Micro CoGen.

Guys:

here is another option that might be fairly inexpensive to implement

the use of an mppt controller is pretty expensive in my opinion, and i am not sure of the benefit other than
the boost converter picking up the amperage from the st head.

then there are those that are using transformers to drop the st voltage to ~80volts or so, so that after rectification
the voltage does not exceed the mppt upper voltage limit, so

if one is to use a transformer to start with, why not just get on to drop the voltage down to perhaps 20 volts or so open circuit
and feed it to a controlled rectifer, which is triggered by a less costly regulator or a 3 step, via a mosfet driver.

using surplus parts, and maybe some adaptation of existing hardware one ought to have the ability to get full wattage from the st head
into dc charging to the batteries, assuming of course they need and will accept it,, in any case i am sure one could get far above
the 60-80amp limit of the common mppt, most especially working with 12 or 24volt systems, where the amperage would be twice or more
over the ability of an mppt controller.

attached is a concept sketch, and yes i probably have a few flaws included  :)

thoughts?

bob g

What the hell is a "Controlled Bridge Rectifier" and why haven't I heard of it before!!! Am I risking life, limb and pocketbook not knowing all the options!!!

What I meant to say was:
Please sir, may I have more information on this "Controlled Bridge Rectifier" thingy?

Thanks, Geno

i think Bruce can explain the function of a controlled rectifier better than i, but here is a feeble attempt

basically we replace the bottom two diodes in the full wave bridge with something like a triac, or maybe an N-channel
mosfet

the rectifier then cannot rectify unless the controlled elements are triggered on, once they are triggered on they stay on
until one of two things happen, the trigger signal goes away or the sinewave crossover zero volts (then the trigger will either remain
on to keep the rectifier conducting or allow it to stay off.

the regulator/driver is basically a pwm unit that samples the battery voltage and adjusts the pwm which in turn drives the mosfet driver, which
fires the controlled elements of the bridge (which in this case are the lower rectifiers of the bridge)

this is all done at frequencies from a few hundred hz to several thousand hz, perhaps much more depending on various criteria.

it of course is the average on time that adjusts the voltage and keeps it regulated to the voltage you want, or program for.
depending on what kind of regulator you use.

i will defer to Bruce for the finer points of operation.

bob g

So Bob,

Quoteit of course is the average on time that adjusts the voltage and keeps it regulated to the voltage you want, or program for.
depending on what kind of regulator you use.

Kinda of like the a modern version of the vibrating dynamo regulator.

Lloyd

Lloyd:

exactly, that is what the modern regulator does, it replaces the vibrator with an electronic pwm control


more on this subject

there are at least three control handles one could use with this system

one would be as described, the controlled rectifier

another would be a pwm control of the AC going into the primary of the transformer, the pulse width would be modulated based
on a feed back sample of the battery voltage, and

another which might be even simpler would be a regulator that controlled the st field and based the pulse width on the same scheme as
above, being a sample sense line from the battery bank

i suspect each has its pro's and con's, or compromises to deal with

but i am thinking that either of these methods would be less expensive, more robust, and higher output capability than the mppt controllers

i got a heck of a book that might be useful in designing one or all of these systems, i guess i better dig it out and start reading again.

bob g

Bob,

With this setup, would the ST head have to remain at 60HZ or can it be slowed as low as 40 hz ?

veggie

upon some further thought, i am  thinking the third option might be easiest because it would require the lowest power electronics
of all the options, the field current is relatively low compared to the AC output and definitely dramatically lower than the DC product of the
step down transformer.

i can see conceptually a marriage of a microcontroller, a battery temp sensor, a driver circuit for the field, a couple look up tables and some
coding, and you would have a nice 3 step st battery charger.

maybe someone wants to jump on this project?  all i know is my hands are full!

but the more i think about it, the more i am liking the possibilities such a system would provide

its is a very large alternator that can put out 7.5kwatts of DC power into a 48volt, 24volt or a 12 volt battery, this system would make it possible
i think.

the deal is, if this concept shows promise, it would mean me being faced with scrapping a good part of my system for the lack of need, and a
huge leap in simplifying things.

so there you are, more questions, and fewer answers

:)
bob g

veggie:

i think a system could be designed with the capability to operate at 40hz, and still allow for operation at 60hz if there was a need
to do so.

you would certainly want to engineer for 40hz, and then allow for pwm tapering back the duty cycle for 60hz operation.

otherwise you might have to have a 100% duty cycle to operate at 40hz if it worked at all, that is if you design for 60hz
and then try to slow it down.

there is some discussion regarding pulsing current not being good for batteries, and there are those on both sides of that arguement
one side likes pulsing for desulfation (which i don't ascribe to) the other wants nice clean low ripple DC (which seems prudent to me)

and there are tons of 60hz battery chargers out there albeit most of the large ones are 3phase and as such low ripple by nature, so maybe
such a system would benefit by a bank of large caps? or a cap/inductor filter? maybe surplus parts?

i have a rather large bank of dc caps from a huge old inverter that i could probably call into duty, but this is something i have no experience in
and would defer to Bruce and other EE types either on this board or elsewhere.

it just seems like a worthy project, at least to me

:)

bob g

Bob,

I was doing some reading on the subject, and trying to come up to speed, but atlas I scrapped it because, my lack of being an EE. I have some pdfs, on a system you are describing, also I think I posted a link in another topic where they were using, various of amplifier switching, fets, and mosfet, to rectifie without the big vd.

My pop was a stellar EE, he started at Otis, then to Texas Inst, then to Litton, being he had a family he had to go as a salaried employee...my Mom wouldn't let him risk the start ups. We ended up in Seattle when, Boeing moved us here from Texas. That was the first wave of the tech boom, back then he was a slide rule king, our basement was full of scopes and tubes.

