Portable energy storage system

benjamin · May 2010

I have done a significant amount of research on all of the various components of alternative energy. I somehow missed the part regarding higher voltages resulting in smaller required cabling for battery banks. So I'll tell you guys where I'm at just to get some thoughts on how to proceed.

Here's what I have:

20 Trojan T-605 6V 210AH batteries
1 Aims 5000W 12V Modified Sine Wave Inverter
1 Xantrex 2500W 12V Pure Sine Wave Inverter/Charger w ACS Remote Panel
1 Morningstar ProStar 30 Charge Controller with Meter
2 2” x 1/4” x 24” copper bar (for bus bars)
600 125MM by 125MM solar cells. (1470W total)
2 1750W Permanent magnet motors for windmills
100' 2/0 Welding Wire and lugs
2 AC Circuit Breaker boxes with multiple breakers
2 AC Master shut-off breakers
Additional components for assembly

I'm going to be building a vacuum chamber in order to build the solar panels, so I've got that part worked out. Once everything is hooked up and running the system will be able to generate 4.9KW. Assuming I get 50% of that for 10 hours each day, I should be able to generate around 25kwh per day, or 750 per month.

Now here's the challenge. We don't have our own property yet and are currently renting a house. I've built a compartmentalized box on caster wheels to contain the heart of the system, e.g. batteries and inverters. It's not easy to move, but it is at least movable by one person. I do of course realize that batteries create hydrogen and so the box was designed so that the inverter compartment is completely sealed off from the battery compartment. Additionally, I'm considering adding a bilge blower that will kick on automatically if certain criteria are met, such as if the voltage rises above the gassing voltage for a given temperature.

There are 10 sets of two batteries wired in series. Each set has a negative and positive lead running to the bus bars. This is where I am looking for input. Coming off the bus bars, I need to run wire to the inverters. Between the inverters and the bus bar there should be a disconnect switch. At peak load, if I was using 7500W, the system would be pulling around 625AMPs because it's a 12V system. I am able to find 500A fuses and smaller for decent prices so fusing the inverters individually is not an issue. I'm not really sure what the best route would be as far as a disconnect switch goes.

Square D makes 700A+ DC breakers and they charge around $15,000 for them. Frankly, the pricing doesn't make any sense and reminds me of those $20,000 hammers from years ago. Anyhow, I am able to find them from second hand sources for around $400. So far, this is the best solution.

At this point I have several questions.

What is best solution, as far as safety and price, which can be implemented in order to add a DC master switch to this setup.
Considering the box is wood, should there be any concerns about the bus bars reaching temperatures exceeding the ignition point of the wood resulting in a fire? It appears that many setups have the bus bars mounted to wood and that this is common practice.
The battery compartment of the box will have a fresh air intake on the bottom. This will allow air to flow across all of the batteries and then up through 14 2” holes leading all the way to the top of the box at which point there will be another vent for outflow. Given this setup and the fact that hydrogen rises, is an additional blower required?
Does the increased number of strands in welding wire reduce the amperage it can carry? How many AMPS can 2/0 welding wire carry? I've designed under the assumption it can carry around 200A.

Cariboocoot · May 2010

Re: Portable energy storage system

The question that needs answering is: what is the purpose of this system? Experimentation? Off-grid power? Back-up? It makes a difference.

It's a lot of stuff you've got there for experimenting with. For serious off-grid power it's a lot of not-so-good stuff. Like the AIMS inverter; good paperweight. Home-made panels? Big risk of failure, potentially catastrophic (fire).

You seem to have missed one of the basic electrical facts: Volts * Amps = Watts. This is the wiring issue you allude to at the start. If your end result is "X" Watts, it takes twice as much Amperage at half as much Voltage:
1200 Watts = 100 Amps @ 12 Volts or 50 Amps @ 24 Volts. The Amperage is what mainly determines wire size (except for line loss calculations).

There is a decided lack of DC Over Current Circuit Protection in your list. Fuses/breakers are absolutely necessary for panels, charge controller output, and inverter.

Your batteries add up to 2100 Amp/hrs! That will require more than 3000 Watts of panel to recharge. This is way too large for one controller. The Morningstar 30 can handle at most about 450 Watts. Normally a 12V system doesn't go over 2kW in power (AC). Again, the inverters are over-sized for a 12V system (and the AIMS is a piece of junk).

You won't find many fans of small-scale wind around here, but DIY wind turbines are often better than commercial units. DO you have enough wind? Find that out before yu go to the trouble of building/erecting them.

Again, the most important question you can answer for us and you is: What are you expecting to do with this set-up?

The basic design method is to calculate potentials loads first, then determine what is needed to supply them.

mike95490 · May 2010

Re: Portable energy storage system

I've missed the part where this is portable ? 20 big lead-acid batteries will fully load a utility trailer.

40' towers for windmills are not too portable either.

Making this into a 12V system is insane, make it a 48V system, solves a lot of wiring problems.

Just my nickels worth

benjamin · May 2010

Re: Portable energy storage system

The purpose is to supply off-grid power. I will not be backfeeding into the grid.

I realize that a 12V system is unconventional. This is what I've ended up with however.

You stated that the Aims is junk but provided no supporting arguments or evidence.

Not one of my questions has been answered.

