Proposed system / Calculations

[morgandc]

I am in the final stages of moving to an off grid house in Sacramento, CA area and am starting my upgrade planning.

Calculated winter daily loads are 15.5kwh
Weekly loads that can be shifted 46kwh/wk and run with generator if needed
Optional load for summers 12kwh (Hybrid car, gas and charge at work in the winter)

Calculate for Winter 15.5kwh*2 days*1.5 losses= 46.5kWH
Calculate for Winter 15.5kwh*3 days*1.5 losses= 70kWH

46.5kwh/48v = 968AH needed for 2 days
70kwh/48v = 1458AH needed for 3 days

Trojan SIND 04 1685 has a 1293ah * 48v 20hr rate = 62,064 kWh
Trojan SIND 02 2450 has a 1489ah * 48v 48hr rate = 71,472 kWh
Trojan SIND 02 2450 has a 1594ah * 48v 72hr rate = 76,512 kWh

2 days @ 20hr rate => 968ah/1293ah => 75% discharge => 25% charge
2 days @ 48hr rate => 968ah/1489ah = 65% discharge => 35% charge
Days of charge to 20% = 1594ah/484ah = 2.63 days

Not ideal, but stays above 80% discharge in emergency, and a generator can be used to help as needed. To increase to 3 days or staying about 50% batteries requires doubling the inverters, panels, etc. to meet the min charge rates. This would translates to a 50% increase in an already expensive system, and 50% more in battery replacement costs forever.
http://www.trojanbattery.com/pdf/dat...04_1685_DS.pdf

So, assuming 1293ah batteries that puts me at a max discharge of c/8 = 161.6amps, and min. charge rate of 129 amps.
Min. Generator size is 129amps*48v = 6.2kW @80% load = 7.7k round up to 8k generator
min. solar array is 129amps * 48v = 6.2kWh
Max draw is 161amps =>7.7kW

Solar array is at 150 degree angle, due to shading and pvwatts says

Month	6.9k DC array Output (kWh)	per 30 days kWh
Jan	488.0	16.3
Feb	658.9	22.0
Mar	871.4	29.0
Apr	1017.0	33.9
May	1085.9	36.2
Jun	1054.5	35.1
Jul	1117.8	37.3
Aug	1146.7	38.2
Sep	1077.5	35.9
Oct	936.6	31.2
Nov	603.9	20.1
Dec	471.7	15.7

Existing system
Solar Array: 2.5kW panels
Inverter/Charger: Magnum MS4448PAE
Batteries: 48v 370ah and 7 years old.
Generator: Champion DuelFuel 7k continuous

Proposed System
1x Schneider Electric Conext XW+ inverter rated at 6800watts
2x Midnite Classic 150
12x 4v Trojan 1685AH batteries
1x top of pole mounts holding 15 60cell panels
15x 295watt mono Solarworld panels (input needed)
12x 205watt poly panels (existing panels)
8k Diesel or LP liquid cooled low rpm generator
1x residential fridge is in the daily load calc (The main fridge, not willing to compromise to propane)
1x 48v Sunfrost RF18 is in the daily load calc (may not happen, but including in loads)

Once I pin down the proposed system, I will then be trying to figure out the best order to do things. The generator brand doesn't instill confidence and the batteries are on their last legs. I don't dare get an expensive set of batteries without a large enough inverter/charger to maintain them. The existing Magnum invertor could charge them, but not avoid stratification.

Proposed order of purchase / install
1. Generator 8k
2. Solar Panels -> upgrade existing system to 4.4kW with the new panels
3. Forklift upgrade the Inverter and chargers / Upgrade to full 11.4kW
?? Batteries

Batteries should be replaced soon, so possibly step 1.5 if I can survive 6-12 months with the existing charger and not kill them. Otherwise step 4 and I hope I can avoid buying a temp cheap set of batteries in the meantime. Possibly a lot of generator time, which is cheaper than a cheap set of batteries

[Mike90250]

15kwh daily ? That is some load. Any of that you can shed will be useful.

[morgandc]

It seems to add up fast with someone in the house all day... I am hoping that the numbers are estimated high, but they are gathered off the net, so we shall see. I can hopefully get some real numbers in a few weeks