Lloyd

it seems I'm ok at understanding just enough to frustrate myself, and those that take my que.

maybe,

We could get halfcrazy to get the boys at mid-nite solar to build such a deal, since an mmpt controller is probable ill suite to create a very effecient gen/controler for bat charging. Especially since the bats are the heart of an efficient off grid.

I think the perfect off grid in a lot of situations is, an array of PV, that can cover some nominal loads while taking the bat through absorption/float, and then let the gen do the bulk. That's how I have my boat set up which is a semi-grid/off grid.

Lloyd

SCR's can certainly be used for power regulation; at one time they were one of the only options for high voltage and power switching, besides BJT transistors.

SCR's or Triacs (which are just two SCR's) are the control element in many AC motor controls and virtually all dimmers.  Since they can't be switched off (they only go off when current goes to zero), they can't do high speed switching, and for DC, would need large inductors and capacitors for filtering.  You do still see SCR's used as solid state relays for AC in a charger or power supply.

So for a DC output,  it is generally much easier and cheaper to just control it via PWM of a MOSFET, as the MPPT units and AC chargers now all do.  In our case, if using a massive inductor for a filter, then SCR's could be used, if desired.  It's outside my design experience to use them for such an application.

The other method- of going back and regulating the ST with feedback from the battery charger DC (voltage of battery, temperature,  and charge current) is a nice one that we've discussed before.  I do have the schematic elements for this (temperature compensation circuit, AVR, current sense, even transfered onto a single schematic page.  But I have no need for it myself and don't have time to work on it just for fun.

There is a lot to be gained by using the MPPT charge controller that is already there for PV regulation (at least in a 48V system) for the AC battery charger.  It already knows how to do temperature compensation and 3 stage charging, and equalization.

The only bugger we hit is that it would be nice to not have to reset the max battery charge current to limit the AC charger current draw.  Reducing the voltage of the transformer ouput via a switch on an AVR (drop the feedback voltage) or a harmonic dropping resistor might be one way to solve the problem.  Alternately a current limiting chopper circuit would do the trick but we are trying to avoid any custom circuit work.

If Midnite solar was to add a secondary battery charge current limit which could be triggered by an input from an AC charger's DC output, then their MPPT unit would solve the problem in a nice way, and regulate for both AC charger and PV, (or wind).  If the unit was capable of tolerating "lumpy" DC (rectified AC with no filtering), that would be even better;  then all it takes is a transformer and rectifier to have a fancy AC charger.  If the unit had a "charge complete" output for shutting down the AC charger, and an "auto gen start" output signal...it could handle a very sophisticated, fully automated setup.

I will try feeding my 250 volt unit with power through a rectifier and give an update. when I get 5 minutes.

two points come to mind here. one is the transformers in the previous thread where rated for 30 amps and he had 80 volts so that would turn into almost 60 amps at 48 volts unless I am missing something here I haven't followed that thread real close as I plan to rectify 120 vac then go through a classic.

Second point I will have to ask our engineer how hard it is to take a signal and trigger a lower output current we do have 2 aux relays on this thing and one can be configured for an input.

Thanks Halfcrazy.  The Midnite solar unit may be the new king of MPPT charge controllers. 
You're right about the buck conversion power efficiency to 48 volts on Marcus's MX80, though it's only 40 amps of charge at a bulk termination voltage of 60V (15V per 12V battery).  An aux input to the Midnight which enables a max wattage input (from an AC charger) would allow the controller to get the most out of the AC charger during bulk charging.  But any implementation of an aux current limit would put it way ahead of the other products.  The MX60/80 has no inputs at all besides the temperature probe.

Llyod-  Perhaps this was a typo; "since an mmpt controller is probable ill suite to create a very effecient gen/controler for bat charging. Especially since the bats are the heart of an efficient off grid."  If you meant that MPPT controllers are ill suited, then you're ill informed.

You should read the specifications and manual on the Flexmax MX80 and the upcoming Midnite product (or Tristar MPPT); they do a very capable job of battery management.  There is no reason they can't be used as the battery management end of an AC charger.  They make a fixed voltage, non-temperature compensated charger look like the barbaric piece of battery abusing  crap that it is. 

In many locations and seasons, PV systems do the entire charging cycle without a problem.  It's only you guys in coastal Washington who don't see the sun very often that think it's only for absorption stage charging. 

Hi Bruce,

It's true that PV can do the bulk in a lot of areas...but it takes a fairly large amount of panels, especially in areas that have sun challenges. The NW is a huge off grid market with all of the vacation cabins on islands, and back woods not close to the grid.

The set up for most is to; PV, gen, conservation, and using small bat banks (400-720amphr). The need for well  pumps, and some other 220 v loads...really hits the banks, so a gen is the answer, just bc of the shear costs of a PV sys that could do it all, with our sun challenges.

I guess I am missing something about the mmpt's. If using as a gen controller, what's the most amps it can bulk charge at?

On a 12 volt sys, with a dc gen and a 250 amp alt, you can get close to 220 amps during bulk, make the hot water, run it twice a day, once in the morning, and maybe 1 in the eve. for 1hr each run and burn a little less than 2 litters of fuel. Let the small PV run absorbtion and float. After amortization of gen, and computing fuel costs, I think that's a pretty efficient sys. Bruce, would an mmpt controller do this on an st? If so that would be a great little system.

Thanks for your help Bruce.

