Casio GW300A-2V Casio Solar, Atomic Watch
Atomic Solar Digital, Shock Resistant, Resin Band, 200 Meter Water Resistant, World Time, Auto Electro-Luminescent Backlight with Afterglow, 1/100 Second Stopwatch, 4 Alarms with Snooze, Hourly Signal, Auto-Calendar, 12/24-Hour Formats
Using the energy from the sun, the BatterySAVER SE 2W will replenish your 12V battery by sending a constant maintenance level charge to the battery of your car, light truck, van or SUV. You will never be caught with a dead car battery again!
The new generation of solar power battery trickle chargers and solar powered battery chargers. Ideal to maintain and charge your car, RV or marine batteries or charge small and medium appliances. Uses highly efficient solar panels that work well under all lighting conditions. Worry free maintenance with easy installation!Maintain your car, light truck, van, or SUV battery. Connects in seconds, and keeps your battery fully topped up when your vehicle is not in use. Works well under low light conditions.
Solar water heating up: a wide range of options exist for ready-to-install, readily certified solar water heating systems. To further heat things up, government and utility incentives are expanding. (Utilities).
Solar water heating is once again gaining market share, and with good reason. The development of HERS and Energy Star, together with technological refinements, is transforming the way home builders look at water heating options. Complete off-the-shelf systems have evolved and are being readily certified for a myriad of rebate programs.
In most applications, solar water heating contributes more to saving energy than any other solar technology. Solar water heating at $1.00-$2.50/W is a better investment than photovoltaics at $6.00-$10.00/W. Solar domestic hot water (SDHW) systems in the market cost $1,000-$2,500/kW for a typical residential system.
According to the national Solar Rating and Certification Corporation, a typical residential SDHW system for a family of four delivers 4 kW of electrical equivalent thermal power under full sun, and when the temperature of the water in the storage tank is about the same as the air temperature. Such a system typically has about 64 [ft.sup.2] of solar collector surface area and produces approximately the same peak power as 400 [ft.sup.2] of PV panels.
Because peak performance occurs infrequently, a more realistic indication of solar thermal system performance is the rated daily energy output of the collectors or system. Using this method, a typical SDHW system contributes 7-10 kWh per day, depending on the solar resource and the type of collector or system.
SDHW is the better energy investment if the backup water heating is electric-resistance heat; if one uses a heat pump or gas-based backup, the economics may vary.
Many new system sales today are to repeat customers who have moved and want new systems installed on their new homes. After 15-20 years of experience with solar water heating systems, these homeowners know the value and performance that these systems deliver. And the newer systems deliver even more value than the older ones as, since the 1980s, the solar water heating industry has seen the development of better systems, certified installers, lower prices, and proven performance. The familiarity with solar water heating, anticipated savings, and confidence in the systems’ performance have led a number of state weatherization programs to incorporate solar as part of their low-income energy savings measures (see “Making Solar Hot Water Affordable,” HE Jan/Feb ‘99, p. 8).
Options for SDHW
Although the array of system choices may seem confusing at first, the choice of a solar water heating system is quite simple. The most important factor is the climate where the system is to be installed. But before I elaborate on climate types, I need to explain four basic solar system terms: direct, indirect, passive, and active.
Direct solar systems heat the water that is consumed or stored in the water heater (see Figures 1, 2, and 3). If the water in the storage tank or water heater is directly heated in the solar collector, it is a direct system. In other words, the water you use in the house is the same water that has been circulated through the collectors.
[FIGURES 1-3 OMITTED]
Indirect systems incorporate a heat exchanger separating the solar collector from the storage tank. An antifreeze solution circulates through the collector, and the heat exchanger transfers the heat from the antifreeze solution to the potable water in the tank. This heat exchanger can be internal or external to the storage tank.
If a solar water heating system has a circulation pump to transfer heat from the collector to the storage tank, the system is classified as an active system. If the system has no pump or control mechanism to transfer the heat to the storage tank, it is a passive system.
Passive systems use no pumps. Instead, they use natural forces like thermosiphon. In thermosiphon systems, thermosiphon action occurs when water heated in the collector becomes more buoyant than the colder water from the storage tank. The heavier, descending, colder water from the tank forces the heated water back to the tank. This is the most popular system design used outside the United States. Travel anywhere in the Caribbean, the Middle East, the Mediterranean, Australia, or Asia, and you will see the thermosiphon system. In these areas, solar has long been considered the only option for heating water in homes and small businesses. Many Americans dislike seeing the thermosiphon tank on the roof, so the solar water heating industry has developed systems with storage tanks that are recessed into the attic or located on areas of the roof not visible from the front of the house, thus providing a low profile for the system (see Figure 2).
