alternate fuel for CHP

[elnav]

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.   

[rcavictim]

Elnav,

That was a very good post! You made some good observations and connected some more of the dots.

[elnav]

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?