Harvesting Electricity from the Greenhouse Gas Carbon Dioxide

10:39 pm

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Electricity Generation

July 23, 2013 — A new method for producing electricity from carbon dioxide could be the start of a classic trash-to-treasure story for the troublesome greenhouse gas, scientists are reporting. Described in an article in ACS' newly launched journal Environmental Science & Technology Letters, the method uses CO2 from electric power plant and other smokestacks as the raw material for making electricity.

Bert Hamelers, Ph.D., and colleagues explain that electric power-generating stations worldwide release about 12 billion tons of CO2 annually from combustion of coal, oil and natural gas. Home and commercial heating produces another 11 billion tons. Smokestack gas from a typical coal-fired plant contains about 10 percent CO2, which not only goes to waste, but is a key contributor to global warming. Hamelers' team sought a way to change that trash into a treasure.

They describe technology that would react the CO2 with water or other liquids and, with further processing, produce a flow of electrons that make up electric current. It could produce about 1,570 kilowatts of additional electricity annually if used to harvest CO2 from power plants, industry and residences. That's about 400 times the annual electrical output of the Hoover Dam. Like that dam and other hydroelectric power facilities, that massive additional amount of electricity would be produced without adding more CO2 to the atmosphere, Hamelers pointed out.

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How to Set Up a Small Solar (Photovoltaic) Power Generator

12:55 am

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Solar Power Generation

The goal of this article is to show how to set up a small solar power generator. While there are a lot of decisions you can make, this particular how to focuses on small-scale solar generation (<1kWh/day), and simplifies it so that just about anyone can set up a functioning system. However, beware that compromises in efficiency, safety, and code adherence may be made for the sake of simplicity.