The simplest solar water heater is the integral (or integrated) collector storage system (ICS), also referred to as the batch or bulk (or breadbox) storage system (see Figure 1). In these systems, the collector and the storage are incorporated into one unit. The hot water generated by ICS systems should be used during the afternoon and evening, so that the stored hot water is consumed or transferred into a separate storage tank in the house before dark. This will reduce overnight heat loss during colder weather. The water is used or transferred when someone makes a draw in the house. When a draw is taken, the water in the ICS unit replaces the water that was used from the backup tank below.
Direct systems should be limited to warm climates or to areas that experience only a couple of freezing days per year. And those freezing days should include only a few hours’ worth of below-freezing temperatures. Direct systems are only intended to be installed in areas that have occasional freezes in the winter, not sustained days or long, clear nights below 40 [degrees] F.
If you live anywhere that experiences regular seasonal freezing weather (most of the United States, except for parts of Florida and California), you need an indirect system. Indirect solar water heating systems incorporate a heat exchanger to transfer the heat energy from the collector to the potable water in the water heater. Freeze proof heat transfer fluids are used in the indirect system collector loop to protect the collector during freeze conditions. Not all indirect systems use antifreeze solutions; some systems have a drain-back design. This design strategy allows all of the heat exchange fluid to drain out of the solar collector into a reservoir when the pump stops circulating. Therefore, there is no solution in the solar collector to be damaged by freezing conditions.
Backing Up the System
What about days when it’s overcast or there isn’t enough sun to heat the water to the desired use temperature? What type of backup water heater should you choose? This is a very important decision (see “Solar Water Heating,” HE Jan/Feb ‘02, p. 6).What are the typical water heating options in the area–electricity, natural gas, LPG or propane? All of these can be used as the back-up heating fuel. Most solar storage tanks have an electric element that heats only a portion of the storage tank when necessary, to increase the potable water to the desired use temperature. A demand water heater will reduce electric water heater tank losses and will save space in the house.
If gas is used in anything other than a instantaneous-demand heater, you should choose a two-tank system. This system consists of a standard gas water heater and a solar storage tank. Because a typical gas water heater has the burner located at the bottom of the tank, whenever hot water is used in the house, cold water entering the tank turns the burner on, which in turn heats the whole tank. To use a solar system with gas as a backup, you must have a separate solar storage tank that has the cold service water entering the system. The solar storage tank will supply preheated water to the typical gas backup heater. Thus the gas burner will run only when it is needed to boost the temperature of the preheated water for delivery into the house. Another advantage of this system is that during the summer the gas heater can be bypassed using valve strategies, eliminating its high standby heat loss.
Many active solar water heating systems use a PV module to generate electricity to run a DC pump motor (see Figure 3). This is one of the better uses for PV; the current generated by the PV panel controls the speed of the pump. This has a direct relationship to the amount of heat energy being generated by the solar thermal collector. This combination is quite elegant: no controller, no battery, no inverter, no grid connection! Used in a solar water heating system, water pumping becomes one of the most cost-effective PV applications.
Government and Utility Support
The development of HERS, the Energy Star programs, and many state energy programs (including those in Florida, Illinois, Arizona, California, and North Carolina, where there is an attractive 35% tax credit for solar water heating) is helping to highlight the efficacy of solar DHW. While I was at the Florida Solar Energy Center, I taught and promoted the Florida Energy Gauge (HERS) program. I demonstrated the advantages of including a SDHW system in a home to qualify for the Energy Star Home program using the Engauge ratings software. In many cases, a simple radiant barrier, a 12-SEER heat pump, and a SDHW system qualified a typical production-built home for the Energy Star label.
Many utility programs are offering rebates for solar water heating. There are also potential federal tax credits for solar water heating.
Home builders are now learning the advantages of incorporating solar water heating systems into new homes. The renewable portfolio standards in some states will allow solar water heating to demonstrate the reliability and performance of today’s systems and offer real savings to buyers and lower risks for contractors and financiers.
Consumers have shown that, given the opportunity, they will choose a solar water heating system. For new construction, working with a solar contractor to identify subdivision lots with good orientation and models that are aesthetically pleasing with new skylight-styled solar water heating systems can simplify the sales process and narrow the options for the builder and consumer. Combining tax credits for the builders of energy-efficient homes and credits for the purchase of solar water heating systems could increase demand nationally.
I would imagine that a few firms have a couple of new designs waiting for the right market opportunities. A solar water heating system may cost $2,000-$4,000 for the equipment, plus the cost of installation, today– but maybe that long-awaited $1,000-$1,500 system is out there on the drawing boards of more than a couple of engineers. Maybe someone is even building it right now.