BB. · May 2010

Re: Portable energy storage system

benjamin wrote: »

There are 10 sets of two batteries wired in series. Each set has a negative and positive lead running to the bus bars. This is where I am looking for input. Coming off the bus bars, I need to run wire to the inverters. Between the inverters and the bus bar there should be a disconnect switch. At peak load, if I was using 7500W, the system would be pulling around 625AMPs because it's a 12V system. I am able to find 500A fuses and smaller for decent prices so fusing the inverters individually is not an issue. I'm not really sure what the best route would be as far as a disconnect switch goes.

7,500 watts * 1/10.5V cutoff * 1/0.80 invtr eff * 1.25 NEC safety factor = 1,116 Amp minimum circuit/breaker/switching

The above, if you are concerned about fire and want to run 7.5 kW off of a 12 volt bank is the current you should design for.

Square D makes 700A+ DC breakers and they charge around $15,000 for them. Frankly, the pricing doesn't make any sense and reminds me of those $20,000 hammers from years ago. Anyhow, I am able to find them from second hand sources for around $400. So far, this is the best solution.

DC current is actually quite a bit more difficult to "break" than the equivalent in AC (if you look around, DC switches are built much heavier than equivalent rated AC switches/breakers/etc.).

Also, in your case, you need to have the breaker/fuse survive interrupting a dead short against, potentially 50,000-100,000+ amps (assuming each battery string is capable of 1,000-2,000 amps into a dead short). A "normal" house circuit breaker/fuse is rated for a interrupt current maximum of 10,000 Amps AC (maximum current provided by a residential pole transformer).

Also, note that batteries and battery strings can be shorted too (plates short, tool drops on battery terminals, etc.)... Each battery string should also be protected by its own fuse.

Another issue with paralleling large numbers of batteries is the difficulty to get current sharing between all strings (I recommend 3 strings or less)... What tends to happen if there are different lengths of cables/bus bars/etc. between the load and individual battery strings is that battery sets near the load/charging source will supply more current and those farther away less (batteries will "wear faster" and bank will appear to have less energy storage than it should). You should calculate resistance/voltage drop (or measure it if already built) and see how much of an issue you may have... Remember batteries/bus voltages should be balanced within 0.100 volts or less).

Also, look at voltage drop overall... If you have a 12 volt battery and want to run it down to 11.5 volts, and the inverter has a 10.5 volt cutoff (typical)--your entire distribution system can have, at most a 1 volt drop.

A 48 volt bank will have 1/4 the current... And voltage drop wise 46 volts - 42 volt cutoff = 4 volt wiring drop...

1/4 the current, roughly, would mean that you could use 6 AWG size smaller wire to carry the same rated power.

At this point I have several questions.
What is best solution, as far as safety and price, which can be implemented in order to add a DC master switch to this setup.

I don't have a good answer on that one--perhaps a marine wrecking yard or EBay may be your best choice for something that can handle 1,000+ amps (rated).

Considering the box is wood, should there be any concerns about the bus bars reaching temperatures exceeding the ignition point of the wood resulting in a fire? It appears that many setups have the bus bars mounted to wood and that this is common practice.

Wood (and battery cases) are flammable... If the bus bars/wiring are getting hot enough to concern you about igniting a wooden box--then they are running too hot already (undersized). If you are worried about shorts, fuses/breakers on each parallel string, and at the bus bar output to inverter (chargers/etc.) will help limit your exposure to elevated temperatures. Would a heavy metal box be better--possibly against fire--but the expense, weight, corrosion issues may out weigh the advantages of metal...

The battery compartment of the box will have a fresh air intake on the bottom. This will allow air to flow across all of the batteries and then up through 14 2” holes leading all the way to the top of the box at which point there will be another vent for outflow. Given this setup and the fact that hydrogen rises, is an additional blower required?

It sounds like you have enough ventilation... Remember that fuses/breakers can be ignition sources and should be well ventilated/out side the box if possible.

Does the increased number of strands in welding wire reduce the amperage it can carry? How many AMPS can 2/0 welding wire carry? I've designed under the assumption it can carry around 200A.

The number of strands (finer strands) just changes the flexibility of the cable--not its DC current carrying capability... For AC, that is not quite true. There is something called the skin effect--and as frequency rises, the current tends to be forced to the "skin" of the conductor.... An inverter has a 120 Hz component to its current flow and 4 ought (0000) cable is approaching the skin depth limitation -- if it was a single solid copper conductor.

An issue with welding cable is that it is very fine wire and actually quite difficult terminate properly (and/or find proper crimp connectors). Unless you need the very fine wire for flexibility, it would be better to stay with standard industrial wire.

We have one user here that has used surplus large AIM inverters and found them to work for his off-grid shop use... These inverters tend to be (from what I recall) MSW type inverters (modified square wave). Probably 80% of what you plug in will work OK. And, perhaps, 10% of your AC loads could have problems (over heating typically, although you can have timer circuits that don't time correctly, some smaller devices with wall warts may over heat, and some motors may over heat too). I guess the big issue is that, for many of us here, we just don't think it is a very good idea to make a 7.5 kW 12 volt inverter (and needing 1,100 amp capable wiring)---there are just so many issues that it is difficult to believe that very many installations will ever achieve their 7.5 kW output.

-Bill

benjamin · May 2010

Re: Portable energy storage system

Thank you for the great information.

Has anyone researched running the power from an inverter through a 1:1 transformer to smooth out the wave? I know there would be an efficiency loss there, but this could very well be what some inverter manufacturers do.

I'll probably limit the DC current draw to between 600A and 800A. I don't think I'll ever have both inverters maxed out and I don't want to wire for 1200A.

icarus · May 2010

Re: Portable energy storage system

Well,, I will answer the questions I can,, in spite of my feeling (echoed by CC and Mike) that at the very least you are trying to do a classic, ready, fire aim!

