Does using solar degrade my batteries?

[Irish Rover]

I have 2 x 580W panels and a 3kw inverter. We use various electrical appliances on the boat such as an airfryer, electric grill, kettle etc. I'm careful to stay within the inverter capacity and I monitor the battery voltage. If it goes below 12v I switch something off or start the generator. Mostly the power I'm pulling out for the fryer, or whatever, is being more or less equalled by the yield from the panels. Does this power inflow/outflow degrade the batteries? It's no big issue. I'm just curious.

 

[PaulRainbow]

I have 2 x 580W panels and a 3kw inverter. We use various electrical appliances on the boat such as an airfryer, electric grill, kettle etc. I'm careful to stay within the inverter capacity and I monitor the battery voltage. If it goes below 12v I switch something off or start the generator. Mostly the power I'm pulling out for the fryer, or whatever, is being more or less equalled by the yield from the panels. Does this power inflow/outflow degrade the batteries? It's no big issue. I'm just curious.

12V is 90% discharged. EDIT 90% is for LifePO4, for LA it would be circa 50%

A 3Kw inverter can draw 300A continuously. Your solar can't match that sort of current draw.

What's your battery capacity ?

 

[Irish Rover]

12V is 90% discharged.

A 3Kw inverter can draw 300A continuously. Your solar can't match that sort of current draw.

What's your battery capacity ?

Battery capacity is 660Ah
When you say "12v is 90% discharged" does that mean I've used 10% of the available power or 90%?
When I'm using something which draws high amps I keep a close eye on the Victron app and if it shows the voltage at 12 or lower I switch something off or start the generator. If I switch off the inverter (without the generator running) the voltage shoots back up to 13+ almost immediately.

 

[PaulRainbow]

Battery capacity is 660Ah

Your inverter could discharge those to 50% in 30 mins

When you say "12v is 90% discharged" does that mean I've used 10% of the available power or 90%?

You've used 90%. 50% But that's only if the batteries are at rest, if subject to a large load the app or monitor will read less than the rested voltage and will recover when you switch the load off, as you say below.

When I'm using something which draws high amps I keep a close eye on the Victron app and if it shows the voltage at 12 or lower I switch something off or start the generator. If I switch off the inverter (without the generator running) the voltage shoots back up to 13+ almost immediately.

I'd try to keep the current draw as low as possible, within reason, you still want to use things. Next time you need new batteries i'd suggest changing to Lithium.

 

[Irish Rover]

I'd try to keep the current draw as low as possible, within reason, you still want to use things. Next time you need new batteries i'd suggest changing to Lithium.

Thanks for the helpful info and advice - as always. I should have changed to Lithium when I bought the batteries last year but it was a rush job and I knew changing involved some other work which was above my pay grade.

 

[Refueler]

Just to add to Pauls excellent advice here ....

Try to only have one high demand item on at any one time - to try and reduce the load on those poor batterys !! TBH - I'be inclined to be running the Genny instead of flogging those batterys .... assuming any neighbours don't mind !

 

[Irish Rover]

Just to add to Pauls excellent advice here ....

Try to only have one high demand item on at any one time - to try and reduce the load on those poor batterys !! TBH - I'be inclined to be running the Genny instead of flogging those batterys .... assuming any neighbours don't mind !

Am I really "flogging" the batteries? I boil the kettle 3 or 4 times per day, use the airfryer or the grill for approx half an hour and a few other smaller low wattage appliances occasionally.

 

[noelex]

Solar input will only be helpful to lead-acid batteries (unless your settings are inappropriate).

You cannot estimate the batteries’ SOC from the voltage under load unless you take the value of the discharging current, the history of this current, as well as other factors such as temperature, battery type, etc. However, a voltage below 12.0 V is not a great sign with the loads you have indicated.

 

[Irish Rover]

However, a voltage below 12.0 V is not a great sign with the loads you have indicated.

Is not a great sign of what?
PS - I'm not sure I understood anything else in your post

 

[Refueler]

Is not a great sign of what?
PS - I'm not sure I understood anything else in your post

Think he's trying to say :

Solar is no problem as long as your settings are so that batts are not being overcharged etc.

As to the longer sentence - that is near rambling on about calculating the energy load demand on the batterys ... because your batts are seriously 'voltage dropped' under load.
As you state they pick up back to ~13V when batts rested .... which is good - but does show that you are are 'hammering' you batts ....

Think of it like this ... a reasonable full charged battery turning over a moderate sized diesel engine will depress a battery under load from 13+ to ~11V while cranking - you are not far off that ...

 

[Irish Rover]

Think he's trying to say :

Solar is no problem as long as your settings are so that batts are not being overcharged etc.

As to the longer sentence - that is near rambling on about calculating the energy load demand on the batterys ... because your batts are seriously 'voltage dropped' under load.
As you state they pick up back to ~13V when batts rested .... which is good - but does show that you are are 'hammering' you batts ....

Think of it like this ... a reasonable full charged battery turning over a moderate sized diesel engine will depress a battery under load from 13+ to ~11V while cranking - you are not far off that ...

