Hi Everyone,

I've had 8kw Sunsynk inverter and 10Kw Sunsynk battery installed.

With these higher levels of load shedding I fear we're not going to make it all the way through as we have a few pumps. On average we seem to be drawing about 1350W (based on the app).

My questions are:

1) How low can these batteries be drawn down safely? (we will be putting in a solar panels soon so that should be a big help).

2) What happens if they run flat during a higher stage of load shedding?

 

Thanks all...

 

All depends on settings but you should be able to go down to 10% SOC after which the inverter will shut down to protect the battery. So below 10% you will most likely be joining the rest of the 95% of dark Africa's population. 

Is it an absolute bust that all the pumps have to run through loadshedding? I would minimize the essential loads and seperate the non-essentials so that they will fall away below a certain SOC%.

Not sure about the setup on the Sunsynk's but this works great on Victron systems. My AC units and borehole pump are connected to the non-essential output but the relay is set to stay closed under certain condition, for example, when the batteries are charging from solar, when grid supply is on and when battery SOC is above 50%. Anything below that the AC and borehole pump will shut down and leave me with about 8 more hours of power on essential loads. Thats enoug to last untill the sun comes up.

 

22 hours ago, JohnMc said:

1) How low can these batteries be drawn down safely? (we will be putting in a solar panels soon so that should be a big help).

2) What happens if they run flat during a higher stage of load shedding?

It depends largely on the battery and its BMS. I give you an example:

My Leoch TB48100 data sheet claims that its BMS will cut out at 40.5V. That corresponds to almost 100% DOD. I set on the inverter the low voltage cutout at 42V. It happened two times during load shedding at night. I had to wait for power coming back, then the off grid Axpert/Synergy inverter automatically turned on bypass mode and to recharge the battery. Everything worked fine thereafter.

22 hours ago, JohnMc said:

Hi Everyone,

I've had 8kw Sunsynk inverter and 10Kw Sunsynk battery installed.

With these higher levels of load shedding I fear we're not going to make it all the way through as we have a few pumps. On average we seem to be drawing about 1350W (based on the app).

My questions are:

1) How low can these batteries be drawn down safely? (we will be putting in a solar panels soon so that should be a big help).

2) What happens if they run flat during a higher stage of load shedding?

 

Thanks all...

 

Generally you will not get more than 90% out of them. At that point either the BMS or the inverter will shut the batteries down.

You have no panels, so if the batteries get down to 10% remaining, and there is no grid, then you start singing "hello darkness my old friend".

What you want is panels. Once you have them then your batteries can get some charge during day time load sheds whilst carrying less load.

If it's done properly, and unless you have foul weather, your batteries will charge during the day. At that point PV drops off to just enough to service loads, so your battery stays charged. 

I have 10kWh of battery. My rule of thumb is that if I hit 16:00 with a full battery, then I am good until at least 7:00 the next day. And at 7:00 I will still have about 50% of the battery remaining, so I can probably survive an early morning load shed. (this morning our slot started at 6:00. Nice sunny day, no problems, my battery was charged all the way by 10:30.

Once you have panels then you can start strategising. You do as much as you can during the sunlit hours. This maximises use of PV and keeps your battery for later in the day. So my water heating all gets done during the day, pool pump runs during the day, appliances get run during the day etc. And then at night we have lights, TV, wifi, fridges, freezer, external lights, security system all working and load fluctuates between 200 and 400 watts, and then evening load sheds make no difference because either way the house is running off of battery.

Here's my system today, so far. Green line is SOC, blue line is PV, yellow line is load. At 7:00, with a little PV coming through, SOC is 55% and so I still have some in the tank. Once the battery is charged, you see PV pretty much tracking the load.

We have been untroubled by stage 6. When the weather is gloomy, there's always a slot in which I can force charge the battery from grid. But really, a properly set up hybrid system (grid, batteries, PV) gives a very high level of protection AND cuts costs. At the moment, you aren't saving anything.

Thanks everyone. This sets my mind at ease that at least its not going to blow up my system if I drain it too far....

@Czauto, we need the pumps to run as it pumps water to the cows drinking troughs (I'm on a dairy farm).

I've ordered 8 x 550W panels so that should take care of the loads during the day. During the night we rarely have as much usage because neither the cows nor the humans are using water requiring pumps to run...

Thanks everyone..

Generally the greater the DOD you are running them to the shorter the life expectancy of the cells. 

Recommended DOD is 90% in the specs so as long as you don't go below that shouldn't be invalidating any warranties.

Other major factors influencing cells life expectancy are the discharge and charge rates, the lower the better. 

 

 

20 hours ago, Sc00bs said:

Generally the greater the DOD you are running them to the shorter the life expectancy of the cells. 

Basically this is correct. But lets give it a thought:

My Leoch TB48100 data sheet guarantees 3500 cycles with 100% DOD. At one cycle per day that amounts to almost 10 years. At a max 80% DOD programmed and with your argument I would expect up to double the life time. By that end we probably will have new technology batteries on the market.