It seems that you have the hardware and you are trying to get that square peg hardware to fit into round holes.

First, vent the battery box! I suggest a voltage controlled fan, with intake and exhaust vents. The shear number of cells suggests that (if you are going to charge at anywhere near optimal currents) there will be considerable off gassing, so safety is a big issue.

Second, if you have buss bars that might get hot enough to ignite a wooden box, you either have a very poor conductor, or a problem. If you are really concerned that under "normal" service your buss bars are going to get that hot, consider lining the box with cement board or sheet metal with an air space behind it.

As for the ampacity of 2/0 wire, it depends on length, and how it is used:
http://www.allaboutcircuits.com/vol_5/chpt_3/2.html
From the above link, 2/0 in free air should carry 200 amps

All that said, I would redesign the entire system, with components sized for the loads, the batteries and the Pv. Anything else will result (IMHO) in a system that is either (or both!) underperforming, unsafe, and in the long run will be more expensive than doing it right in the first place.

48 vdc battery bank, MPPT controller(s) and a proper sine wave inverter. ( the loses using a MSW get pretty big as the inverter gets big).

Good luck, and welcome to the forum.

Tony

PS If you are counting on 50% output for 10 hours/day, I think you are going to be very disappointed. In any real world, 4 hours of good output is considered "average".
I like to figure name plate rating of the PV/2 to account for all system loses *4=the amount of power you can harvest with a battery based system. (Your mileage may vary, but it isn't likely to be 50% for 10 hours on average, even in a sunny climate.

1470/2*4=2,900 wh/day or 2.4kwh/day is what you MIGHT be able to use on a average day in/day out basis. I would guess with home made panels, you output is likely to be lower.

BB. · May 2010

Re: Portable energy storage system

Charging current wise--a good starting rule of thumb is 5-13% of the 20 Hour battery capacity.... Below 5%, it gets difficult to fully charge/equalize batteries (plus keep up with self discharge for older cells, and simply a lot of batteries for little charging current--and for over 13%, many flooded cell storage batteries can start overheating, plus it is a lot of money for a lot of battery charger).

You have a 12 volt bank and 1,050 Amp Hour of batteries (again, rough rules of thumb):

1,050 AH * 0.05 charge = 52 amps minimum recommended
1,050 AH * 0.05 charge = 136 amps maximum recommended

Charge wise in Watts:

52 amps * 14.4 volts = 750 watts
136 amps * 14.4 volts =1,960 watts

Also, note that many charge controllers (typically the larger ones and many MPPT type)--they have a maximum output current rating... So a large(ish) 60 amp 12/24/48 volt charge controller:

14.4 volts * 60 amps = 864 watts
58.6 volts * 60 amps = 3,516 watts

So, the same controller, when operating at 4x higher battery bank voltage, can manage 4x the amount of solar array. (would take 4x the number of controllers to run a 12 volt bank vs 48 volt bank).

-Bill

BB. · May 2010

Re: Portable energy storage system

benjamin wrote: »

Has anyone researched running the power from an inverter through a 1:1 transformer to smooth out the wave? I know there would be an efficiency loss there, but this could very well be what some inverter manufacturers do.

No, there is really no practical way you can "filter" a MSW waveform into a TSW (True Sine Wave) waveform using passive components. If you could filter out the higher frequency sine waves (see Fourier series) would just be converted to heat... Start with a pure sine wave inverter in the first place.

All About Inverters
Choosing an inverter for water pumping

There are Ferroresonant Transformers -- And they are used to filter/ride through AC line problems... However, they tend to be big, heavy, expensive, and very frequency dependent (can be a big issue when running on a standard AC genset).

If you need sine wave power (highly recommended), you should start with sine waves.

-Bill

benjamin · May 2010

Re: Portable energy storage system

icarus wrote:

It seems that you have the hardware and you are trying to get that square peg hardware to fit into round holes.

Yes I am. So far I have probably saved around $20k or so as well. It's either this or nothing as I have to work within my budget.

icarus wrote:

First, vent the battery box! I suggest a voltage controlled fan, with intake and exhaust vents. The shear number of cells suggests that (if you are going to charge at anywhere near optimal currents) there will be considerable off gassing, so safety is a big issue.

Agreed.

icarus wrote:

Second, if you have buss bars that might get hot enough to ignite a wooden box, you either have a very poor conductor, or a problem.

I doubt they will get hot, it was just a passive question.

icarus wrote:

As for the ampacity of 2/0 wire, it depends on length, and how it is used:
http://www.allaboutcircuits.com/vol_5/chpt_3/2.html
From the above link, 2/0 in free air should carry 200 amps

It says 225A to 300A what am I missing? (You said 200A)

icarus wrote:

All that said, I would redesign the entire system, with components sized for the loads, the batteries and the Pv.

It would be expensive for me to repurchase 48V inverters.

icarus wrote:

Anything else will result (IMHO) in a system that is either (or both!) underperforming, unsafe, and in the long run will be more expensive than doing it right in the first place.

Under-performing is OK, since the system is over-built. Really, my only concern is fire, so I'll be taking measures to ensure that doesn't happen. e.g. having the system reviewed by electrical engineers, getting advice from you guys, adding insanely sized 800A DC breakers.

icarus wrote:

Good luck, and welcome to the forum.

