All posts by mgdpost

Researchers uncover new method in electrification of waste heat

From computer chips to car engines, from cell phones to laptops; they all release excess heat in order to perform at their optimal level. More than half of the energy consumed worldwide is wasted, most of it in the form of this excess heat. According to researchers from the Massachusetts Institute of Technology this waste heat is a great potential source of energy if harvested correctly. They recently uncovered a new method of obtaining electrical power from otherwise wasted heat.

Waste heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found, and is regarded as a waste by-product. The burning of transport fuels is a major contribution to waste heat. When excess heat is released the efficiency of the equipment will decrease below 100 %. When, for instance, the waste heat from a car engine in the winter is being used for the car radiator, the efficiency will increase. In theory the same principal would apply for cell phones and laptops. If this wasted energy is cleverly harnessed and utilized we might not, for instance, have to recharge our phones or computers that often.

There are many different approaches to transfer thermal energy to electricity, these approaches are mostly still in development. Peter Hagelstein, one of the main researchers from MIT, is of the view that the existing solid-state devices that are already available to convert heat into electricity are not very efficient. It is known as high-throughput power. According to Hagelstein it converts heat from a less efficient system  and you get more energy. But it is a larger and a more expensive system in which you get either high efficiency or high throughput. But the MIT team found that by using their new system, it would be possible to get both.

Theoretically a limit is set on the maximum amount of efficiency any device van achieve when converting heat to electricity. This limit is called the Carnot Limit, based on a formula set in the 19th century. Hagelstein found that current devices can only go as far as one tenth of that limit. Hagelstein and collegues claim to have reached an efficiency as high as 40 % of the limit by using their new technology. They say in the future it might be possible to achieve up to 90 %.

The MIT researchers chose to not try upon improving existing devices but to start from scratch designing the ideal thermal-to-electric converter. It’s not entirely clear how the new system works. It involves a single quantum-dot device – a type of semiconductor in which the electrons and holes, which carry the electrical charges in the device, are very tightly confined in all three dimensions. Such devices are still in development and will not appear on the market for a couple of years to come.

http://web.mit.edu

Sandia developes four new SunCatchers

After more than a decade of innovative engineering and validation testing Stirling Energy Systems (SES) and Tessera Sol have presented four newly designed solar power dishes .These four new dishes are the follow-up model of the original SunCatcher system and will be ready for commercial production in 2010.  

The six first-generation SunCatchers are currently planted in the New Mexico desert where they are producing up to 150 KW of grid-ready electrical power during the day.  The new dishes have been upgraded and tested a Sandia National Laboraratories to allow for a high rate of roduction and cost reduction.  Sandia’s concentrating solar-thermal power (CSP) team has been working closely with SES over the past five years to improve the system design and operation which uses a Stirling engine.

The modular CSP SunCatcher uses precision mirrors attached to a parabolic dish to focus the sun’s rays onto a receiver, which transmits the heat to a Stirling engine. The engine is a sealed system filled with hydrogen. As the gas heats and cools, its pressure rises and falls. The change in pressure drives the piston inside the engine, producing mechanical power, which in turn drives a generator and makes electricity.

The new SunCatcher is about 5,000 pounds lighter than the original, is round instead of rectangular to allow for more efficient use of steel, has improved optics, and consists of 60 percent fewer engine parts. The revised design also has fewer mirrors — 40 instead of 80. The reflective mirrors are formed into a parabolic shape using stamped sheet metal similar to the hood of a car. The mirrors are made by using automobile manufacturing techniques. The improvements will result in high-volume production, cost reductions, and easier maintenance.

SunCatchers have numerous environmental advantages.  They are said to have the lowest water use of any thermal electric generating technology, require minimal grading and trenching and require no excavation for foundations. And more important they will not produce greenhouse gas emissions while converting sunlight into electricity. Tessera Solar is planning to build a 60-unit plant generating 1.5 MW by the end of the year either in Arizona or California. One megawatt powers about 800 homes. The proprietary solar dish technology will then be deployed to develop two of the world’s largest solar generating plants in Southern California with San Diego Gas & Electric in the Imperial Valley and Southern California Edison in the Mojave Desert, in addition to the recently announced project with CPS Energy in West Texas. The projects are expected to produce 1,000 MW by the end of 2012.

Clean cars run on urine

How does this sound; using urine, the most abundant waste on earth, as the new fuel source? And, to catch two birds with one stone, it helps clean-up municipal wastewater at the same time. Urine-powered cars should be available in six months according to scientists from the Ohio University, who developed an electrolysis method to retrieve hydrogen from urine collected from livestock.

electrolysis
electrolysis

Hydrogen fuel cells are one the cleanest burning fuels ever developed. Hydrogen was, until now, taken out of water and then put into fuel cells as a gas that can power a vehicle.  The only emission that is said to come out of this fuel cell powered vehicle is water vapor. Urine’s major constituent is urea, which incorporates four hydrogen atoms per molecule – importantly, less tightly bonded than the hydrogen atoms in water molecules. By placing a special nickel electrode into a pool of urine and applying an electrical current, hydrogen gas is released. Once the urea is removed from the waste pool, a farm is left with water that is significantly less polluted than it was, with irrigation as one possible use.

One of the hurdles facing this alternative fuel source is that hydrogen gas requires high pressure and low temperatures to be stored. It becomes somewhat easier to store when it’s binded back to oxygen to create water, but even then it still requires large amounts of electricity to be released. The Ohio University scientists who developed the urine technology found that attaching hydrogen to nitrogen in urine allowed it to be stored without the strict requirements of ordinary hydrogen, and allowed it to be released with less electricity (0.037 volts versus 1.23 volts needed for water). A fuel cell, urine-powered vehicle could theoretically travel 90 miles per gallon according to the Ohio scientists.

 Some argue that hydrogen-fueled cars won’t offer a cost-effective way to reduce automotive air pollution or reduce
emissions of climate-changing carbon dioxide gas for at least several decades. Environmental scientist  David Keith is one of them. He doesn’t oppose the use of hydrogen fuel cells but argues saying it makes far more sense to first use this fuel in ships, trains and large trucks rather than cars. Such uses could achieve large reductions in air pollution without the need for the extensive hydrogen distribution infrastructure which would be required for refueling automobiles. Such an infrastructure is very expensive (approx $5.000 per vehicle or more), according to the researchers’ work. Also around 10-20% of the hydrogen would escape into the atmosphere. He says that if hydrogen fuel cells replaced all of today’s oil and gas-based combustion technologies, such losses would double or even triple the total hydrogen deposited into the atmosphere at the Earth’s surface.

Other researchers say that the use of hydrogen on large scale would oxidize when reaching the stratosphere, which would cool the stratosphere and create more clouds and, in effect, making the holes in the ozone layer larger and longer lasting. However it is not yet known on what scale this process will take place and there is also uncertainty how soil absorbs hydrogen from the atmosphere. The bottom line is that hydrogen could still be considered the far better option when it comes to competing with the toxic elements that are released into the air with gasoline burning cars. It might have its downsides but weighed against all the positives, they don’t seem to stand a chance.
It seems like we have a winner here.