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Is it a good idea to buy used batteries?


Muchachos
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Hi ,

I just had my grid tier installation completed two weeks ago. 

It’s a 10kVa Victron inverter, 3xPylontech US3000 batteries, 16xCannadian Solar 405W Panels and a 250V/100A MPPT.

The system is running fine during the and the batteries are charged by 10 in the morning. I however don’t have enough battery storage to make it through the night. My minimum SOC is set to 30% and I am shot of another 3kWh to make it through the night. 

I am now considering getting used Pylontech US3000 batteries and I wanted to know if it’s a good idea.

Am I better if getting 2xUS30000 used batteries for R30,000 or buying one new one and saving for another one later?

What are the things to look out for when buying used Lithium batteries?

Is the a way of checking the warranty validity on the Pylontech batteries?

Is there a way of testing the number of cycles used on the Pylontech batteries?

 

Thanks,

Muchachos

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You've already spent north of R150k on your brand new system. Trying to save R5k per secondhand battery could potentially handicap your R150k system. It's simply not worth the risk. Spend the R20k, get another new US3000 and you won't have this nagging feeling in the back of your mind that there could be issues down the line. It's probably cheaper trying to get your night time consumption down a little...

Edited by gbyleveldt
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Check the Victron VRM cloud to see if you can find any spikes of power usage during the night that you can identify and try and move those to the daytime. 

But I agree: try and reduce your usage. Replace some lights or appliances with more efficient versions could cost much less than R20k

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On 2020/09/12 at 2:11 PM, gbyleveldt said:

You've already spent north of R150k on your brand new system. Trying to save R5k per secondhand battery could potentially handicap your R150k system. It's simply not worth the risk. Spend the R20k, get another new US3000 and you won't have this nagging feeling in the back of your mind that there could be issues down the line. It's probably cheaper trying to get your night time consumption down a little...

I am trying to keep my cost going forward low going forward. My end state is to have back up for up to 3 days to cater for rainy days and for that I will need a total of 6xUS3000.

 

On 2020/09/12 at 2:53 PM, Krokkedil said:

you have 10kw of backup power and it is not enough.

I have a 300Lt geyser with a 3KW element. I have installed Geyser wise thermostat with the display and it need about 2 hours to get to about 45 degree in the morning.

23 hours ago, Louisvdw said:

But I agree: try and reduce your usage. Replace some lights or appliances with more efficient versions could cost much less than R20k

I have done this bit, install LED light and even moved some of the oven cooking to an airfryer which is half the power.

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10 hours ago, Muchachos said:

I have a 300Lt geyser with a 3KW element. I have installed Geyser wise thermostat with the display and it need about 2 hours to get to about 45 degree in the morning.

You're running your geyser off the batteries during the night? 

I'd drop a 2Kw element in there and heat the geyser up mid afternoon rather. 

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13 hours ago, Muchachos said:

No, just 2 hours in the early morning before work.

Run it off the grid if you are running it that time. At least that is what I do. Not for it for me to save a few bucks on the one hour of a geyser heating up every day and abusing my batteries like that. I set a scheduled charging slot for my batteries between 05:00 and 07:00 during which time my geyser comes on. The scheduled charge is set to stop at 30% SoC, which is lower than my minimum SoC of 50%, so all that really happens is it prohibits my batteries from being discharged during that morning geyser slot.

Or get a heat pump for your geyser. That might be a better investment than another battery and cost about the same.

Edited by jykenmynie
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I have a schedule charge for the morning which I have disabled whilst I am exploring to see if I can have my system supplying our demand without taping into the grid.

This should help with reducing the payback on my investment whilst getting the benefit of the spare capacity for load shedding and any other power outages since I am working from home.

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You’ll be hard pressed to have batteries reduce your payback period, unless you strike a lucky deal somewhere.

Something like Pylontech US3000B is about R23.5k. You get 6000 cycles at 80% DoD and at that point 60% of the original capacity will remain. Assuming that the degradation is linear, you’ll be able to pull:

6,000x3.5x0.8x0.8 = 13,440kWh from it.

At R2 per kWh from Eskom, that is barely the original purchase price. Assuming that Eskom increases are in line with investment return on assets you would invest the R23.5k in.

My view: Size the battery bank for your inverter, so you don’t damage the batteries in trying to draw more current from them than they could give. Beyond that, there’s better investments, like a heat pump on your geyser, in my opinion. And it saves you money even when the sun isn’t out and you need to buy electricity from Eskom and can’t generate the PV.

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3 hours ago, jykenmynie said:

You get 6000 cycles at 80% DoD

i agree that batteries (at the current price) are not saving you money. Another thing to remember is, that you will only achieve about 200 cycles/year. Assuming a life expectancy of 10 years that is only 2000 cycles. Batteries at the moment only make sense if you need them to bridge load shedding or if you are forced to live off grid (or if it is your hobby 🙂).  

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2 hours ago, jykenmynie said:

My view: Size the battery bank for your inverter, so you don’t damage the batteries in trying to draw more current from them than they could give.

I have a 10kVa Victron Quattro, what is the optimal size with Pylontech US3000?

3 hours ago, jykenmynie said:

Beyond that, there’s better investments, like a heat pump on your geyser, in my opinion. And it saves you money even when the sun isn’t out and you need to buy electricity from Eskom and can’t generate the PV.

My geyser is the Kwikot Indieect Solar. The water is just not warm I. The mornings for work.