Thanks!

icarus wrote:

If you are counting on 50% output for 10 hours/day, I think you are going to be very disappointed. In any real world, 4 hours of good output is considered "average".
I like to figure name plate rating of the PV/2 to account for all system loses *4=the amount of power you can harvest with a battery based system. (Your mileage may vary, but it isn't likely to be 50% for 10 hours on average, even in a sunny climate.

I said 4.9KW at peak output, which would of course never happen. However, 3.5KW of this is coming from wind generation, so if I estimate power from this at 30% for 6 hours per day that would be 6.3KWH. The solar cells will be homemade, but I'll be using starphire glass and using the same production technologies as the major manufacturers. I have already designed a vacuum chamber and the production methods in order to ensure a high end product on par with what can be purchased commercially. I understand being conservative, but I estimate that I will get 1000W x 6 hours on a nice sunny day, in addition to lower output for several additional hours. So this would be another 6KWH for a total of 12KWH so far. It has been incredibly windy this spring so far here in the midwest. I wish I had the mills up right now actually.

BB. wrote:

You have a 12 volt bank and 1,050 Amp Hour of batteries (again, rough rules of thumb):

Maybe you are just giving an example but I actually have 2,100 AH. So based on the equations you provided I would need 105A (1,512W) min and 273A (3,932W) max.

Here are pictures of what I have built so far. As you can see in the second picture, the bus bars are rather large, I doubt they will get hot.

Cariboocoot · May 2010

Re: Portable energy storage system

Despite being persona non grata I shall make another suggestion.

If you don't need 5kW for any one device, you can break up your total loads into several smaller inverter set-ups. These can have entirely separate battery banks/charging or a central system for power.

The thing that's wrong with AIMS inverters is exactly the trouble you're finding: they try to get thousands of Watts of power out of 12 VDC, requiring very large amounts of current which is difficult to handle:

5000 Watts @ 10.5 VDC (low cut-off point) = 476 Amps

If you want to limit your maximum output capacity you can under-size the wiring providing you use a fuse sized to the lower output limit:

2500 Watts @ 10.5 VDC = 238 Amps requiring a 300 Amp fuse instead of a 600 Amp one.

I'll say this before anybody bawls me out for suggesting the above: Under-sizing wires is not recommended!

You're still going to have trouble charging that huge battery bank:
2100 Amp/hrs @ 10% = 210 Amps charging @ 14.2 Volts = 2,982 usable Watts = 3727 Watts of panels.
Not to mentioned at least 3 charge controllers of the expensive type (Outback FM80 handles 80 Amps - most only handle 60).

Maybe you could sell some of those batteries to finance other aspects of the system?
This is why we drone on and on about loads and the need to minimize them.

BB. · May 2010

Re: Portable energy storage system

You are correct about the AH--I took one too many "1/2" converting from 20 x 6 volt batteries to 10x 12 volt batteries...

One concern is how do you plan on checking electrolyte levels and specific gravity?

You probably will need to get to all cells at least once per month to check levels and specific gravity (once you have a good handle on your batteries, you may be able to check a bit less often). Are you planning on an automatic watering system?

-Bill

benjamin · May 2010

Re: Portable energy storage system

Cariboocoot wrote:

Despite being persona non grata I shall make another suggestion.

On the contrary.

Cariboocoot wrote:

If you don't need 5kW for any one device, you can break up your total loads into several smaller inverter set-ups. These can have entirely separate battery banks/charging or a central system for power.

I'll ponder this, but I may not need to. It is doubtful I will ever use more than 50% or 2500W from the AIMS.

Cariboocoot wrote:

The thing that's wrong with AIMS inverters is exactly the trouble you're finding: they try to get thousands of Watts of power out of 12 VDC, requiring very large amounts of current which is difficult to handle:

5000 Watts @ 10.5 VDC (low cut-off point) = 476 Amps

This is concerning, because their own manual states that you should connect them using 1 set of 4/0 wire or two sets of 1/0 wire. I was going to use 2 sets of 2/0, but I may need to use 3 sets of 2/0. The runs will be very short though. 30” max.

Cariboocoot wrote:

If you want to limit your maximum output capacity you can under-size the wiring providing you use a fuse sized to the lower output limit:

I'll probably run 3 sets of 2/0 and fuse the AIMS at 500A. I may never use that much power, but there may come a time when I need that much on occasion.

Cariboocoot wrote:

You're still going to have trouble charging that huge battery bank:
2100 Amp/hrs @ 10% = 210 Amps charging @ 14.2 Volts = 2,982 usable Watts = 3727 Watts of panels.

The owner of the place I bought these from said that they like to be brought up slowly, so I don't know where that fits into the math from you and BB. The Xantrex inverter I have has a built in 100A charger, so I can give them a nice boost once in a while if needed.

Cariboocoot wrote:

Not to mentioned at least 3 charge controllers of the expensive type (Outback FM80 handles 80 Amps - most only handle 60).

It wouldn't be a problem for me to pick up 3 more of the Morningstar charge controllers, or maybe move up to a larger model.

Cariboocoot wrote:

Maybe you could sell some of those batteries to finance other aspects of the system?
This is why we drone on and on about loads and the need to minimize them.

Nooo! These are my babies.

BB. wrote:

One concern is how do you plan on checking electrolyte levels and specific gravity?

I've built the box with enough room on the bottom shelf to check these via access panels. The top two shelves will require another access panel and possibly removal of the top 4 batteries to gain access to the 4 batteries on the second shelf. I'm estimating 3 months between checks. Due to the size of this bank, it will charge and discharge slowly so I feel that will increase the time between checks.