For more information:
To find certified installers across the country, go to www.seia.org.
The Database of State Incentives for Renewable Energy (DSIRE, at www.dsireusa.org) provides a wealth of information on incentives, programs, proposed policies, and existing legislation that promote renewable energy. DSIRE, a project of the Interstate Renewable Energy Council (IREC), is funded by DOE’s Office of Power Technologies and managed by the North Carolina Solar Center.
Annual, site-specific energy savings for domestic water heating systems are available at www.solar-rating.org for all systems certified by the Solar Rating and Certification Corporation. According to these data, a typical SDHW produces about 3,400 kWh per year, depending on local conditions and type of collector. Additional useful information may be found at the FSEC Web site (www.fsec.ucf.edu); and the Florida SWAP program Web site (www.alpha.fsec.ucf.edu/swap/).
Two of the manufacturers in this field are heliodyne (www.heliodyne.com) and Duke Solar (www.dukesolar.com).
William T. Guiney is the Water Heating Division manager of Duke Solar Energy, LLC, in Raleigh, North Carolina. Prior to joining Duke Solar in 2001, Bill was a solar thermal specialist and instructor for the Florida Solar Energy Center.
COPYRIGHT 2002 Energy Auditor and Retrofitter
Byline: Fairley, Peter
Publication Date: 07-01-2004
Cheap, flexible solar cells could help avert the world’s impending energy crisis. That’s a big promise. But a handful of startups and established companies are vying to make good on it, by developing printable devices made of plastics and nanomaterials.
Endless energy: Konarka’s solar cells (red) on flexible plastic convert sunlight into electricity over large areas.
Endless energy: Konarka’s solar cells (red) on flexible plastic convert sunlight into electricity over large areas.
ON THE TEST BENCHES OF KONARKA TECHNOLOGIES IN LOWELL, MA, A NEW KIND OF SOLAR CELL IS BEiNG PUT THROUGH ITS PACES.
Strips of flexible plastic all but indistinguishable from photographic film bask under high-intensity lights. These strips, about 10 centimeters long and five centimeters wide, are converting the light into electricity. Wire a few of them together, and they generate enough power to run a small fan.
Solar cells, of course, are nothing new. But until now, solar power has required expensive silicon-based panels that have relegated it, largely, to niche applications like satellites and high-end homes. What’s remarkable about Konarka’s power-producing films is that they are cheap and easy to make, using a production line of coating machines and rollers. The process is more akin to the quick-and-dirty workings of a modern printing press than to the arcane rituals performed in the clean rooms of silicon solar-panel manufacturing. The company literally has rolls of the stuff; its engineers plan to cut off usable sheets as if it were saran wrap.
Konarka’s technology is just one example of a new type of printable solar cell, or photovoltaic, that promises to go almost anywhere, paving the way for affordable and ubiquitous solar power. Not only are the cells inexpensive to produce-less than half the cost of conventional panels, for the same amount of power-but they’re also lightweight and flexible, so they can be built into all sorts of surfaces. Flexible films laminated onto laptops and cell phones could provide a steady trickle of electricity, reducing the need to plug in for power. Solar cells mixed into automotive paint could allow the sun to charge the batteries of hybrid cars, reducing their need for fuel. Eventually, such solar cells could even cover buildings, providing power for the electricity grid.
A growing number of startups, like Konarka, and big corporations, such as General Electric, Siemens, and chip maker STMicroelectronics, are vying to realize this vision (see “Printable-Solar Revolution,” p. 38). Konarka hopes to start selling its solar films next year for use in consumer electronics and defense applications. And this winter, Siemens announced that it had boosted the power output of its own prototype plastic-based solar cell to new heights-an achievement that could finally make the technology viable for widespread use.
What’s making all this possible is recent breakthroughs in materials science, including advances in nanomaterials. Some of the most promising solar devices are made from conducting plastics and nano-based particles, far too small for the eye to see, that are mixed in a solution. This solution can then be printed, in a process similar to ink-jet printing, onto a surface; there the nanomaterials assemble themselves into structures within the plastic, forming the basis of a solar cell. And all this is done with little human intervention. “The fabulous notion here is that we may be able to put this active agent in some spreadable medium and basically print these things,” says Rice University chemist Richard Smalley, who shared the 1996 Nobel Prize in chemistry for the discovery of soccer-ball-shaped carbon molecules known as bucky-balls, a key ingredient in many nano solar cells.
