Assistance Program. The Weatherization Assistance Program works in partnership with states and more than 900 local service providers to weatherize homes of eligible low-income families.

The purpose of the proposed SERC grants are to speed delivery of weatherization assistance services, promote increased leveraging of federal funding with other funding sources, and identify and develop sustainable energy funding models that are not currently deployed by the Weatherization Assistance Program network.

The Department seeks comments from potential applicants, which include state weatherization agencies and local services providers, and also from other stakeholders.

Contact: scotty@stlouisrenewableenergy.com for additional info

PAYGO imposes spending restrictions on Congress

As someone who has contacted me with your concerns about the budget deficit and the national debt, I wanted to reach out to you now to let you know about important legislation, known as PAYGO (Pay-As-You-Go), that has just been signed into law. PAYGO imposes spending restrictions on Congress and will help bring down the deficit.


PAYGO rules require spending increases and revenue cuts to be paid for by offsetting cuts or revenue-raisers elsewhere in the budget. For example, a proposal to increase spending on highway construction would have to be balanced by increased fees on drivers or a cut to education spending. PAYGO rules were in effect and contributed to the balanced budget of the 1990s, but they were allowed to expire in 2002, leading to irresponsible budget deficits during the past decade.

PAYGO will require Congress to spend wisely on what works and only fund programs and tax cuts that deliver the most bang for the buck. To this end, the legislation also requires the Government Accountability Office (GAO) to assess initiatives across the government to find inefficient or duplicative programs.

PAYGO will help us bring down the deficit responsibly over the long-term. For now, however, the deficit will remain large because the recession has reduced tax revenues and has required the government to take extraordinary measures to save the economy. Extending unemployment and health insurance benefits to the unemployed, temporary and targeted tax cuts to boost demand, and investments in infrastructure, schools and alternative energy help save jobs now and will deliver benefits for years and decades to come. In fact, the nonpartisan Congressional Budget Office recently concluded that the Recovery Act of last year has already saved or created 1-2 million jobs, and economists agree that many more jobs will be saved or created this year.

Restoring fiscal responsibility will also require us to address several long-term challenges, such as spending on defense and Medicare. Last year, I was pleased to vote in favor of a new law to reform wasteful contracting procedures for military spending. Congress is also continuing to debate health insurance reform legislation that will reduce the deficit over the next decade by spending our health care dollars more effectively. PAYGO will help Congress maintain its discipline in these efforts to reduce spending.

Please do not hesitate to contact me with your views on the budget deficit or any other issue of concern. I also hope you will find my website, carnahan.house.gov, a useful resource for keeping up with my work in Washington and the 3rd District of Missouri, and I welcome you to sign up for my e-newsletter at carnahan.house.gov/update.

A New Solar Energy Source

A New Solar Energy Source from the Common Pea
Provided by: http://www.stlouisrenewableenergy.com/  Submitted by Green Prophet Staff on March 5, 2010 – 2:38 pm

If harnessing the unlimited solar power of the sun were easy, we wouldn’t still have the greenhouse gas problem that results from the use of fossil fuel. And while solar energy systems work moderately well in hot desert climates, they are still inefficient and contribute only a small percentage of the general energy demand. A new solution may be coming from an unexpected source — a source that may be on your dinner plate tonight. Peas!

“Looking at the most complicated membrane structure found in a plant, we deciphered a complex membrane protein structure which is the core of our new proposed model for developing ‘green’ energy,” says structural biologist Prof. Nathan Nelson of Tel Aviv University’s Department of Biochemistry. Isolating the minute crystals of the PSI super complex from the pea plant, Prof. Nelson suggests these crystals can be illuminated and used as small battery chargers or form the core of more efficient man-made solar cells.

Nanoscience is the science of small particles of materials and is one of the most important research frontiers in modern technology. In nature, positioning of molecules with sub-nanometer precision is routine, and crucial to the operation of biological complexes such as photosynthetic complexes. Prof. Nelson’s research concentrates on this aspect.

