I'm really new to this, I would like to know the opinion of the experts.

I'm a bit concerned regarding the usage of my battery. I'm not sure if I'm using it correctly in order to maximize it's life span.

Not using BMS, I'm using the settings on the Growatt to charge, discharge and float voltages.

I have 2 X 5 KW growatt inverters and 12 X 400 W 

1 X 5 KWH LI Battery

On a nice sunny day by about 10:00 AM my battery is fully charged, and my PV is generating over 3,5 KW.

I then switch the geyser on, in about an 1 hour and  1/2 the geyser thermostat switch the geyser of.

After 12:00, the system is idling, basically just trickle charging the battery.

From about 16:00 in the afternoon wife starts cooking and we start to use some of the accumulated battery power.

Usually by about 22:00 PM battery is at about 10% SOC and switches over to mains.

During the night every 2 hours or so when battery voltage drops to +_ 48 V the system uses mains to charge the battery to about 51 V.

See picture bellow of the last 24 hours.

Please some advice will be highly appreciated.

 

 

 

Edited October 19, 20214 yr by Antonio de Sa
to add more info.

What i did was monitor the evening usage for a few days , this then thought me that i can go down to +-60% SOC in the evening , then from 00:00(next day) the battery starts to gets used again and it ends up at about 10% just as the sun starts to come out and it starts to charge ..  then you are not using any grid to top up ever. You will obviously have different values of SOC  depending on usage and battery size so it takes a few days or so dialing it in. This also leaves you with enough capacity should loadshedding occur through the night. How deeply you discharge every day will be one of the main lifespan determining factors.Deeply discharging everyday affects some chemistry's more than others. So go according to your batteries warranty ,for me if i get 6000 cycles @ 90% DOD i would be more than happy(and this is what you should expect from most LFP batteries).

@Nexuss, thanks for the feedback.

Unfortunately by the time the wife finishes with the cooking there is only +_40% SOC, thus not enough to run the all night. With 60% SOC I'm pretty sure would have enough energy accumulated in the battery to last until sun rise.  Maybe I should invest in a new battery.

The spec on my battery.

 

 

My settings cut voltage is set at 46 V, hence I never fully discharge the battery.

Battery spec call for floating voltage @  54 V and the inverters do that exactly.

Presently, according with the battery info I'm using two cycles per day, I think with an average of 2 per day my battery should last at least 7 to 8 years, possibly longer.

I've reduced my grid consumption from an average +_ 24 units/day to +_ 4, tremendous savings on my electricity bill, I'm very happy with that indeed.

 

 

Edited October 19, 20214 yr by Antonio de Sa
to add more info.

@Antonio de Sa I can't remember why you are not using the bms.

Since you have enough power to charge one more battery then it sounds OK.

I'm just wondering how you are using the battery to cook? Is it an induction stove? In that case you can compare going gas for cooking vs the price for another battery. 

In my case we use the airfryer some nights this doesn't need any adjustment from my side since it doesn't happen every day.

@Buyeye I had a problem with the BMS tripping my AC supply breaker to the inverters, I think that was because I was feeding the inverters from my earth leakage on the Distribution Board, I've since changed that, the inverters are now supplied direct from the mains via a 63 Amp double pole CB and back to the DB via a 63 Amp earth leakage.

I have not yet tested the BMS with the new set up, will do it next weekend.

So far I don't have a problem switching on my 3 KW geyser, when I switch on the geyser I make sure there is enough PV generated by my panels to do the job, I have about 4 KW of power on a sunny day by about 10 o'clock.

The stove is a normal reactive power stove.

Usually we  use about 3 KW/H of power to do the cooking every day, so I have enough stored energy in the battery to cope with that consumption..

Just a question ? I'm I doing something wrong ? so far I don't have any problem, apart from discharging the battery during cooking from 100% SOC to +_ 40% SOC.

As you can see from the picture bellow I've switched geyser on just before 10 O'clock using 3 KW and my PV was generating just over 4 KW

From about 11:30 it's just idling basically just keeping battery at float voltage

 

 

 

Edited October 19, 20214 yr by Antonio de Sa

@Antonio de Sa

I apologize if it sounded like I said you are doing something wrong.

My comment in induction vs gas for cooking is because that is the usual debate that people normally have when going renewables route.

If you have enough batteries to power a normal stove every night then you are doing very well. Not long ago that would have been an extremely(prohibitively) expensive. 

@Buyeye No, it did not sound as you saying I was doing something wrong.

I think here the main issue is having is having 10 KVA of power from the inverters. That is why I can comfortably use the stove, if not enough power in the battery, the system will switch over to mains. so far so good, did not have to do that yet. 

If I had another 5 KWH battery in days like we been having  lately I would be completely of grid. As I can see from my monitoring system' allot of solar energy is waited between 12:30 until about 16:00. 

I presume when the rains finally arrive will be a different scenario. 

Also let's see what happens in the winter.