Steps

1. Decide how much power you need. To do so, determine which electronic devices you would like to use, then find out how much power they use. Most devices have wattage ratings, which can then be multiplied by the number of hours of use to produce "Watt-hours" (Wh), which is a unit of power consumption. For example, if you intend to use a 15W device for 2 hours a day, that's 15W x 2h = 30Wh. Note, however, that ratings are usually higher than the actual power consumption. To determine how much a device actually draws, you can use a meter like the Kill-a-Watt. Once you have all the Watt-hours, add them up. If the total exceeds 1000Wh (or 1 Kilowatt-hour), this How to may not be suitable for you.
2. Determine how much unobstructed sunlight you receive in the location you intend to set up solar panels. Unobstructed literally means that there are no shadows. If a tree, neighboring building, or anything else casts a shadow in that particular spot, don't count the time during which a shadow exists. So, if you get 12 hours of sunlight, but the sun is beyond the fence for 2 hours in the morning, then behind a tree for an hour at noon, then shadowed by your neighbor's barn for 2 hours before sunset, you only get to count 7 hours. Note also that days are shorter in Winter. If you intent to use your set up in Winter, use your Winter hours.
3. Divide your total power consumption from Step 1 by the number of hours you came up with in Step 2. If you decide you need 600Wh and that you get 6h of sunlight, that's 600Wh / 6h = 100W. This is the amount of power you need to generate per hour of sunlight to meet your needs. To be safe, multiply that by at least 2 or more. This is to account for the fact that solar panels only generate their rated output when pointed directly at the sun, and if your solar panels are fixed, they won't be facing directly at the sun most of the time. After various inefficiencies, you may lose another 20% or more of the power generated. If you expect regular and sustained cloud coverage, you may need to multiply by 5 or more (or simply reduce consumption to live within your means).
4. Buy solar panels. Broadly speaking, there are 3 types of solar panels (strictly speaking, photovoltaic cells): amorphous silicon, polycrystalline, and monocrystalline. Amorphous silicon panels are relatively inexpensive, relatively unaffected by small shadows, but are very inefficient in terms of space (for the same power rating, amorphous silicon panels will be larger and heavier). Polycrystalline panels are more efficient, cheaper than monocrystalline, but also less efficient. Monocrystalline panels are the most efficient, but also the most expensive. Output from mono- and polycrystalline panels can be halved or less by even a tiny shadow because of the way individual cells are wired. Mono- and poly-crystalline panels can be purchased these days for as little as $3-5/Watt. Consider "B-grade" panels which are significantly cheaper, yet come with reasonable warranties. While some people want their panels to last 25 years, the reality is that the cost of PV cells are coming down so rapidly that replacing or augmenting your panels in another 5-10 years may actually be cheaper than paying more now for ones that last longer. If the solar panels are more expensive than your budget allows, consider lowering your power consumption. Turning off or forgoing some devices won't kill you (and if it will, this How to is not for you).
5. Calculate the amount of battery capacity you need. To do this, take the power consumption estimated in Step 1, then double it, because only about half the batteries' capacity should be considered usable to avoid over-discharge. Then, multiply by the number of days' reserve you would like. For instance, if you want to use 600Wh, you need 1200Wh (or 1.2kWh) of capacity, so if you had 3.6kWh, you'll be good for a few days even if the sun disappears (though you may have other problems at that point). Since most batteries have capacities in Amp-hours, it may be best to convert Wh to Ah. To do so, divide the capacity you calculated by the battery's voltage, so 3600Wh / 12V = 300Ah (divide by 6 for 6V batteries).
6. Buy batteries. While normal car batteries will work (for a while), it is best to use "deep-cycle" batteries, which are generally marketed for use in RVs and boats. Some people prefer 6V golf cart batteries, which are designed to withstand repeated deep discharges. If using 6V batteries, connect two in series (positive terminal of one connects to negative of the other), then connect pairs in parallel (positive of one pair with positive of the other pair, negative with negative). If your budget allows, you may consider AGM batteries, which can take more "abuse", but also cost 2-3x what lead acid batteries cost. Make sure the Ah ratings of all batteries added together is higher than the capacity you calculated in the previous step. If using multiple batteries, make sure to get multiples of the same battery, and to get them all new (or reconditioned) at the same time. Mixing different capacity, model, or age batteries can shorten all of their lifespans.
7. Buy a charge controller. Charge controllers can cost as little as $10 or over $100. The most important thing is to actually use a charge controller. If you hook up solar panels directly to some batteries, the batteries will charge for a while, but they could quickly be ruined. Whichever charge controller you get needs to support the amount of current your solar panels produce. Most charge controllers are rated in Amps, so divide the Watt rating of your solar panels by 12V (e.g. 200W / 12V ~= 17A). Find a charge controller with a rating higher than your theoretical estimate. This will give you a safety margin, as well as some headroom for growth in the future. Beyond that, exactly which charge controller to buy is basically a trade-off between cost vs efficiency and battery-life. The more expensive charge controllers will use different charging algorithms best suited to the type of battery you have. They also may compensate for temperature to better protect your batteries.
8. If you plan on running devices off of AC power (i.e. use normal wall plugs), you will also need an inverter. There are broadly two types of inverters: modified sine wave and pure sine wave. Pure sine wave inverters give you power that is closer to city power, but these inverters tend to be more expensive ($150+ for a 600W inverter). Modified sine wave inverters can be much cheaper ($30+ for a 400W inverter), but some devices may not work, or work well with them. Note also that inverters have 80-90% efficiency, which means you lose some power in the DC to AC conversion. However, if you've followed all previous steps as recommended, your set-up should have the excess capacity to absorb this inefficiency.

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Off-Grid Sterilization With 'Solar Steam'

8:49 pm

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Solar Energy

July 22, 2013 — Rice University nanotechnology researchers have unveiled a solar-powered sterilization system that could be a boon for more than 2.5 billion people who lack adequate sanitation. The "solar steam" sterilization system uses nanomaterials to convert as much as 80 percent of the energy in sunlight into germ-killing heat.

The technology is described online in a July 8 paper in the Proceedings of the National Academy of Sciences Early Edition. In the paper, researchers from Rice's Laboratory for Nanophotonics (LANP) show two ways that solar steam can be used for sterilization -- one setup to clean medical instruments and another to sanitize human waste.

Researchers show two ways that solar steam can be used for sterilization — one setup to clean medical instruments and another to sanitize human waste.

"Sanitation and sterilization are enormous obstacles without reliable electricity," said Rice photonics pioneer Naomi Halas, the director of LANP and lead researcher on the project, with senior co-author and Rice professor Peter Nordlander. "Solar steam's efficiency at converting sunlight directly into steam opens up new possibilities for off-grid sterilization that simply aren't available today."

