"basically don't put in a 2000amp hour battery bank that you are taking more than 30% out of on a daily basis if you have only a 50 or 100amp generator,, it will be running all night just to get you ready for the next day."
This does not make sense to me. If you plan to use a genset for your power then using one that roughly matches your needs and running it for long hours will be more efficient than running a huge one for an hour or two each day. and spending a fortune on batteries. Only use batteries at times when the power draw is too low to make engine use worthwhile. If you use 300 amphours per day and you run your generator during the four hours of maximum power usage then it will probably only have to (also) charge the battery at 50 - 70 amps to keep the battery charged for the remaining 20 hours of the day.
Just because you have a large battery capacity, that does not mean that you need a huge generator. Hopefully you will be keeping the battery charged with wind and solar energy anyway but there are always times when these sources fall a bit short of the mark, and then a generator is a good way to save the battery. Again, a small genset that meets your demands and puts a bit into the battery at the same time will keep from over-discharging it until such time as the wind/sun come back to help you get it fully charged.
my 2 pence Hugh Piggott http://www.scoraigwind.co.uk[ Parent ]
the problem with small gensets is they get horrible fuel economy in gr/kwatt/hr
larger ones get better economy "if" they are run at or near full capacity, but not many folks have need for this amount of power on a continous basis, or are willing to schedule around or startup a genset to provide for a load.
batteries therefore become a reality in most cases, and will allow a much more efficient larger genset to run fewer hours to recharge with, at which times those heavy loads that can be scheduled can also be provided for... such as washing clothes, power tools, and a few other heavy loads that can also be scheduled or controlled with a bit of thought, such as refrigeration and domestic water heating.
certainly it would be most desirable from an efficiency standpoint to use the power as generated without another conversion link in the chain.
bottom line my point should have been, don't buy a huge battery bank if you don't have adequate charging means to maintain it properly. it certainly does not make sense to put in a 1000amp/hr battery bank if all you have to maintain it is either a harbor freight solar panel set (~50-60 watts) or an 8 foot windgenerator that is sited in a catagory 1 wind area. if one finds themselves with this setup, he probably ought to start seriously thinking about some serious generator capacity to maintain those batteries while he is working on a taller tower or many more solar panels.
i have spent the last several months, (nearly a year now) running endless tests on a diesel powered trigenerator, S195 changfa (rated 12hp at 2000rpm) driving directly an ST7.5kva generator and, a pair of prestolite 110-555jho alternators and, a sanden rotary refrigeration compressor. the results are generally as follows
1. the engine gets better and better fuel economy based on gr/kwatt/hr consumption the more load that is applied, up to approx 40% over rated output where the head gskts fail. (i mention this to show the engine is not smoke limited, but gskt limited)
a better recommendation might have been to
i just read about too many folks spending a buttload of cash on a large set of batteries without any forethought into how to manage their charging. big batteries come with big responsibilities. the time to find out you are deficient in the charging arena is not after you buy/install/and the rundown the set, then be in a panic trying to figure out how to get them recharged before the sulfation starts to harden and crystallize rendering the set injured or worse damaged or murdered by means of a slow death.
i also read about too many folks having read some article in some magazine or webpage thinking that they can take a scrap lawnmower engine and cob together junkyard 10 dollar alternator, using cheap harware store drive componenents such as aluminum or potmetal pulleys and a fractional hp belt, and have something that will maintain their expensive batteries as they need. the reality is generally not very good to say the least, what happens more times than not is the battery owner now thinks he has the problem solved, but in building and tinkering with the substandard genset he has allowed even more time for the batteries to harden. So by the time he finally finds out the genset he has just put together does not meet the need more unnecessary injury or damage has taken place.
for most folks that need batteries, their batteries represent the largest outlay of cash invested. most can cut costs building their own windgens, gensets, maybe hydro, salvage solarpanels, or buy them used. most folks understand how they can work around most other parts of their systems, but these same folks are stuck with buying batteries. my belief is the focus should be centered on the batteries first after all reasonable conservation has been considered.
the central focus being on the batteries would naturally extend to how and by what means am i going to efficiently charge these babies?
only after i have figured that one out, would i feel comfortable starting to tap their power in any meaningful way.
don't know if this makes sense or not?
bob g[ Parent ]
It is in the long term cheaper to run with the minimum size battery bank possible, as defined by a correctly designed system. Therefore running a back up generator as required, a battery bank that can supply your needs for 7 days of little input is of no use if you can not recharge it from renewable sources in short order and in a controlled manner.
Also my understanding is that most lead acid batteries respond best to a recharge rate of 10% of amp hour rating, correct me if I am wrong but that is my experience.
It is a complicated path to find and install a reliable Re system, not that the theory is hard but the client is!