BB. wrote:

Are you planning on an automatic watering system?

Yes, I don't want to pay $20 per cell though. If I can find/build something for a decent price to automatically water the cells that would be great.

My girlfriend and I will be moving off-grid sometime in the future. We currently use around 820KWH per month without optimizing our usage. We have a very efficient fridge, and other than that the only things we really need to run are computers, lights and clocks. We are moving to laptops because they are much more efficient.

mike95490 · May 2010

Re: Portable energy storage system

benjamin wrote: »

Has anyone researched running the power from an inverter through a 1:1 transformer to smooth out the wave? I know there would be an efficiency loss there, but this could very well be what some inverter manufacturers do.

Been there, done that, the inverter sees the huge inductive load, and will refuse to start.

As for dropping a huge inductive load onto a energized MSW inverter, I did not have the nerve to do that.

Mike

BB. · May 2010

Re: Portable energy storage system

I am not sure I would aim at a 3 month water/s.g. check schedule and requiring partial dis-assembly to boot... Working around high current battery connections can be hazardous (bolting/unbolting/etc.).

Regarding moving off grid---I have always liked the 100 kWH per month number... At that power level and below, your off-grid power requirements are somewhat affordable and maintenance levels/costs are reasonable. Of course, you can go more or less based on your needs and location.

-Bill

icarus · May 2010

Re: Portable energy storage system

"Maybe you are just giving an example but I actually have 2,100 AH. So based on the equations you provided I would need 105A (1,512W) min and 273A (3,932W) max."

I believe, (and I may be misunderstanding something,,, wouldn't be the first time) but your ~2100 ah of battery is at 6 vdc. double the voltage/halve the ah capatcity,, same power available, but the math is different.

"It says 225A to 300A what am I missing? (You said 200A)"

I said it depends on length. Lower voltage=greater voltage drop. Add length and you lose more power in the wire. You will have to do a calc to determine what is acceptable.

"It would be expensive for me to repurchase 48V inverters."

See next:

"Under-performing is OK, since the system is over-built. Really, my only concern is fire, so I'll be taking measures to ensure that doesn't happen. e.g. having the system reviewed by electrical engineers, getting advice from you guys, adding insanely sized 800A DC breakers."

"It wouldn't be a problem for me to pick up 3 more of the Morningstar charge controllers, or maybe move up to a larger model."

Weren't you concerned about the price of an 800 amp DC breaker?

"I understand being conservative, but I estimate that I will get 1000W x 6 hours on a nice sunny day, in addition to lower output for several additional hours. So this would be another 6KWH for a total of 12KWH so far."

I hope you're right,, but I would be surprised. You might get that on a bright sunny day,, but on average, clouds, hot temps, shading, is going to drop your net (IMHO) closer to where I predict.

"Nooo! These are my babies."

They may be your babies, but they have a very finite life, and if you mistreat them, you will significantly shorten that life! By the way,, what are you doing to keep them FULLY charged as they sit now?
Finally, I don't want to sound too much like a naysayer, and in fact I applaud your industriousness. That said, part of our job (as I see it), is to relay what we believe is the best advice we can. With that in mind, I would read all you can about wind. I think you may find that very few people (especially here) have been very satisfied with (small scale) wind as a very good solution. The reality is if one has enough wind to be very useful, ironically one usually has too much wind to keep the hardware reliable.

Once again,

Good luck,

Tony

PS If you haven't read these I STRONGLY suggest doing so:http://www.batteryfaq.org/

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

dwh · May 2010

Re: Portable energy storage system

icarus wrote: »

PS If you are counting on 50% output for 10 hours/day, I think you are going to be very disappointed. In any real world, 4 hours of good output is considered "average".
I like to figure name plate rating of the PV/2 to account for all system loses *4=the amount of power you can harvest with a battery based system. (Your mileage may vary, but it isn't likely to be 50% for 10 hours on average, even in a sunny climate.

1470/2*4=2,900 wh/day or 2.4kwh/day is what you MIGHT be able to use on a average day in/day out basis. I would guess with home made panels, you output is likely to be lower.

Exactly my first thought on reading the OP. It *might* be possible to get 10 hours/day of full output from a solar system - on a mountaintop on the equator using a really good tracking system.

But in the real world Tony's formula is proper - 50% of the PV rated output will be eaten up by system losses, and 4 hours is a good day for solar harvesting.

And that isn't accounting for cloudy days. It's also common around here to plan enough battery capacity to supply your off-grid needs if the sun doesn't shine for 3 days. If you do that, then you upsize your battery bank and thus also end up usually needing to increase charging capacity (PV+charge controller(s)).

Or adding a generator to charge the batteries on cloudy days, which often works out to be cheaper over the long run.

And yea...I highly doubt you're going to get full rated output from home-made PV modules.

Kamala · May 2010

Re: Portable energy storage system

There is plenty about this plan to be concerned about. IMO, the use of homemade solar panels is foremost. Especially for a domicile.

You say you have built a "vacuum chamber" for use in constructing your panels. How do you evacuate the chamber? Can you measure the "pressure" of this vacuum? I'm no engineer, but I get queasy trying to imagine the cost of an industrial grade vacuum chamber, to say nothing of the adhesives, sealants and bonding materials required to preserve that vacuum in the finished product. Over and over.

Sorry if I sound harsh but I think you've taken a pretty big bite out of a pretty bad apple. Swallow if you wish but I think you will be looking for a remedy sooner than later.

Still... good luck.

