Additonal battery back-up for solar/wind

I barely understand the basics of electricity, yet it seems the big issue with solar is the lack of storage ability and draining during low sunshine/night usage.

Would it work to have a separate battery bank that could be hooked up and charged during the high yield times when electricity then can be used is produced, yet disconnected during regular usage periods, and then that battery bank is only "connected" for use to supply power when the standard capacity is drained?

Andy John wrote:I barely understand the basics of electricity, yet it seems the big issue with solar is the lack of storage ability and draining during low sunshine/night usage.

Would it work to have a separate battery bank that could be hooked up and charged during the high yield times when electricity then can be used is produced, yet disconnected during regular usage periods, and then that battery bank is only "connected" for use to supply power when the standard capacity is drained?

it's an interesting idea but would result in uneven wear. Batteries last longer if they are not pushed too hard so a larger single battery bank will outlive a smaller one that gets occasional breaks from a second one.
Cheers, David

Okay so one ginormous battery bank is always best?

it's an interesting idea but would result in uneven wear. Batteries last longer if they are not pushed too hard so a larger single battery bank will outlive a smaller one that gets occasional breaks from a second one.
Cheers, David

I wasn't thinking of "smaller" and larger battery banks more like 2 -3 equal battery banks, that could be charged and drained optimally. Also, I've heard draining a system to low and incomplete recharging creates efficiency issues. So my theory would be to "duplicate" the house's power needs via multiple battery banks.  

I wasn't thinking of "smaller" and larger battery banks more like 2 -3 equal battery banks, that could be charged and drained optimally. Also, I've heard draining a system to low and incomplete recharging creates efficiency issues.

If the batteries were lead acid, this would likely lead to a slight betterment, as they do not want to be heavily discharged, and also need a full charge and even equalization charge now and again for optimal cycle life. It would add a LOT of fiddly work remembering to switch your batteries, and of course a bunch of duplicated breakers, wires, battery monitors and so forth. It would be expensive and complicated to automate everything.

The solution? Modern batteries! Seriously, 1858 called; they want their batteries back :). With lithium the problem you are describing goes away. Because lithium batteries are happiest between 30 and 70% SOC, and will still give you thousands of cycles from 0 to 100%, you can just make one bigger bank that you maybe do not always use. They are expensive up front, but they are getting cheaper every year. Once you factor in the much longer lifespan, they end up being a better deal.

The big mistake that many people have made with traditional batteries, is coupling large battery banks to small solar arrays back in the 80's and 90's.  It left a large trail of many ruined batteries, with people soured on solar.

That was back in the days when solar was 4$/W.  Today it's different, in that you can get 4W/$.  You can get excellent service and longevity with traditional lead batteries today because the panels are now so cheap, that every system can be overloaded with panels.  The result is happy long-lived batteries.

Michael Qulek wrote:The big mistake that many people have made with traditional batteries, is coupling large battery banks to small solar arrays back in the 80's and 90's.  It left a large trail of many ruined batteries, with people soured on solar.

Absolutely Michael,   They tried to under charge the batteries then pull out twice what they put in.  My personal formula is that battery size should be 25% of available power generation.  I try to get my batteries to float by 10 AM in summer and 2 PM in winter.  It works very well for us.  We made that mistake first time around.

I have purchased 24 reconditioned, AGM, 90A 12v truck batteries at a local, used battery store in Albuquerque, for $50 (now $65) each, and feel I have figured put a way to get the benefits of maintenance-free, durability, economy, and finally, Replaceability, as these batteries can be sourced and replaced virtually anywhere, as oppossed to the expensive, "solar" batteries.

My system is 48 V.  I have 20, "175 watt" panels, and often/always shut 15 of them down because the huge battery bank is often charged up within a few hours of sunlight with only 400-500 watts of true input, and the excess energy is a tax on my system.  I turn the other 15 on when I am running larger power tools (1800watt) for more than 30 minutes, so as not to use the battery life span for these tasks.  

Toby White wrote:I have purchased 24 reconditioned, AGM, 90A 12v truck batteries at a local, used battery store in Albuquerque, for $50 (now $65) each, and feel I have figured put a way to get the benefits of maintenance-free, durability, economy, and finally, Replaceability, as these batteries can be sourced and replaced virtually anywhere, as oppossed to the expensive, "solar" batteries.

My system is 48 V.  I have 20, "175 watt" panels, and often/always shut 15 of them down because the huge battery bank is often charged up within a few hours of sunlight with only 400-500 watts of true input, and the excess energy is a tax on my system.  I turn the other 15 on when I am running larger power tools (1800watt) for more than 30 minutes, so as not to use the battery life span for these tasks.  

Don't you have a charge controller to monitor the power and automatically divert when too high? With this amount of power you need a charge controller?

Toby White wrote:I have purchased 24 reconditioned, AGM, 90A 12v truck batteries at a local, used battery store in Albuquerque, for $50 (now $65) each

Are these batteries 90Ah now, or were they 90Ah when first made?  These batteries were made for engine starting?  That means they are a poor choice for off-grid applications.

Toby White wrote:My system is 48 V.  I have 20, "175 watt" panels, and often/always shut 15 of them down because the huge battery bank is often charged up within a few hours of sunlight with only 400-500 watts of true input, and the excess energy is a tax on my system.  I turn the other 15 on when I am running larger power tools (1800watt) for more than 30 minutes, so as not to use the battery life span for these tasks.  

Murphy's Law.  If you need to "shut off" panels to keep from overcharging, sooner or later something's gonna happen and all your batteries get trashed.  As Kimi says, you should have a charge controller doing this.