Can I harvest 2,000 Watt*Hours per day with....

Himins

I know math pretty well, but electricity does throw me a curve so here is the question...

With 4 6v exide Golf Cart batteries wired 12v
Outback Cc fm80
psw inverter 600w pulling .8amp at idle
6 230w panels...see side bar for specs
3.5 hours of direct sunlight per day in my location (N.W. Minnesota)

Can I harvest 2000 kw per day, and how deep will these batteries by cycled per day(more than 70%?)
Would a 24v inverter make enough difference in effeciency to keep the dod below 70%?

I am sooooo close with a bank of murdered batteries, I am comfortable with the gauge of wire, and overall effeciency of the wiring lengths and diagram etc..
I just survived -36 degrees for 3 days without using my furnace fan or my generator...BUT I had to use about 2 gallons of kerosene per day to supliment heat source....If I can harvest 2000 kw per day instead of the currant 1.4 kw per day...I could use the fan on my furnace instead of kerosene ...this would save cord wood and fossil fuel use on the coldest day during the winter months.


exide GC2 GC-145 6v 145 20hr amp rate245 ah rc min @25 amps=525 rc min @75 amp=145



Short Circuit Current (Isc): 8.80 Amps
Open Circuit Voltage (Voc): 36.75 Volts
Maximum Power Current (Ipm): 8.14 Amps
Maximum Power Voltage (Vpm): 29.00 Volts
Temperature Coefficient (Voc): -0.351%/°C
Temperature Coefficient (lsc): 0.053%/°C

Electrical Characteristics
Maximum Power (Pmax)*: 230 Watt
Tolerance of Pmax: +10%/-5%
Type of Cell: Polycrystalline silicon
Cell Configuration: 60 in series
Module Efficiency (%): 14.7%
Maximum System (DC) Voltage: 600 Volts
Series Fuse Rating: 15 Amps

Rybren

Re: Can I harvest 2000 kw per day with....

Himins wrote: »

d how deep will these batteries by cycled per day(more than 70%?)

I'm about the farthest thing from an expert that you'll find, but to answer this question, I believe that you'd need to define your load (in WH or AH)

westbranch

Re: Can I harvest 2000 kw per day with....

Not only how much they are but what are you powering? motors? heaters? lights? etc

Cariboocoot

Re: Can I harvest 2000 kw per day with....

Can you harvest 2kW hours per day from 1380 Watts of panel?
Yes. Depending on location and what day. Using the Icarus formula you get:
1380 Watts * 4 hours minimal equivalent good sun * 52% over-all efficiency = 2870 Watt hours AC.

Will you get this much? That depends on the particular circumstances. With an off-grid system more power can be had if you can utilize the panels' output potential once the batteries are charged (opportunity loads) otherwise this potential goes unrealized.

Now about those batteries. Is that eight 12 Volt 145 Amp hours all wired in parallel? If so, that's two problems right there. One would be the eight parallel connections, the other would be trying to charge 1160 Amp hours @ 12 Volts from a 1380 Watt array; not enough current (about 88 Amps when you need 116), and if there were it wouldn't all be handled by one charge controller.

Rybren

Re: Can I harvest 2000 kw per day with....

In the body of the OP, he says that he has >>4 6v exide Golf Cart batteries wired 12v<<

His sig block says >>8 deep cycle 12v batt<< Guess he changed them out for the 6V

BB.

Re: Can I harvest 2000 kw per day with....

There are some typo's in the title of the post:

2,000 kW is a "rate"... Like Miles Per Hour and Gallons per minute.

Watt*Hours is an amount... Like miles driven and gallons pumped.

kW is 1,000 x Watt...

So, you typed 2,000 kW but I think you mean 2,000 Watt*Hours or 2kWH per day...

Math wise, just from the solar array powering an AC off grid inverter:

6x 230 watt panels * 0.52 overall system efficiency * 3.5 hours of sun per day = 2,512 Watt*Hours = 2.5 kWH per day

So--Technically, you could do that... However, 3.5 hours of sun sounds pretty high for N.W. Minnesota in the dead of winter... Using PV Watts for Fargo North Dakota with an array tilted to vertical (to shed snow):

Month    Solar Radiation
(kWh/m 2/day)
1      3.61     
2      4.58     
3      4.12     
4      3.62     
5      3.13     
6      2.97     
7      3.16     
8      3.53     
9      3.66     
10      3.58     
11      2.95     
12      2.92     
Year      3.48

And tilted to latitude:

Month    Solar Radiation
(kWh/m 2/day)
1      3.42     
2      4.66     
3      4.94     
4      5.28     
5      5.57     
6      5.71     
7      5.83     
8      5.71     
9      4.94     
10      4.11     
11      2.98     
12      2.75     
Year      4.66      

Looks like you may have a fair amount of sun in the winter--But perhaps some cloudiness in summer.

So, depending on your panel tilt, snow on the ground (reflections), it looks like it may be possible...

Are you planning on running the loads during the day or during the night--or split between day/night?

-Bill

Photowhit

Re: Can I harvest 2000 kw per day with....

So are the 12V batteries dieing and thinking of replacing them with 6V golf cart batteries?

I'm guessing you have no capacity left in your current battery bank, so your not running your fan?

Can you not supliment your solar with your genny for these cold days so you could run your fan?