-Dwight

	Qty	Watts	Daily Hours	Daily Total WH	Weekly Hours	Weekly Total	Notes
Car - Surplus KW / Generator / @work	1			12,195			Winter I will run on gas kicker engine or Generator
Annette PC - Business style 2x monitors	1	400	9	3,600
LP Heat (fans)	2	70	16	2,240
Dwight PC, 2x monitors - Gaming style	1	700	3	2,100
Refridge - LG Residential	1			1,959
Refridge - Sunfrost RF19	1			1,019
Air Filters	2	20	24	960
LED Lights	2	20	17	680
Cameras	2	12	25	600
Security System	1	22.5	24	540
TV	1	150	3	450
Microwave	1	1200	0.3	360
Keurig	1	1500	0.2	300
Toaster	1	1200	0.2	240
Clock Radio	1	7	24	168
Vacuum	1	1000	0.1	100
Blender	1	500	0.1	50
Toothbrush	2	0.9	24	43
ipads	1	2.5	12	30
router	1	2.5	12	30
electric razor	1	0.9	24	22
phones	2	10.5	1	21
apple tv	1	0.5	24	12
smart watch	1	1	1	1
Well Pump (150ft water level, 1.5HP)	1	2760		-	7	19,320	15gpm - Large Cistern with gravity feed - Gen or sunny days
dryer	1	1800		-	7	12,600
dishwasher	1	1500		-	2	3,000
washer	1	800		-	7	5,600
LP Oven	1	90		-	4	360
Rice Maker	1	1000		-	1	1,000
Pressure Cooker/Crock Pot	1	160			8	1,280
			Total with car	27,720		41,880
		Summer	Daily with car	41,580		62,820	x1.5 for off grid inverter innefficiencies
		Winter	Daily without car	17,887			x1.5 for off grid inverter innefficiencies

[bcroe]

I am in the final stages of moving to an off grid house in Sacramento, CA area

Trojan SIND 04 1685 has a 1293ah * 48v 20hr rate = 62,064 kWh
Trojan SIND 02 2450 has a 1489ah * 48v 48hr rate = 71,472 kWh
Trojan SIND 02 2450 has a 1594ah * 48v 72hr rate = 76,512 kWh

1293ah * 48v = 62,064 WATT HOURS, NOT KWH. Better check everything again. Bruce Roe

[SunEagle]

1293ah * 48v = 62,064 WATT HOURS, NOT KWH. Better check everything again. Bruce Roe

Damn that 3 place decimal point for "k" always getting in the way of good numbers.

[morgandc]

LOL, good thing that is from the word document and not the spreadsheet!

[morgandc]

One the reasons the battery capacity is not larger, is due the max charge rate on the WX+6848 being 140amps. Following the min. 10% charge rate rule of thumb, 1400ah @20hr is the max battery bank it can charge properly without sunshine to help out. How firm is this recommendation? Could I bump up the batteries to the next size up? Say the 2v 1547ah Trojan industrials? This would put be below 10% without solar to help. The solar plan can add up to more than 100 amps if I were to run the gen during the day. On the other hand, the battery size is already pushing based on the 6.9kW panel size alone. But that could be upped a little bit easily.

[Mike90250]

Have you figured how much solar and charge controllers it's going to take, to get your 10-13% charge rate for a larger pack ? And figured it for only the high performance part of the day, you don't get noontime sun all day long

[morgandc]

The 2x midnight solar controllers can handle up to 96amps each so that would be 192amps enough for any non parallel Trojan industrial line configurations at 10%. I have no problem bumping up the solar array a bit more to match the 10%, just really don't want to add another invertor for the additional generator charge rate. The length of that charge time is what I was hoping someone would chime in with. If I went to 1547ah, I would be at 9% on the gen charge capacity plus whatever solar I have. How long does the charge rate have to be above 10% to mix the electrolyte properly? Is mid day enough...

[Mike90250]

Are you sizing batteries for loads, or for expected long days of clouds ? To stir the electrolyte with bubbles, you have to get the battery charging voltage above the gassing point. That happens in the latter half of the Absorb stage. If you have drained batteries down low, you may not have enough solar to get the batteries recharged to the gassing point, forcing you to run generator.
The electrolyte only needs weekly stirring, it takes it a while to separate out to different layers, but you still need to recharge to prevent sulfation,

[morgandc]

The sizing is based on a balance of a couple days of min. winter load combined with staying below the threshold for moving to a 2nd inverter, 3rd charger and more panels to keep up with a larger battery bank.

If bubbling is caused by voltage/bubbling, why the need for a min c/10 charge rate? Couldn't you in theory get to the same point with a longer charge period?

[Mike90250]

......If bubbling is caused by voltage/bubbling, why the need for a min c/10 charge rate? Couldn't you in theory get to the same point with a longer charge period?

Because you need enough power to get the batteries to that voltage. With solar, you only have so many hours to work with. And these are "Guidelines", you can play outside the lines, but understand things may not work as expected.

[morgandc]

Thanks, it helps to understand it is voltage/charge related and not a certain period time of amperage.

[morgandc]

Well, I have been living on the existing system now for 6 months. No car charging, no crock pots, no kuerig, no dishwasher (yet), no well usage (use gen). But otherwise during summer I can live on10KWh in a day no problem. I really wish I had decent monitoring of usage off the charger/inverter for better numbers instead of just looking at the solar charger numbers. Winter was another story... the generator was being run every day for a couple of hours.

Moral of the story, real life usage doesn't match up with the theoretical numbers all that well.