Is it a good idea to buy used batteries?

[Louisvdw]

31 minutes ago, Muchachos said:

Can I connect a pump to the my Kwikot Indirect solar geyser

I'm not sure. Best to check with Kwikot

[jykenmynie]

2 hours ago, Muchachos said:

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? 

Get an installer to do a site inspection. I received a quote for full installation (everything that is required - excluding a geyser of course, I have one) and a 4.7kW ITS heatpump for about R25k. Keep in mind that, while this is close to the price of one battery, it will actually save you more money (and off-grid battery time) than a 3.5kWh battery will. That battery will be empty after an hour of running your 3kW element. Then you won't yet have enough hot water (obviously depending on how much water you use, but you mentioned 2 hours of running). The heatpump would use about:

6kWh / 4.7kW ~= 80 minutes @ 1.17kW ~= 1.5kW.

So you just saved 4.5kWh (that is 1.6 US3000B batteries if you discharge them 80%). My above calculation have quite a bit of margin for error in before it is equivalent to one battery only. Also, when the sun isn't shinning, a heatpump would still save you money while your batteries won't be able to be charged properly with the available PV.

Edited September 15, 2020 by jykenmynie

[Muchachos]

9 hours ago, jykenmynie said:

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.

I have a gas stove with an electric oven which pull about 5KW when it starts up and the my three batteries go over 100A. Would the 6 Pylontech be able to run the over?

[Muchachos]

2 hours ago, jykenmynie said:

So you just saved 4.5kWh (that is 1.6 US3000B batteries if you discharge them 80%). My above calculation have quite a bit of margin for error in before it is equivalent to one battery only. Also, when the sun isn't shinning, a heatpump would still save you money while your batteries won't be able to be charged properly with the available PV.

Thanks, this makes sense. With this I can put the geyser on critical loads because I would have enough PV or bakery power to run it.

[jykenmynie]

21 minutes ago, Muchachos said:

when it starts up and the my three batteries go over 100A.

One US3000B is okay with running at 100A for something like 10 seconds (can’t remember the specs exactly), so your three in parallel can do 300A for a burst. I’d be more concerned with your inverter’s ability to pull up to 20kVA for short periods of time or run at 10kVA for long.

Disclaimer: I’m very much a layperson when it comes to the technical aspects of these parts and my observations should be considered in that light.

If you haven’t had any issues with the batteries shutting down to protect itself yet, you probably don’t need to worry about it from a troubleshooting perspective. From a warrantee perspective, I’ve heard that it is possible that some suppliers might not honour these if the batteries were under spec for the inverter they were supporting.

[Muchachos]

23 hours ago, Louisvdw said:

I'm not sure. Best to check with Kwikot

Gave Kwikot a call and they have conformed that u can install a heat pump with my solar geyser. Thank you.

[Muchachos]

18 hours ago, jykenmynie said:

One US3000B is okay with running at 100A for something like 10 seconds (can’t remember the specs exactly), so your three in parallel can do 300A for a burst. I’d be more concerned with your inverter’s ability to pull up to 20kVA for short periods of time or run at 10kVA for long.

The recommend and max discharge current on each of the batteries is 37A and 74A. With three of them in parallel I am assuming I should get 111A without the inverter or batteries being strained.

If I where to have 6 batteries in parallel then the recommend discharge for all 6 will be 222A limited by the 140A on the inverter since its a 47V/10kVa/140A.

Is this how it is?

At what point do I get into warranty problem on the inverter and the batteries?

Edited September 16, 2020 by Muchachos

[Bobster.]

On 2020/09/15 at 3:45 PM, Muchachos said:

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

I don't know. I don't have any plumbing skills (I have an urge to fiddle with the plumbing, but this is not the same as actually having a clue. I have learned to ignore this urge.) I imagine a competent installer would be able to answer this sort of question.

[Bobster.]

8 minutes ago, Vassen said:

It depends where you look. I’m not sure about the kwikot HP but I purchased an alliance 5KW HP around March for around 11K. It’s identical to the heat tech HP. 
 