In a previous study last year, Halas and colleagues showed that "solar steam" was so effective at direct conversion of solar energy into heat that it could even produce steam from ice water.

"It makes steam directly from sunlight," she said. "That means the steam forms immediately, even before the water boils."

Halas, Rice's Stanley C. Moore Professor in Electrical and Computer Engineering, professor of physics, professor of chemistry and professor of biomedical engineering, is one of the world's most-cited chemists. Her lab specializes in creating and studying light-activated particles. One of her creations, gold nanoshells, is the subject of several clinical trials for cancer treatment.

Solar steam's efficiency comes from light-harvesting nanoparticles that were created at LANP by Rice graduate student Oara Neumann, the lead author on the PNAS study. Neumann created a version of nanoshells that converts a broad spectrum of sunlight -- including both visible and invisible bandwidths -- directly into heat. When submerged in water and exposed to sunlight, the particles heat up so quickly they instantly vaporize water and create steam. The technology has an overall energy efficiency of 24 percent. Photovoltaic solar panels, by comparison, typically have an overall energy efficiency of around 15 percent.

When used in the autoclaves in the tests, the heat and pressure created by the steam were sufficient to kill not just living microbes but also spores and viruses. The solar steam autoclave was designed by Rice undergraduates at Rice's Oshman Engineering Design Kitchen and refined by Neumann and colleagues at LANP. In the PNAS study, standard tests for sterilization showed the solar steam autoclave could kill even the most heat-resistant microbes.

"The process is very efficient," Neumann said. "For the Bill & Melinda Gates Foundation program that is sponsoring us, we needed to create a system that could handle the waste of a family of four with just two treatments per week, and the autoclave setup we reported in this paper can do that."

Halas said her team hopes to work with waste-treatment pioneer Sanivation to conduct the first field tests of the solar steam waste sterilizer at three sites in Kenya.

"Sanitation technology isn't glamorous, but it's a matter of life and death for 2.5 billion people," Halas said. "For this to really work, you need a technology that can be completely off-grid, that's not that large, that functions relatively quickly, is easy to handle and doesn't have dangerous components. Our Solar Steam system has all of that, and it's the only technology we've seen that can completely sterilize waste. I can't wait to see how it performs in the field."

Paper co-authors include Curtis Feronti, Albert Neumann, Anjie Dong, Kevin Schell, Benjamin Lu, Eric Kim, Mary Quinn, Shea Thompson, Nathaniel Grady, Maria Oden and Nordlander, all of Rice. The research was supported by a Grand Challenges grant from the Bill & Melinda Gates Foundation and by the Welch Foundation.

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Noise reduction innovation for power stations

2:59 am

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Electricity Generation

Schiller Biomass Power Station in New Hamsphire uses the innovative noise reduction technology [Credit: PNSH]

New technology deployed at the largest US biomass power plant prevents creation of noise from fans while reducing power consumption.

The solution developed by the Industrial Noise and Vibration Centre (INVC) from Berkshire, UK, relies on active noise reduction instead of suppressing the noise by silencers and acoustic enclosures.

“We have developed a way to prevent the noise being generated in the first place instead by designing aerodynamic inserts that fit inside the fan casing. You can think of these as akin to the aerodynamic features used on Formula 1 cars to control airflow,” said Peter Wilson, the INVC technical director.

The technology was installed at the 50 MW Schiller biomass power plant in New Hampshire - the largest biomass power plant in the US. The site had had problems due to the noise produced by the station’s ID fan. The installation itself only required 12 hours. According to a technical review evaluating the solution, not only noise reduction has been achieved but the plant  has also been consuming considerably less energy.

"We recorded a 10dB drop in noise, which is huge. We also recorded a reduction in the power used by the ID fan after Quiet Fan technology had been installed." said Jim Granger, the Senior Engineer at Schiller.

Conventional silencing technology to suppress the drone of large ID fans is rather costly and increases down-time of the installation. According to the evaluation data, the Quit Fan technology managed to achieve similar level of noise reduction costing about 80 per cent less.

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