Misleading Capabilities of Backup Mode?

[BIC1]

Already had a new 12.1kWh PV system. After much research (unfortunately, not on this forum) comparing one PW2 with a natural gas generator, I decided on the PW. As I have net-metering, the PW's only purpose is as backup---same as the generator.

For the same net money as one PW, I could have installed an 18kWh NG generator that would have easily powered my whole house. I decided the limitations of the storage of one PW would be outweighed by the unlimited off-grid solar capability, assuming sunshine.

Putting aside the 50F temperature issue, which is not applicable to me as I installed in conditioned basement space, one week after installation, I'm learning the Tesla marketing is extremely misleading and I am regretting the PW.

After running some power-outage tests, I discovered there are extreme limitations on off-grid solar power with the sun shining. Counter-intuitively, the more the sun is shining, the less one can use the solar capability due to various limitations that one can read about elsewhere on this forum. Talk about crazy.

My installer, a relatively new partner with Tesla, was not told about these restrictions during Tesla training and is searching for a solution, i.e., some way to divert the excess solar and dissipate it, such as with a capacitor. I'm guessing from what I've read on this forum, there is no such capability. Tesla markets this simply as your PV system will work off-grid with sunshine. No little asterisk about the restrictions & complications with those restrictions.

That is my question; is there any way to divert/dissipate the excess solar while off-grid in backup mode so that the PV doesn't shut down? Thanks.

 

[miimura]

It sounds like the problem you're describing is the 12kW solar overwhelming the 5kW Powerwall inverter. If you have more than one solar inverter, you can turn one or more of them off during an outage and during high solar generation hours. As the sun goes lower in the sky, you can turn on all the inverters. That is the generation side. On the consumption side, the easiest thing to do is to charge an electric vehicle to balance the consumption and generation. Unfortunately, there is not an easy automated way to do it. Perhaps Tesla will address that automation in the future if you have a Tesla vehicle.

 

[Shygar]

I think when the grid is out, the PW2 will go down to 95% then solar kicks back on and charges it back to 100% and keeps cycling like that. Is that causing you an issue? I would only think that would be a problem if you need to sustain over 30 amps (max a single PW2 can handle), but then your solar would kick on shortly.

 

[power.saver]

It's unfortunate that your installer didn't recognize the PW limitations when integrating it with your 12kW solar system. But it's not crazy, a 5kW PW inverter cannot accept 12kW of inverter output when the grid is down. If you have two inverters, you should call your installer back out to move one outside the GW so that the other remain functional during an outage. If you want all the 12kW solar capability, you should install another PW.

 

[BIC1]

Yes, the 12kW PV is overwhelming the 5kW PW. On the generation side, I have 38 panels and 19 APsystems YC500A microinverters. I don't think there's any way to selectively turn off microinverters.

Yes, later in the afternoon, the battery would drop to 96% and then charge back up to 100%. But, mid-day, the solar shuts off. I don't have an EV car to soak up the excess (nor anything else for that matter that could soak up that much excess solar). I could turn my two AC units to freezing temps (if it's summer), but that would bust the 28 (30?) amp limitation.

At any rate, it's pretty complicated to manage if at home. If I'm away from home, it seems useless.

 

[BIC1]

But it's not crazy.... If you want all the 12kW solar capability, you should install another PW.

By crazy, I mean intuitively, not literally. I understand the situation---now. Yes, Tesla support suggested another PW. Great idea if they want to pay for it. My budget is maxed for this.

 

[miimura]

Yes, the 12kW PV is overwhelming the 5kW PW. On the generation side, I have 38 panels and 19 APsystems YC500A microinverters. I don't think there's any way to selectively turn off microinverters.

Yes, later in the afternoon, the battery would drop to 96% and then charge back up to 100%. But, mid-day, the solar shuts off. I don't have an EV car to soak up the excess (nor anything else for that matter that could soak up that much excess solar). I could turn my two AC units to freezing temps (if it's summer), but that would bust the 28 (30?) amp limitation.

At any rate, it's pretty complicated to manage if at home. If I'm away from home, it seems useless.

I have 18 Enphase micro-inverters and they are separated on two 20A 240V breakers. So, I could turn off half of them if I wanted. You should look at your setup more carefully to see if it's possible.

 

[LargeHamCollider]

Heck I’d just wire a switch into the panels and turn it off whenever need be.

 

[getakey]

why can't you use the PWs to cost shift if you are on net-metering?

 

[BIC1]

why can't you use the PWs to cost shift if you are on net-metering?

I don't think there's anything to gain. The kWh are settled up at the end of each month. If I under-produce, they just bill me the same rate for total kWh, regardless of when they were used. Same for over-producing, they pay me the same rate regardless of time of day usage. The grid is my storage.

 

[BIC1]

I have 18 Enphase micro-inverters and they are separated on two 20A 240V breakers. So, I could turn off half of them if I wanted. You should look at your setup more carefully to see if it's possible.

They may be broken up into three groups.

 

[SteveInCal]

My single PW is scheduled for installation on 4/24 and I've found this website to be an amazing source of information - thanks to all who contribute!

