15.93kW off-grid solar array batteries?

[SunEagle]

The same thing could have been said 10 years ago.

You would think that the battery scientists would have developed a tried and true battery to last a decade by now.

[mzs112000]

So, I think I will use the Trojan Solar AGM 375Ah 6V batteries.
375Ah is the 20 hour rate. Based on the 10 hour rate, it's 329Ah.

So based on that, a 8S7P bank of them should give me 48v @ 2303Ah or 110.5kWh. According to the datasheet, it will last 1700 cycles at 50% Depth of Discharge, so I should be good for 55.2kWh with this pack...
Now, 55.2kWh is more than the house uses in a day, so that should be fine. The Volt only needs to charge once every 3 days or so, that should fit in quite nicely, and it will take me down to 65% Depth of Discharge every 3 days, or 55% Depth of Discharge every night.

[ButchDeal]

So, I think I will use the Trojan Solar AGM 375Ah 6V batteries.
375Ah is the 20 hour rate. Based on the 10 hour rate, it's 329Ah.

So based on that, a 8S7P bank of them should give me 48v @ 2303Ah or 110.5kWh. According to the datasheet, it will last 1700 cycles at 50% Depth of Discharge, so I should be good for 55.2kWh with this pack...
Now, 55.2kWh is more than the house uses in a day, so that should be fine. The Volt only needs to charge once every 3 days or so, that should fit in quite nicely, and it will take me down to 65% Depth of Discharge every 3 days, or 55% Depth of Discharge every night.

um 7 parallel strings ... wow, you are ambitious. I would highly recommend you reconsider that and look at using 2V batteries instead.

[jflorey2]

So, I think I will use the Trojan Solar AGM 375Ah 6V batteries.
375Ah is the 20 hour rate. Based on the 10 hour rate, it's 329Ah.

So based on that, a 8S7P bank of them should give me 48v @ 2303Ah or 110.5kWh.

1) Don't use AGM. They don't last as long and are less tolerant of abuse.
2) Don't put so many in parallel. Going more than 2 (3 at the most) is asking for trouble. The Rolls-Surette 2YS31P is a 2400 amp-hour battery; get 24 of them and you will be much better off than with 56 smaller batteries. They will last longer, be cheaper over time, be more reliable, be easier to maintain etc etc.

[organic farmer]

You would think that the battery scientists would have developed a tried and true battery to last a decade by now.

It certainly seemed like some big breakthrough was likely to happen any day, back in 2008.

[mzs112000]

1) Don't use AGM. They don't last as long and are less tolerant of abuse.
2) Don't put so many in parallel. Going more than 2 (3 at the most) is asking for trouble. The Rolls-Surette 2YS31P is a 2400 amp-hour battery; get 24 of them and you will be much better off than with 56 smaller batteries. They will last longer, be cheaper over time, be more reliable, be easier to maintain etc etc.

Wow. The Rolls 2YS31P seems perfect for my usage...
A bank of those should be perfect for running my house... And with 2500 cycles at 55% Depth of Discharge, they should last almost 7 years. Looks like those should fit the bill nicely...

[mzs112000]

Okay, I have layed out my (hopefully) final plan for the system...

First is the array, which is a 15.93kW array, it is ground-mounted, on kind of a truss/frame system, tilted south by the number of degrees needed for optimal sun-exposure year-round, and out of the way of any trees or other objects that could cause shading.

Batteries are 24x Trojan Solar Industrial series 2450Ah 2V Flooded Lead-Acid, I have calculated my kWh of capacity based on the 10-hour rate which is 1712Ah, the 2450Ah quoted from Trojan is the 100-hour capacity rating. The 48v 1712Ah bank gives me 82.1kWh, or 55kWh usable for my purposes, based on the cycle-life stated in the datasheet That should work, because my house will only ever use 55kWh maximum per day anyways. And it should be possible to add a second parallel string, if I ever need it.

My charge controller(s) are mounted on the array truss, under the panels safe from direct sunlight, wind and rain, since the batteries are also under the array, in a well-ventilated custom enclosure to protect from water, heat and such, that minimizes the length of my 48v wire run, so I can avoid excessive voltage drop and heat buildup on the cables.

My inverters(MagnaSine, they are stackable so I can put in up to 4 inverters if I ever need them), are also mounted under the truss, again so they are close to the batteries, to reduce wire run length and voltage drop.

From the inverter, my 240VAC line is ran in PVC conduit underground from the array, to the house service panel(standard 200A service panel). Also, I do have a second 240v line, going from the main service panel to a secondary disconnect/breaker-box on the garage, this is to run the 3.3kW Chevy Volt charger, lighting and other random items that may be used from time to time.
The Chevy Volt uses less than 7.2kWh per day, and my area has plenty of "free" level 2 chargers, so that is not a major issue. Also, any random items in the garage are used very rarely and mostly during summer anyways when there is plenty of daylight.

P.S., in my area, there is a year-round average of 4 peak sun-hours. I was told that a good ball-park estimate for daily energy output of a solar array is ARRAY-SIZE / 2 * (AVERAGE-PEAK-SUN-HOURS * 2). Lastly, during peak-sun hours, I am at work, I can easily have any high-power loads running during peak sun hours. The home is well insulated, the air-conditioner(which is a high-efficiency unit, and uses only 1500W) can be timed to run during peak sun hours to cool the house down to 60 degrees(F) and then shut off, by the time I come home from work/errands, the house has warmed up to about 70 degrees(F) and the sun is going down anyways to where summer lows are 75 degrees(F) anyways. Also, climate is nice, so AC may rarely need to run anyways. Clothes washing can be timed to run while I am at work, same with dish washing. Pretty much, other than the Chevy Volt, anything that uses large amount of power/energy can be timed to run during peak sun hours, and only small loads have to run at night.

So, all-in-all, what do you guys think, do you think this is a workable system? Is there anything you think I should change, or expound upon with this design? Is there any suggestions?
P.S.S, Year-round average daily PV output should be around 63kWh, unless it is a cloudy day, but cloudy days are usually cooler, so no AC usage is needed, and heavy loads(other than the Volt) usually run once every 4 days or so anyways.

Aaaannndddd another edit: For what it's worth, it does not usually get very cold where I live, and since the house is well insulated, heater usage is negligible, this last winter I started a heater for about 4 hours, just to make sure it still worked. If it does get cold enough for a heater, stored away somewhere I have an old computer, I could fire up that thing, and have it do Folding@Home or SETI@Home for a few hours, it will warm up a room quite nicely, and be doing something useful at the same time. PowerPC G5 CPU's are very toasty, AFAIK just the heat from one of those is like equivalent to 1,000 BTU/hr.