One of the things I have become interested in during my research into alternative power for off-grid applications is methane digesters.
This is probably a technology as old as the original Lister engines. Methane is created naturally as a byproduct of decaying biological material. Although quality and quantity varies depending on feed stock it is sucessfully used as both a cooking, heating and engine fuel. Being naturally renewable it is a environmentally green as using vegetable oil for fuel.
If you google Methane digesters you will find all manner of hits ranging from US goverement funded studies and pilot projects to You tube videos showing sizable generators powered by methane.
If you live off grid and have a flock of chickens for eggs or a couple of animals being raised for food you have the necessary resources to create your own methane fuel. A number of Google hits illustrate home made digesters ranging from a couple of used drums to giant industrial digesters that can feed generators to supply electricity to the utility grid.
Several of the government funded pilot projects involve commercial farms that are now totally energy independent and can resell electrical power to the utility. One mid western farm also collects and bottles methane to fuel all their farm vehicles.
It seems to me this is a very viable option for off-grid CHP.
As a follow up to the above post I would like to mention another old technology that would fit well with Lister engined CHP. If you do not want or need to run a generator 24/7 it is desirable to store excess electrical energy in batteries for powering inverters during the silent times when the generator is not running.
Edison developed a battery using iron and nikel plates commonly referred to as NiFe batteries. The electrolyte is not acid but an alkaline solution of potassium hydride.
Two notable features about NiFe batteries is the fact they do not wear out since the plates are not consumed the way lead acid batteries do. Secomndly when a NiFe battery is depleted you only need to flush out the plates with distilled water then replace the electrolyte, not the plates or the whole battery. Life span in service is unknow since the original Edison cells manufactured 75 yers ago are still running. One company located in Montana is going to be manufacturing NiFe batteries domestically.. I found another company advertising NiFe in australia.
I also found a videon Youtube showing how you can fabricate your own. One down side to NiFe batteries is the fact each cell only develops 1.2 volts instead of 2.0V so you need 10 cells for a 12V battery instead of 6 but in most off grid applications footprint size is not so critical.
Admittedly the battery efficiency is not as great but the discharge characteristics is better since you can discharge deeper with out damage such as you incur with lead acid.
I live in Montana so naturally I would like to visit with them. Where in Montana is the company? How can I contact them?
Thanks .... Ken Gardner
www.zappworks.com/
Guys name is Stephen Ellis.
Quote from: elnav on May 03, 2010, 12:25:11 PM
..... Admittedly the battery efficiency is not as great
And that's the killer. Who wants to install 20% more generating capacity ? Solar panels are pretty pricey
"Who wants to install 20% more generating capacity ? Solar panels are pretty pricey"
REPLY
Who is talking solar panels as a supplement.
Jens lives down in the canadian banana belt but up here we have frost for six months of the year. I do not think I would be able to get by running a CHP genset for only 2 hours per day. Based on how long I would need to run a heat producing motor I would be producing way more electricity than I could store or use. If I was to use free or nearly so free fuel does it matter if the battery is somewhat less efficient? It just means I run the genset a bit longer.
Same thing if I was running a Stirling engine generator from a wood stove heat source. Even a steady 1kW genset running 24/7 would produce more power than I normally use. My uncle in law runs his off grid home on a single outback inverter. But he has now replaced his battery bank twice in 8 years at several thousand $$ each time. The only way he could get more longevity from his battery bank is to spend much more on capacity in order to reduce his DoD kevel.
Mike you raise some interesting points. I can see your point if you are generating power by using solar panel and they barely keep up with demand. However this being a CHP forum I was not thinking in that direction. In climates with very cold winters -30 Below for example a CHP plant would be running fairly steady. Under such conditions even with just 1kW of generation power it would more than cover your power consumption for the day.
OK, so you are using iron batteries, and you've run your genset 20% longer. Once your batteries are charged, you will have to kick on your electric heaters (multi hundred gallons of storage) or else your low electrical load, will unload your genset, and your diesel is no longer seeing much of a load, and it will carbon up. Wood gas or methane may not matter unless you are using spark ignition.
Quote from: elnav on May 03, 2010, 01:49:39 PM
I do not think I would be able to get by running a CHP genset for only 2 hours per day. Based on how long I would need to run a heat producing motor I would be producing way more electricity than I could store or use. If I was to use free or nearly so free fuel does it matter if the battery is somewhat less efficient? It just means I run the genset a bit longer.
