How may KW of solar panels for 10 kwh powerwall

C

Charles Francis Speakman

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Almost completed the battery testing phase, have at least enough high energy cells for 10 kwh DIY Powerwall.

Have 2 grid tied SolarEdge Inverters, 7.6 kw StorEdge Inverter for 9.86 kw panels, and 5 kw SolarEdge Inverter for the other 6 kw of panels.

Am still concerned that will not be able to make my DIY Powerwall interface with EITHER of my SolarEdge grid tied inverters. Am looking at the LG Battery that can be purchased for $6200 US, and is supposed to play nicely with my StorEdge Inverter. But am uncertain as to how to add my DIY Powerwall into that system without problems/warranty issues etc. Would love to do it if possible.

I DO have room on my roof for 5 more panels, about another 1.5 kw. Considering a non-grid tied inverter to tie to those panels and my DIY Powerwall as an alternative. But that would only produce about 6-7 kwh per day, and not enough to charge my DIY Powerwall to full each day. BUT, if could charge it up with late night grid energy ($0.015/kwh), that could work also.

Interested in comments from the group...
 
Depends o were you live and how many solar hours you get, but you can figure it out. Assuming you have 4 solar hours, you'd need 2.5kW of panels assuming 100% efficiency. Assuming 80% efficiency you need closer to 3kW of solar panels... does this answer your question?
 
You must consider too the consumption of your appliances in real time that will substract to generated power and won't go to batteries, and if your numbers is that you will empty your batteries every day and need to recharge them, then you must need a higher capacity or with a full cycle every day your cells wont last.
 
Since you should use all energy from your battery bank you really dont need that much solar panels. You can always charge from the grid as well when you got surplus energy from the grid tie system. Doing that way you will loose energy but its still solar energy.

Most off-grid inverters can do that. Thats my recomendation.

1.5kw for 10kw of bank is kind of same as i got
I got 16kw of solar to a 100+kWh battery bank ;)
 
Thanks for the input. Considering 10kwh LG battery tied to my 9.86 kw panels/StorEdge Inverter. Add 5 more panels, 1.5 kw to charge my DIY 10 kwh Powerwall. 6 hours of sun 70% efficiency most likely. Can still charge from the grid at night as needed.

Recommend leave it all DC from the roof to the Inverter that will charge the DIY Powerwall? Recommendations appreciated for a southeast USA based system.
 
Charles Francis Speakman said:
Recommend leave it all DC from the roof to the Inverter that will charge the DIY Powerwall? Recommendations appreciated for a southeast USA based system.
Click to expand...

My understanding is you want to limit the dc/ac and ac/dc conversions as much as possible. If you have a low Voltage system and long cable runs you might have to calculate the voltage drop vs multiple transformers inefficiencies...
 
With offgrid inverter or just a charger you will most likely leave it dc all the way down. For only 6 panels a normal system where you run 2s3p will be ok in same 6mm2 wire.. Though some losses. Otherwise go for a high voltage system but 6s only gives you 200VDC out.
 
VERY GOOD NEWS. Had time for some roof measurements today, and have room for 8 Canadian solar 290 Watt panels for my OFF Grid array to charge my DIY Powerwall. Looking for recommendations on which charge controller to purchase, and how to wire...all 8 in series, or 2 strings of 4? All in series would be easier if the charge controller can handle the voltage.

And...can I use the PV 10 gauge wire all the way from the panels through the attic (in conduit) to the garage...about 60 feet, to the charge controller and my DIY powerwall?

Thanks again for all the great input.

Charles
 
daromer said:
With offgrid inverter or just a charger you will most likely leave it dc all the way down. For only 6 panels a normal system where you run 2s3p will be ok in same 6mm2 wire.. Though some losses. Otherwise go for a high voltage system but 6s only gives you 200VDC out.
Click to expand...

Will the PCMX60 handle the voltage of all 8 panels in series? Read it was rated for 145 volts maximum input. So would be better off to have 4s2p or 2s4p???

Also need advice on wiring these, as have only done series wiring in the past for my SolarEdge system.

Charles
 
No it cannot handle 8s.
Are the panels 60 cells or 72 cells? If they are 72 cells 2s4p will work fine meanwhile if they are 60cells 2 in series may be tiny bit to low. Need to check specifications. I run the PCM with 3 in series.
 
ELECTRICAL DATA / STC
Power Optimizer connected to a SolarEdge Inverter CS6K 285MS-SD 290MS-SD
Nom. Max. PWR (Pmax STC) 285 W 290 W
Nom. Max. PWR (Pmax NOCT) 207 W 210 W
Open Circuit Voltage (Voc STC) 39.1 V 39.3 V
Output Voltage Range (Vout) 5-60 V 5-60 V
Max. Output Current (Imax) 15 A 15 A
Max. Series Fuse Rating 20 A 20 A
Module Efficiency 17.41 % 17.72

These are the specs for the 290 watt panels planning to use. Looks like 39.3 Voc. This is listed as specs as attached to a power optimizer and SolarEdge Inverter. I am not going to be using those for this setup however.

So how would you wire all 8 panels? Would like to use the same PV wire from the panels, through the roof entry, through the attic, run about 60 feet to enter my garage where the charger and Powerwall will be located.

Going to start with 14 packs of 80 cells for around 10 kwh, but would like to have 28 for 20 kwh eventually. Will one PCMX60 charger work for all of it, or would it be better to have 2 chargers, one for each 10 kwh Powerwall pack?

And do you have a recommendation for Inverter to use on the other side of the packs to send AC to my house during the evening hours? Only looking for about 4-5 hours until can get to the really cheap electricity after 11 pm, 1.5 cents per kwh.
 
But above states its power optimizers on them? If so you have 60V max and then you cannot have more than 2 in series for the PCM for example.

