How much AGM battery?

Hi all
A friend of mine has had bad luck (experiences) with his off grid system. The original installer made a mess of things leaving the owner with a badly executed system. Undercharged batteries for the first year, no way to find out why (no generator either at first). The first set of L16's experienced a runaway charge event and many of the 16 batteries were toast. He ran a little longer on some scavenged/salvaged L16's.
He then installed a 10kw system like mine, straight feed to the grid, no net metering possible (or use of any of the power). At the same time an electrical service was installed for the house and the off grid system was de-commissioned. Batteries sold for scrap value.
My system (with batteries still) allows me to use the grid when I want, charge or just have the utility carry the loads and let renewables charge and or charge and charry all the loads. I think I've convinced my friend to get some batteries so he can still use the valuable MX60 and double Outback inverters etc, and use the solar power available to him.
Here's the question: How much battery capacity is required to really just have the system act like a big UPS? Cost is a factor. Enough battery to be off grid for 3 days...not needed, the propane generator is always available still. 1.8kw of pv, 2x 3600watt OB inverters and one MX60. I'm thinking a minimum of 400amp hours (48 volt system). AGM would be better than FLA's, time and inclination to work with FLA's is lacking on his part.
Contributions and suggestions are appreciated.
Ralph
A friend of mine has had bad luck (experiences) with his off grid system. The original installer made a mess of things leaving the owner with a badly executed system. Undercharged batteries for the first year, no way to find out why (no generator either at first). The first set of L16's experienced a runaway charge event and many of the 16 batteries were toast. He ran a little longer on some scavenged/salvaged L16's.
He then installed a 10kw system like mine, straight feed to the grid, no net metering possible (or use of any of the power). At the same time an electrical service was installed for the house and the off grid system was de-commissioned. Batteries sold for scrap value.
My system (with batteries still) allows me to use the grid when I want, charge or just have the utility carry the loads and let renewables charge and or charge and charry all the loads. I think I've convinced my friend to get some batteries so he can still use the valuable MX60 and double Outback inverters etc, and use the solar power available to him.
Here's the question: How much battery capacity is required to really just have the system act like a big UPS? Cost is a factor. Enough battery to be off grid for 3 days...not needed, the propane generator is always available still. 1.8kw of pv, 2x 3600watt OB inverters and one MX60. I'm thinking a minimum of 400amp hours (48 volt system). AGM would be better than FLA's, time and inclination to work with FLA's is lacking on his part.
Contributions and suggestions are appreciated.
Ralph
Comments
http://members.sti.net/offgridsolar/
E-mail [email protected]
http://zoneblue.org/cms/page.php?view=off-grid-solar
First 5-13% rate of charge:
- 1,800 Watt array * 1/59 volts charging * 0.77 panel+controller derating * 1/0.05 rate of charge = 470 AH @ 48 volt bank maximum (weekend/seasonal/emergency off grid)
- 1,800 Watt array * 1/59 volts charging * 0.77 panel+controller derating * 1/0.10 rate of charge = 235 AH @ 48 volts nominal (full time off grid)
- 1,800 Watt array * 1/59 volts charging * 0.77 panel+controller derating * 1/0.13 rate of charge =181 AH @ 48 volts minimum "cost effective" battery bank for array
Roughly, a 3,600 Watt AC 48 VDC input inverter would be a 360 AH battery bank minimum (to run inverter at rated power).So--Back to what will "work" for your friend... Does he want to run an AC inverter at 100% rated power (and 2x surge power)? Or does he want to run closer to 2,350 Watt maximum?
My suggestion would be a string of "golf cart" batteries in flooded cell at ~220 AH... That would be a nice sized system and ~2,200 Watts maximum. The 3,600 Watt inverter would be "over sized" for that bank--But would give him 3-5 years to experiment.
Assuming >4.0 hours of sun ~7 months of the year (Ottawa?):
http://solarelectricityhandbook.com/solar-irradiance.html
- 1,800 Watt array * 0.52 off grid system eff * 4.0 hours sun per day minimum average = 3,744 Watt*Hours per day average minimum
That would run a home "off grid/emergency power" pretty nicely (one energy star refrigerators, lights, computer, cell phone charger, washing machine, possibly a well pump).-Bill
http://zoneblue.org/cms/page.php?view=off-grid-solar
Ralph