Lloyd

i just finished an article on this topic from sandia labs a few weeks ago,and will find it again
and link to it when i can.

the concern of that article was solar panel battery systems often  lose capacity of the batteries
because there is not enough sun hours per day in most area's , most of the year, unless
the system is very well engineered, which acccording to the article most are not.

folks like to live an ongrid lifestyle offgrid and to do so requires a mountain of batteries,
just like horse,  big horse need lots of oats

so you find you have to have a huge panel investment, and then find you need more than one controller
to handle the amount of power, and it gets very expensive real fast, unless of course you engineer well

get it wrong and it gets out of hand in a hurry.

doing bulk charge with a genset makes sense to me, as it is the most efficient part of the charging cycle
and if you are recovering heat for domestic uses, then the overall efficiency can be quite good in my opinion.

the problem as i see it is it is a moving target and no one answer will fit every application

where we need 4, obviously 2+2 will get you there, or 3+1, or 1+1+2, or 1+1+1+1 will get you there as well
and none are the same as 2+2 or each other for that matter.

that makes recommendations very problematic, especially if the user refuses to educate himself beforehand.

personally i think every one of the options discussed on the forum is viable, under certain conditions, and there
is probably one of the options that fits better than all other for each individual application.

it is nice to have a forum populated with folks willing to try and test each option and sort out the pro's and con's
maybe what won't work for one guy, might be the perfect solution for another?

bob g

Hi Bruce,

QuoteThey make a fixed voltage, non-temperature compensated charger look like the barbaric piece of battery abusing  crap that it is.

I haven't used on of these, unless it was in the shop recovering a bat that had been abused. Even the best multi stage ac charger running from the ac plug of a generator is very poor, as compared to an efficient dc gen. The need to size the ac gen to the largest load, makes them run most of the time in a very inefficient manner.

Thanks for your help Bruce.

Lloyd

Llyod,  The MPPT charge regulator as AC charger back end approach is better suited to a 48V system, as the 80 amp units represent a 3500 watt+ charging capacity, which is a good match for a genset. As a single unit they don't have enough current capacity for a 12V system, though they can be put in parallel to do so.  (Hang onto your wallet.)

Few people recommend 12V systems for new off grid systems, these days.  200 amps is not an easy amount current to work with, and real world losses in these systems are problematic.

In your case, with a bunch of 12V marine equipment, I can understand why you'd want to stick with 12V, and your direct DC charging system will make that work well.  There is at least one company making a custom alternator regulator that does temperature compensated, 3 stage charging.




I

Hi Bruce,

Thanks for your input....I appreciate you knowledge and incite(I get a little crusty too), along with your willingness give it so freely.

Don't take this as being argumentative, and as Bob said everyone has different needs, with different answers.

While I like many of the attributes of the 48 v sys.

12v has some complementing reason also. Take 6 t-240 6v Trojans series/parallel and you get a fairly resilient 720 amphr bank(for under $600.00)., I've yet to find a lower cost per kwh then this set up.

With the same Trojans, 4 will get you a 24v 440 amphr bank @ under $400.00 dollars, but no resiliency, so you have to ad 4 more(another $400.00, bc if you loose one bat in the 4 group the whole bank is down.

Getting into a resilient 48v sys changes all the parameters, and the cost skyrocket bc now your looking at a whole different bat, and those mothers are big money.

Other factors in favor is the sheer number of 12 v based users ie motors, pumps lights, chargers and any other thing that you need that runs on dc voltage. It's been my experience that once you leave the 12v realm, you have fewer options, at a much higher price point.

There are other issues with 12v, but there are at least 6 that I know of multi-stage charge controllers, w/temp, and true bat sense.  I know that a 24v ho alt is almost 2/3 more then a 12v alt. I have no idea the premium for a 48 volt alt, this is where the mmpt controllers appear to step in.

Other things like high current, and resultant voltage drop. One way of dealing with the voltage drop, is using a distributed panel system, while it may add some complications for the electrically challenged, it's not a big issue for those skilled in dc systems.

Not to mention that a smaller PV can be used...

I'm just talking out loud, so don't get frustrated with me.

Lloyd

Now this is a resilient Bat Bank, if you can afford it.
(http://www.windsun.com/pictures/Mexico-01.jpg)

Quote from: BruceM on February 17, 2010, 02:54:06 PM
Llyod, Your case for 12V for an off grid system of respectable size doesn't hold water, technically.  There are lots of different AH wet batteries.  A failed battery in either a parallel or series string is equally problematic.  Other arguments of yours are equally erroneous:  smaller PV?  Busses solving distance/loss problems?  AH comparisons for battery banks of different voltages?  Must have a 12V system for a few items that need 12v?  Egads, Llyod.

It's great that you like 12V, know how to work with it and can get by with it for your boat, with some custom engineering work.   But there really are good technical reasons why 48V is being used in most new off grid systems of moderate or larger size.  In the future I think you'll see even higher voltage systems, as you do now in larger facility UPS systems, and in electric vehicles.

12V is still king for small setups, for obvious cost reasons.

Hi Bruce,

While I agree with you on many levels...just not all.

Unlimited dollars and we can do anything...and I agree that the future maybe higher buss voltages.

Now if I have a 6 string 12 v group and I loose a bat, I disconnect that pair, and I still have a 440 amphr bank to limp along on, and since we cant just replace 1 bat in the string bc age, and condition, I have to replace the whole bank.

Now if I have a 4 string 24v and loose one bat. I'm out of business until I replace the bank. Sure we can go to 12 volt bats, but you have be willing to pay about twice as much for the same amphr bat that will preform the same, and your amortized kwh cost will be greater.

I haven't set down to do an amortization of a resilient 48 v bank, but I know going in that the inverters and bats, are going to be more per kwh after amortization, and my upfront cost will be much greater. That being said, I think there will be a day, once production cost are driven down, but we are still early in the manufacture cycle.

At this time in the manufacture cycle, the cheapest even in figuring associated losses is 12 v it's cheaper per kwh, until you start hitting what is larger then 80% of the installed systems.

Lloyd


This may be one of the best info sites on batteries. I will forgo a WP and just add this to the WP section on bats.
http://www.windsun.com/Batteries/Battery_FAQ.htm (http://www.windsun.com/Batteries/Battery_FAQ.htm)

Llyod, I disagree with most of your technical assessment, but I'm glad you like 12V and it works for you.
I wouldn't use it or recommend it for an off grid power system myself unless it was a very small system. In this regard I am in agreement with most engineers and system designers.

Clearly, 12V is king for small systems, for cost reasons. 

Bank costs.