The kwikot and heat tech / alliance looks almost the same to me with regards to specs. All heat water to 60 degrees. I know the ITS claim to get water a lot hotter but I heard some not so good reviews about them and they were not willing to sell to me directly so decided to try the alliance. It worked fine through winter and uses around 1.3kw. I have a 200l geyser. 
 

after installing solar, I now use excess solar to heat the water with the electrical element at mid day. Heatpump only works evening and early morning. 

I did do some googling. On the face of it if you can do the install yourself you'll almost halve the price you pay. But the install (or a decent install) includes isolation valves, insulation, an isolation switch and associated wiring, and the routing of piping - IE not just the heat pump.

As regards temperature, that is controllable on mine. I can also set it to only turn on at certain times of day.

The advantage for me is that the current draw is nowhere near that of an element, and so I have been able to put the heat pump on the backed up circuits.

Edited September 16, 2020 by Bobster
Correct spelling. I must lay off the sauce

[Bobster.]

1 minute ago, Vassen said:

I agree. It makes sense if you can install yourself. But honestly, the install in pretty straightforward. Installers just like to make it sound complicated. 
 

i got quotes for around 24k for a standard install not higher than 2 meters from the ground. 
 

I needed to install mine about 5meters high so didn’t bother getting additional quotes.

Brackets, 4 ball valves ( I added 2 inside the roof and 2 at the pump), copper / brass fittings and diverter valve, isolator, new cabling, lagging was another 4-5k. Still a lot less than the 24k. 

Please see my earlier comments about the disconnect between my actual knowledge of plumbing and the urge to do it myself. If you do know what you're doing then you can probably get the pump installed for less than I paid.

NB! It will eventually need a regas. I noticed that my pump was running longer and longer in the mornings. I got a guy in to check the gas. He topped it up and now it heats nice and quickly again.

[Muchachos]

3 hours ago, Vassen said:

It depends where you look. I’m not sure about the kwikot HP but I purchased an alliance 5KW HP around March for around 11K.

These are selling for around R16k it seems. The disadvantages of a pandemic and high ROE.

 

3 hours ago, Bobster said:

I don't have any plumbing skills (I have an urge to fiddle with the plumbing, but this is not the same as actually having a clue. I have learned to ignore this urge.) I imagine a competent installer would be able to answer this sort of question.

Same here, the urge is great but sometime the results are not so great and I would not want to mess up my expensive equipment.

3 hours ago, Bobster said:

I did do some googling. On the face of it if you can do the install yourself you'll almost halve the price you pay. But the install (or a decent install) includes isolation valves, insulation, an isolation switch and associated wiring, and the routing of piping - IE not just the heat pump.

Let me google and see if I think I can do it.

The 5KW HP at 1.5KW battery use is way better than my current 6KW to warm up the water in the mornings.

Edited September 16, 2020 by Muchachos

[Muchachos]

50 minutes ago, Vassen said:

Hmm. It seems you are right. That’s a 50% increase in 6 months. Installers probably charge like 30k for a 5kw HP install. Even at 24k, I’m not sure if it is worth it if you take into account the limited lifespan. 

Yeah, at this cost two US3000 seem very appealing until the clouds come.

 

51 minutes ago, Vassen said:

You already have a geyerwise and you say that your batteries are fully charged by 10am so are you using the excess solar capacity that you have to heat the water to the maximum 65 degrees during the day.

Yes, in most case the water just needs 2 hours to heat up. There are case where one your is sufficient but since the geyser wise is only one week I can't confirm.

 

53 minutes ago, Vassen said:

If this is still not enough, then perhaps add another geyser in series and heat that up to max as well. That should give you enough hot water for the morning by basically using the geyser as an energy storage device. It’s a lot cheaper than using another battery to heat the water. 

A second geyser which is smaller that the current 300Lt might be an option. The warm water from the 300Lt can be heated by battery in the morning and this could be a 2Kw element that only consumes 4 kWh if not less depending on how much time it take to heat up the water. I could leave the 300Lt Solar only. I would then need a second geyser wise to keep the water in the 150Lt geyser at a good temperature.

Not sure if the 150Lt needs to be solar. Sounds like adding more cost when not needed

[jykenmynie]

10 hours ago, Muchachos said:

The recommend and max discharge current on each of the batteries is 37A and 74A. With three of them in parallel I am assuming I should get 111A without the inverter or batteries being strained.