K

solarvic · May 2010

Re: Portable energy storage system

Are you planning on setting this up at the house you are renting? I know if I was the landlord I would either evict you or else raise my insurance policy to pay for the fire. If you go thru with it at your rented abode get the solar panels far enough away so you don,t burn your landlords house down. S:Dlarvic

benjamin · May 2010

Re: Portable energy storage system

BB. wrote:

I am not sure I would aim at a 3 month water/s.g. check schedule and requiring partial dis-assembly to boot

Yeah, that's something I'll have to work on.

BB. wrote:

Regarding moving off grid---I have always liked the 100 kWH per month number

Sounds good. I'm really not sure how we even use 800kWH per month. I've got a meter, so I'll start monitoring what is using how much.

icarus wrote:

I believe your ~2100 ah of battery is at 6 vdc

There are 20 210AH batteries at 6V DC. So it would be 4,200AH / 2.

icarus wrote:

Weren't you concerned about the price of an 800 amp DC breaker?

Yes, but even if the breaker and extra fusing costs $1k, that is still less than the half the price of one decent 48V inverter.

icarus wrote:

By the way,, what are you doing to keep them FULLY charged as they sit now?

Right now I bulk and float charge them once a month in pairs until they are fully charged. Once I have the wire lugs crimped I'll wire them up to the Xantrex and let it take care of them.

icarus wrote:

The reality is if one has enough wind to be very useful, ironically one usually has too much wind to keep the hardware reliable.

I was concerned about this as well. I'll take it into consideration when I design the blades and drive mechanism.

icarus wrote:

If you haven't read these I STRONGLY suggest doing so:http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Thanks, I'll check those out.

Kamala wrote:

There is plenty about this plan to be concerned about. IMO, the use of homemade solar panels is foremost. Especially for a domicile.

There's only two things to be concerned about. First is the high amperage from the bus bars to the inverter, a distance of several feet. Second is the homemade solar panels. I'm not worried about the solar panels in the least. The only solar panels I saw, and I believe it was on this forum, that started on fire were made out of Plexiglas and soldered incorrectly. My solar panels will be made out of starphire glass, be soldered correctly and have an ABS plastic backing, which is common industry practice.

Kamala wrote:

You say you have built a "vacuum chamber" for use in constructing your panels. How do you evacuate the chamber? Can you measure the "pressure" of this vacuum? I'm no engineer, but I get queasy trying to imagine the cost of an industrial grade vacuum chamber, to say nothing of the adhesives, sealants and bonding materials required to preserve that vacuum in the finished product. Over and over.

With a vacuum pump
With a vacuum gauge.
Yes, they cost upwards of $80k.
Yes, the sealant is $1.5k per gallon I believe.

I'm aware of the details and intricacies of building solar panels. I have studied various manufacturing techniques and equations used to calculate moisture penetration using various sealants. I currently consider this knowledge and my design plans, including the design plans for the vacuum chamber itself to be intellectual property, because I may manufacture these for retail. I can however say with great confidence, that these will be durable, completely submersible and last at least 25 years at a very wide range of temperatures.

solarvic wrote:

Are you planning on setting this up at the house you are renting? I know if I was the landlord I would either evict you or else raise my insurance policy to pay for the fire. If you go thru with it at your rented abode get the solar panels far enough away so you don,t burn your landlords house down.

I certainly appreciate your invaluable comments. I'll just go ahead and give up because I'm too stupid to do this without lighting myself, my friends and my family on fire.

Actually, last I checked, tempered glass isn't flammable. Neither are the solar cells, nor the sealants I will be using, nor the aluminium frame. The ABS plastic backing is flammable, however last I checked many manufactures use this.

benjamin · May 2010

Re: Portable energy storage system

So here is where we are at. Based on comments here and from a few other guys I have been talking to:

The positive leads coming off of each battery pair will be fused at 200A. This will protect the system in case something was to short the bus bars. This is something that will probably never happen, but it adds an extra layer of protection. So with these fuses, the bus bars will never be able to draw more than 2000A.

Wires will be run from the bus bars to a 700A DC Circuit breaker. This will require 3 sets of 4/0 wire. Estimated length is 18” or so.

Wires will be run from the DC breaker to each inverter. The 5000W inverter will be fused at 500A and the 2500W inverter will be fused at 350A. Multiple runs of 4/0 or 2/0 will be used to meet the amperage demands.

Is this pretty solid? Anything else you guys would add?

BB. · May 2010

Re: Portable energy storage system

Sounds like a good start. When testing the system out, you probably can use a couple portable electric heaters on your inverters to test the loading (voltage drop, look for any hot spots).

Also, a DC clamp on Amp Meter -- if you don't have one, you can generally use a DVM set to 200 mV full scale and check the battery jumper cable voltage drop for each of your 10 strings. If they are all sharing current properly, the voltage drop should be similar for each of the (hopefully) identical jumpers (you would be using them like a current shunt resistor).

-Bill

lorelec · May 2010

Re: Portable energy storage system

benjamin wrote: »

At this point I have several questions.
What is best solution, as far as safety and price, which can be implemented in order to add a DC master switch to this setup.

Considering the box is wood, should there be any concerns about the bus bars reaching temperatures exceeding the ignition point of the wood resulting in a fire? It appears that many setups have the bus bars mounted to wood and that this is common practice.

The battery compartment of the box will have a fresh air intake on the bottom. This will allow air to flow across all of the batteries and then up through 14 2” holes leading all the way to the top of the box at which point there will be another vent for outflow. Given this setup and the fact that hydrogen rises, is an additional blower required?

