I am on-grid, and about 2 month ago had my geyser re wired to run from my inverter, this enables me to harness much more of my free PV power. I manually switch on my Geyser during peak solar time (LOL) for around ¾ of an hour. The Geyser pushes the load to around 4.4 Kwh and on average PV then provides around 1.5 Kwh short, which is supplemented by the battery. Fairly often my solar panels provide just enough power to cover that load.

I currently have a Hubble 5.5 KW AM-2 Hubble AM-2 (Max. Continuous Discharge Current 100A) battery and have just purchased another so will double up witch should provide me with a significant benefit.

What I do not understand is how many KW’s can I safely draw from the battery when there is no PV power?

“just multiply the amps by the voltage (and then divide by 1,000 to get kilowatts): at 120 Volts, 20 amps of current would be 2,400 Watts or 2.4 kW of power. Easy, right?”

AMPS VOLTAGE KW's

100 220 22

 

Is this correct?

6 minutes ago, Rodbuilder said:

I am on-grid, and about 2 month ago had my geyser re wired to run from my inverter, this enables me to harness much more of my free PV power. I manually switch on my Geyser during peak solar time (LOL) for around ¾ of an hour. The Geyser pushes the load to around 4.4 Kwh and on average PV then provides around 1.5 Kwh short, which is supplemented by the battery. Fairly often my solar panels provide just enough power to cover that load.

I currently have a Hubble 5.5 KW AM-2 Hubble AM-2 (Max. Continuous Discharge Current 100A) battery and have just purchased another so will double up witch should provide me with a significant benefit.

What I do not understand is how many KW’s can I safely draw from the battery when there is no PV power?

“just multiply the amps by the voltage (and then divide by 1,000 to get kilowatts): at 120 Volts, 20 amps of current would be 2,400 Watts or 2.4 kW of power. Easy, right?”

AMPS VOLTAGE KW's

100 220 22

 

Is this correct?

200 amps @ 50 volt is 10kW (on the DC side). Your inverter is going to be your limiting factor.

Batteries have an amp hour rating. Multiply battery volts times amp hours to get watt hours then divide by 1000 to get kilowatt hours.

That is the same sum I have already made, but I get a very high number as you say more then the inverter can handle.

If I run say my geyser @ 5 kwh on battery only, this will discharge my battery quickly, but not damage it?

Thanks

Hi Rob, Power = Volts x Amps. 

48ish Volts x 100A = +-5,000W.

Rough 48V battery guide. Every 20A of battery draw is 1000W. 

So if you have 1 battery with a 100A continuous rating. When you draw 5000W that 100A will divide by 2 of the batteries doing duty. So each battery will deliver 50A each or 2500W each to make up the 5kW. You will not hurt the batteries pulling 5kW from two of these batteries. If you only had a single battery I'd say you close to the limit & to not put on the geyser with just the one battery. With 2 you in a comfortable position. 

What I do not understand is how many KW’s can I safely draw from the battery when there is no PV power?
 

Hubble AM-2 is a "1C" rated battery
As @Steve87 said ~5kW - remember to set the Charge & Discharge Amps

In my case I've set the limit to 150A x 48V ~7.2kW.
My 4xAM2 can do 4x100Ax48V ~19.2kW
The Sunsynk 8k can handle 8kW (or 8.8kW)

Edited December 1, 20223 yr by system32

I would change the geyser element to a 2000W one, then your solar should be ok to power the geyser without the battery. May take slightly longer to heat but the sun is free.

11 hours ago, system32 said:

What I do not understand is how many KW’s can I safely draw from the battery when there is no PV power?

If you have 4 AM-2's they can deliver 100A each, according to the manufacturer, so you could draw 19,2kW at 48V theoretically. They should also protect themselves if the inverter tries to go outside of the spec (that is what the BMS is for). I am going to guess that your 150A limit is set up because you have 160A fuses installed?

Edited December 1, 20223 yr by P1000

On 2022/11/24 at 1:25 PM, Peter V said:

200 amps @ 50 volt is 10kW (on the DC side). Your inverter is going to be your limiting factor.

This!

My batteries are capable of supplying more than my inverter can handle. So check the inverter too, and then the lowest of the two figures is what you can draw without something failing.
 

