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Despite the world's financial and economic crisis, electric energy consumption in Brazil is growing at 5% a year. The current installed generating capacity is 101 GW. Since supply and demand are balanced these days, it means that the required expansion is 5 GW/year just to make sure the market is supplied in the years to come. However, the approved, licensed and under construction power plants add up to 4 GW/year. There is a 1 GW/year deficit.
This scenario stimulated the Federal Government to offer special stimulus for renewable, up to 30 MW projects. The official development bank – BNDES - offers special credit lines for such projects, and mainly the end users who contract energy out of these projects get a 50% discount on the wire fees (related to demand charges).
There is a list of renewable projects that fit in very well here in Brazil. The sugar mils took the lead and are now cogenerating energy as much as they possibly can, by burning excess sugar cane bagasse to produce and sell electricity through the public grid. Elephant grass might be a very interesting option too:
The power plants are the same ones that are already and extensively used to burn other biomasses such as wood chips and sugar cane bagasse;
The elephant grass grows very quickly as compared to other biomasses (2 to 4 harvests per year), it is resistant to drought and disease;
It is neutral in terms of emissions;
It may be built and start operations in less than 2 years.
A 30 MW power plant requires about 5 000 hectare of elephant grass to produce firm energy throughout the year. Since this is a considerable land size, only remote areas are good candidates for such farms. Therefore, special attention is needed when it comes to selecting the location. The closer to the public grid, the better in order to reduce transmission line investments. The good news is that there are states in the country that fit very well these requirements.
Elephant grass power plants may be of special interest to independent power producers and to end users such as industrial, commercial and institutional to "self-produce" energy. The regulations are very well prepared in Brazil to accommodate such projects. There is an established electricity spot market which may be used to balance the power plant's production versus contracted volumes.
The elephant grass power plant makes sense for the investors and for the client.
Energy is being sold at R$ 180/MWh (1 USD = 2.3 R$ as of November 08) in the deregulated energy markets in Brazil.
A potential client for this energy will receive a 50% discount on the wire fees. The following calculations show the final price as seen by a 13 kV industrial energy user. Typically the wire fees are:
On-peak demand: R$ 33/kW
Off-peak demand: R$ 8/kW
Assuming an industrial client with a 24 x 7 operation and a 80% load factor the wire fees as referred in terms of R$/MWh may be calculated:
Total demand cost: R$ 41/kW
Number of hours per month: 720 h
Equivalent demand cost: 41/(720 x 80%) = 0,071 R$/kWh = 71 R$/MWh
The 50% discount represents therefore R$ 35/MWh.
Energy billed by the plant is R$ 180/MWh. The end user will see it as R$ 180/MWh – R$ 35/MWh = R$ 145/MWh.
The most important challenges associated with a project like this are:
Find a competitive 5 000 hectare land close to a public grid. There are states very conveniently located in the central and or southeaster states which might fit this "job description";
Contract the turn key package (thermal power plant) from world class providers. There are very well established companies with decades of tradition in the sugar mill industry;
Develop a long term energy contract with a client (or clients) so as to facilitate access to official loans (especially from the BNDES) which offer special terms and conditions for such projects;
Contract elephant grass from a local producer or develop its production on-site so as not depend on third parties;
Contract back up power before the local utility company. If the power plant for any reason is not able to produce energy the final client will not be affected at all;
Develop a strategy to take advantage of the spot markets. In Brazil where 75% of the electric energy is produced out of hydro power plants, the rainy and dry season have a major influence in the spot prices. Combining the thermal power plant with these seasonal variations will only but increase internal rate of returns!
For information on purchasing reprints of this article, contact Tim Tobeck ttobeck@energycentral.com. Copyright 2010 CyberTech, Inc.
Mr. Herzberg: Elephant grass combustion in a power plant IS NOT emission neutral ! The carbon dioxide generated in the power plant going into the atmosphere has a >10 yr. "half life" which means only 1/2 of the carbon dioxide is reduced by environmental means. However, one of the largest "environmental means" is dissolving in the ocean which changes the pH. The pH of the ocean has already gone slightly acidic which is slowly dissolving the coral. The coral is necessary for fish life. This pH change has been recorded all over our globe via buoy pH meters. In addition, we do not (U.S.) have enough arable land to grow crops and the elephant grass. So, forget elephant grass it is not practical nor environmentally safe. Dr. Warren Reynolds Solar-Hydrogen Energy Consultant
bill payne 12.23.08
Tractors we see presumably use diesel. Both for planting and harvesting.
