The curse of inefficient conversions plagues everything from microchips to massive factories and power plants. When you boot up your laptop, the microprocessor inside is spewing heat that has to be dissipated by a heat sink and fan; the power brick that you plug into the wall is leaking energy in the conversion from AC to DC; and about 7 percent of the electricity generated at a distant power plant is wasted in transmission losses while traversing the grid before the juice ever reaches your home. The most common form of waste energy by far is heat, but power can also be squandered in unproductive motion (as in walking) or even in the millions of tons of edible food tossed into landfills. A 2010 University of Texas study estimated that discarded food contains more than 2000 trillion Btu of embodied energy each year.
No single solution can address all these different types of waste. Instead, we need to engineer creative approaches to fit each situation, as the University of New Hampshire learned after installing a gas-fired cogeneration plant in 2006. "The plant completely changed the way we think about managing energy on campus," says Paul Chamberlin, the university's assistant VP in charge of energy and campus development. The obvious gain was capturing excess heat that the turbine gave off while producing electricity and using it to heat campus buildings, boosting the generator's overall efficiency from 35 percent to a maximum of about 85 percent. Better yet, the university realized that landfill gas from a nearby dump, which otherwise would have simply flared into the atmosphere, could provide valuable extra fuel. Less obvious, though, was what to do with all that extra heat in the summer—"free steam," as Chamberlin puts it. The solution: The new UNH business school currently under construction will have steam absorption chillers instead of electric air conditioners, and other campus buildings will follow suit.
sphaeroides has been identified as the bacterium having the highest hydrogen-producing rate (260 ml/mg/h) (7), with a photoenergy conversion efficiency (energy yielded by combustion of produced hydrogen/incident solar energy) of 7%, determined using a solar simulator (7, 8).
determined that outdoor solar incubation for a period exceeding one month in California, resulted in an average energy conversion efficiency (energy yielded by combustion of produced hydrogen/incidence solar energy) of 0.2% (6).
Bacterial mechanisms for photosynthetic hydrogen production are summarized in Figure 2-4.
Food is a highly efficient energy-storage mechanism: a 2-ounce granola bar contains as much energy as a 12-pound lithium battery. Rotting organic matter in landfills releases some of that energy as gas, typically about 50 percent methane, which can be captured, cleaned and burned to generate electricity and heat. Before its 7.9-megawatt EcoLine cogeneration project could start operating, the University of New Hampshire had to build its own gas processing plant to enrich the gas from a nearby landfill. This facility is necessary to remove carbon dioxide, as well as strip out contaminants like sulfur and volatile organic compounds. Nationally, there are 558 landfill gas-to-energy projects operating out of 2400 possible landfills. The EPA has identified another 510 sites as highly promising but untapped, with the potential to produce enough electricity to power 690,000 homes.
Further steps toward a long-term stability goal of 1000 hours are already underway.
Next goals visible
"Forecasts indicate that the generation of hydrogen from sunlight using high-efficiency semiconductors could be economically competitive to fossil energy sources at efficiency levels of 15 % or more.
How we'll fuel our future is often framed as a misleadingly simple, two-sided debate: We either have to produce more energy or use less. But that picture ignores a basic thermodynamic truth: For the same reason you should never pay cash for a perpetual motion machine, you can never make use of 100 percent of the energy you consume. Something is always lost in the conversion from fuel to work. While that may sound like bad news, it also introduces a third way to address future energy needs. Right now, our energy conversion is abysmal, nowhere near the theoretical limits of efficiency. But with smarter design and new technologies, we can get a lot closer to those limits.
The light-independant reactions of photosynthesis occur in the stroma of the chloroplast and involve the conversion of carbon dioxide and other compounds into glucose. The light-independent reactions can be split into three stages, these are carbon fixation, the reduction reactions and finally the regeneration of ribulose bisphosphate. Collectively these stages are known as the Calvin Cycle.
The biggest obstacles facing the quest for efficient energy conversion aren't just technical. We have an awareness problem. When it comes to curb appeal, a nearly invisible diode that converts AC to DC with virtually no loss can't compete with a shiny solar panel, even though the latter is less efficient. And, as a rallying cry, "Run your engine as close to the Carnot efficiency limit as possible without violating the second law of thermodynamics" will never replace "Drill, baby, drill!" So a philosophical shift is in order. Yes, we need to keep pursuing new energy resources, but we must also make the most of what we have now. "When it comes to solving our problems with fossil fuels and the environment, these technologies are really the low-hanging fruit," Nelson says. "They're available now; they just need to be pushed."
Using a now patented photo-electrochemical process, May could modify certain surfaces of these semiconductor systems in such a way that they functioned better in water splitting.
"We have electronically and chemically passivated in situ the aluminium-indium-phosphide layers in particular and thereby efficiently coupled to the catalyst layer for hydrogen generation.
Every time you plug your cellphone, laptop, HDTV or other electronic device into the wall, you're converting AC power from the grid into electronics-friendly DC power. The reverse happens when DC power from solar panels or wind turbines is converted to AC to feed into the grid. "Power conversion is happening everywhere, in every appliance that uses energy," says Umesh Mishra, CEO and co-founder of Transphorm, a Google-backed startup. "These conversions are very lossy: 10 to 12 percent of electrical energy generated in the U.S. is lost to conversion." The solution, according to Mishra, is to make the diodes and electrodes that help perform this conversion out of a semiconducting material called gallium nitride rather than silicon. Since the atomic structure GaN is capable of holding three to five times the voltage of silicon without leaking, it can reduce waste by 90 percent at each conversion step. Transphorm's converters are already slated for use in large-scale data centers but could ultimately be incorporated into virtually any electric product, Mishra says.
Recapturing waste heat from an enormous power plant is a no-brainer, thanks to the superhigh temperatures and economies of scale. But much more common are small industrial facilities with furnaces, ovens, incinerators and engines, where the amount of waste heat is too small to efficiently power a full-fledged turbine. Florida-based Cyclone Power has developed a versatile Waste Heat Engine that can tap into the exhaust of pretty much any industrial process, using more modest heat from 500 to 1000 degrees Fahrenheit to power reciprocating radial pistons in a Rankine cycle generator. "Our target is much smaller scale distributed power, from about 5 to 500 kilowatts," says Cyclone president Chris Nelson. One of the first uses is actually mobile: running refrigeration and auxiliary power in long-haul trucks, saving 5 to 10 percent on fuel. The company estimates that there are also 10,000 industrial installations in the U.S. that would be suitable for the Waste Heat Engine, which could save 13.5 billion kilowatt-hours a year.