Does the increased number of strands in welding wire reduce the amperage it can carry? How many AMPS can 2/0 welding wire carry? I've designed under the assumption it can carry around 200A.

For high amperage switching, you're probably going to want to use a contactor of some sort. A brief scan of the surplus stores turned up one 600A contactor for ~$300 (towards the bottom of the page at: http://www.surplussales.com/Relays/REcontacts-1.html). They also have some 200A devices for $45 each. You'll want to make sure they're DC rated, of course (the 600A one appears to be rated for 28VDC). Use fuses as necessary for overcurrent protection.

2/0 wire (by NEC standards) is rated for 300A in free air if you're using 90degC THHN, for example. I definitely prefer welding wire. The flexibility can't be beat, the cost is reasonable, and the neoprene jacket with withstand much higher temps and a much more corrosive environment than your average building wire. You can buy crimpers and attach the lugs proper-like (good ones are costly). Harbor Freight actually has a decent hydraulic crimper for ~$75 that they claim is good up to 2/0...but they have the dies mislabeled (haha...this IS Harbor Freight, after all!), so in reality it's only good for 4AWG max. I managed to fabricate a couple of new dies for it and it works really well with the 2/0. Crimp the lugs, and then use a propane torch on directly on the lug with some 60/40 solder to carefully make a really good connection. Then slip a piece of adhesive-lined polyolefin heat shrink over the joint, and you'll have a cable that will probably outlast you!

I think the concerns that others here have with a 12v, several-thousand-watt inverter are justified. Sizing conductors large enough to carry the current is easy enough, but since higher current translates directly into more heat inside electronic equipment, the longevity of the inverter might suffer. Building your system to accomodate very high currents, and the expense (and possibly hazards) that it entails, might outweigh the cost of a higher-voltage inverter to begin with.

Marc

benjamin · May 2010

Re: Portable energy storage system

Good information. I am using welding wire. I am having a friend crimp them at work since I don't want to buy a crimper. I did buy the HF crimper but returned it because it was too small. I should have kept it and made some dies like you did.

Anyone see anything wrong with these fuses? They are the cheapest I could find.

http://www.go-fast-parts.com/5734043.html
http://www.homegoodz.com/i60550-blue-sea-5126.html

BB. · May 2010

Re: Portable energy storage system

When dealing with fuses and breakers, a rated voltage and maximum interrupt current is really needed to know if they will work in the application.

I believe the company that makes those fuses is a car stereo firm and I don't think the fuses are UL/NRTL listed and I did not see a voltage rating--although, they are probably rated for at least a 12 volt circuit.

But, finding this information has been difficult even for other fuses... Our host does sell high current fuses... You can look at a catalog page for one series here (PDF).

These fuses appear to be rated to 300 VAC and 200,000 RMS Amps --- The DC rating would be less (I could not find one)--but I would guess that they have higher ratings than the other Scosche fuses you looked at. But a 400 amp fuse is almost $50 and almost 3" across.

Oh, here is the fine print on the DC interruption capabilities of the "T" (JJN-T-TRON) fuses from NAWS:

*15-600A rated 160Vdc, 601-1200A rated 170Vdc and 10 KAIC.

160 VDC and 10,000 Amps Interrupt Current...

I don't know of an inexpensive way to do fusing (fuse-able links maybe?)--But please be careful--Those batteries are capable of huge amounts of current into a dead short.

-Bill

benjamin · May 2010

Re: Portable energy storage system

So coming off the batteries I have two options it seems.

1. $10 fuses that have a max AIC of 6,000A ($100 total)
2. $45 fuses that have a max AIC of 500,000A ($450 total)

* Ignition protected (conforming to SAE J1171)- safe for installation aboard gasoline powered boats
* Silver-plated connector blades for corrosion resistance
* Visible indication of blown condition
* 6,000 Ampere Interrupt Capacity (AIC) satisfies ABYC requirements for main DC circuit protection on large battery banks
* For use with Blue Sea Systems' ANL Fuse Blocks

BB. · May 2010

Re: Portable energy storage system

Good deal--I missed the AIC rating (late, was working on a 7" netbook screen, ...:roll:).

I cannot give you any additional guidance... 6,000 amps is a lot of current at 12 volts -- you may never get a short that could sink 6,000 amps in your system and those fuses would be fine.

The larger 400+ amp fuses, I was looking at those for possibly your Inverter main fuses (high AIC rating)... But, again, your system, your choices (and I am not saying they are wrong/bad choices--I really don't know).

And certainly what you are looking at using is vastly better than no protection at all.

-Bill

icarus · May 2010

Re: Portable energy storage system

I know I will get static for this but sometimes I think things must be said.

You seem to have all the confidence in the world to build this system.

To me, this reeks of ready, fire, aim. The fact that you have a couple of thousand dollars worth of batteries before you have you PV built is, IMHO, silly. The batteries will require care and attention (not to mention energy) to keep in top form, for some number of months (or years) until you are ready to use them. In the meantime they will have used up some of their life sitting on a shelf.

Far be it for me,or anyone else to dictate to you (or anyone) what you should do. That said however, it seems that you keep finding justification for square pegs in round holes. I am reminded of the guy who contracted a grid tie system and was proud of what he was going to do. He was advised from post #2 that there were some flaws in his yet to be installed system, and that it would likely perform ~2/3 as well as expected. Rather than listening to the advice of those folks here with way more experience than he, he constantly argued and justified his ready, fire, aim. When the system was up and running,, it performed just about as well was predicted by the experts here,, ~2/3 as well as he thought. The net result was a system that had, in effect cost more and performed less.