The mighty PSI

To generate useful energy, plants have evolved very sophisticated “nano-machinery” which operates with light as its energy source and gives a perfect quantum yield of 100%. Called the Photosystem I (PSI) complex, this complex was isolated from pea leaves, crystalized and its crystal structure determined by Prof. Nelson to high resolution, which enabled him to describe in detail its intricate structure.

Described in 1905 by Albert Einstein, quantum physics and photons explained the basic principles of how light energy works. Once light is absorbed in plant leaves, it energizes an electron which is subsequently used to support a biochemical reaction, like sugar production.


“If we could come even close to how plants are manufacturing their sugar energy, we’d have a breakthrough. It’s therefore important to solve the structure of this nano-machine to understand its function,” says Prof. Nelson, whose lab is laying the foundations for this possibility.

Since the PSI reaction center is a pigment-protein complex responsible for the photosynthetic conversion of light energy to another form of energy like chemical energy, these reaction centers, thousands of which are precisely packed in the crystals, may be used to convert light energy to electricity and serve as electronic components in a variety of different devices.

“One can imagine our amazement and joy when, upon illumination of those crystals placed on gold covered plates, we were able to generate a voltage of 10 volts. This won’t solve our world’s energy problem, but this could be assembled in power switches for low-power solar needs, for example,” he concludes.

Solar Power News

Article supplied by: Scotty, St Louis "Renewable Energy" Missouri, written By: JAD MOUAWAD

c.2010 New York Times News Service

INDIANTOWN, Fla. — In former swamplands teaming with otters and wild hogs, one of the nation’s biggest utilities is running an experiment in the future of renewable power.

Across 500 acres north of West Palm Beach, the FPL Group utility is assembling a life-size Erector Set of 190,000 shimmering mirrors and thousands of steel pylons that stretch as far as the eye can see. When it is completed by the end of the year, this vast project will be the world’s second-largest solar plant.

But that is not its real novelty. The solar array is being grafted onto the back of the nation’s largest fossil-fuel power plant, fired by natural gas. It is an experiment in whether conventional power generation can be married with renewable power in a way that lowers costs and spares the environment.

This project is among a handful of innovative hybrid designs meant to use the sun’s power as an adjunct to coal or gas in producing electricity. While other solar projects already use small gas-fired turbines to provide backup power for cloudy days or at night, this is the first time that a conventional plant is being retrofitted with the latest solar technology on such an industrial scale.

The project’s advantages are obvious: Electricity generated from the sun will allow FPL to cut natural gas use and reduce carbon dioxide emissions. It will provide extra power when it is most needed: when the summer sun is shining, Floridians are cranking up their air-conditioning and electricity demand is at its highest.

The plant also serves as a real-life test on how to reduce the cost of solar power, which remains much more expensive than most other forms of electrical generation. FPL Group, the parent company of Florida Power and Light, expects to cut costs by about 20 percent compared with a stand-alone solar facility, since it does not have to build a new steam turbine or new high-power transmission lines.

“We’d love to tell you that solar power is as economic as fossil fuels, but the reality is that it is not,” Lewis Hay III, FPL’s chairman and chief executive, said on a recent tour of the plant. “We have got to figure out ways to get costs down. As we saw with wind power, a lot has to do with scale.”

For solar power, scale is still a relative term. At its peak, the solar plant will be able to generate 75 megawatts of power, enough for about 11,000 homes. But that is dwarfed by the adjacent gas plant, which can produce about 3,800 megawatts of power. (A megawatt is enough to power a Wal-Mart store.)

Utilities are being pulled in different directions. They must ensure that the lights remain on at all times as well as provide the lowest-cost power to their customers. At the same time, they are being pressed to find ways to reduce their greenhouse gas emissions and invest in renewable power sources.

The latter is critical if the nation is to succeed in reducing its emissions of carbon dioxide. Power plants account for over a third of domestic greenhouse gas emissions that are responsible for global warming.

“We believe there is a cost to society associated with carbon emissions and not having energy security and not having domestic energy supplies,” Hay said. “But it’s not a level playing field for renewable versus fossil fuels right now.”