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2 minutes ago, Muchachos said:

I have a 10kVa Victron Quattro, what is the optimal size with Pylontech US3000?

So the "rule of thumb" as I have it, is 1kWh per 1kVA your inverter can invert. So 10kWh for you. However, Pylontech's BMS has some more restrictive discharge current allowances. So the way I have it is that for my 5kVA MP II, I should really run 3xUS3000B. So for you, 6 would probably be optimal. I'm not an expert on these items, so I'd rather wait until someone more knowledgeable replies.

8 minutes ago, Fuenkli said:

Batteries at the moment only make sense if you need them to bridge load shedding or if you are forced to live off grid (or if it is your hobby 🙂)

Agreed, so both of those are "luxury" purchases for me - So if you like it and can afford it - Do it!

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49 minutes ago, Fuenkli said:

Another thing to remember is, that you will only achieve about 200 cycles/year.

How does this work? I thought it was 365 based on the number of days.

49 minutes ago, Fuenkli said:

i agree that batteries (at the current price) are not saving you money.

What would be the best price for a US3000 to save me money on electricity?

 

49 minutes ago, Fuenkli said:

Batteries at the moment only make sense if you need them to bridge load shedding or if you are forced to live off grid (or if it is your hobby 🙂).  

I got a ridiculous bill from Tshwane for electricity and I decided they are not getting my money anymore. I would rather star a new hobby than give them my money 🤣

Edited by Muchachos
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29 minutes ago, Fuenkli said:

yes you would get 365 cycles if you empty the battery completely every day. This is however almost impossible to achieve. 

Thanks, good information for me.

 

7 minutes ago, Fuenkli said:

it would have to fall to about 50% of the current price. 

Was hoping for 75%

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On 2020/09/13 at 9:37 PM, Muchachos said:

I have a 300Lt geyser with a 3KW element. I have installed Geyser wise thermostat with the display and it need about 2 hours to get to about 45 degree in the morning.


I have about the same battery capacity as you, and we easily get through a night without SOC dipping below 40%. So, like @Rclegg, I'm surprised you don't get through the night. 

I have a heat pump that, at present, starts up at 6:30 in the morning. In the current warm weather it is up to 55 degrees after about an hour, and it uses 1.2 kw to get there. In the winter it is about 90 to 100 minutes.  In your scenario you use about 6kw/h - which is a big chunk of your battery. Currently I am using 1.2 kw/h to get hotter water. Still a chunk, but not nearly as big.

So maybe check the price of heat pumps and factor in that you are actually giving yourself more battery time in the case of load shedding. My heat pump is on the backed up circuits, so it will always run, even if we don't have grid power.

Edited by Bobster
Temperature is in degrees, not percent.
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PS: I don't know the size of my geyser, but Kwikot recommend my pump for a 200 to 250 l geyser. The next model up is recommended for up to 400 l and is rated at 8.6 A (compared to 6A for mine). If it works as efficiently as mine then you're still looking at a good saving power wise.

Edited by Bobster
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On 2020/09/12 at 1:15 PM, Muchachos said:

Hi ,

I just had my grid tier installation completed two weeks ago. 

It’s a 10kVa Victron inverter, 3xPylontech US3000 batteries, 16xCannadian Solar 405W Panels and a 250V/100A MPPT.

The system is running fine during the and the batteries are charged by 10 in the morning. I however don’t have enough battery storage to make it through the night. My minimum SOC is set to 30% and I am shot of another 3kWh to make it through the night. 

I am now considering getting used Pylontech US3000 batteries and I wanted to know if it’s a good idea.

Am I better if getting 2xUS30000 used batteries for R30,000 or buying one new one and saving for another one later?

What are the things to look out for when buying used Lithium batteries?

Is the a way of checking the warranty validity on the Pylontech batteries?

Is there a way of testing the number of cycles used on the Pylontech batteries?

 

Thanks,

Muchachos

Well, it depends on what you mean by 2nd hand.

You can check how many cycles the battery has done by using the batterymon.exe, just connect to the battery and then check how many cycles the battery has done. You can also check the charge states of the individual cells....Then you can make an informed decision as to whether or not the cells/battery is worth the money.

 

Read here:

 

 

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55 minutes ago, Bobster said:

I have a heat pump that, at present, starts up at 6:30 in the morning. In the current warm weather it is up to 55 degrees after about an hour, and it uses 1.2 kw to get there. In the winter it is about 90 to 100 minutes.

This would be my ideal case. What is the difference between a heat pump and the solar geyser?

 

28 minutes ago, Louisvdw said:

I have the 3.5kW Kwikot heatpump on a 150L geyser. It takes 1h 15min in winter to heat. 45min in summer. (use 900W).

I should really check the heat pump out.

 

 

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44 minutes ago, Muchachos said:

This would be my ideal case. What is the difference between a heat pump and the solar geyser?

A heat pump doesn't use solar power. It is like a back to front aircon. It has a condensor, a compressor, refrigerant gas. It draws heat from the air and sends that to a heat exchanger which heats the water. It runs off electricity, but less of it than an element does.

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1 hour ago, Louisvdw said:

I have the 3.5kW Kwikot heatpump on a 150L geyser. It takes 1h 15min in winter to heat. 45min in summer. (use 900W). During the day that comes from the solar array, but early morning Eskom heats it for me. 

Just look at the price of the 5.5kW Kwikot pump. It's more than the price of one battery. 😀

Can I connect a pump to the my Kwikot Indirect solar geyser which I got before installing the solar system? 

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