What is Energy Returned On Energy Invested [EROEI] in BTUs?
What is the HEAT RATE for Elephant Grass electricity?
"The power plants are the same ones that are already and extensively used to burn other biomasses such as wood chips and sugar cane bagasse"
The figure below shows low pressure steam which goes into a condenser to produce hot water.
This looks like a loss of BTUs?
Why isn't the low pressure steam fed directly back into the boiler preserve BTUs?
Energy is an area of INTEREST, not an area of EXPERTISE or ABILITY.
I am hopefully learning.
Don Hirschberg 12.23.08
Bill, you ask good questions. The output and thermal efficiency of a steam turbine goes up with the pressure drop available. The way to get a large ratio of pressure in (steam supply pressure) to turbine exhaust is to condense the exhaust with coolant. The steam rates, i.e. the pounds of steam needed to make a kWh are quite sensitive to this exhaust pressure (vacuum). A power plant that can have an exhaust pressure of 1 inch of mercury, 29/30th of a perfect vacuum, will be more efficient than one attaining 2 inches of Hg absolute pressure. Hence a plant will often be a bit more efficient in winter than in summer as the only thing determining the pressure (vacuum) is the temperature at which the exhaust is condensed. Sure, it can get a lot more complicated, but this is the crux and I think answers your question.
Tom Butler 12.24.08
Bill, the low pressure steam would have to be compressed to the turbine inlet pressure, then heated in the boiler. The power cycle is actually more efficient if you condense the steam, pump the liquid up to turbine inlet pressure, and boil the liquid. It takes a lot less work to pump water than compress steam. In fact, if you compressed the steam to the turbine inlet pressure it would consume more work than the turbine produced by expanding the steam.
Don is correct that higher turbine inlet pressures and lower condenser pressures increase efficiency, but he didn't really address your question about returning steam to the boiler instead of condensing the steam. Don is correct that things can get complicated, and I can't prove what I just said without a lot more explanation, but all steam plants operate pretty much like the one shown in Mr. Herzberg's article.
Rafael Herzberg 12.25.08
Actually the thermal cycle's design depends on the potential customers for low pressure steam. This is the ideal situation - a cogeneration mode.
If there is a customer for low pressure steam then there is no need for the condenser and a higher efficiency is obtained. This would be the ideal arrangement!
If there is no low pressure stteam customer then a low pressure boiler may be used.
The cost as per indicated in the article shows that it is feasible even in the worst case scenario (thermal cycle with no low pressure use - process steam).
Malcolm Rawlingson 12.26.08
Seems a bit nuts to me. Using sugar cane waste makes some sense as the crop is being grown for another purpose. Growing a crop purely for the purpose of burning it in a boiler seems a rather dumb idea.
The author notes a 1GW shortfall in capacity that could be filled by this method. That is roughly 33, 30MW plants. Each requires 5000 hectares "in a remote location". That is a total of 165,000 hecatares for just one GW. That is about 608 square miles of land. To farm that is going to require a lot of diesel driven machinery and diesel driven trucks to haul it from the remote location to the plant.
I don't think it makes economic, environmental or energy sense. A 1 GW nuclear plant will produce less CO2 emissions and takes up only 10 hectares. Seems to me 5 new nuclear plants will solve Brazils energy problems for many years to come and you won't have to chop down what remains of the Amazon rain forests in Brazil to do it.
Malcolm
Malcolm Rawlingson 12.26.08
By comparison 608 square miles is about 5 times the size of Malta in the Mediterranean. Of course 608 sq mi doesn't include the roads and other infrastructure required to get the stuff from the growing areas to the plants.
Hope there is a contingency plan in the event mother nature deals a crop failure.