I suffer from the same problem except I have very cheap fuel so extra run time is not a huge expense, it just wears out the generator and engine. In our setup we pump hot water through the concrete floor to store engine heat. We have found that it takes a long time to fully heat the floor but more importantly, it returns the heat to the rooms long after the engine is shut down. During the winter with longer nights and colder days, in an attempt to get more value from the fuel burned, we use electric heaters to warm the house while the floor is soaking the heat from the engine. At the same time the batteries are charging to power the inverters for use when the generator is down. With proper management, once the floor is heated, we can get by running the generator a few hours in the afternoon and evening and provide almost all our domestic hot water, house heat, as well as all of our electricity.
Where our rub comes is in the summer months. With passive solar heat the house stays warm, even hot. We shut off all engine heat from the generator to the floor, heating only domestic water. Yes we use less lights during the summer months but still have other electrical demands that require the generator to run. This is when we do not get full value from our fuel. The batteries become charged, the hot water is hot but due to the heavy electrical demands the generator still is required to run and the heat is wasted, the extra available electrical power is not used and the windows on the gen shed are open. This is when I am the most thankful for cheap fuel.
I plan to incorporate solar and wind power into our setup as time and money permit. I am also looking at a much smaller standby generator for backup power in the winter and primary generator power during the summer.
You mentioned the cost of replacing the battery bank. I too am looking at doing that. The cost is kicking our tail right now. Our batteries don't power the inverters very long so we end up runing the generator just so the kids cam watch a movie. Ouch. :o
Ken Gardner
Mike I think you are jumping to conclusions regarding what system I am envisioning . Ken Gardener is using thermal masss to store heat in between genset runs. This is prefectly viable. During periods of low electrical demand it is possible to run a much smaller genset for Battery charging. Minor supplemental heat can be derived from solar heat collector panels for domestic hot water etc.
My uncle in-law normally runs a 25 kW Lister to power his resort but when its only him and the wife, he only runs a small 4-5 kW genset . His brother who is also off-grid runs his entire house on a 3 kW Outback inverter and only needs the genset running when charging batteries or to run the well pump on a 350Ft deep well. He uses a wood burning boiler for heat because wood is free except for the fuel for the chainsaw.
I got to thinking about methane digesters because a couple of ranchers I know has begun raising a few hundred chickens for eggs so the manure is already there as raw feed stock for making methane gas which in turn can be used to generate electrical power.
Last year I started reading about Nickel Iron batteries, and found only China and Europe. As I recall, the big down side was the low efficiency meaning that there were significant losses involved with the charging process. I could mistaken, but I believe I read 30% loss was a norm and higher.
Interesting read on the ZappWorks web site, but are you sure these batteries are actually manufactured here in the US? I would suspect a Chinese import is porbably involve. I would be interested to know more. If I even installed a NiFe battery string, I would certainly drive with trailer to Montana and ship back myself to avoid expenses involved with shipping thousands of pounds. Besides, I love Montana, one the most fantastic places I have even seen I.e. (Glacier National Park, road to sun, etc).
Back to batteries, can anyone provide more information on these batteries or the ZappWorks vendor?
Bruce
Wet lead acid batteries may not be as efficient as we thought. Take a look at this eye opening report from Sandia Labs:
http://photovoltaics.sandia.gov/docs/PDF/batpapsteve.pdf
You must keep batteries frequently full to avoid sulphation and loss of capacity, but for the last 90% of charge, you are looking at 45% in the test above, and THAT WAS NOT POWER, just amps in, amps out at 3 amp charge rate. By the time you factor in 2 volt loss on the 12V battery(15%), and Peukert losses (perhaps 15-20% for a higher rate of charge like on a generator), you could likely be under 30% energy efficiency!!!
Note that at 50% depth of discharge, they got 85% (not counting Peukart and voltage in/out losses). But only because the first portion of that was 95%. If you are prolonging the life of your batteries by reducing depth of discharge...you will pay dearly in energy efficiency.
NIFE may actually have a better overall efficiency for typical off grid operations, since they don't have to be kept full. Some of the NIFE vendors now say 80% using the nicad nickel pocket forming method, but even 60% is great compared to a shallowly cycled wet lead battery. Now if only the prices would come down on NIFE or LIFEPO4. I'd need a boat load of cells for my 120V bank!