I don't disagree with your general comments just need to make my point.
allan down underDare to be free![ Parent ]
your points are well taken
having had some time to sleep on this topic, i think i am on solid ground here.
as you stated "Also my understanding is that most lead acid batteries respond best to a recharge rate of 10% of amp hour rating, correct me if I am wrong but that is my experience."
in general i would expect this statement to be true, but a battery that is 50% to approx 80% SOC, can accept upwards of 25% of its amp/hr rating without issues, before you must taper back (when the battery starts gassing) we all know the part about tapering back when things start to boil.
what is not apparent at first glance is overall life costs of the batteries, generally speaking it does little good to charge at 10% even if it extends the life 50% (which is an exageration and likely would never happen in any event) but costs you twice what the batteries first cost were in fuel/repairs/maintenance of the genset (which is a very conservative estimate given fuel prices propensity to sky rocket)
i haven't done the math lately, but off the top of my head one could cut the engine time in half, along with fuel consumption if he has the 25% capacity charge capability over that of having a 10% charge capacity.
otherwise you are absolutely correct, this isn't rocket science, but it is a multivariable arithmetic equation one must work through to get an optimized system.
believe me when i say, i argue these topics not so much to teach what i know, but rather learn what i don't know (which turns out to be much more than i thought going into this thing), so i can rethink my position, go back and do more research and study, and wear out a bunch more pencils
i learn a lot from you guys that have tons of experience in the field, where else is there as much practical experience on this topic but here?
thanks bob g[ Parent ]
Seems everyone is looking at it from the opposite extremes.
Since 80% of us are on grid, when the battery is too low, we move the extension cord from the inverter outlet to the grid outlet. I hope.
I personally do not see a problem if a $10 handyman gen set is used to fill in the occasional RE gap. And I figure that is how most are used. The RE controller will still be doing a majority of the 'fancy control'. And what are the other options? Candles and kerosene? Gas powered AC gen for a reading lamp? Run the battery down to 10.5V and hope the wind or sun is abundant tomorrow?
Maybe the gen is run for a pint or quart of gas 3 times a month for 2.5 months during the poor RE times of the year? Most people are not going to be overly concerned about the fuel efficiency of something using 1 or 2 gallons a year. Certainly the handyman-types will not spend 100X more money for double the fuel efficiency in the hope of saving 2 to 4 quarts of gas a year.
It would be a different story if the $10 gen was the only charging system, or a major percentage of the charging power, but I doubt many are. G-[ Parent ]
you are likely correct in that it all comes down to perspective
if you are ongrid, and have a small battery bank, a small budget homebrew gas power genset likely will suffice in some cases.
now my reality :)
most of the folks i am dealing with are offgrid, no chance of grid connection and wouldn't connect if it were given to them free.
a few of which have 2400amp/hr @48 volts, several of which have a couple thousand amp/hrs at 24 and even more that have over 2000 amp/hrs at 12 volts.
none of which could even recharge their battery banks even one time with 2-4 quarts of gasoline. to suggest otherwise would lead to disappointment in my opinion.
if one were to have a large battery installation and even has a suitable sized windgen in a good wind area, or sufficient solar panel density, or hydro of sufficient size.. its not so much what happens when the time comes when as is said the wind don't blow, sun don't shine, the streem run's dry,, but what happens if there is some other major failure? an unusually high wind, hail, lightening, or other calamity that takes out your AE generating capacity for a protracted length of time?
here is the thing, i am not suggesting what size battery bank one should put in, or that one need spend a small fortune on charging capacity, what i am suggesting is the most efficient use of whatever size battery one decides he must have and what the most efficient means of charging is likely to be.
like i said, i am not hear to be arguementative just relating my reality as i see it, and trying to support my assertions.
btw, if one were to have a large installation of AGM batteries, even higher capacities would be beneficial in reduction of runtime :)
BUT -
I agree that a larger generator is more efficient when heavily loaded, and that batteries can accept heavier charge rates in the lower SOC window. The way I see it, everyone has made very valid points, but they need to be combined into something that makes more sense as a whole... so here goes:
The way I see it, use the genset to augment RE in recovering from deeper discharges after extended periods without renewable input, and maybe somewhat during, to the extent that one is able to forecast such things.
Start it up at say 60% or less SOC. Forget the idea of trying to just use it as the charger. Make it big, load it hard, and run it short; 'emergency' recovery and peak loading only.
Kill the genset above 70%, and let the RE do the lighter, less critical charging that unpredictability won't have such a negative effect on when it's not there (sulfation).
You're killing two birds with one stone here - Your batteries aren't as 'desperate' to get out of the danger zone at that level, and the transition happens at about the same time the genset/batteries will collectively begin to really start losing efficiency as a system anyway.
Load begins to reduce, and the acceptance rate is decreased - so thats a double hit if you just kept running the generator by itself. Since RE is flaky anyway, and comes and goes in spurts, it makes sense to have it as your primary source when the bank level is higher, because you won't 'feel' the efficiency losses as much as with gasoline or diesel.
And yes, run the genset during peak load times to help keep the batteries from dipping in the first place. I'm sure this is a trade off that requires some additional thought, depending on if the collective load is more or less a steady drain, or transient in nature, and for how long, etc etc...
Oh, and before I forget - I prefer perpetual motion to home built nuclear - it is much safer, and has an infinitely more predictable failure rate... >;P~[ Parent ]