"Flogging", "hammering". Is that
not what they're for, the same as your cranking battery analogy?

 

[Refueler]

"Flogging", "hammering". Is that
not what they're for, the same as your cranking battery analogy?

My point about comparing with starting an engine is to illustrate the sort of load being put on the batts ... not something you want to be doing for too long ...

 

[noelex]

Is not a great sign of what?

A 660Ah lead-acid battery bank should not be regularly dropping below 12.0V with the loads you describe. The most likely cause would be a low battery state of charge, loads that are too high, a battery or batteries performing poorly, a wiring problem upstream of where the voltage is measured, or a combination of these factors.

PS - I'm not sure I understood anything else in your post

That is also not a great sign.

 

[Irish Rover]

A 660Ah lead-acid battery bank should not be regularly dropping below 12.0V with the loads you describe. The most likely cause would be a low battery state of charge, loads that are too high, a battery or batteries performing poorly, a wiring problem upstream of where the voltage is measured, or a combination of these factors.

That is also not a great sign.

If I have the fryer @1500w or the grill@ 1500w or the kettle @1200w running on their own the victron connect app shows the voltage in the high 12's but if I put 2 together it drops close to 12 or below depending on what the panels are producing at that given time. Switch off the inverter and it comes back up to 13+ almost immediately.

 

[Refueler]

If I have the fryer @1500w or the grill@ 1500w or the kettle @1200w running on their own the victron connect app shows the voltage in the high 12's but if I put 2 together it drops close to 12 or below depending on what the panels are producing at that given time. Switch off the inverter and it comes back up to 13+ almost immediately.

Which is what I would expect to see ...... nothing wrong there. Its just hard life on your batterys !

The Solar will of course be trying to charge the batterys during this - effectively adding their energy to the batterys ....

 

[Irish Rover]

Its just hard life on your batterys !

OK. That's why I started the thread to determine if I was was doing untoward harm to the batteries. I prefer to avoid using the generator as much as possible and to use the available green energy - strange, I know, for a guy with 640HP under the bunks. If it shortens the life of the batteries so be it, as long as I'm not doing anything which will lead to a sudden and complete failure of the house bank.

 

[Baggywrinkle]

Imagine it like this ...

The solar charger and the batteries are providing a pool of energy, and the inverter is drawing from that pool to power your devices.

For arguments sake, we can ignore conversion losses and say that your fryer is drawing 1500W and your grill another 1500w from the pool.

The battery will be providing 3000W minus what is currently coming in due to solar, for simplicity sake lets say 1000W of solar.

3000W(Load)-1000W(Solar)=2000W which must come from the battery.

For arguments sake, lets say your house bank is 3 x 220Ah batteries @12V in parallel.

This means each battery will be providing 2000W/3= 666W each, which at 12V is 666/12= 55A

You have 220Ah available, so the battery will go from 100% to dead in 220/55 = 4 hours.

You don't really want to discharge to zero as it damages the batteries, realistically keep them above 50% ... so you have 2 hours when your solar is working hard before your batteries are dead, you can do the sums again with no solar (evenings) .... the load then will be closer to 80A and you'll have 2 3/4 hours to empty ... this is indeed verging on abuse of leisure batteries.

The inverter is rated to run your loads, but the batteries are under-specced for using the full capability of your inverter.

Run the generator when cooking IMO - especially if there is little solar and you want to use more than one of your AC loads.

 

[Refueler]

OK. That's why I started the thread to determine if I was was doing untoward harm to the batteries. I prefer to avoid using the generator as much as possible and to use the available green energy - strange, I know, for a guy with 640HP under the bunks. If it shortens the life of the batteries so be it, as long as I'm not doing anything which will lead to a sudden and complete failure of the house bank.

No - I actually commend you Sir .... too many I know just fire up the genny and don't think about those around them who have to listen to it and also suffer possible exhaust fumes.

But I would as said before - look at running the genny fror such short time loads ... saving the batts for other lesser stuff.

 

[PaulRainbow]

A 660Ah lead-acid battery bank should not be regularly dropping below 12.0V with the loads you describe. The most likely cause would be a low battery state of charge, loads that are too high, a battery or batteries performing poorly, a wiring problem upstream of where the voltage is measured, or a combination of these factors.

It's a sign that you're posting drivel again. The OP has stated, more than once, when the load switches off the terminal voltage goes back up to 13+ volts. None of the things you list above are an issue.

That is also not a great sign.

If you post gobbledygook how do you expect anyone to understand it ?

 

[PaulRainbow]

OK. That's why I started the thread to determine if I was was doing untoward harm to the batteries. I prefer to avoid using the generator as much as possible and to use the available green energy - strange, I know, for a guy with 640HP under the bunks. If it shortens the life of the batteries so be it, as long as I'm not doing anything which will lead to a sudden and complete failure of the house bank.

You're not.

Sticking to one high load device at a time minimises the stress on the batteries. They might not last quite as long as if you only used them for powering a few low current devices, but who want to be camping onboard with no amenities for the sake of replacing the batteries a bit sooner ?