On 2022/11/24 at 1:15 PM, Rodbuilder said:

Is this correct?

yes, but, read all of the above, but also realise, if your HWC has a 3kW element and you run it for only one hour on the batteries (your two 5kWh NMC's) then are down to approaching 66% SOC remaining only...  assuming you have no other major draws at that same hour... we don't have a HWC with electric element, so this kind of consumption is less of an issue... but by my calculations, if I want to sit comfortably on a household that consumes, maybe 15 to 16kWh per days, I'd think I'd want double that in battery capacity at least to cover ourselves without worrying too much about the odd cloudcover etc... we do not have a grid connection other than an extension lead to the neighbour which can cover 2kW max...

Edited December 1, 20223 yr by Kalahari Meerkat
quesition was never answered

I really appreciate all the input from you guys, is extremely helpful!

This is a very nice forum with no rudeness and other BS.💯%    I also like the software!

Today I am installing another battery, expensive for a pensioner but I think well worth it.   I will be able to run on battery throughout the night (or nearly) and will program the inverter at some point to charge from grid only at certain times.

I have been heating my 400 W Geaser from the battery & PV for 2 month now and this is working well and I see no negative consequence.   I do this manually at the moment and switch on when there is good sun outside.   Usually I run the geyser for about 3/4 hour in summer.   Winter will be another learning curve for me.

 

On 2022/12/01 at 10:47 AM, P1000 said:

If you have 4 AM-2's they can deliver 100A each, according to the manufacturer, so you could draw 19,2kW at 48V theoretically. They should also protect themselves if the inverter tries to go outside of the spec (that is what the BMS is for). I am going to guess that your 150A limit is set up because you have 160A fuses installed?

Nothing is "set up" anywhere I have programmed some of the initial setting by reading from Sunsynk manual.    Am to cautious to do anything at the moment😀

4 hours ago, Rodbuilder said:

Nothing is "set up" anywhere I have programmed some of the initial setting by reading from Sunsynk manual.    Am to cautious to do anything at the moment😀

Caution is the better part of valor!!!!  Do be careful. 😀

It's all been said above, but I'll try to summarize briefly.

You could do this using KWh or Ah as the base for calculations. I prefer to use the KWh because that takes care of the fact that your DC and AC are running at different voltages.

• Batteries have a Capacity - usually expressed in KWh.
  • e.g. A 5KWh battery can provide 5KW for one hour. or 1KW for 5 hours. In theory.
  • That answers the question: HOW MUCH power is stored?
• Batteries also have a "C" rating - usually expressed as a simple number with "C".
  • e.g. 1C, or 0.5C. This basically tells you how much of the battery's total Capacity you may use in one hour. You could convert it to a percentage - That makes more sense in my head. 0.5C = 50% of Capacity per hour.
  • That answers the question: HOW FAST can the power be delivered?

My battery is 4.8 KWh, 0.5C. This means that I should only pull 50% x 4.8 = 2.4KW max load at any time. If I do that I could (theoretically) pull that load for 2 hours. (Except - don't do the full 2 hours because you don't want to go below about 20% SoC.)

So - check your battery spec - if you have 5KWh 1C (mentioned by one of the responders above) - you should be able to pull 5KW from it, but it will only last an hour (less 20%).  So please check your battery's specs.  And, if you have two batteries, then you can ADD them together. Effectively you have a 10KWh Battery, still with 1C rating...

And then set your Inverter to limit the current accordingly - that will protect your batteries from accidental abuse and damage. (PS, though may battery is rated 0.5C, I set my Inverter to max at 45%, or 0.45 C.)

The mistake I made was to use Grid volts i.e. 220 volts in my calculation, that's why I got to a very high number.    I could instinctively see it was incorrect.

Thanks again, this is now clear.

On 2022/12/06 at 9:01 AM, Rodbuilder said:

Today I am installing another battery, expensive for a pensioner but I think well worth it.   I will be able to run on battery throughout the night (or nearly) and will program the inverter at some point to charge from grid only at certain times.

With 2x Hubble AM-2 batteries, in the battery setup, (Batt type) tab on your SunSynk 8.8 kW inverter, Batt capacity = +- 220 Ah, Charge Amps = +- 50A (or up to 200A), Discharge Amps = 185A.  ⚫ Lithium, ⚫ CAN. (Shut Down) tab, ShutDown = 20%, Low Batt = 35%, Restart = 50%. If you have an emergency need for battery power, you can change the Shutdown = 10% on the odd occasion to get through the night.

When connecting your new battery to your old battery (parallel), check the voltage difference of the two before connecting them. If the difference is 2V or greater, you MUST charge the new battery separately first, or the old battery and inverter will try and supply more than 100A to the new battery, and the new battery BMS will trip out.

You have a great setup with your inverter and batteries, hope they serve you for many years to come.