So what makes you think your only harvesting 1.4Kwh per day? is this from your Charge controller? Are you running the fan on you furnace during the day when your batteries are topped off?

How many cloudy days do you have during these winter needs? This is important in figuring out you batter bank capacity. If you use the top 30% but can't recharge shortly following you'll run the batteries past the 70%.

BB.

Re: Can I harvest 2000 kw per day with....

Have a little more time to type here...

Regarding battery usage... You have 4x 6 volt 220 AH batteries, if you use 25% per day (a more or less "balanced" usage):

• 4x 6 volt * 220 AH * 0.85 inverter eff * 0.25 discharge = 1,122 WH = 1.1 kWH per day

So--You should have ~2x larger battery bank to run a 2kWH load at night. Currently, you would be at almost 50% discharge if you used 2kW per night. Could be OK--But you certainly need to get the batteries pretty fully charged the next day

For a 6x230 Watt array, with 5% to 13% to 25% typical rates of charge:

• 6*230 watts * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.05 rate of charge = 3,644 AH @ 12 volt maximum battery bank
• 6*230 watts * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.10 rate of charge = 732 AH @ 12 volt nominal
• 6*230 watts * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.13 rate of charge = 564 AH @ 12 volts max cost effective for solar
• 6*230 watts * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.25 rate of charge = 293 AH @ 12 volts max with thermal management

Your current bank is 440 AH @ 12 volts... So, you appear to have a slight "excess" of solar panels... A "nice balance" for a 2kWH per day battery bank with 2 days of storage and 50% maximum discharge would be (assuming charge during daylight and run loads at night from battery bank):

• 2,000 WH * 1/0.85 inverter eff * 1/12 volts * 2 days of storage * 1/0.50 max discharge = 784 AH @ 12 volts

And the array sizing would be (5-13% rate of charge):

• 784 AH * 14.5 volts * 1/0.77 panel+controller derating * 0.05 rate of charge = 738 watt array minimum
• 784 AH * 14.5 volts * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,476 watt array nominal
• 784 AH * 14.5 volts * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,919 watt array "cost effective maximum"

Your current array of 6*230Watt=1,380 watts is not too far off of running at 784 AH @ 12 volt battery bank.

If costs were an issue, I might be real tempted for 3 parallel strings of golf cart batteries and leave the array as is (you will have a bit more generator runtime in winter).

If not, I would look at 8*230 panel array and a 24 volt battery bank (new inverter, probably use the same MPPT Solar Charge Controller). And get a larger battery to try and keep the string down to 1 series string (2-3 parallel battery strings is the most I would recommend unless you have no other options).

If you stay with 12 volts, you would need 100 amps or more of charge MPPT solar charge controller--The single FM80 would toss out 20+ amps of available array current in the middle of the day. But you could keep your 12 volt AC inverter.

Personally, I look at the battery bank as the "weak link" in any system. Larger AH cells in series, vs smaller cells in series/parallel is always my first suggestion.

But, it does come back to loads... A 12 volt battery system really starts to struggle with >~1,200 watts of loads (well over 100 amps of DC current). So--if you have plans/needs for higher loads (or higher starting currents such as fridge/well pump/etc.)--Then as your bank AH capacity needs rise, you really should look at 24 or 48 volt systems... The Outback FM is good for 12/24/48 volt batteries--So each time you double the bank voltage, you also double the size of solar array you can support, without needed to buy an new/second/third charge controller (if only AC inverters where so "nice").

-Bill

Himins

Re: Can I harvest 2000 kw per day with....

i'm currantly using 5 murdered 12 volt batterys wired to 12 v...My new battery(if its size works) will be 4 exide 6v GC batts. still wired for 12 v untill I can purchase a 24 v psw inverter. I am very happy so far with my 600w psw Go Power inverter. I should have gone up one more notch to a 1000 W as it offeres a sleep mode.
The murdered battery is working extreemly well considering they were in the junk pile, free. I'm guessing actual battery's designed for GC would be a marked improvement. I am running one box fan, and would like to run one furnace fan during the coldest winter days...I'm very very close now...with the murdered battery.

Himins

Re: Can I harvest 2000 kw per day with....

You are correct BB...it was a type o... kwh according to my kilowatt meter. I'm kind of optimistic as this system has been awesome so far. the colder its been the more i need the furnace fan....and when the temprature drops this low...we get brilliant sun as a side benefit.

Himins

Re: Can I harvest 2000 kw per day with....

To Photowit...I am changing the batt to 6v golf cart Exide. I use about a gallon of gasolene per week to supliment the currant system. When its cloudy, its generally warm enough to get by running a single box fan. I am averaging 1400 kwh actual use per day...I need to up it to 2000 kwh, then I can use the furnace fan a tiny bit after sundown...and during the coldest days after the battery is topped off during daylight...if possible.

Himins

Re: Can I harvest 2000 kw per day with....

Thanks Bill...BB...that helps a whole lot, I didn't thing of 3 strings of 6v...for some reason I thought I would have to go with 4 or 8...You have solved my puzzle here and I really appreciate everyone's help. Thank you again.

Photowhit

Re: Can I harvest 2000 kw per day with....

Some of the larger box fans use close to 100 watts, not sure what yours does, you might look into a 10" fan like and O2cool Which is closer to 10 watts but really moves a lot of air for a 10" fan.

The link is to WalMart who doesn't sell them over winter, but I think Amazon does.