(http://ep.yimg.com/ca/I/wind-sun_2094_32399334)
2-Volt 1766 Amp-Hour Deep Cycle
Surrette 2KS-33PS Deep Cycle Battery
Item# 2KS-33PS
Regular (MSRP) price: $950.00
Our Discounted Price: $780.00
Availability: Usually ships in 5-7 business days.

12v = $4,680.00
24v = $9,360.00
48v = $18,720.00

(http://ep.yimg.com/ca/I/wind-sun_2094_45555961)
Concorde PVX-2580L (8D) Deep Cycle AGM Battery 12 Volt, 255 AH
Sun Xtender PVX-2580L AGM Sealed Battery
Item# PVX-2580L
Regular (MSRP) price: $918.43
Our Discounted Price: $585.00, 2 for $1,164.00, 4 for $2,320.00

12v = $  585.00
24v = $1,164.00
48v = $2,320.00

(http://ep.yimg.com/ca/I/wind-sun_2094_32913238)
Crown Battery, 1090 AH @ 20 hr rate, 12 volt, 850 lbs
rown Industrial Battery 6-125-15
Item# 6-125-15
Regular (MSRP) price: $4,452.00
Our Discounted Price: $3,172.00

12v = $ 3,172.00
24v = $ 6,344.00
48v = $12,688.00

things to consider every time you increase the voltage you drop the amp load by almost half that's good, you increase the real estate required the house the bank, and the cost by dbl...that's some thing to consider, As you increase the initial cost you have to increase the fail safes to protect your investment...that's something to consider.

A 48 volt array will take more panels to match the 48v bats, with all of the associated controllers. This increases upfront investment and maintenance costs.

Something that most don't amortize into the deal is loss prevention...1 catastrophic event could wipe out a large investment, and it's likely your home owners policy isn't going to cover that loss. That is unless you purchase a rider upfront, which is another increase in up voltage costs.

Last but not least is the labor cost...up voltage also increases the labor...I'll bet by square.

Bruce...a systems efficiency, have to consider all associated issues, not just those that pertain to electrical losses.

Lloyd

http://www.thesolarguide.com/solar-power-uses/cost-faq.aspx (http://www.thesolarguide.com/solar-power-uses/cost-faq.aspx)

Solar Cost FAQ

What will solar energy cost me:

   if I want to use (a) solar panel(s) to help power my home?

   Solar electricity costs about $10 to $12 a watt installed, though you may be eligible for state incentives. Check your utility bill to see your monthly usage. A robust solar electric system will cost about $20,000. You can spend as much money, to receive as much solar electricity, as you feel comfortable with.

http://solarpanelspower.net/solar-panels/solar-panel-insurance (http://solarpanelspower.net/solar-panels/solar-panel-insurance)
Does Your Insurance Cover Solar Panels?
What does your homeowner's insurance company think about solar panels?  Do you know?  You may be surprised to learn that your insurance company views renewable energy installations as a potential additional liability, rather than an integral part of your house for which coverage is provided in the event of a loss.  Do you need special solar panel insurance?

Insurance companies have cancelled insurance because of solar panel installations when they view them as "too risky."  95% of the time, these assessments are based on misinformation – or a complete lack of knowledge – regarding solar panels.  I have read about insurance companies that decided solar panels were a fire hazard due to the potential of overheating, and other companies that thought there would be water leaking around the installation.

Still, purchasing solar panel insurance can run you up to an additional $1000 a month!  You'll never save that much in electric bills.


NOW HERE IS A TOOL..everyone should visit http://ideas.4brad.com/solar-economics-spreadsheet (http://ideas.4brad.com/solar-economics-spreadsheet)

here is my take

a 12volt system can work, and work well "if" you can locate generation and storage very close together.

the big limitation is the availability of high output high quality inverters to make AC from your 12vdc

stepping up to 24volts  helps some, but you don't really get your best bang for the buck till you go to 48volts, but

there is tons of appliances that run on 12, lots on 24, and very few that run on 48volts, which is kinda nuts in my books

even jacobs figured that he would have to produce appliances to run off his 32volt wind gens, why the 48volt manufactures
haven't taken a lesson from history is beyond me, i guess they just figure we will just convert to AC and live a happy life?

the assessment of battery costs, is not really an apples to apples comparison, because the figures don't illustrate
that while the 48volt banks cost 4x the 12volt banks they also have 4x the kwatt/hr capacity.

where i would go with 12volts would be "if" i had a ready source of inverters, and where i could install everything
batteries, generators, panels etc on and in a storage container, and do all the power conversion in a close linked system
and then transfer the 120/240 to the house in a conventional manner.

one thing i now know for sure, is if i were concerned about efficiency of the generation in BSFC, i would go with at least the 24volt
system as outlined in my white paper, and likely would recommend going to 48volts because i am fairly sure there will be another increase
in efficiency of the alternator.

if i were a single guy, i would buy two 20ft shipping containers, set them about 20ft apart, live in one, generate my power in the other
and have room for all the mechanicals and a small shop area to maintain them.  a completely autonomous house. with a greenhouse between
along with a small courtyard area, for a couple rabbit hutches, and put a view deck patio up topside.

then a 12volt system would probably suffice quite nicely.

bob g

Professor,

I am not in any camp as a 1 voltage fits all, especially in the state of manufacture cycle we're in...availability of devices is directly proportional to cost and over all efficiency.

I used to be one of those guys whom had to have the latest greatest motherboards, and associated hardware...then I realized I was one of the fools with money(not receiving a return on investment), investing in research and development that funded their(manufactures) bottom line, as profit to the share holders and more funds for the engineers(to tinker with)...this all kept their bean counters happy...and ultimately technology advanced.

But now that I have started to consider amortization into my everyday purchases...I might look like the slow adopter, but....I am getting more bang for my buck...which is good for my bottom line.

So while 48 volt looks to be the most efficient from an engineer's stand point...stop and do a bean counter stand point....based on the current price of the system over all., and net ROI.