I have an existing PV system with 24 microinverter panels and have been concerned about the same issue. But according to this photo, my panels are on two separate two-pole circuits inside the Enphase Collector enclosure. I'm assuming I can turn off one two-pole breaker and shut down half of my panels. Is this correct? Do you have a similar enclosure?

 

[getakey]

I don't think there's anything to gain. The kWh are settled up at the end of each month. If I under-produce, they just bill me the same rate for total kWh, regardless of when they were used. Same for over-producing, they pay me the same rate regardless of time of day usage. The grid is my storage.

very different here. Net metering means we can solar charge back at peak rates and power house at PW stored rates

 

[miimura]

very different here. Net metering means we can solar charge back at peak rates and power house at PW stored rates

The Net Metering part is the same. In California we have Time-of-Use rates, so it makes more sense to time shift the energy to avoid paying peak rates and letting the solar all go to the grid during Peak hours. When the Peak rate is double or triple the Off-Peak rate in $/kWh, it makes a lot of sense. Some utilities don't offer it yet or have very small differentials.

 

[Ampster]

That is my question; is there any way to divert/dissipate the excess solar while off-grid in backup mode so that the PV doesn't shut down?

I guess it depends on where you are standing. One way to look at it is that the excess solar energy is being diverted into the ether when the inverters are shut down. If you wanted to dissipate the excess you could put a dump load on them to create heat or as you mentioned, turn down the temperature on one of your air conditioners. With an AC the cold you are creating inside just moves the heat to the outside.
The difference between solar and a generator is that the fuel in a solar PV system is free whereas a generator uses fuel that you have to pay for.

I am not sure there is much difference between turning off half of your solar during an outage and having the PowerWall turning off all of your solar half of the time. There probably is a way to set up some sensors to see when the solar is not producing and you could set up some relays to turn on some large space heaters oursdoors which could keep the solar going. It would have to be on a timer so it did not operate at night, but it could be done if it would make you feel better that your solar was working more often.

 

[Shadious]

Not that it helps, but it would seem that the installer would have discussed the limitations of the PW prior to installation. We have 2 powerwalls and 11.4 Kw system and they work perfectly together. If anything we underproduced a bit while running off grid tests. As was stated, you are using the PW to store energy for the night time. The real challenge is living off that power overnight without running our. My guess is that the one PW would take a lot of sacrifices in electric useage

 

[bob_p]

Tesla's website used to recommend 1 PowerWall per 4 KW of solar panels. We have 15.4 KW of solar panels and 4 PowerWalls, so when we're operating off grid, and the PowerWalls aren't full, the PowerWalls are able to take all of the solar power.

Based on initial results on our new system, we're likely going to shift to a "free nights" electric plan in a few months and use the PowerWalls to eliminate as much grid usage as possible during "day" hours. And if we end up sending excess power to the grid, even without net metering, it appears we'll see a 50% reduction in our electric bill (compared to using a standard per KWh plan with our solar panels/PowerWalls).

 

[BIC1]

I called the electric company. Net-meters are not eligible for the new, voluntary, time of use plan. If anybody wants to look at the program out of curiosity and tell me if it would make sense for me if someday allowed, check out:
Time of Use Plan

 

[BIC1]

Not that it helps, but it would seem that the installer would have discussed the limitations of the PW prior to installation. We have 2 powerwalls and 11.4 Kw system and they work perfectly together. If anything we underproduced a bit while running off grid tests. As was stated, you are using the PW to store energy for the night time. The real challenge is living off that power overnight without running our. My guess is that the one PW would take a lot of sacrifices in electric useage

Unfortunately, the installer, who I like and think is competent, is new to Powerwalls. They've only installed a few and apparently this topic was not covered in their Tesla sponsored training. I think they'll be discussing this with potential clients in the future.

Yes, I carefully thought out the sacrifices to be made operating off the battery at night, with snow on the panels for a few days, etc. I decided I could live with that believing no sacrifices have to be made when the sun is shining. The Tesla website says:

"Powerwall can detect an outage, disconnect from the grid, and automatically restore power to your home in a fraction of a second. You will not even notice that the power went out. Your lights and appliances will continue to run without interruption. If you have solar and Powerwall, then solar energy will continue to power your home and recharge Powerwall. Without Powerwall, solar will shut down during an outage."

No asterisk/footnote about the issue we're discussing. I find the above quote misleading. To me, it means when the sun is shining, no worries, all systems are a go. Tesla says, "Without Powerwall, solar will shut down during an outage." They should also say, "under certain common circumstances, even with PW, solar will shut down during an outage."

 

[CA-Gbm84]

Unfortunately, the installer, who I like and think is competent, is new to Powerwalls. They've only installed a few and apparently this topic was not covered in their Tesla sponsored training. I think they'll be discussing this with potential clients in the future.

No asterisk/footnote about the issue we're discussing. I find the above quote misleading. To me, it means when the sun is shining, no worries, all systems are a go. Tesla says, "Without Powerwall, solar will shut down during an outage." They should also say, "under certain common circumstances, even with PW, solar will shut down during an outage."

You're asking about 'dissipating' energy - how is that different to turning off the inverters?


It's in pretty much every technical document that is written about Powerwall and the Tesla.com website.
Your installer rushed through training and design - that's not Teslas fault.

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