vprinc:Questions about my off grid solar power system and battery options

Vprinc,

Fee free to start your own thread--If you want futher discussions. It keeps your Q&A in "your thread"... Anyway, per Estragon, the hours of sun per day by month gives you a pretty good way to estimate how much your system will generate (or how large of solar array you need).

For example, a fixed array in Phoenix AZ:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Phoenix
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle from Vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.92	5.55	6.45	6.83	6.74	6.57
Jul	Aug	Sep	Oct	Nov	Dec
6.08	5.78	6.03	5.82	5.24	4.74

If you are in Phoenix, and you have very good sun, the array set for "average" best year round production... Worst case is December:

• 10,000 WH per day * 1/0.52 off grid system performance * 1/4.74 hours of sun (Dec) = 4,057 Watt array "break even" December

Or, 24 panels * 320 Watts per panel (=7,680 watt array):

• 24 panels * 320 Watts * 0.52 off grid system eff * 4.74 Dec hours of sun = 18,930 WH per day (Dec average) ~ 18.9 kWH per day (Dec)

Your battery bank, if 2 days of storage (no sun) and 50% discharge:

• 1,110 AH * 48 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 max typical discharge = 11,220 WH of storage (2 "days" with 50% max discharge)

To recharge your battery bank, rule of thumb recommendation is ~5% to 13% rate of solar charging... 5% minimum (weekend/sunny seasonal usage) to 10%+ for full time off grid:

• 1,110 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.05 rate of charge = 4,214 Watt array minimum
  
• 1,110 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.10 rate of charge = 8,429 Watt array nominal
  
• 1,110 AH * 59 volts charging * 1/0.77 panel+controller losses * 0.13 rate of charge = 10,957 Watt array "cost effective" maximum
  

Arizona has lots of sun--So your minimum charging current array is pretty near your "worst case" month of sun and loads...

And for a 1,110 AH @ 48 volt battery bank, the "recommended" maximum "useful" AC inverter size (for a flooded cell lead acid battery bank) would be around 5,500 to 11,000 Watts (more than that, is a substantial drain on the that size battery bank (basically 1kW per 100 AH of storage for a 48 volt battery bank).

The above is just a generic start about your system. At least with first guesstimates--Your system seems pretty well configured for full time off grid usage (possibly no genset needed) as you have configured.

Monitoring your battery bank with a hydrometer (logging temperature corrected specific gravity for each cell, once a month or so).

Keeping electrical connections clean and torqued.

Get a DC Current Clamp DMM (like this one from Sears, "good enough" for our needs). You can use it, for example, to measure the DC current for each string in you array and make sure each is carrying its fair share of the current (no bad connections, failed panels, etc.).

-Bill

vprinc,

I have moved your questions to your own thread--It helps keep things simple (your questions, answers to your questions).

What is it you want from your battery bank? Low cost, reliability, easy maintenance, long life, or all of it (not going to happen).

Well maintained Fork Lift Batteries seem to be a nice solution with >15 year life if well taken care of (kept clean and water, not discharged to dead, not sitting around with less than 75% discharged, etc.).

NiFe batteries--Seem to be very rugged, but need lots of "extra" solar power (~65% efficient batteries vs Flooded Cell Lead Acid batteries that are >~80% efficient). Plus every few years you have to dump and refill with new electrolyte (absorbs CO2 from air)--Not an easy job.

-Bill