Making these cells efficient enough to compete with coal, wind, and nuclear power remains an ambitious goal, but it’s one that experts say is attainable. Though mainstream applications are early-stage, “the way has been opened,” says Serdar Sariciftci, a materials physicist at Johannes Kepler University in Linz, Austria, and a Konarka advisor. “The avalanche has started.”
In 2003, more conventional solar panels were manufactured than ever before, yet all of them, together, yielded just 750 megawatts of electricity-the equivalent of one average-size coal-fired power plant. What’s holding up the solar industry is cost. Most top-of-the-line solar panels are made with 15-centimeter wafers of crystalline silicon, and those materials are very expensive. As a result, solar power is four to ten times more costly to produce than electricity from conventional power plants.
For decades, solar-cell researchers have tried to develop cheaper alternatives to silicon. The problem has been efficiency: other materials just don’t generate enough electricity. But Siemens’s achievement earlier this year of the highest efficiency to date in plastic solar cells could change that. The Siemens design combined two of the most important advances in materials science in the past 30 years: electrically conducting polymers and buckyballs.
The idea of combining these materials to capture solar power first gained credence in the early 1990s, when physicists Sariciftci and Alan Heeger at the University of California, Santa Barbara, created primitive photovoltaic devices by pouring a solution of conducting plastic and buckyballs onto a glass plate, spinning the plate to spread the solution into a film, and sandwiching the film between electrodes. The conducting polymer absorbed photons, kicking off electrons that were then attracted by the buckyballs and routed to an electrode.
In short, the film acted like a solar cell. Originally, the power output was meager (less than 1 percent of the energy of incoming sunlight). But the principle of the printable solar cell was proved: you could layer a photovoltaic material on a surface and make it work without complex preparations.
Day in the sun: Christoph Brabec, Siemens’s plastic-solar-cell leader
For Sariciftci, printable solar cells became an obsession. In 1996, after moving to Kepler University, Sariciftci began assembling a research team to boost the power output of his devices. One of his first recruits was Christoph Brabec, a young polymer scientist. By 2000, Sariciftci and Brabec had found a mix of solvents, temperatures, and drying conditions that delivered a better blend of plastic and buckyballs. The result: more electrons made the jump from plastic to buckyball, more than doubling the power output (see “Solar on the Cheap,” TR January/February 2002).
In 2001, Brabec left Sariciftci’s lab to head a new research effort in polymer photovoltaics at Siemens. It was his team at Siemens that earlier this year significantly increased the power output of the buckyball-plastic cell by tweaking the nanomaterials and shifting to a more industrial-style coating method. Exactly why the power jumped is not yet clear, says Brabec, though he suspects that the explanation has to do with a more regular structuring of the cell’s polymers and buckyballs. What is clear to Brabec is that he and his colleagues can squeeze even more power out of these cells, at least doubling their efficiency once more to capture 10 percent of incoming solar energy-a percentage that experts consider to be a threshold for rooftop applications. “We are absolutely sure that efficiency will continue to climb,” says Brabec.
Now, he says, it is time to demonstrate that large-scale production is feasible. “What we did was in a clean room, and the maximum module size is [ 15 centimeters],” he explains. “The logical next step is to get out of the lab and try reel-to-reel production under industrial conditions.” he hopes to get there next year.
At least one startup may beat Siemens to that goal. Konarka is now gearing up to manufacture its novel photovoltaic film, which it expects to start selling next year. Unlike Siemens’s, Konarka’s films don’t use buckyballs, instead relying on tiny semiconducting particles of titanium dioxide coated with light-absorbing dyes, bathed in an electrolyte, and embedded in plastic film. But like Siemens’s solar cells, Konarka’s can be easily and cheaply made.
Konarka sees a short-term payoff in consumer products. Power-hungry electronics such as cell phones and laptops-and anything else with a battery and access to light-could make good use of Konarka’s flexible film, according to executive vice president Daniel McGahn. And the solar films could eliminate the need to run power cords to many other electronic devices installed in homes or businesses, such as the temperature, gas, and process sensors scattered throughout manufacturing plants.
Down the road, researchers hope to boost nano solar cells’ power output and make them even easier to deploy, eventually spraying them directly onto almost any surface. PaIo Alto, CAbased startup Nanosolar, which has raised $5 million in venture capital, is working on making this idea practical. The company is exploiting the latest techniques for automatically assembling nanomaterials into precisely ordered architectures-all with a higher degree of control than ever before possible.