I think in another post you hit the nail on the head when you suggested we need to think differently,  conservation, and load timing, added with system design.

Conservation is the biggest ROI. If we can scale back the sys requirements bc of new and better equipment, more efficient design, load management, Conservation is the guy driving the truck, and that guy will save us money at every turn if he's not a lead foot.

Lloyd

Llyod, you don't seem to realize you can reduce the AH of batteries of a 48V bank by 3/4 and still have the same power storage capacity as a 12V bank. You  pay about the same yearly costs for the same power storage capacity of bank, regardless of voltage or design service life of batteries.  That's consistent with conventional wisdom on wet lead acid batteries and the Windsun battery info article you posted, your statements are not.

First you argue for redundant parallel strings, then you trot out prices for monster 2V cells, which certainly wouldn't be used in parallel.  Or high dollar AGM batteries???

I don't agree with any of your assertions, including the nonsense on PV insurance making PV power worthless ($1000 per month for home power PV).  Your signal to noise ratio is below my tolerance limit, I won't respond further.

Bob,
You beat me to posting the above.  

I agree, for small systems, as I said before, the equipment cost advantage of 12V is there. There is no real advantage in battery costs, as Lloyd has tried to claim.

Most of my off grid friends don't use DC appliances;  they use new high efficiency AC units for a fraction of the cost, that perform in the real world (not marketing brochures) nearly as well.  They would rather put that extra $1500 towards more PV or wind power, or better batteries.

12VDC is very handy to have around.  I have a separate small, low current 12V system for house and shop use in my own off grid setup. It provides the power for the 10 watt house heating circ pump, my fiber linked cell phone receiver, and some other very low power electronics.

Getting a great deal on some surplus equipment would certainly influence  system voltage choice.  If I could get along with inverters, and had some bargain gear and a free set of monster Surrette or HUP 2V cells, I wouldn't mind that 12V system one bit.  Alas, inverters and I don't mix.

Bruce , don't get frustrated my noise will result in a more profitable signal.

QuoteLlyod, you don't seem to realize you can reduce the AH of batteries of a 48V bank by 3/4 and still have the same power storage capacity as a 12V bank. You  pay about the same yearly costs for the same power storage capacity of bank, regardless of voltage or design service life of batteries.  That's consistent with conventional wisdom on wet lead acid batteries and the Windsun battery info article you posted, your statements are not.

First you argue for redundant parallel strings, then you trot out prices for monster 2V cells, which certainly wouldn't be used in parallel.  Or high dollar AGM batteries???

As I posted, redundancy is important in an off grid, and there's know way to provide redundancy without additional parallel bats over nominal voltage.

The bats I posted are in a range from the biggest money the the mid sized money, it doesn't matter which tier(price point) you decide to buy bats in.

Let's just take  a known, well performing bat that is in the low dollar tier...the trojans t240's

12v  6 X 6v= 3 parallel 12 volt string, with an AH of 720 x (6 x 89.00)= $534.00 that's  0.74 per AH
24v  4 X 6v= 1 series   24 volt string, with an AH of 240 x (4 x 89.00)= $356.00 that's  1.48 per AH
48v  8 X 6v= 1 series   48 volt string, with an AH of 240 x (8 x 89.00)= $712.00 that's  2.96 per AH

Now to get any redundancy in the the 24 or 48 volt bank you have to dbl the cost of each choice. From here it doesn't matter what voltage bank we choose, all we need do is break down to actual wattage used(charge-discharge) to calculate, the true costs of the bat bank on kwh.

Just because the higher voltage has more available, doesn't mean we  are getting a value from that investment...much like the situation where the stand by ac gen is sized to the to the highest load it has to run as opposed to being able to sacle up and down to the actual load.

My whole point is to be true, we have to calculate over all efficiency...and that is in no uncertain terms, the total cost of the system as it relates to our actual energy usage.

QuoteI don't agree with any of your assertions, including the nonsense on PV insurance making PV power worthless ($1000 per month for home power PV).  Your signal to noise ratio is below my tolerance limit, I won't respond further.

This is not my assertions, if you read the article you'll see that it was written by an attorney, on her blog whom is very keen on solar.

So, Bruce...the point of this forum and the resultant discussions is an attempt for us all to exchange our knowledge, and drill down to what is the best for each of our own situations.....one size doesn't fit all....and I am not proposing that it does.

My point is consider all the cause and effect.

Lloyd

Quote from: Lloyd on February 17, 2010, 04:35:33 PM
Bank costs.


things to consider every time you increase the voltage you drop the amp load by almost half that's good, you increase the real estate required the house the bank, and the cost by dbl...that's some thing to consider, As you increase the initial cost you have to increase the fail safes to protect your investment...that's something to consider.

yes Bruce...I do understand

QuoteLlyod, you don't seem to realize you can reduce the AH of batteries of a 48V bank by 3/4 and still have the same power storage capacity as a 12V bank. You  pay about the same yearly costs for the same power storage capacity of bank, regardless of voltage or design service life of batteries.  That's consistent with conventional wisdom on wet lead acid batteries and the Windsun battery info article you posted, your statements are not.

Lloyd

Lloyd,

I've missed the forum for the past day, so there was a lot to read.

Please remember, in a battery bank you can't go by amp-hours unless you're comparing the same voltage battery banks.   Like Bob says, you're comparing apples to oranges.   Amp-hours works great when you're at Walmart buying a battery for your truck:  they're all 12 V batteries.

You have to use kwh when comparing battery banks of different voltages.   Using the values in your last post as an example:

12 v bank:   6 batteries = 8.64 kwh     = $61.80 per kwh
24 v bank:   4 batteries = 5.76 kwh     = $61.80 per kwh
48 v bank:   8 batteries = 11.52 kwh    = $61.80 per kwh

See, cost per kwh is the same, unless you are getting a discount by buying batteries in volume.    The total potential stored energy in the banks is proportional to the number of batteries in the bank, not the voltage configuration of the bank.

