House/solar battery opinions

[seraphim]

My current battery space is 20"L x 14"w x 10"H

Going solar, and want to packs as much AH in there as I can (reasonably). Currently looking at 250 - 300. Price is not THE deciding factor, unless all else is equal.

I don't have experience with a lot of different companies, so I don't know who may a poor reputation. Some I am looking at:


http://www.apexbattery.com/group-8d-gel-solar-battery-solar-batteries.html $609 + $109 shipping)

http://www.atbatt.com/product/23216/sla/power-sonic/12v-150ah/battery#tabs ($774 for 300ah no nipping)

http://www.batterygiant.com/Product/8D%2DGEL (allegedly $577 (maybe $669) for 225AH can pick up locally)

http://www.mastervolt.com/marine/products/agm-slimline-12v/agm-sl-12-150/#specifications (can fit 2 185AH units in my space - haven't found an online price yet, which tells me something lol)

Any thoughts on these, or others you are aware of?

[full_mosey]

seraphim wrote:
It's not the smallewr attage I've been looking at, but the number of amps after the mppt converts the current from, let's say, 39 volts to 12. I may be wrong, but it seems to me the charging amps being pushed into the battery is the key factor. Am I wrong?

Doing the math, I've been finding single high voltage panels which - after the dc to dc conversion - put out the same or slightly higher amperage than a group of 100 watt 12v

Basically, MPPT does Watts in = Watts out; less operating efficiency.

Nominally speaking, if your battery is accepting 30A at 14V, then 30A*14V=420W will be drawn from the array.

At 14V, up to 480W/14V=34A can be drawn from the array.

The actual array Watts will be governed by temperature, tilt and insolation.

HTH;
John

[time2roll]

As long as you have MPPT wattage is what matters.
Divide wattage by 14 to get approximate amps.

Conservation is the other side of the equation to keep the battery full.

[seraphim]

I'm confused here. How'd you jump from amps (480) to watts? Is .06 a magic number of which I don't know the significance lol? Plus, in the Midwest, the charts only show about 3 hours of usable sunlight a day rather than 5.

We're back to the question I posed Almot - which is more important; the wattage of a panel irregardless it's voltage, or the number of amps being put into a battery at its charging voltage?

I'm curious about both of your answers...

Pianotuna wrote:
Posted: 08/21/13 08:56am Link  |  Quote  |  Print  |  Notify Moderator
Hi seraphim,

I prefer to calculate *grin*

480 x 0.6 = 288 watts minimum.

288 x 5 hours = 1440 watt hours

1440 watt hours /12.8 volts = 112.5 amp hours

parasitic loads are typically 36 amp-hours per day

seraphim wrote:

It seems that 480ah is the most I can squeeze into the available space.

And if I use 100ah a day, then I only have two days of battery power to use, unless I can recharge that amount on a daily basis - which I doubt lol.

[seraphim]

Posted: 08/20/13 10:55pm Link  |  Quote  |  Print  |  Notify Moderator
seraphim,

Sorry about that, but I believe I was mistaken as it doesn't sound just right.
You are right, you should have more than 0.01 amps when charging. Besides, the Trimetric only reads in 10th's of an amp, not 100th's. Is it possible that you have the wrong shunt resistor? Without shore power connected, try turning on one incandescent 12 volt light bulb, the current (negative to indicate out of the battery)should increase by about 1.2 amps.
Also, you may want to set P1 to ~13.5 volts.
Again, you may be best served by contacting Bogart Engineering directly to verify correct setup.

Steve

Good idea. They allegedly sent the 500amp shunt. Before I call, I may open up the monitor and make sure a wire didn't pull loose.

[seraphim]

It's not the smallewr attage I've been looking at, but the number of amps after the mppt converts the current from, let's say, 39 volts to 12. I may be wrong, but it seems to me the charging amps being pushed into the battery is the key factor. Am I wrong?

Doing the math, I've been finding single high voltage panels which - after the dc to dc conversion - put out the same or slightly higher amperage than a group of 100 watt 12v

[Almot]

seraphim wrote:
It seems that 480ah is the most I can squeeze into the available space. If I could put 600 in, I would. Now I'm trying to get the best charging available for that 480 ah bank I can, using a limited amount of available roof space.

I highlighted what seems most important to me. The best charging = higher panel wattage. Max up the wattage. It will cost more for 4*100 12V panels than one 300W, but not much more in total, considering cheaper PWM controller. And it sounds like price is not your biggest concern.

I hear you about limited battery bank. In solar homes they recommend bank big enough for 10 days. In RV I think 3-5 days is good enough. With low daily draw, 480 AH bank should work well if you can fit that much. 400 AH bank will be still good though you will have to be more energy-savvy.

But you need enough solar to charge the bank fast - there can be rain and clouds, and larger panel could do it better then - and keep the bank close to full. There is no benefit in getting a smaller solar wattage. Rule of thumb is 1W per 1 AH of the bank, so 4*100W solar is not too much for 480 AH bank.

[BFL13]

No idea with MPPT and tracking confusion issues, but I did report on my success with parallel PWM controllers on one array on one battery bank.

In this case the question was whether you could put a Y in the array to controller wiring and have one controller on each leg of the Y. The controllers have their own controller -battery wires to the same battery.

It worked just fine. I was not able to measure how many amps of the total each controller did, but it would not be half each unless the Y were perfectly even for R.

You don't need two separate array-controller sets of wires iaw. You can put the Y close to the controllers and save a bunch of wire.

The reason for that set-up was that each controller was under-sized for the total amps of the array, but the two controllers sharing kept each under its rating. Worked great.

[full_mosey]

smkettner wrote:

mena661 wrote:
Can you use parallel controllers on one PV panel?

Why would this be helpful?
Not a best practice even if it works.

He doesn't have solar. We have no idea which MPPT controller mfgrs are being considered.

However, I can't see how multiple MPPTs could cooperate from a single panel due to the constant testing of the panel's parameters.

I vote no.

HTH;
John

[time2roll]

mena661 wrote:
Can you use parallel controllers on one PV panel?

Why would this be helpful?
Not a best practice even if it works.

[mena661]

Same bank. MPPT controller.

[full_mosey]

mena661 wrote:
Can you use parallel controllers on one PV panel?

To same bank or separate banks?

MPPT or PWM?

Morningstar has some very informative documents. Don't know whether they apply to non MS controllers.

PWM with separate banks, yes with diodes.

HTH;
John

[pianotuna]

Hi mena,

In theory yes, but all leads would have to have identical resistance. It's probably a bad idea. That magic blue smoke is just waiting to escape.

[mena661]

Can you use parallel controllers on one PV panel?

[full_mosey]

seraphim wrote:

So rather than attempt to calculate our usage, I bought a monitor to SHOW me our usage. But our usage will not change how much AH we install. We want to install the max reasonably possible.

You're doing it right.

A pair of 240W 24V panels with a MS MPPT 45 is a good fit. This controller will allow for tilting.

If the panels need to be far apart, and flat mounted, you might consider two MPPT 15 with separate parallel wiring to the bank.

Have you decided on the battery bank?

HTH;
John

[pianotuna]

Hi seraphim,

I prefer to calculate *grin*

480 x 0.6 = 288 watts minimum.

288 x 5 hours = 1440 watt hours

1440 watt hours /12.8 volts = 112.5 amp hours

parasitic loads are typically 36 amp-hours per day

seraphim wrote:
It seems that 480ah is the most I can squeeze into the available space.

And if I use 100ah a day, then I only have two days of battery power to use, unless I can recharge that amount on a daily basis - which I doubt lol.