If I where to have 6 batteries in parallel then the recommend discharge for all 6 will be 222A limited by the 140A on the inverter since its a 47V/10kVa/140A.

So the Pylontech BMS will allow higher rates of discharge, up to 100A for limited time. I have not tried to push mine, but I only have a 5kVA MP II so it is capped at pulling 100A from both my batteries, so 50 from each. Never had to do that before though. Have seen it get up to 80A perfectly fine for a short amount of time.

When we get into Quattro territory, maybe @plonkstercould help out? My pedestrian Multiplus knowledge might not apply. 

My gut feeling is that the Quattro would be able to invert 10kVA from DC to AC (to probably about 9kVA after losses), so it can attempt to pull 200A from your bank for extended periods, but possibly up to 400A in short bursts.

On the warranty, this is something you need to check with your supplier. Not sure who did your installation and supplied the parts but have read on the forum before that some suppliers might not honour warranties on batteries if it wasn’t appropriately specified for the inverter.

4 hours ago, Muchachos said:

The warm water from the 300Lt can be heated by battery in the morning and this could be a 2Kw element that only consumes 4 kWh if not less depending on how much time it take to heat up the water.

You will not use less energy to heat up your water with a smaller element, it will just need to run for longer. The temperature you want to get your water to and the temperature it is currently are the only determinants of the energy required. If you normally run the 3kW element for 2 hours you’ll run the 2kW element for 3 hours. I’ve got a 2kW in my 150l geyser, will not suggest going 2kW in 300l unless you don’t mind waiting.

5 hours ago, Vassen said:

Hmm. It seems you are right. That’s a 50% increase in 6 months. Installers probably charge like 30k for a 5kw HP install. Even at 24k, I’m not sure if it is worth it if you take into account the limited lifespan.

Just remember the conversation here is about buying another battery or two to heat his water in the early hours of the day, or getting a heat pump to heat it from his current bank. The heat pump and the batteries have a similar expected lifetime, so we only need to consider which one will cost more over its life.

A heat pump plus installation and one battery cost about the same. The heat pump will for 10 years use less than a third of his current energy to heat the water. The battery will only be able to help with half of it if the battery had been fully charged with solar. That would not always be the case.

I’m not sure there is any argument to be made for more batteries, unless his bank is currently too small for his inverter’s instantaneous demands. 

[Muchachos]

6 hours ago, Vassen said:

7 hours ago, Muchachos said:

 

Do you already have the solar collectors installed on this geyser? If yes, what system is it. Thermosyphon or pumped and flat plate or evacuated tube. 

Yes I have the solar pumped flat plate. That is why I had to install the geyserwise

[___]

3 hours ago, jykenmynie said:

When we get into Quattro territory, maybe @plonkstercould help out? My pedestrian Multiplus knowledge might not apply. 

A Quattro is just a Multi with two AC inputs. The inverter component is the same as for the equivalently-sized Multi. So your Multi-knowledge will be applicable in most cases

[Muchachos]

7 hours ago, Vassen said:

Over the last week, the  evacuated tube 200l has been reaching 70-80 degrees

I need to get my geyser checked. Im not getting this performance 

[Muchachos]

4 hours ago, jykenmynie said:

My gut feeling is that the Quattro would be able to invert 10kVA from DC to AC (to probably about 9kVA after losses), so it can attempt to pull 200A from your bank for extended periods, but possibly up to 400A in short bursts

   On 2019/10/27 at 8:59 PM, Ironman said:

I have a stack of 4 x US3000.  The current charge and discharge limit that the Pylontech BMS sends through to the Victron Venus is 148 Amp.  And the thickest cable they provide for that current is 25mm?

They say their cable is 25mm and its 2 meter long. 

The volt drop over 2 meter with 148 Amp is 0.552 Volt or 1.15%

The volt drop over 2 meter with 296 Amp is 1.1 volt or 2.3%

I read this  on Youda's Lab post. 

@plonkster, should I be able to run my Quattro 10kVa with the 3 US3000 at 111 without the battery or the Quattro throwing an alarm?

