Told my Powerwall won't charge off Solar

[jjrandorin]

Not sure why all the negativity... anyway. Suns out pumpin'... It's the summer solstice in only a couple of hrs! Rock on Tesla!

You actually started this in this thread, by assuming to know what someone "should" be able to use as far as electric usage in their home, then definitely "telling" them they were doing it wrong, basically.

On that note, Im shutting down the discussion in this thread on what someone should or shouldnt be able to "exist" on as far as electric usage. if someone wants to discuss that they should make another thread.

 

[wwu123]

Did you actually look at the graph? There's at most a 25% increase in efficiency over the past 10 years.

My array of 250W panels just passed the 10-year mark, they're rated at 15.1% efficiency (when new), a modern 480W panel I checked is 21.4% efficient - that's 33% better (or conversely, we can say the older panel is 25% less efficient). It's higher wattage also because it's much larger in area.

Of course, whether 25%, 33%, 100% even, all moot for OP who's trying to solve a battery storage problem, not a solar production problem - and prohibitive to swap a 10-year old solar system and be subject to NEM3 instead of NEM1. Even if a new system were totally free, I think it'd be financially disastrous, as in net loss every year....

 

[buckets0fun]

Not sure why all the negativity... anyway. Suns out pumpin'... It's the summer solstice in only a couple of hrs! Rock on Tesla!

Calling out bs isn’t “negativity”, it’s discourse. The doubling down and still being told you were wrong likely hurt your feelings, which may have changed your perception of the facts at hand.

Who knows. Enjoy the sun down unda. Don’t let the dingo near the baby, toss some shrimp on the barbie and knock down some vegimite for us.

 

[GasDoc]

Sorry that I've been absent from this thread. Thanks for all the input.

This is going at our second home, up in the hills, which we might retire to someday.

My primary motivation currently is to have some backup in the event of an outage. I generate enough power that PGE sends me a check for about $400 annually. No need to time shift or generate more excess power.

Tesla is installing today. They tell me that I will be able to charge my Powerwalls from Solar when I'm on grid. The excess will be exported to the grid. The issue is that during a power failure, my panels may generate more power than the inverter is rated to handle. So they recommend at least one more powerwall.

The installer knows my plan for another PW sometime in the future and will place this one in a spot where it can have a companion next to it down the road. I'm not in a position to shell out the cost for a second powerwall at this point and would rather pay the additional install fee rather than delay this project with the winter months coming. The installer says that I will be fully functional at the end of the installation and, with my existing solar, no need to wait for permission to operate from PGE.

 

[CrazyRabbit]

But given my experience of having to wait this many years for this first (free) Powerwall, I just want to get it done and deal with the second one later. The purpose of this thread was to try to get an understanding of why I can't charge off solar with just one unit.

Solar inverters are current power supplies, meant to push as much current as they can and they don’t throttle like a voltage supply or generator. And since your single powerwall can’t accept all the 10kw that extra current will fry something.

 

[miimura]

Solar inverters are current power supplies, meant to push as much current as they can and they don’t throttle like a voltage supply or generator. And since your single powerwall can’t accept all the 10kw that extra current will fry something.

This is not technically correct. If you configure a Powerwall system with too much solar it won't self-destruct or "fry something". It will simply not work well. When the solar ramps up and the Powerwall gets full or approaches the maximum charging rate when off-grid, it will raise the frequency to try to curtail the solar. Most solar inverters don't do good proportional curtailment, so it will simply shut down. This means that the Powerwall could be empty and need charging, but the solar is too powerful and the Powerwalls won't charge. This is why it is treated as a design rule.

I have solar based on Enphase micro-inverters. I have one old system (M215) and one new system (IQ8). On both of these systems, it's possible to simply shut down sections of the solar by turning off breakers in 20A increments. So, I would not hesitate to put all the solar on the backup side of the system because I could just turn off portions of the system to remain below the maximum Powerwall charge rate. When you are in a grid-down situation, it's best to have all the solar available.

I should mention that if you have variable loads available like a Tesla car to charge, you can keep all the solar running full blast and vary the car charging to absorb the surplus solar that the Powerwall can't accept. However, this is an interactive solution just like turning off part of the solar. As I recall, the OP mentioned that this is like a vacation home, so he should really see if he can divide the solar so a portion is on the non-backup side of the Gateway so that the whole system can run fully autonomously without overloading the Powerwall.

 

[BGbreeder]

This is not technically correct. If you configure a Powerwall system with too much solar it won't self-destruct or "fry something". It will simply not work well. When the solar ramps up and the Powerwall gets full or approaches the maximum charging rate when off-grid, it will raise the frequency to try to curtail the solar. Most solar inverters don't do good proportional curtailment, so it will simply shut down. This means that the Powerwall could be empty and need charging, but the solar is too powerful and the Powerwalls won't charge. This is why it is treated as a design rule.

I have solar based on Enphase micro-inverters. I have one old system (M215) and one new system (IQ8). On both of these systems, it's possible to simply shut down sections of the solar by turning off breakers in 20A increments. So, I would not hesitate to put all the solar on the backup side of the system because I could just turn off portions of the system to remain below the maximum Powerwall charge rate. When you are in a grid-down situation, it's best to have all the solar available.

I should mention that if you have variable loads available like a Tesla car to charge, you can keep all the solar running full blast and vary the car charging to absorb the surplus solar that the Powerwall can't accept. However, this is an interactive solution just like turning off part of the solar. As I recall, the OP mentioned that this is like a vacation home, so he should really see if he can divide the solar so a portion is on the non-backup side of the Gateway so that the whole system can run fully autonomously without overloading the Powerwall.

Don't your IQ8s under a California grid setting do a throttling of the output as the frequency increases?

All the best,

BG

 

[miimura]

Don't your IQ8s under a California grid setting do a throttling of the output as the frequency increases?

All the best,

BG

I actually don't know. I just got the IQ8 system installed in September and haven't even done an off-grid test yet. I should grid charge up to 100% and see what happens when I turn off the main breaker. I am not working between Christmas and New Year, so I may add this to my list of home projects.

 

[jjrandorin]

I am not working between Christmas and New Year, so I may add this to my list of home projects.

Not working "At work" but probably plenty of work around the house, I would imagine, lol.