Charging multiple powerwalls

[RedBall]

Hi,

Im in the UK, and really struggling to get an answer to what I think should be a basic question. Cant find the answer in any tesla publications either.

With multiple Tesla Powerwalls, can you charge them concurrently at their maximum rate.

i.e. if a single powerwall can charge at 5kW, can a bank of 3 charge at 15kW? (5kW each)

The reason for my question is that whilst I have a high electricity usage, I dont have the space or correct facing rooftops (or enough sun in the UK) to fully charge the powerwalls.

The reason I want 3 is that would just about cover an entire days usage outside of the off peak charging period.

So - on sunny days, use whatever solar I can and put the rest into the batteries.

On dull days, charge the batteries fully on off peak, and use that power during the peak. Problem is our off peak is only 4 hours, so I have 4 hours to fill up 40.5kWh of powerwalls, so need to be able to charge a bank of three at a rate of 10-11kW or about 3.5kW into each.

So far ive had the following:

No, they share the max 5kW, so a bank of three would charge at 1.6kW each (a bank of 10 would charge at 0.5kW each etc..)
It would require a gateway on each battery as its the gateway that limits the charge rate
Yes they can but need grid permission to charge them at that rate.

Im close to just forgetting the entire thing and using the money for something else, it just seems so difficult to get an answer to a basic question.

 

[bkp_duke]

I have 3, live in Southern California. I have a 12kW DC system and I've seen my powerwalls charge at up to the max that system will produce. They definitely do NOT share the 5kW for the entire system, it is per powerwall.

 

[RedBall]

I have 3, live in Southern California. I have a 12kW DC system and I've seen my powerwalls charge at up to the max that system will produce. They definitely do NOT share the 5kW for the entire system, it is per powerwall.

Is that when grid charging though?

I.e. can you charge your 3 at 15kW from grid?

Sorry dont know what the max charging rate for a powerwall is in the US.

 

[bkp_duke]

In the USA we are not allowed to grid charge if we have solar. The system blocks that function.

 

[RedBall]

In the USA we are not allowed to grid charge if we have solar. The system blocks that function.

I thought you could use it to grid charge during off peak, time of use etc.

 

[bkp_duke]

I thought you could use it to grid charge during off peak, time of use etc.

Only if it is not coupled with solar.

 

[miimura]

I thought you could use it to grid charge during off peak, time of use etc.

In the UK, you can charge from the grid. You should check with some of your countrymen, grid charging may max out at ~3kW per Powerwall. No sure because I'm in the States and we can only charge from the grid during StormWatch events.

Thinking back to other UK users experiences, I don't think you can force it to charge fully from the grid. You are usually at the mercy of the Tesla algorithm to decide how much to charge during Off-Peak. People have complained that it's only backward looking and doesn't consider weather forecast. So, the changeable UK weather frequently leaves them short because the system expected more solar generation on that day. Tesla has unofficially hinted that more advanced controls might be forthcoming.

 

[oleboyredw]

I can answer part of your question, but as I only have one powerwall I cannot give the full answer. My comments below are UK specific (may be valid elsewhere but I do not know if they are).

In the UK the powerwall will top up on cheap time electricity if you configure it to do so by setting the time zones in it. You can set up peak, shoulder and cheap. You can only set up one cheap time a day, so I have mine set to 02:30-07:30. I have a second cheap time from 22:30-00:30 which I cant exploit because the Powerwall only supports one per day.

A powerwall has an internal restriction (inverter I believe) that has a limit of 5Kw, so I’ve seen mine max out a few times, but very few due to my usage profile.

Do not assume that if your Powerwall is 10% full when time enters the cheap period that it will fill your batteries as much as possible in the cheap period. The internal algorithm for doing this is not too smart and takes account if behaviour in last few days as far as I can work out. Not ideal for the ‘randomness’ of British weather, with odd miserable days here and there, probably more suited to California(?)

Having said the above, which may sound quite negative, I’m really pleased I included a battery in my config, we’re only occasionally seeing peak electricity use, which probably averages out to less than 0.3Kwh per day. (Sunnypeacs on pvoutput if you want a look at my stats).