Marcus boiled it down to the core issue, in my opinion

also

a few years back i set out and got the best prices i could find for all the popular flooded lead acid batteries

when i took into account all the factors, cost, amp/hrs, cycle life, etc it was amazing that there was almost no
difference per kwatt/hr between the highest quality and the lowest

you pay more for a high quality battery and get my cycles, so it all comes out in the wash

it was as if there was a conspiracy or something

on topic

there are other factors too

taking the same battery that make up a 12volt bank, and using it for 48 provides more kwatt/hrs or it will provide for shallower discharges
which lead to longer lifespan in more cycles, here the relationship is not linear and the advantage in lifespan tips to the use of 48volts, "if"

you have a means of efficiently charging at the upper end of the charge cycle where battery efficiency is poorest, so there is no advantage
with 48 if you are burning fuel to do the charging, but is an advantage for solar where we don't pay for sunlight (at least not yet)

for me:

system voltage was determined by the ability to get the mx series exeltech inverter system, which was 48vdc
had the inverters been 24 or even 12volts that would have been my determining factor as the low cost of surplus
inverters was more than enough to offset the cost of a very large battery bank of the best quality batteries made.

once the voltage was set, then came the journey to determine the most efficient method of charging them, i got enough
solar to do the job, so i  was left to determine which voltage of generation provided the most kwatt/hr per gram of fuel
consumed.

this is where 12volts gets kicked to the curb in my opinion, there really isn't much available that will provide 250amps charging
at 14.4 volts dc, with efficiency over about 52-54% (ad copy notwithstanding), 24volt alternators are about the same, but
after much research and testing i found that i can reach close to 80% with my system at 28.8vdc that pretty put the last nail
in the 12volt coffin, and if as i suspect, my 48volt project x alternator clears the 80% efficiency ceiling there is no way i would
use or recommend a 12volt system. 

except as outlined for very specific applications like Lloyd's boat, or a cabin?

its only after taking all the factors into consideration that for me a 48 volt dc system is the only way to go

conclusion:

if you have to burn fuel to charge your battery bank, 48volt  system will pay for the battery bank in fuel savings
over a 12volt system of similar kwatt/hr capacity. (or at least it should if the system is setup right)

bob g

Firsts things first.

I am not advocating one voltage over another.

Second, ohms law says it doesn't matter...watts or amps it is a metric only, dependent on voltage.

Amp hr or kwh(just a different way to measure) its' the same if you ascribe to ohms law..to which I do.

Bat banks are marked in amp hrs, not watt hrs.

Bat banks are storage only, not watts or amps consumed, or regenerated.



Now that we got that settled...my only point is the initial investment, over amortization.

How much does a 12v bank for storage cost?

How much does a 24v bank for storage cost?

How much does a 48v bank for storage cost?

What is the 24 hr watt/amp load? no matter what bank voltage you choose.

How much fuel does it cost to replenish that 24 hr watt/amp hr load?


Fuel is the cost of equipment and amortization, no matter the voltage.

Fuel equals, a diesel/gas/propane gen set dc/ac, acquisition costs, repair and maintenance, plus the actual fuel burned replenishing the watts/amp hrs burned.

Fuel can be a solar PV system, acquisition costs, repair and maintenance.

All associated systems require loss prevention costs. Insurance, security.....

All of the above are independent of the nominal voltage of the system of your choice.



Now what are the savings of one voltage over the other .

Efficiency in regenerative time?

Increased cost of the lower voltage, due to VD..which equates to bigger conductors, and associated?



Now just as an example we run a 12volt(i used this voltage bc I'm crusty) a little perky\cat/volvo, spinning a 250 amp alt..regenerating 220 amps/2640watts at 14volts back into a bank in one hour, on 1 liter of diesel $2.45 per gal= 0.264172051 x 2.45=$0.65 cents.

220amps over 24 hrs = 9.16 amps burned every hr non stop for 24 hrs. Now we have to amortize the equipment? Is it  a dc or ac gen, does it include solar, how big should the bat bank be.

How many amps/watts are you burning over 24 hours?
How many are burning more then 220 amps in 24 hrs? remember ohms law do the math and convert to 12 volts so that we may compare apples to apples.

How much do our system really costs.

Remember omhs law..it doesn't matter what the nominal voltage of the system is, we burned the same in a 24 hr period, almost, bc there may be some efficiency at the higher voltage...but the metric is going to be small on a 24 hr period.

In the end a bat bank will increase the system costs the higher you go in voltage....if you use a well tested bat manufacture...the higher voltage may increase the storage value...but if that exceeds the required storage between regeneration...that's a loss not a gain.

Since there is no redundancy in a single series string, we have to add redundancy, no matter the nominal voltage, what is the cost of this redundancy?


Lloyd

Quote from: mbryner on February 17, 2010, 10:08:52 PM
Lloyd,

I've missed the forum for the past day, so there was a lot to read.

Please remember, in a battery bank you can't go by amp-hours unless you're comparing the same voltage battery banks.   Like Bob says, you're comparing apples to oranges.   Amp-hours works great when you're at Walmart buying a battery for your truck:  they're all 12 V batteries.

You have to use kwh when comparing battery banks of different voltages.   Using the values in your last post as an example:

12 v bank:   6 batteries = 8.64 kwh     = $61.80 per kwh
24 v bank:   4 batteries = 5.76 kwh     = $61.80 per kwh
48 v bank:   8 batteries = 11.52 kwh    = $61.80 per kwh

See, cost per kwh is the same, unless you are getting a discount by buying batteries in volume.    The total potential stored energy in the banks is proportional to the number of batteries in the bank, not the voltage configuration of the bank.

Hi Marcus,

I think I was pretty clear about the kwh relation to a bat bank.

Quote from: Lloyd on February 17, 2010, 09:03:31 PM
Bruce , don't get frustrated my noise will result in a more profitable signal.



