battery tables,charts, etc

lotek

Im trying to figure out how many batterys I need, how long a 250 vs 400 AH battery takes to charge ,how big an array I need to charge them, how long it will take, etc, Is there an online source for conversion tables, charts, that I could use?

If I'm using 9000 to 12000 watts a day, with 13 205 watt panels, can I get by with 8 250 AH 6v golfcart batteries? or will it depleat them beyound 40 %

BB.

Re: battery tables,charts, etc

First, I think you intended to type 9,000 to 12,000 Watt*Hours per day.

Assuming you have 13*205=2,665 or 2.665 kWatts of watt panels, mounted at your latitude, fixed mount in South Georgia near Columbus (USA--not the country of the same name ). Using the PV Watts website with a derating of 0.52 for an off grid system (note the 52% overall efficiency number accounts for all "average" losses in an off-grid system--if you use AGM batteries and/or DC power only, then we can adjust the derating number up a bit):

[FONT=Fixedsys]Results

Month
Solar Radiation (kWh/m2/day--"Hours of Sun" per day)
AC Energy (kWh per month)
Energy Value ($)
1      3.80          154        12.17   
2      5.05          186        14.69   
3      5.27          207        16.35   
4      5.97          221        17.46   
5      5.84          220        17.38   
6      5.48          195        15.41   
7      5.56          201        15.88   
8      5.72          210        16.59   
9      5.43          196        15.48   
10     5.26          201        15.88   
11     4.29          163        12.88   
12     3.47          138        10.90   
========================================
Year   5.09          2293       181.15 [/FONT]

Assuming your array will give you 100% power for 9 months of the year (other months will backup with genset)... February @ 186 kWhrs per month (divided by 30 days per month) will give you an average of 6.2 kWhrs per day (6,200 watt*hours).

Your need of 12kWhrs per day * 30 days = 360 kWhrs per Month which would require ~2x your current 2.6 kWatts of solar panels.

Regarding your battery bank... Assuming 12kWhrs per day * 3 days of battery backup (no sun) with a maximum of 50% discharge, and an 85% efficient inverter:

12,000 WH * 3 days * 1/50% * 1/0.85 * 1/12 volt battery bank = 7,059 AH 12 volt bank

Now--either I misunderstood your power requirements (9-12kWhrs per day) or you are planning on using a whole bunch of power a day.

2.66 kWatts of solar panels is not enough, and 8x 250 AH 6v golf cart batteries (or 4 strings of two 6 volt batteries each * 250 AH = 1,000 Amp*Hours) is way undersized.

If you plan on using a generator all year long (~1-4 gallons of fuel per day) to help. And, I would guess you need a 48 volt battery bank to handle the peak loads (unless you have some special application that draws an average 500 watts 24 hours per day)--the system as stands is not going to make you happy.

Also, 13 solar panels? With this sized system you should be using a large 60+ amp solar charge controller (or several if 12 volt system). Most people with wire up strings of panels in series/parallel (say 4 panels in series, the three strings in parallel) to reduce the the wire size/gauge and voltage drop of their PV panel to charge controller run.

13 panels in parallel will work--but makes for an expensive amount of copper if your panel wiring run to battery shed is long.

-Bill

PS: The above is based on our typical rules of thumb (or rule of thumbs :roll: ) that allow a quick and dirty sizing to the "average" off-grid user's needs--if you have special needs/applications, the numbers can certainly be adjusted to give you a more cost effective system.

lotek

Re: battery tables,charts, etc

I actually figured my expected usage at around 6000 watts daily.( I hope thats right) It may be less. and Im 30 miles north of tallihassee Fla.
I have room for 15 panels on my roof but was going to put 2 skylights (same size as panels) in. I could put in 3 and use 12 panels if I need to make all my panel connections to the combiner box equal.
I do have room on the ground in front of the greenhouse for another 5 panels, but they would be more vulnerable to damage at 2 ft off the ground.
With a 48v inverter, and a generator for cloudy days to keep the charge up, just how many batterys should I be using? or how much power should I reduce to

BB.

Re: battery tables,charts, etc

OK, assuming 6kWhrs per day and Tallahassee Fl -- we get:

[FONT=Fixedsys]Results

Month
Solar Radiation (kWh/m2/day)
AC Energy (kWh)
Energy Value ($)

1      4.10          165        14.85   
2      4.86          177        15.93   
3      5.07          196        17.64   
4      6.05          227        20.43   
5      6.15          229        20.61   
6      5.73          203        18.27   
7      5.28          191        17.19   
8      5.52          203        18.27   
9      5.38          194        17.46   
10     5.32          201        18.09   
11     4.51          169        15.21   
12     3.92          153        13.77 
=======================================  
Year   5.16          2309       207.81    [/FONT]

Assuming 9 months of average power from panels.

177 kWhrs per month / 30 days = 5.9 kWhrs per day

So, you are pretty close to meeting your average load with average weather.

Earlier, you talked about using an XW inverter... So lets assume 48 volts and 6kWhr average daily load with 3 days of no sun, 50% maximum discharge:

6,000 Watt*Hours * 3 days * 1/0.50 * 1/0.85 invtr eff * 1/48 volts = 882 Amp*Hours @ 48 volts

-Bill

Solar Guppy

Re: battery tables,charts, etc

Near Florida huh?, where is the juice for the AC coming from?


It takes a 14kW PV system for my home to net-out usage ... and I have a well insulated attic and high efficiency appliances including the AC

lotek

Re: battery tables,charts, etc

Ive lived here for 20 yrs and never used anything but a fan. My new project
(home in the swamp) Is on 6 ft poles and gets good wind,( when its blowing)
I will also be adding underground duct( 6" PVC pipe into the swamp and under water) to bring in cooler air. + LP and wood stove + solar and LP on demand hot water. My biggest electrical draw should be the LCD TV. computer. frig, and freezer, Still looking at the best models to pick from.
>next project, trying to figure out how to tie in an electric scooter moter(DC 24 or 36 volt generator) to the battery bank , Well that, and hook it up to a bike.