M
Don Hirschberg 12.26.08
These days we often see power plant efficiencies expressed taking full Btu for Btu credit for using low pressure steam for low temperature heating. Heating, say, nearby buildings could very well be a good design choice, but a Btu so used is not the equivalent of a Btu going over the fence as electricity.
Using this rationale the efficiency of my car goes up when I turn on the heater. If I roll down the windows on a cold day it goes up even more. Maximum efficiency woud be reached when there is no heat being rejected by the radiator.
This kind of efficency improvement requires at least an asterisk.
Malcolm Rawlingson 12.26.08
Thermodynamics dictates that the efficiency of any steam system cannot be greater than about 40%. (Carnot Cycle). The bigger the delta P across the turbine the greater the efficiency. So higher steam inlet pressures and lower condenser pressures all make for efficiency improvements but you'll not get much more than 40% out of it. if you figure out how to do that please patent it and send it to every steam plant manager in the world. You will be an instant millionairre.
A pass through turbine replaces the condenser with some process that uses the decreasing energy content of the steam. The problem there is that these processes increase the pressure at the back end of the turbine so any gains in efficniency from using the steam in a process are lost because the back pressure is higher. The back pressure would be at least atmospheric.
The condensing process while it does indeed throw away all the latent heat of the steam extracts more energy from the steam because it is discharged at near pure vacuum.
Recycling steam as opposed to water back to the boiler would require a gigantic boiler and steam return system. Steam takes up an awful lot more volume than its equivalent weight of water. So big big pipes, big big boilers and low low efficiency....not economic sad to say. M
Don Hirschberg 12.26.08
Malcolm, Thanks. Well designed and well operated Rankine Cycle plants operate at about 34% thermal efficiency, quite near the theoretical max. I dug out my first edition Keenan and Keyes. Saturated steam at 1 mm Hg is 79 F and one pound of this steam occupies 653 cubic feet.
Don Hirschberg 12.27.08
Oops. Make that one inch of Hg, not one mm.
Len Gould 12.29.08
Onto the list of good (and bad) points raised above one should add the problem of earth's known phosphorous resources (that's the P in NPK of all fertilizers) being good for only about another seventy years at PRESENT rates of use. Agreed, by reverting to less concentrated resources we may be able to double the estimated resource, but that's still a very finite amount. How well do the proposed generation plants recover phosphorous and potasium from the flue gases?
Bottom line is, growing ANY plant only converts about 1% of the available solar energy resource to carbohydrates, and we already know how to convert about of 60% of the available solar resource to turbine-quality heat using simple mirror collectors. Agreed, also required are some tanks of sand and gravel for overnight storage, but a simple 3-1 ratio of collector power rating to turbine power rating allows 83% availability in many otherwise usless dry areas.
I just don't get it. Why is everyone so determined to refuse to apply solar thermal which for all the reasons raised above (esp. EROEI of agricultural processes, alternate uses of fertile land, mineral fertilizer availability, etc. etc.) is a far better solution? With a baseload of 50% of energy supply from nuclear, some intelligence in real-time-pricing, and emergency gas-fueled backups, solar thermal with thansmission can easily provide the other 50%. It's a no-brainer.
Don Hirschberg 12.30.08
Len, perhaps it’s because we have had solutions of the energy dilemma de jour so many times over so many years. I am looking at US power generation data through July 2008. It tells me that 99.98% of our power generation ain’t from solar sources (voltaic + thermal). While I am aware that there is a sizeable thermal solar generation plant in Spain I am also aware that a decades (?) old US thermal solar plant in California (?) has been abandoned. Are the Spaniards the only ones exempt from no-brainerism?
Jim Beyer 12.30.08
It would seem to me the first/best use of biomass is for making biofuels as their main attribute (compared with wind/solar) is that they already represent a stored energy. Just burning the stuff does not seem very cost effective, at least in the long run.
Len,
You've brought this point up before. Not sure you've gotten an adequate answer to it. In fact, I'm sure you haven't. Don makes a point that systems in the past have not be particularly effective. For one thing, I think the technology is largely regional; you need lots of sun and lots of space. I think you have quite a bit of mechanical stuff per square meter, don't you? How does that really scale up in terms of cost and maintenance? For example, what would a 500 MW thermal plant look like? I'm not sure the solar thermal storage has been adequately demonstrated to date. I think it probably will work, but the devil is in the details. (My tiny thermal knowledge tells me there's gotta be some efficiency loss in transferring the heat and then in recovering it. How big is that in reality?)