Now to get any redundancy in the the 24 or 48 volt bank you have to dbl the cost of each choice. From here it doesn't matter what voltage bank we choose, all we need do is break down to actual wattage used(charge-discharge) to calculate, the true costs of the bat bank on kwh.

Just because the higher voltage has more available, doesn't mean we  are getting a value from that investment...much like the situation where the stand by ac gen is sized to the to the highest load it has to run as opposed to being able to sacle up and down to the actual load.

My whole point is to be true, we have to calculate over all efficiency...and that is in no uncertain terms, the total cost of the system as it relates to our actual energy usage.

Marcus,

maybe you can tell me how much a 48 v bat bank costs?

Lloyd

I can only tell you about my 48 volt system (soon to be doubled in size):

8 x L-16 Deka batteries in series @ $300 each = $2400
370 Ah x 48 V = 17,760 wh or 17.8 kwh 
$134.83 / kwh

Of course these could be arranged in series/parallel at 12 V:

2 x 6 V in series = 12 V
Then 4 of those parallel.   Still 8 batteries.  Still same cost.
370 ah at 12 V x 4 parallel groups = 4440 wh x 4 = 17,760 watt-hr
Hmm, it's exactly the same total energy as in the 48 volt bank.

No arguing Ohms law with me.   I know what it says.   Done here.

Quote8 x L-16 Deka batteries in series @ $300 each = $2400
370 Ah x 48 V = 17,760 wh or 17.8 kwh
$134.83 / kwh

Marcus,

How many kwh's are you burning per 24 hr period?

What is your generator run time for regeneration?

Why are you adding the duplicate bank?

I know you have a big PV planned, but lets leave that out for now.

Lloyd

Lloyd:

correct me if i am wrong, i have been wrong before, just ask my ex!

:)

amp/hrs vs kwatt/hr are two different terms all together

the former has no factor of voltage while the latter considers the voltage of a bank, that is what makes it an apples to apples comparison
irregardless of ohms law.


any time you try to calculate the true cost of a battery bank, you will end up in doing so in kwatt/hrs delivered to the load over the lifespan
of the battery, amp/hrs are not part of that equation at that level.

as an example lets work with 12volts first

i could buy a single 100amp/hr battery that is 12volts,  for say 100dollars  it can deliver 1.2kwatt/hrs over 20 hours
it is good for maybe half that if we only ask it to do 50% depth of discharge, so each cycle it can deliver us .6kwatt hours
at that rate it can do 1000cycles so
the battery over its life will deliver .6kwatt hours x 1000 cycles = 600 kwatt/hrs for the 100 dollar investment, or 16.7 cents per kwatt/hr
delivered to the load over its useful life.

now lets look at 48volts,  one of two ways, the first using the same battery as in the previous 12v example

we would need 4 such batteries, 4  twelve volt 100amp/hr batteries= a 48volt bank at 100amp/hrs, but that equals 4.8kwatt/hrs
48volts x 100amp/hrs = 4.8kwatt hours, now if we use this bank to 50% it too will last 1000 cycles and deliver 2.4kwatt/hrs each cycle
so 2.4 kwatt/hr x 1000 cycles = 2400kwatt/hour over its lifespan for our 400 dollar investment
2400 kwatt/hrs / 400 dollars = 16.7 cents per kwatt/hr... which is the same as  the 12volt example

so where is the rub? its a wash, except for two things

charging efficiency and do we need the added kwatt/hrs delivered each cycle

lets make things really apples to apples

if we engineer a system that only needs .6kwatt/hrs per day, then the 48volt battery bank has the capability of delivering 4x the daily requirement
so rather than increase the loading we stay with .6kwatt/hrs, and instead of using 50% of the battery capacity as we would in the 12volt example
we now use 12.5% of its capacity!

remember the non linearity of capacity as it relates to lifespan?

at a draw of 12.5% per day the battery will now last 3000 cycles, which is so

if the 12volt bank cost us 16.7 cents per kwatt/hr based on a 1000 cycle lifespan
and the 48 volt bank also cost us 16.7 per kwatt/hr based on a 1000 cycle lifespan, then
the increase lifespan in cycles reduces our cost per kwatt hour delivered to maybe one third
that of the 12volt system

now lets compare charging efficiencies, using an engine driven generator

in order to recharge the 12volt 50% depth of discharge bank will require about 25amps for our example
in charging capacity 25 amps x 14.4 volts = 360 watts / typical 12volt alternator efficiency of 54%= 667watts mechanical power

to recharge the 48volt bank at 12.5% depth of discharge will require about 6.25amps at 57.6volts or
6.25x 57.6 = 360 watts (same as above, but) 360 watts / typical 48volt alternator efficiency of 80% = 450 watts mechanical power

so the 12 volt system requires 667 watts mechanical and the 48 volt system requires 450 watts

667/450 = 1.48 or  in other words the 12volt systems fuel requirements are 48% higher than that required by teh 48volt bank.

to recap
the nonlinear relationship between depth of discharge and lifespan in cycles plus the decrease in fuel consumption to recharge
makes the use of 48 volts very attractive. the savings in fuel alone might well pay for the battery bank all by itself, and in any
event surely would pay the premium or added cost of a 48volt bank over a 12volt bank.

note: my numbers above are fictional, but non skewed, they are meant for illustrative purposes only. while some of the numbers
might well be higher or lower, the relationships will remain the same and the bottom line advantage will remain in favor of the 48volt
bank.

where am i wrong in this assessment?

bob g

Hi Bob,

Here it is:

   
Ohm's Law
   Ohm's Law defines the relationships between (P) power, (E) voltage, (I) current, and (R) resistance. One ohm is the resistance value through which one volt will maintain a current of one ampere.

( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from negative to positive on the surface of a conductor. Current is measured in (A) amperes or amps.

( E ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts.

( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms.

( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts.[/b]
Now with this equation, I can determine the watts if I know the volt and amps, or I can determine the amps if I know the watts and voltage, I can even determine the voltage if I know the watts and amps. Now that I can get an answer for watts I can get a kwh.


I fear this is degrading, and going nowhere fast.

My point all along is something you know very well.......make all you decisions based on test results.

I am just using economics as my test bed.

Bruce, and you agree that 12v makes a good small system voltage, I also agree.

We all agree that 48 volts is the best voltage in large systems. Maybe even higher voltages...I think that won't happen until we get better, and more affordable bat tech.

What I was trying to drill down to, is at what size kwh system, does it makes sense to change from 12 volt to 24 volt to 48 volt? Not based on the factor of higher voltage being more electrically efficient...bc in all cases 48 volt would be the choice.

So the only way to test over all system efficiency, is to determine the cost per kwh, against the cost to build the system, and arrive at the true costs per kwh. It's hardly arguable that as you increase system voltage, that it also increase system costs.

The question is at what point does the higher efficiency of 48 volts systems, amortize the increased system costs.

Lloyd

Lloyd:

i understand ohms law about as good as the next guy  :)

my point with my dissertation is simply this

if you are going to have to recharge with an engine driven genset, 48volts will win out over 12 in "all" cases, even small systems.

while it may well cost more for the 48volt bank it really need not be dramatically more, because

i left out one more option in my analysis

that being the use of smaller lower capacity 12volt batteries to make up the 48volt string

while the ratio is not quite linear, a 25amp/hr battery will be dramatically less expensive than a 100amp/hr battery

so in the end you would be faced with using 50% depth of charge just as with the 12volt example, the addional cost would
not be 4x such as in the previous 48volt example, so you would not get the advantage of shallower cycling and the battery
life would be similar at 1000 cycles, but

you would still be more efficient in charging, enough so to pay for the bank of batteries in fuel savings within the lifespan of the batteries.


now having made the case for 48volts, a similar case can be made for 24volts as well, and

there is still a place for 12volts for certain applications, but there will have to be much research and development to come up
with a means of engine driven alternator to get the efficiency of either a 24 or 48volt system,, this much i know probably as much about
or more than most anyone you want to talk to.

i have put a lot of years in research and then more years in hands on research and development of alternators for high efficiency charging
and 12volt units albeit a long and reliable history, are not very efficient compared to what can be done at higher voltages.

it maybe that from your viewpoint and experience with 12volt systems, you see things from a completely different angle than i am because i am viewing the issue from the engine driven alternator viewpoint

you are looking at first cost of installation, and amortization of that bank 12v vs 48

i am looking at how many gallons of fuel at X dollars per gallon will an engine driven genset burn over the life of the batteries 12v vs 48v
and factoring that against first cost and amortization of the banks 12v vs 48v

to be fair i have to admit that it is possible to get the efficiency of an engine driven alternator up to around 75 plus % for 12volts, i just have
not seen anyone working on getting it done, and for now i have little interest in exploring that avenue myself.

although i would be happy to help in that area, via some idea's and discussion

i am working now on the threephase transformer pack and remote rectifier for 12volt battery charging, and am going to be setup to do relative
efficiency testing this weekend,  while i have no real need for such a system, i do have an interest to see if it can be done and to find out
what can be done to increase efficiency.

believe me, a 12volt system would be nice, and i would prefer on if i could get the overall efficiency up to anywhere close to what i can do with 24 or 48volts.

bob g

Bob,

Just for the record I agree with you.

Redundancy is an issue, so to have that in a bank we need at least two parallel groups of system voltage. This is good  for life cycle of the bats as well, it also in most cases covers the Peukert factor, that most don't think about.

As far as bat choices...I don't know of any bats, in the 100 amphr range that I would want to depend on. To me a conventional lead acid wins out over AGM, bc of costs, even with the more efficient charge characteristic.

All this no matter what voltage we choose.

The cheapest entrance into a well tested bat is the trojan t240 no matter the voltage choice of the system.

And again, in other threads you have hit the nail on the head. Usage on an off grid system has to improve dramatically. If we look at the economics of a true off grid solar/bat/gen. We would never choose the off grid bc we could never recover the investment, bc there is flat out no way we can make electricity cheaper then we can buy it from the grid. At the same convenience factor.

Now if we can scale back system costs bc we change our usage pattern, by conservation, more efficient equipment, we lower our over all investment, which lowers our cost per kwh produced.

Lloyd

Bob, I do thank you again for all you have done in testing my proposition on the 12v system.... Now if you would just send me your shipping address, and the specs, and schematic on that diesel cat....I have a present for you.


And here is an excellent online ohms calculator http://www.the12volt.com/ohm/page2.asp#9

here is a link for the cat

magnaflow 54014D

http://www.car-sound.com/02product/displayuniversal.asp?universal=54104D

bob g

Now, i haven't read the last replies scrupulosly, but do have cable sizing and stretch in mind when choosing DC voltage. :)

painful???

painful?????

whatcha talkin about willis?

:)

sometimes it is out of what some would call a painful discussion/debate/arguement that something totally unrelated comes to light and is helpful
to others.

just taking folks assertions on faith, is what got us into AWG, carbon trades, cap and trade, and now the epa regulating CO2 as a dangerous gas.

you guys think this has been painful, try following the global warming is a hoax over on the LEF.

just kidding, i like to argue so it isn't fair  :)

i often forget most folks don't like confrontation and heated debates, and find them painful and tedious.

guess i better keep that in mind!

(what am i saying???)

NAH,,, not me!

:)

ok, back on topic

this whole debate of voltages has led to some interesting research that i find interesting anyway.
and it centers around the common need for massive cables for 12volt power transfer, the goal
of all the testing is to see how much power can be transmitted over a significant distance using
10/3 cable instead of dual 4/0 positives and dual 4/0 negative cables

it may prove to be helpful to others down the road?

bob g

bob g