 

[JohnRatsey]

I'm also in UK and confirm that Tesla's algorithm for off-peak charging isn't very suitable for UK conditions (we all need to keep hassling Tesla to provide some manual control). For example, if it's been a sunny day then the battery won't do much, if any, off-peak charging which the user wants because they know that the next day is going to be murky.

On a more technical side the grid won't be worried about the amount of power used to charge the batteries provided it doesn't blow the main fuse. I've seen a charge rate of about 3.3kW. Three batteries charging at this rate is therefore about 10kW which is well within the fuse capacity provided no one runs an electric shower during the charging period. Unless I'm mistaken, one gateway will manage three batteries. You can see my battery charging on PVOutput (click on the right-most blob under the date to see the battery data then change the date to 3rd Feb 2019).

However, you may fall foul of the 16A limit on the Powerwall output unless you get permission from the network operator to have a device which generates more (perhaps you already have this for your solar system). My PW (strictly speaking, the gateway which controls the battery) is set to comply with the 16A limit so it only produces about 3.3kW. This is a bit daft as there's something wrong if the PW starts pumping power back to the grid until such time as Tesla lets us export power for profit during peak periods.

 

[miimura]

However, you may fall foul of the 16A limit on the Powerwall output unless you get permission from the network operator to have a device which generates more (perhaps you already have this for your solar system). My PW (strictly speaking, the gateway which controls the battery) is set to comply with the 16A limit so it only produces about 3.3kW. This is a bit daft as there's something wrong if the PW starts pumping power back to the grid until such time as Tesla lets us export power for profit during peak periods.

That sounds horribly daft. It should not matter how much the Powerwall is outputting if it is being self-consumed on your side of the meter. The Gateway should be measuring the Grid flow, so it should not be exporting anything, ever, thereby avoiding the 16A export limit. You should definitely ask Tesla to remove this limitation if you periodically need more than 3.3kW of output to balance your consumption.

 

[CWheels]

Only if it is not coupled with solar.

I live in Southern California and I recently had 2 PW2s installed, plus I have it coupled with solar. I have seen the PW2s charge from both solar AND grid simultaneously for 10kW combined into the PWs. In the hour leading up to Peak, it was attempting to fill the PWs before Peak period set in, so it cranked up the charging rate for about an hour. I was also under the impression that they will not charge up from the grid, but it has proven me wrong.

 

[DZeckhausen]

I live in Southern California and I recently had 2 PW2s installed, plus I have it coupled with solar. I have seen the PW2s charge from both solar AND grid simultaneously for 10kW combined into the PWs. In the hour leading up to Peak, it was attempting to fill the PWs before Peak period set in, so it cranked up the charging rate for about an hour. I was also under the impression that they will not charge up from the grid, but it has proven me wrong.
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This is crazy making. Everything I've read on the Tesla site, everyone I've spoken with at Tesla, and (until now) all the posts I've seen from USA Powerwall owners has indicated a PW can charge from the grid or solar, but not both.

I understand the tax consequences of letting a residential Powerwall draw anything at all from the grid - you lose your Federal Investment Tax Credit (ITC). This prohibition lasts 5 years from date of install. But Tesla rep told me yesterday it was physically impossible to connect a Powerwall to both the grid and the solar panels.

 

[MorrisonHiker]

This is crazy making. Everything I've read on the Tesla site, everyone I've spoken with at Tesla, and (until now) all the posts I've seen from USA Powerwall owners has indicated a PW can charge from the grid or solar, but not both.

I understand the tax consequences of letting a residential Powerwall draw anything at all from the grid - you lose your Federal Investment Tax Credit (ITC). This prohibition lasts 5 years from date of install. But Tesla rep told me yesterday it was physically impossible to connect a Powerwall to both the grid and the solar panels.

Powerwalls with solar can charge from the grid just fine. It's a software restriction, not a hardware limitation. When Storm Watch is enabled, the Powerwalls can charge directly from the grid.