How Combined Heat and Power generation can propel electric cars 22 times further than ethanol.
Open Access Article Originally Published: August 18, 2009
Cheap fossil fuel has allowed us to waste the majority of our energy, filling the planet with pollution and waste heat. Our car engines are only 25% efficient and coal power plants are not much better. Corn ethanol is one of the worst wastes of biomass: An acre of corn produces about 330 gallons/year if you cook it using fossil fuel. Use the ethanol as a heat source and the net yield drops to 214 gallons/year. Car gas mileage is 25% lower with ethanol. At 25 miles/gallon we can only drive 25 X 214 = 5350 miles per year on an acre of corn.
If we take that same acre of corn and burn it to make electricity to charge an electric car, we will be able to drive the car 22 times as far! About 117,096 miles per year!
The energy content of dry corn biomass is about 7000 Btu/lb or 4100 kWh/ton.
With an 85% efficient CHP plant the net power out is .85 X 4100 = 3485 kWh/ton
An acre of corn yields about 8.4 dry tons/yr or 8.4 X 3485 = 29,274 kWh per year
The Nissan Leaf, Tesla Roadster and even the Chevy Volt can all travel 4 mi/kWh. 4 X 29,274 = 117,096 miles!
Combined Heat and Power (CHP) plants achieve 85% efficiency by using the waste heat and the electricity. It’s as though part of the fuel generates electricity and the rest generates heat. Since the heat generally replaces fossil fuel burning, carbon credits are gained for both products. The trick then is to locate the plant where heat is needed. Fortunately, we use more heat than electricity.
In the U.S. we don’t have very many 85% efficient CHP biomass power plants yet. In fact, only 8% of our power plants are CHP plants. But Denmark has 53%, Holland 39% and Finland 38%. CHP plants are extremely efficient many exceeding 90% efficiency! The secret of CHP is to locate the plant near where heat is needed. The only real waste then is the heat that escapes into the air and past the heat exchangers in the stack.
CHP requires a different way of thinking. You must look first for places you can sell heat. Electricity is easy to distribute but heat is harder so location and sizing of plants must follow the heat demand. Mammoth gigawatt power plants cannot do CHP unless they are built adjacent to a mammoth cement plant, kiln or steel plant. Most mammoth plants today dump about 2/3rds of their power into a stream or ocean just to get rid of it. A horrible waste!
High-rise buildings, hospitals, industrial parks, shopping centers, apartments, housing tracts and hotels are all excellent candidates for CHP power. Hot water, heat and cooling needs are generally comparable to electric power needs so 50% efficient electrical generators are a perfect fit: The wasted heat from the generator is simply used as heat. Fortunately, the needed technology is appearing just on schedule. Fuel cells can generate electricity with 50-60% efficiency from natural gas or syngas from biomass. One of the reasons mammoth power plants were built in the past was that only very large turbines were efficient. The other reason was pollution control. Neither reason applies today, as gas and biomass burn clean, particularly in a fuel cell.
Fortunately, we have a glut of natural gas from new shale bed discoveries. Gas is very convenient in cities, while biomass can generate carbon free power in more rural areas. Switching from coal power to CHP gas power has a massive impact on greenhouse gas emissions. Natural gas produces only 55% as much carbon as coal. CHP plants are three times as efficient (85% vs. 28%) so the resulting emissions are only .33X.55= 18% of a coal plant producing equivalent power! That’s a better improvement than the planned 40% CO2 output of Futuregen and we don’t have to wait decades for it to happen. With 3X better fuel economy, natural gas is way cheaper than coal and we won’t run out of natural gas for a long time.
Giant power plants are custom designed and take 10 years to build. Smaller, modular CHP plants can be based on standard pre-approved designs with components built on mass-production lines like cars. The capital cost can be much lower than large plants. There are several mass-produced home-sized CHP units coming on the market now based on fuel cells. Honda already shipped 50,000 of their Ecowill units in Japan. These units are 85.5% efficient by using generator-wasted heat to make hot water.
What we need now are standard CHP generator designs in the 1 MW to 5 Mw size that can run on natural gas or biomass. A biomass unit could be used on a farm to heat greenhouses, cold storage, fish ponds or brick production. Burning 2 MW of biomass would produce 1 MW of heat and 1 MW of electricity. 1 MW of electricity is 8,760,000 kilowatt-hours per year, worth about $876,000 per year. The heat is worth about 1/3 as much. Carbon credits and Renewable Energy Credits add to the income. Fuel cell power plants are already a commercial reality. One company has 50 installations that have already generated 275 million kilowatt hours.
