A Few DIY powerwall queries.

singlecell

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I am currently in process of collecting lithium cells and deciding which hardware to buy for my project. Currently we dont even have solar installed, seemed kinda a waste to not be at home all day to use it and feed the energy company power for almost nothing.

I am wondering if with the setups I am seeing on the site if they allow to feed back to the grid once the batteries are full? Not asking because of money, but because if that's the case what stops the batteries from feeding the grid?


Also I am trying to decide if to get one or two charger inverters, I am leaning towards a MMP 5048MG. If you attempt to draw more than what the 5KW inverter can supply, say 6KW, will that continue to feel 5K from the inverter and also 1K from the grid? Or do they just switch over from battery to mains for the full 6K?

And finally, with having everything installed, I know an electrician will need to install the panels and the inverters and whatever new meters are required in the powerbox but are they involved with the battery at all? I ask as I am considering having everything installed battery-less (hence the MG model) and then installing the batteries at a later date. I guess the answer would also then include if batteries are to be expanded later on.

Thanks,
David.
 

Redpacket

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In Australia, the only electricians who are supposed to do this work are CEC certified ones & they usually won't allow any DIY, especially for grid feed connected systems.
Ie you may have to let them install what they are OK with. I would not buy anything until you have agreed with them what gear will be used.
 

AZ_Tekkie

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singlecell said:
Also I am trying to decide if to get one or two charger inverters, I am leaning towards a MMP 5048MG. If you attempt to draw more than what the 5KW inverter can supply, say 6KW, will that continue to feel 5K from the inverter and also 1K from the grid? Or do they just switch over from battery to mains for the full 6K?

FYI, when an inverter is rated at 5KW that's going to include if it's pulling from the grid or batteries. Even if it's doing bypass, 6kw will overload the inverter as that power is still channeling through the inverter. If you plan to run more than it's rated capacity then you'd need two inverters or one bigger one. Some inverters will also do momentary surge. I don't believe the surge is very high on MPP, though i've never tested it.
 

singlecell

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Redpacket said:
In Australia, the only electricians who are supposed to do this work are CEC certified ones & they usually won't allow any DIY, especially for grid feed connected systems.
Ie you may have to let them install what they are OK with. I would not buy anything until you have agreed with them what gear will be used.
I will definitely been finding someone to do the work before I buy anything. I assumed that most companys will just want to install their own supplied gear and not vary much from that.


AZ_Tekkie said:
FYI, when an inverter is rated at 5KW that's going to include if it's pulling from the grid or batteries. Even if it's doing bypass, 6kw will overload the inverter as that power is still channeling through the inverter. If you plan to run more than it's rated capacity then you'd need two inverters or one bigger one. Some inverters will also do momentary surge. I don't believe the surge is very high on MPP, though i've never tested it.
I see, I always thought it would have just connected the mains input to the output bypassing the inverter all together.
 

daromer

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Some Hybrids can do battery/solar + mains and combine but it is still overload. 5kW is 5kW. Also note that the cheaper ones ratint is there MAX rating meanwhile other have it as nominal. There is a reason why some cost 3x to others ;)

So its important to read the instruction for the inverter you look at since it differs.
For instance the one I got can do up to 16kW combined with grid and battery for short time but its 10kW nominal....

Also if you want it to be installed properly you NEED to talk to your electrician before you get any material or do any work. Many of them arent certified and even more of them wont even touch DIY stuff. (As said earlier by others)
 

singlecell

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Thanks guys, I found the manual and it does have a line mode which bypasses the inverter and just connects the input and output, but it doesnt have any specs so I will agree its just going to be 5kW all up.

Will start making some phone calls to see who is willing to do what over the next couple of weeks. I am 450 (untested)cells into collecting 1400 after a week of pulling batteries apart so hopefully not too far off of being able to do something, as long as my box at used batteries doesnt go missing at work....

Another thing I need to look up, with the longmons whats the most amount of cells each one handles? I did have a quick read of the webpage but I couldnt see any figures. I was thinking a 14s100p setup but I dont want to aim for that to start and find out each longmon could only do a 80p. If that makes sense...
 

daromer

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450 untested should yield around 140 cells that are decent. Generally 30-35% good cells is a god rule of thumb so you dont get disapointed.
 

singlecell

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daromer said:
450 untested should yield around 140 cells that are decent. Generally 30-35% good cells is a god rule of thumb so you dont get disapointed.

Oh that is a disappointingly low rate. Hopefully the fact the cells I am getting have only had 2years use and and haven't been through many cycles I come up a bit better. But I am.probably dreaming....
 

jdeadman

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It's been my experience that it all depends on what your source is. For the Medical Packs Ive been getting recently are 2 yeas old and used for those 2 years I get about 90% good cells Of that 10% Bad 50% of those are Dead the rest are just below my mah threshold.

For "Dead" laptop batteries My success rate is what Daniel was saying about 30-40% good cells another 10% below mAh threshold and the rest recycle.
 

hermitdave

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jdeadman said:
It's been my experience that it all depends on what your source is. For the Medical Packs Ive been getting recently are 2 yeas old and used for those 2 years I get about 90% good cells Of that 10% Bad 50% of those are Dead the rest are just below my mah threshold.

For "Dead" laptop batteries My success rate is what Daniel was saying about 30-40% good cells another 10% below mAh threshold and the rest recycle.
I've had close to 60% recovery rate..


singlecell said:
daromer said:
450 untested should yield around 140 cells that are decent. Generally 30-35% good cells is a god rule of thumb so you dont get disapointed.

Oh that is a disappointingly low rate. Hopefully the fact the cells I am getting have only had 2years use and and haven't been through many cycles I come up a bit better. But I am.probably dreaming....

I have been harvesting using laptop batteries.. in most packs i have 2 bad cells. On rare occasion, 4 bad cells.. last week for the first time, HP 63kWh pack has all cells at 0V..

Most of the times, good cellsare at 2.5V or higher
 
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