BruceM
Bruce:
thanks for the link, it is an important one in that most folks don't consider the true cost of ownership of a battery bank
when they get all caught up in wanting to shallow cycle the set in order to extend their lifespan.
yes you can greatly increase the lifespan of a battery by short cycling them, but generally at a huge cost in fuel consumed to
charge them.
now if that fuel is low cost (waste veggie) or free (solar pv, hydro, wind) maybe that makes sense to short cycle and get a dramatically longer
life out of the batteries.
btw, nice to see you again, you have been missed.
bob g
Quote from: BruceM on May 04, 2010, 11:19:42 PM
Wet lead acid batteries may not be as efficient as we thought. Take a look at this eye opening report from Sandia Labs:
Well, that's a buzz kill :-\
Quote from: Bruce on May 04, 2010, 10:30:44 PM
Last year I started reading about Nickel Iron batteries, and found only China and Europe.
Interesting read on the ZappWorks web site, but are you sure these batteries are actually manufactured here in the US? I would suspect a Chinese import is porbably involve.
REPLY
I contacted Zapp Works and was informed that at the moment they were busy refurbishing some Edison cells (olld U.S. mfg.) in order to do some testing. I had asked for data curves instead of single data point information. The correspondent indicated they expected to have this testing done in six months and be able to post data curves then.
He clearly indicated actual manufacturer would be done domestically. And why not? a metal shear to cut iron and nickel sheet stock into plates plastic cases to hold plates and electrolyte. The formula for mixing electrolyte from powder and water is readily available. the case tops will be removable so you can open up the cells and flus the plates prior to replendishing the electrolyte.
One of the problems with charging lead acid is the need to taper off the charge during the latter stages from 80% to 100% full charge status. This in itself unloads the charging plant. On one recent boat system I coupled a water maker belt driven to the generator motor so it could load up the 10HP Kubota engine during the latter stages of charging. This resulted in fully loading the engine and doing something useful besides tapering off the charge . On land this could also be accomplished by pumping water into a resevoir on an off-grid ranch for example or use the resevoir as pumped storage to run a micro hydro turbine. This is the approach used near Niagara Falls . During low demand from grid, they pump water into a natural resevoir then use that power to help buffer peak demand periods.
If you do not trickle charge lead acid batteries right through to the float stage you end up with some residual sulfation and the accumulation grows each cycle. Eventually this will kill the battery prematurely.
One of the things I recently found out about wind and solar controllers; is the fact the controllers do not usually employ ' smart charging' techniques. Instead these controllers simply shut off when the high voltage set point is reached.
Most solar panel controllers simply disconnect the PV panel from the load and the better Wind generator controllers divert the output to a diversion load which could be a hot water tank but is often just a bank of resistors. Either approach is not optimum.
In recent years AGM has gained popularity due to the fact lead acid batteries impose shipping restrictions.
AGM has been exempt from these restrictions and can even be carried by air craft. Which is why you now see chinese made lead acid batteries delivered overseas for domestic sales. The environmentalist have sucesfully closed down most batter fabrication shops in this continent.
Lithium Ion batteries look good on paper but look at the cost. They have not been around long enough for us to have a long history of use. NiFE made by Edison have been around long enough for us to have some idea of comparative performance relative to lead acid. Their ability to be deep cycled and replendished when the electrolyte is exhausted makes them attractive despite the apparent lower efficiencies. This is something you cannot easily do with lead acid.
I asked but did not receive an answer regarding how Peukerts Co-efficients apply to NiFe instead of Lead acid.
I'm showing my age but my electricity lab had NiFe batteries to drive the motor generators we used to perform experiments with . This constituted a substantial load that was comparable to driving a big inverter like a 3 kW unit. Considering we ran those motors for hour long classes at a time I have the feeling NiFe can in fact handle sustained heavy loads as well or better than lead acid. Why else would they have equipped the school with them instead of lead acid?
If NiFe can in fact stand up as well or better to deep cycling and sustained high discharge current and frequent recharging it means you can support an off grid home with less amp hour capacity relative what it takes with lead acid batteries. And charging a deeply discharged NiFe battery makes for better efficiencies than charging a lesser discharged lead acid battery if the Sandia test results apply on a broad range of brands and types.
Elnav,
That was a very good post! You made some good observations and connected some more of the dots.
I have recently been asked to make a proposal for an off grid residential project in Mexico. Each residence would probably need 5 kilowatts of solar panel and a substantial battery bank. The scale of this project is such it may well be a good candidate to try this NiFe approach.
Unless I can figure a way to convert waste heat into air conditioning it does not look good for a true CHP installation. I am looking to see if the waste heat is sufficient for the desalination system. Otherwise I am looking at a few hundred kilowatts of generator power to power desalination RO pumps plus the sewage treatment system.
Anybody have good suggestions?