Nanosolar’s approach is disarmingly simple. Researchers spray a cocktail of alcohol, surfactants (substances like those used in detergents), and titanium compounds on a metal foil. As the alcohol evaporates, the surfactant molecules bunch together into elongated tubes, erecting a molecular scaffold around which the titanium compounds gather and fuse. In just 30 seconds a block of titanium oxide bored through with holes just a few nanometers wide rises from the foil. Fill the holes with a conductive polymer, add electrodes, cover the whole block with a transparent plastic, and you have a highly efficient solar cell.
In theory, at least, energized electrons in Nanosolar’s columns of plastic need only jump a few nanometers to reach the titanium compounds. From there, the electrons shoot straight through the vertically oriented titanium compounds to an electrode. “It’s a fast path out,” says Nanosolar’s CEO Martin Roscheisen, an Internet entrepreneur who founded the company two years ago.
This technology could enable Nanosolar to spray-paint photovoltaics onto building tiles, vehicles, and billboards, and wire them up to electrodes. At first, the cells would be applied in manufacturing, but eventually they might be sprayed onto existing surfaces. When will this approach become prevalent enough to feed electricity to power grids? Roscheisen won’t say, but he vows that by the end of next year, Nanosolar will have prototypes that capture 10 percent of incoming solar energy.
CATCHING SOME SUN
In their initial applications-such as powering cell phones and laptops, as Konarka envisions-printed solar cells won’t need to produce that much power or run for decades at a time. But sealing them up from personal electronics to rooftops is a whole other story.
Handheld power: Konarka solar film is light and flexible and could be laminated onto portable devices.
On a roll: Cheap nano solar cells can be made using rolls of plastic sheets, like this one at Konarka.
Unlike the crystalline silicon in conventional solar panels, the polymers and dyes employed in printable solar cells are exquisitely sensitive to oxygen. Protecting these materials from blowing sand, intense sunlight, extreme temperature shifts, and the myriad other forms of abuse that nature heaps on solar panels will require hermetic seals. But Brian Gregg, a solar expert at the U.S. Department of Energy’s National Renewable Energy Laboratory, predicts that materials scientists will soon develop workable seals that will protect the delicate devices over the long term. “There’s no reason to believe that we can’t make [printed] solar cells that will last for 30 years,” says Gregg.
Indeed, the recent advances in printable solar cells-and the growing possibilities presented by nanotechnology-leave many experts more optimistic than ever that the technology is nearly ready to tackle one of the world’s most troubling problems: how to create a ready and renewable supply of energy. Nanotech pioneer Richard Smalley, for one, is convinced that a solar-powered grid is not just possible but also inevitable-and indispensable. Nanotech could help solve the energy problem, Smalley contends, by providing new tools and materials that make widespread use of solar cells economically viable. But he believes it will take billions of dollars in funding and the focused efforts of the world’s top chemists and physicists to make that happen. So for the past two years, he has been crisscrossing the United States, evangelizing for nothing short of a modern-day Manhattan Project to use nanotech to deliver a sustainable energy system.
That’s the long-term vision. In the meantime, the Konarkas and Siemenses of the world are taking some critical first steps toward changing how we think about harvesting energy from the sun, and how we use electricity in our lives. It may not yet be the Manhattan Project urged by Smalley, but it’s a fast-growing effort that could quickly reach critical mass.
PRINTABLE SOLAR CELLS COULD be BUILT INTOTHE SURFACES OF CELL PHONES, LAPTOPS, CARS, AND EVEN BUILDINGS, PAVING THE WAY FOR AFFORDABLE AND UBIQUITOUS SOLAR POWER.
GENERAL ELECTRIC, Schenectady, NY
Adapting methods developed for printable lighting panels to make solar cells; pushing for 10 percent energy efficiency in a practical cell
KONARKATECHNOLOGIES, Lowed, MA
Manufacturing solar cells made of semiconductor particles; plans to market 5 percent efficient cells by 2005
NANOSOLAR, PaIo Alto, CA
Testing titanium compounds and conductive plastic that can be sprayed on surfaces to form solar cells; seeking 10 percent efficiency by late 2005
NANOSYS, PaIo Alto, CA
Developing self-orienting nanoparticles in conductive plastic for photovoltaic coatings; plans to incorporate them into commercial roofing tiles in a few years
SIEMENS, Erlangen, Germany
Researching buckyballs and conductive plastic for solar cells and photodetectors; seeks practical flexible cells by 2005 STMICROELECTRONICS, Geneva, Switzerland
Blending buckyballs with carbon-based molecules containing copper atoms to make solar cells; conducting research into efficiency and feasibility
Peter Fairley, a Technology Review contributing writer, covers technology, energy, and the environment from Victoria, British Columbia. His last story for TR was “Hybrids’ Rising Sun” (April 2004).
Copyright Technology Review, Inc. Jul/Aug 2004