Ie 2s4p. You need a rather thick wire down or atleast 2*6mm2 that is generally default. Ie 4 wires in total down.

Unless i missed something?


PCM only cares about the solar input. As long as that isnt far above 3.5kW that should be fine.
 
daromer said:
But above states its power optimizers on them? If so you have 60V max and then you cannot have more than 2 in series for the PCM for example.

Ie 2s4p. You need a rather thick wire down or atleast 2*6mm2 that is generally default. Ie 4 wires in total down.

Unless i missed something?


PCM only cares about the solar input. As long as that isnt far above 3.5kW that should be fine.
Click to expand...
The PCM charger looked like it only had entries for ONE plus and ONE negative PV DC voltage wire.So the way I understand itwith 8 panels, I would connect the plus and negative leads together on 4 panels in each string. I would then have a remaining plus and negative on the end panels...and would connect the + to the - in the other parallel string to make the 2 four panel parallel strings connected in series. Then I would have to connecta PV wire to the plus and minus remaining from the end panels of each string, and I would have just 2 wires making the entry into the attic???Am I missing something?

And these wires come in lengths up to 100 feet. They have very thick covers, and the less connections the better. Planning to allow the 2 PV wires and the ground wire to make the trek into the attic, in conduit as required, and to the garage.

Still new to this, sorry for all the questions. Maybe this will help others also.
 
Yes its only + and - going down to the inverter... But you need to have enough thickness on the wire to support that length. Having 4 panels in paralell on a single 6mm2 is not enough when we talk about over 30A. those lines will get hot and you will loose some.
I recomend atleast 10mm2 or larger for that many. In my case i always do 6mm2 per 2 paralelled panels. In my case max 17A.
 
daromer said:
Yes its only + and - going down to the inverter... But you need to have enough thickness on the wire to support that length. Having 4 panels in paralell on a single 6mm2 is not enough when we talk about over 30A. those lines will get hot and you will loose some.
I recomend atleast 10mm2 or larger for that many. In my case i always do 6mm2 per 2 paralelled panels. In my case max 17A.
Click to expand...
From conversion table, looks like 6 AWG wire. Doubt the PV wire is that thick. So, may have to use a Soladeck terminal and make the connections on the rooftop to larger wire to make the trek to the garage.

Those Canadian Solar panels have only a + and - connector wire, and will not connect to each other except in series with the native wires attached, so guess I will have to find some short PV connector wires that have + connectors on each end and - connectors on each end.
 
My suggestion is you define very clearly what exactly you are trying to do with your system ...

Why on earth would you want to buy a battery for $6,000 ??? you can adjust your powerwall to MAKE it work fine with your inverter ..do you have a reliable grid connection ??? Why do you even need a powerwall??

daromer said:
Yes its only + and - going down to the inverter... But you need to have enough thickness on the wire to support that length. Having 4 panels in paralell on a single 6mm2 is not enough when we talk about over 30A. those lines will get hot and you will loose some.
I recomend atleast 10mm2 or larger for that many. In my case i always do 6mm2 per 2 paralelled panels. In my case max 17A.
Click to expand...
Let's look at the numbers ...

Resistance of 6mm2 copper wire is3.08 Ohms/Km

Let's say the distance from panels to regulator is 25 meters ... length of wire is 50 meters

Resistance of this 6mm2 wire is 3.08/ 20 = 0.154 ohms power lost is I squared R at 30A = 900 x .154 = 138W

There is absolutely no danger of the wire getting hot, but this lossmaybe unacceptable.....If panels are in parallel (open circuit voltage 21v?) operating voltage is about 17V @ 30A power is 510W

So with 25 meters distance to regulator ,using 6mm2 , resistiveloss is 138 Watts ...27%
But most of the time you will not be operating @30A ......@15A loss is only 69W ...13.5% of power transmitted.


....


If you doublethe thickness of wire to 12mm2 loss @ 30A is68 Watts ...13.5%

If you put panels in series(open circuit 42 V , op. V 34 V ) then loss @ 30A is 138W ...13.5%

This highlights the advantages of micro grid tied inverters , installed on the back of panels ..transmitting power at 240 /110V (AC) should keep losses below 1% ....

Or keep regulators, batteries and inverters close to panels ...

Or if you have to have a long distance between panels and regulator use aluminium power cable ... 35mm2 is very cheap where I am ...

35 mm2 Aluminium has same resistance as 22mm2 copper
 
In my area most people dimension the wires from the panels to roughly 3 to 4 %. But yeah its all up to the user :)

Ozz ocv is more like 40v
 
ozz93666 said:
Resistance of 6mm2 copper wire is3.08 Ohms/Km

Let's say the distance from panels to regulator is 25 meters ... length of wire is 50 meters

Resistance of this 6mm2 wire is 3.08/ 50 = 0.0616 ohms
Click to expand...

3.08/1000*50 = 0.154 Ohms

Even worse numbers, a voltage drop of 4.28 v and a lost of 138 watts at high distances is more convenient install in serie and increase voltage keeping low amperage.
 
jesusangel said:
ozz93666 said:
Resistance of 6mm2 copper wire is3.08 Ohms/Km

Let's say the distance from panels to regulator is 25 meters ... length of wire is 50 meters

Resistance of this 6mm2 wire is 3.08/ 50 = 0.0616 ohms
Click to expand...

3.08/1000*50 = 0.154 Ohms

Even worse numbers, a voltage drop of 4.28 v and a lost of 138 watts at high distances is more convenient install in serie and increase voltage keeping low amperage.

............

Wow ....well spotted angel , I should have divided by 20 not 50 .... that's a big difference ...I'll edit my post !!

I wonder how far the average distance of panels to regulator is ... perhaps not as much as 25 meters??
Click to expand...
 
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