 

5 hours ago, jykenmynie said:

You will not use less energy to heat up your water with a smaller element, it will just need to run for longer

Yes. I wax reffeing to in the case of me having 2 geysers and the 150lt with 2kW.

 

5 hours ago, jykenmynie said:

The battery will only be able to help with half of it if the battery had been fully charged with solar. That would not always be the case

The heat pump does make sense when you look at these numbers. The disadvantage is that I can take the heat pump when I move house.

[___]

1 hour ago, Muchachos said:

@plonkster, should I be able to run my Quattro 10kVa with the 3 US3000 at 111 without the battery or the Quattro throwing an alarm?

Sure... but the question doesn't have a yes/no answer. It has a "how long" answer. I don't know. As long as the battery stays under 40°C and you stay under 2C discharge rates.

10kW is 200A. A US3000 has a 70Ah capacity iirc, so 280A is 2C.

Remember also that the Pylontech batteries keep a log of what you do with them. As in literally... it has event data in it. If there is a warranty claim, they will pull that data down and see what you've done. Personally, I'd advise doing 2C discharges for no more than maybe 60 seconds.

So in my mind, though a 10kVA will run fine, you won't be able to actually use the whole capacity of the inverter. a 5kVA is better matched, or double-up on the battery.

Edit: I made a math mistake. You said you had 3 of the racks. That's 200Ah, so a 10kW discharge is 1C. The battery can handle that for as long as it remains cool enough. It exceeds the recommended 0.5C discharge though, and as I said, the batteries log it.

Edited September 17, 2020 by plonkster

[jykenmynie]

28 minutes ago, Muchachos said:

The heat pump does make sense when you look at these numbers. The disadvantage is that I can take the heat pump when I move house.

True, but if you plan on moving soon, maybe all of this isn't necessary.

[Muchachos]

1 hour ago, jykenmynie said:

True, but if you plan on moving soon, maybe all of this isn't necessary.

Probably another three years. And will definitely take my inverter and batteries.

[jykenmynie]

In that case I wouldn't bother with the geyser.

[Muchachos]

1 hour ago, plonkster said:

So in my mind, though a 10kVA will run fine, you won't be able to actually use the whole capacity of the inverter. a 5kVA is better matched, or double-up on the battery

I am more keen on getting batteries as they seem easier to move. And 3 more batteries means I can run the oven without affecting warranty on the batteries even better. 

If I 2 more batteries can put the stove on critical supply?

[Muchachos]

12 minutes ago, jykenmynie said:

In that case I wouldn't bother with the geyser.

With all the information received that is my thinking as well. 

And I have a solid sign for my next install. The criteria is it must be one of the estate that has good rates for feeding into the grid. 

[___]

1 hour ago, Muchachos said:

If I 2 more batteries can put the stove on critical supply?

I edited my original post because I got the math wrong. 5*70 = 350Ah. At 10kW or 200A, that is a little over C/2. Which should not be an issue for an LFP cell. So 2 (extra, in addition to the 3 existing ones) will do it, but 3 is better.

During testing, I've never seen a Pylontech battery raise a high current alarm... but that may just be because we haven't done it long enough. Hence, I don't know when it raises such an alarm. Other batteries I've worked with tend to allow you some abuse as long as they remain cool, below 40°C.

Edited September 17, 2020 by plonkster

[Bobster.]

20 hours ago, Vassen said:

That shouldn’t really be the case as it’s a completely sealed system.... or it should be.  It’s not like an aircon where there’s a pipe run between the indoor and outdoor and this often results in some pressure loss. 
 

I’ve had an aircon run perfectly fine for more than 10 years in my previous home Without needing any top up. Just need to hose down the outdoor unit and clean the indoor filters every so often. 
 

With the heatpump, you need to also ensure that the strainer is cleaned once a year because of the poor water quality we get. 

The guy who serviced it did clean various parts and had some device that showed how much gas was in the system and used that to refresh to the level shown on the stickers on the side of the pump. He said it was low on gas, but not empty. He found one filter that was blocked with scale.

It didn't cost the earth, and it has run a lot quicker since. Maybe it was the cleaning that made the real difference.