over sized battery banks

Re: over sized battery banks

You are drawing (a guess) around 10% of the power from your battery bank. Lead acid batteries will be a bit happier if you draw them down by 20% (or to 80% state of charge)--You can do that, as BC04 says, by simply turning off the solar charge controller for 1 day.

Another issue is that you really need a minimum amount of charging current to stir up the electrolytes (and possibly even to help "unplug" the pores on the plates...

• 1,110 * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,045 Watt array minimum
• 1,110 * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,090 Watt array nominal
• 1,110 * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 2,717 Watt array cost effective maximum

Your 850 Watt array in a typical location that gets a minimum of 4 hours of sun per day (9+ months of the year), would generate a minimum of:

• 850 watt array * 0.52 end to end system eff * 4 hours of sun = 1,768 Watt*Hours per day of 120 VAC power (minimum typical clear day)

So--Here you are--The batteries, if everything is going well will last you--Call it 8 years as they are now.

If you had 1/2 the battery bank, the batteries will last you ~8 years again. For 2x the amount of cash, and 2x the risk if those covered batteries you cannot check are actually "unhappy" right now.

And you will have a much better rate of charge for the battery bank (well over 5%) without adding one solar panel.

The amount of power you can pull from your bank if you use the 25% discharge rule of thumb (nominal--25% per day for two days, recharge 3rd day to keep battery from going much below 50% State of Charge):

• 1,110 AH * 12 volts * 0.85 inverter eff * 1/2 days storage * 0.50 max discharge = 2,831 WH per day

Or almost 2x your present load...

Unless you have some large surge load (like starting/running a large well pump or similar)--You are just driving around in a bus when a 2 door car will do just as well.

Not exactly wrong (although, I would still recommend you add some more panels to your array to get you >5% rate of charge), it is just not optimum.

If you cannot run the genset very much in bad weather (hard to get fuel, don't like the noise and fumes, etc.)--Then, perhaps the larger battery bank is a good solution for your needs (again, I would suggest a larger solar array for better average charging current--And running down the batteries 1-2 days without recharging once a month like BC04 suggests to cycle the banks--Floating/shallow charging can be hard on lead acid batteries).

Energy is a highly personal set of choices. What works for me (Grid Tied in a major metro-area) or a couple moderators in the middle of the Canadian wilderness, may not work for you.

And, you may need to re-rack your batteries. Maintenance (measuring/logging temperature corrected specific gravity, cleaning/tightening wiring connections, checking/logging per batter voltages once a month, etc.) will help you better understand your bank and catch problems before they happen. In a bank your size, you could have an open cell or cable and ever even notice it--until years later when the bank capacity falls--and you find out 1/3rd of your bank is already long dead.

Besides a hydrometer, I suggest a DC Current Clamp DMM (like this inexpensive one from Sears--good enough for our needs). You can monitor the DC charging and discharge current per string and make sure that everything is reasonably balanced and you don't have any shorted or open cells (or bad connections).

Also, watch your automatic watering system--Do not let it run unattended... There are a few folks here that have had 5 gallons of distilled water filling a 1 gallon battery (all on its own).

-Bill