I will anxiously await the results to see if they live up to your expectations.

Tony

BB. · May 2010

Re: Portable energy storage system

I would recommend that we ease off the Wind/Home Built Solar Panel warnings... One polite warning about safety issues and let the poster ask questions or not.

For the original poster, people are warning because they are concerned with you and your family's health and safety.

We have users here who's entire solar+battery+generator shed burn down (I think it was a generator/fuel issue); another poster that had a permitted Grid Tied System install that turned to have non-UL/NRTL listed panels and mounting (many home built systems are constructed from wood and plastic)--and it ended up catching the roof on fire but a watchful neighbor/close fire department saved the home; down to multiple post with failing wind turbines and towers (falling metal--even "commercially" built units).

Frequently the printed word is pretty harsh (no context, body language and feedback, etc.).

Every one here cares for health and safety--and many of us have made one or more of the mistakes of which we type. Batteries, solar panels, and fuel powered gensets all have their safety issues and concerns.

In the end, there are many levels of experience out there and the best we can do is give a friendly warning and let people take their own path.

-Bill

benjamin · May 2010

Re: Portable energy storage system

Listen, I appreciate the warnings but I don't appreciate comments such as, “You are going to burn your house down”.

I have a significant amount of experience in breaking down complex problems into individual components. The job of each component is to work well independently of other components.

An example would be a breaker box. It doesn't care how the power is generated or where the power is going. It only cares how much current is flowing through it. It's job is to stop the current if it exceeds set levels.

Each component of my system is designed to work independently. The batteries supply power. The cable transfers the power from the batteries to the bus bars. This cable is sized to handle 200A (300A based on what lorelec wrote) and there are 10 of them. Without fuses the bus bars could safely draw 2000A - 3000A. This cable will be fused at 110A or 130A, limiting the max current to 1300A, so there is no problem here. Each of these components serve their purpose and are assumed to be built correctly. I didn't build the batteries, or the wire, or the fuses. I don't even know how. But I know what they do and I know how to put them together.

The next component is the bus bars themselves. The bus bars must be able to handle the maximum Amps that will ever flow through them. The bus bars are quarter inch thick, two inch wide, two feet long solid copper. There will be a 700A or 800A fuse/circuit breaker between the bus bars and the load. This is another component and is built correctly.

I could go on and on for each component and you can quibble about my analogies here. The point is that if you are going to make a claim that this is a fire hazard and you want me to listen to you, you need to specify which component is dangerous and why. Claiming that a component is dangerous simply because the amperage is high, even though the component can clearly handle the amperage is not a valid argument.

Same with the solar panels. A few of you have stated that the performance of my homemade solar panels will be lower than what you can buy commercially, but you haven't stated specifically what component is the root cause of this, why it happens, or what can be done to prevent it. A few of you have stated that they may catch fire but you haven't specified what component is the root cause of this, why it happens, or what can be done to prevent it. These are issues I have already researched and am aware of.

I'm certainly not saying I have more experience than any of you. I am by no means an electrical engineer. I do however know how to look up what I need to know, I know how to build each component and build them well, and I know how to put them all together. You may argue that I made a mistake by building a 12V system, however there must certainly be benefits to this, even if only cost.

At the end of the day, I'll get this working properly and safely. I'll wire it up to some portable heaters as BB. advised and it will probably give me more power than I will ever need.

BB. · May 2010

Re: Portable energy storage system

Regarding reduced solar panel output--Commercial panels (generally) use thin (1/8" or so) Low Iron / Tempered Glass (standard glass transmits less light because of the iron)... And obviously, the tempering part needs to be done after cutting the glass and before you laminate your package.

Also, depending on the rear backing material's thermal properties--you could end up with more insulation than a "commercial panel"--Could cause cells to run a bit hotter--causing the Vmp to be depressed a bit wrt to other panels...

Part of limiting fire risks is limiting flammable materials (and having UL/NRTL traceability of all materials from the point of manufacture). And even "fire rated" plastics all demonstrate some sort of ability to burn (plus, add a high resistance connection or arc of 300-400 volts at 5 amps for a continuous ignition source)--It becomes a real engineering/test to make "good" panels.

You obviously have been working hard to locate suppliers and setup a process to manufacture your own panels. Hopefully you are successful.

There will be limitations in that non Listed panels are (in the US) generally "not legal" for use with Grid Tied solar systems.

For places where the NEC does not apply (off grid cabins)--nobody is going to stop you from installing your own panels. If you ever have any electrical fire--it is possible that the insurance company (if you carry insurance) could decline to pay the claim--blaming the non-listed panels--but I have not ever read of that happening.

There was a thread/newspaper article about UL Listing of Solar Panels:

UL testing of solar panels from the San Jose Mercury

Chris Paxton, who manages much of the solar testing at the lab, says the majority of "failures" occur with the "humidity freeze" test. The panels go through a 10-day testing cycle where they are exposed to 85 percent humidity — much like the environment in the tropics. Wet modules are then brought down to frigid temperatures of negative 40 degrees Celsius, where the moisture freezes and expands. UL technicians then scour the panels for any defects or inconsistencies in construction.

Not a lot of information -- but interesting none the less.

If nothing else, you will end up with a wealth of knowledge, experiences, and new skills.

Good Luck!
-Bill

Portable energy storage system

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