To feed the gasifier 2 MW with corn, the farmer would need only about 68 acres of land. Other, more prolific feedstocks like elephant grass could probably get by with only 23 acres. In Germany they have straw bale gasifiers that simply require the farmer to throw in a new bale periodically. The control microcomputer rings the farmer’s cell phone with a text message whenever a new bale is needed.
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Reader Comments
6 comments so far...
07-Sep-2009
67951
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Let us not forget that our current energy sources (large plants) are security risks in a post-9/11 world. Distributed power generation places the power generator near the need for power and greatly decreases the efficiency of terrorist acts. A multitude of simultaneous acts would be required to cause the entire grid to collapse. Currently, a concentrated effort on just a few key installations here in Quebec would be a disaster, one which would be very difficult to recover from.
Posted by: David Lemieux
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20-Aug-2009
67762
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Excellent article! One more way the US lawmakers need to "get the lead out."
Posted by: Richard Noe
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23-Aug-2009
67804
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The key to making these types of ideas work is to broaden the Renewable Fuel Standard to includes renewable electricity. If a car is powered by electricity that comes from corn, solar, wind, etc than it also get the $ subsidy at an etahnol gallon equivalent level plus can be used to meet the RFS standard.
Posted by: Jigar Shah
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24-Aug-2009
67812
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Very good statement. However, the 85% energy efficiency is combined for thermal and electric efficiency. The simple electric efficiency actually even drops slightly in a CHP. This is not a bad thing as such, but flaws the nicety of your results. That is, you cannot produce
.85*4100=3485 kWh/ton, but rather something along the lines of
.45*4100=1845 kWh/ton. This will still generate some 15,498 kWh, not taking into account the energy used for growing and transporting the biomass. So let's say its 14,000 kWh. At a mi/kWh this yields 56,000 miles. However, no electric car can deliver this performance under real life conditions. Try that in winter or after a year of battery use.
In the end, though, you will always, even in worst case scenarios end up better than an ICE car, but this not that difficult after all.
The bottom line is: Yes, CHP is a totally neglected (because not sexy and high tech), but real and ready technology that could help countries with urban settlements to cut carbon emissions AND save money - provided the fuel is priced right. CHP was pretty much on the rise in the 90s, but when gas prices (here in Europe mostly meaning Russian gas) soared, the development of new CHP plants stumbled. Power plant developpers told me that they could easily increase efficiency further, but this would be too costly to sell the product on the market.
It is a real dilemma: With peak oil and high gas prices, but cheap coal, it is very difficult to invest in CHP, although this is the most promising thing one can do and would help the environment much more than PV (except in very sunny areas such as the SW), wind (except in very winddy areas such as the MW), hydro (always a good way to destroy an entire area with just one project).
CHP offers the option of generating electricity in a semi-centralised manner, meaning that operations are possible within residential areas as the air is almost clean. This allows more grid flexibilty and opens the gates for more renewables. Actually, I believe that renawbles need to go hand in hand with CHP, since gas fired plants can easily regulate their output, which is much less an option with coal or even nuclear (so called base load plants).
Very good article.
Cheers,
Max
Posted by: Max Gruenig
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25-Aug-2009
67835
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Hello, Highway Hay!..A crew of restored low center of gravity farm tractors like the Ford 8N, for example, move along the highway right of way: Two are fitted with sicklebar mowers, one pulls a windrower, another pulls a small 'round-baler' and a final one has a scoop-loader and 'rear-blade' to smooth the tops of bumps-n-moguls: All are equipped with safety rollbars, strobe flashers, and painted 'school-crossing' flourescent-yellow. All are converted to run on straight ethanol. Instead of chopping and blowing the grass/plants alongside the road, the crew cuts, windrows, and bales the biomass into moderate-sized bales [the size of an oil drum] which the 'scooper' can pick up and place on an old military 6x6 truck [running on bio-algae-fuel]. When loaded, the truck carries the bales to a biomass refiner/distiller/cooker? and returns. A military 4x4 service truck refuels the tractors and carries tools/parts/etc...Think of how many thousands of miles worth of 'highway hay' grows along our public roads...Rather than pay folks to chop the 'hay' down, let 'em 'harvest' it and use it for fuel?!. Aaron..
Posted by: Aaron Allen
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26-Aug-2009
67844
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Yes! helo highway hay, and goodby fosil fuel. Aaron Allen it is shame your not the director of The Department of Energy. The world would be a better place.
Posted by: Thomas becker
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