Mark Brownstein, an energy and grid specialist at the Environmental Defense Fund, praised FPL’s innovative thinking. “When we talk about getting to a low-carbon, clean-energy economy,” he said, “we know there is not going to be a single technology that is going to transform the industry.”

Currently, 29 states require utilities to increase the amount of power produced from renewable energy, which includes solar, wind, hydroelectric, geothermal and biomass. Last year, Congress considered a federal mandate for 25 percent of renewable power by 2025 as part of its energy and climate legislation. (The bill has since stalled.)

Utilities have been scrambling to meet the state requirements, and many will not be met, according to electrical utility experts.

While renewable power is growing, its share of the nation’s electrical generation remains small. Wind power, which has surged in recent years, accounts for less than 2 percent of the nation’s electrical output. Solar is even smaller. Coal, meanwhile, generates half of the nation’s electrical output, followed by natural gas and nuclear energy.

Part of the challenge in increasing the share of renewable energy sources is to make up for their variable nature — at night, for example, or when the wind does not blow. Because electricity cannot be stored easily, utilities must always produce enough power to meet electric demand at any given time. In practice, this means they need keep a lot of idle plants that can be fired up rapidly when demand spikes.

About 20 percent of the generation capacity overseen by PJM Interconnection, a regional transmission operator covering 13 northeastern and mid-Atlantic states, is used less than 100 hours a year, according to Lester B. Lave, a professor of economics at Carnegie Mellon’s school of business.

“As long as the contribution of wind and solar is very small, utilities can handle it very well,” Lave said. But what happens once the share of renewable power rises to 10 percent? Or 20 percent? “No one knows what the magic number is.”

Spain, which generates more than 12 percent of its electricity from wind, has struggled with wind variability, Lave said. Similar problems are also cropping up in the United States, especially in states where solar and wind power are on the rise. In 2008, for example, Texas narrowly avoided a blackout when wind power, which supplied 5 percent of demand at the time, experienced an unexpected lull, driving wind electricity generation down to 350 megawatts, from 2,000 megawatts, in less than four hours, according to Lave.

It is a problem the industry is beginning to focus on, and hybrid plants could provide part of the answer. By adding renewable power to existing fossil fuel plants that operate around the clock, the thinking goes, utilities could have readily available power that could be fired up instantly whenever their wind or solar resources dropped off.

The Electric Power Research Institute is working on two pilot programs that seek to integrate solar power with traditional coal and gas plants in New Mexico. A dozen hybrid projects similar to FPL’s plant are planned around the world, said Cara Libby, the institute’s project manager for renewable energy.

“Intermittency is probably the challenge utilities are putting the most efforts into researching at the moment,” Libby said. “The biggest concern, of course, is how to keep the power on.”

Instead of adding new capacity, smart grid designs and investments in transmission lines could also help balance the contribution of intermittent resources, said Tim Stephure, an analyst at Emerging Energy Research, a consulting firm. Some regional operators, such as PJM, are also encouraging their large customers to cut consumption when demand is at its peak to reduce the overall power requirements on the grid, said Brownstein of the Environmental Defense Fund.

At FPL, part of the challenge will be to fine-tune the system so that its gas and solar components provide just as much electricity as needed at any given time — day or night, cloudy or clear. At a cost of $476 million, the solar project, known as the Martin Next Generation Solar Energy Center, will be second-biggest, after the 310-megawatt Solar Electric Generating System in the Mojave Desert in California. That system, also owned by FPL, was built in the 1980s.

FPL estimates it will cut its natural gas use by 1.3 billion cubic feet each year, the consumption of 18,000 American homes. It will also cut carbon emissions by 2.75 million tons over 30 years, the equivalent of taking 19,000 cars off the road. The solar panels concentrate the sun’s rays into a vacuum-sealed tube that contains a synthetic oil, which heats up to 748 degrees Fahrenheit. The oil is then used to produce steam that is fed into an existing turbine to produce electricity. Using small sensors, the mirrors will be able to rotate during the day to track the sun’s movement. In case of a hurricane, they will flip upside down for protection.