I think the corollary to solar thermal is long distance transmission (1,000+ miles). Well, I don't think this is a no-brainer either. I think this is a big expense and will again recover some gov't approval to fund it. Which means politics, etc., and more cooks to spoil the broth.
While I am not a fan of solar PV, you have to appreciate it's simplicity and modularity that it provides. You can put them right on your own roof without bothering your neighbors that much.
Cooper Schieffelin 12.30.08
This concept would be very challenging due to the following
1. Securing financing from BNDES or a BNDES member bank is a long, bureaucratic process with significant costs for technologies which are proven such as wind and even more so for a novel idea such as using elephant grass to fuel a biomass plant. The BNDES applicaiton and approval process is so inefficient, messy and costly very few developers have enough risk capital and view the returns as high enough to justify such a project
2. How many plants are currently using elephant grass as fuel...to my knowledge none. Elephant grass is different than bagasse.
3. How do you ensure a reliable long term supply of feedstock (elephant grass)? Surely, the farmers are not credit worthy entities willing to contract at fixed prices long term?
In my opinion, this type of project would be difficult to pull off in the US or Canada much less Brazil. I do not have anythign against Brazil but have found the business environment to be somewhat inefficient.
Malcolm Rawlingson 12.31.08
Thanks Don....Bit rusty on my Thermodynamics there....you're right most plants run at about 34% thermal efficiency....and that is about as good as it gets. Although I had read somewhere that fluidized bet coal plants can run up to 39% due to the very high steam inlet temperatures available. But stand to be corrected on that.
All these renewable systems are fine...I am sure they work on a small scale. But the grid is no small scale enterprise and like many power engineers...I heard it all before. Sure you CAN put solar panels on your roof to produce a few kilowatts in the summer time in the day when the Sun is shining...but the grid MUST work 24 hours a day seven days a week. It must work in the depths of winter with feet of snow covering the solar panels. It MUST work when the wind is not available. It MUST work when water levels in dams are low.
What makes it work under these conditions is Big coal plants, Big nuclear plants and Big gas plants. That is why despite all the promises all the money and all the subsidies and dare I say it - all the hype...these sources make up 99% or more of the grid supply and always will.
The bottom line is that in order to provide electricity at all times of the day and night under all weather conditions the fuel source MUST be under human control NOT natural control. If you intend to rely on mother nature for your electrical supply you are in for a big surprise....she may not co-operate.
I am not against using any supply of energy to produce electricity but the oft quoted claim that renewables can power the grid without support from nuclear and coal is complete and utter nonsense and the sooner that is realised the better.
Happy new year to all.
Malcolm
Malcolm Rawlingson 12.31.08
Len, Your concept of solar thermal makes a bit more sense to me... certainly much more than Solar Photovoltaic. It is OK for relatively warm climates - not sure it would be very effective in Canada in winter time but sure it can offset water heating requirements and displace some gas and electrical supplies used for hot water tanks. I had an indoor swimming pool heated this way and it worked well in Summer but was pretty hopeless in the winter time. Also prone to springing leaks as I recall. Had to climb up on the roof many times with sealer to fix the holes. Not sure all the Grandma's of the world will be too pleased about having to do that to keep their hot water tank running.
And of course one needs a roof. The average Condo/apartment/high rise dweller would have a bit of a problem finding one of those.
So like all these ideas it does work but widespread application is really not feasible except in single family homes. And I suspect the payback times are quite long.
Len: Thanks for the link. I have been looking for information on CSP technologies. My first scan of the (more than 300 pgs) document has convinced me that these technologies are much more financially attractive than wind power. Recovering the capital cost per megawatt of capacity remains daunting. However, unlike wind, the energy produced by CSP is during the time period needed (midday) and most valuable. Also, with intermediate heat storage being feasible, that would allow for load following. Finally, I can see that there are likely many ways to improve operations so as to improve values.
