Two Powerwalls V2 not meeting expectations, why?

[SolarInAZ]

Hi, new to forum, here in Cornville, AZ, where it's almost always sunny.

We had a solar panel system installed september last year (2018) and it's not acting like we wanted. First off, the saleslady seriously mislead us. We told her we wanted a 13.KwH system, and instead of giving us that much in panels, she gave us 8.5Kw panels and TWO Tesla Powerwalls. She is no longer working there.

So here's what happens: When I turn them on, I send less power to APS, and I use more power.

It's really that simple.

Talking to Tesla for months about this, I've been told, that's because when you are running them as a backup, the house is drawing its energy from the batteries constantly. And they are less than 70% efficient. Meaning I will use 130% of my normal power consumption.

power -> batteries -> Home use.

When I run them for cost savings, there isn't any. Again, that power efficiency problem. You get less out than you put in. I guess I didn't understand that initially. I thought you get out what you put in.

So if I charge them during the morning it costs me 130% of the energy I will get from them during peak hours. So much for saving money.

End result: I turned them off, and had a power bill credit of $65 in December. I turn them on, and it's $31 for January. I do not have electric heating (well, I do, but I didn't use it, since that can vary, I used my gas furnace for both months.

We bought them, and they've told us, "It's too late to return them". So here I am with TWO powerwalls turned off in my Garage.

My wife keeps telling me to have an electrician come out and disconnect them, then sell them on Ebay. I'm hoping there is some other solution.

 

[Achilles]

Hi, new to forum, here in Cornville, AZ, where it's almost always sunny.

We had a solar panel system installed september last year (2018) and it's not acting like we wanted. First off, the saleslady seriously mislead us. We told her we wanted a 13.KwH system, and instead of giving us that much in panels, she gave us 8.5Kw panels and TWO Tesla Powerwalls. She is no longer working there.

So here's what happens: When I turn them on, I send less power to APS, and I use more power.

It's really that simple.

Talking to Tesla for months about this, I've been told, that's because when you are running them as a backup, the house is drawing its energy from the batteries constantly. And they are less than 70% efficient. Meaning I will use 130% of my normal power consumption.

power -> batteries -> Home use.

When I run them for cost savings, there isn't any. Again, that power efficiency problem. You get less out than you put in. I guess I didn't understand that initially. I thought you get out what you put in.

So if I charge them during the morning it costs me 130% of the energy I will get from them during peak hours. So much for saving money.

End result: I turned them off, and had a power bill credit of $65 in December. I turn them on, and it's $31 for January. I do not have electric heating (well, I do, but I didn't use it, since that can vary, I used my gas furnace for both months.

We bought them, and they've told us, "It's too late to return them". So here I am with TWO powerwalls turned off in my Garage.

My wife keeps telling me to have an electrician come out and disconnect them, then sell them on Ebay. I'm hoping there is some other solution.

Keep me in mind if you do. I have two right now but feel I need another.

 

[SolarInAZ]

Keep me in mind if you do. I have two right now but feel I need another.

Well, what are we doing wrong?

I would have to sell them together. They are joined together:

 

[SolarInAZ]

Another view of them - they were linked together (big hole through sides, conduit installed, then the black spacer kit shown, to make them one big unit.

So it's a 26KwH battery? All I know is I don't generate enough electricity to make it worthwhile.

Or, alternatively, is there some other solution?

 

[zanary]

I have two Powerwalls, and 10 panels. The AI/NN for the Powerwall takes about a month to learn your power usage, and then make decision on when to charge them, when to net meter, and when to run the house, or any combination of them.

This is during the winter, but I suspect that during the summer I'll be over generating and then net metering even more back to PG&E which will offset my consumption from them during the winter months.

If you don't want you use them then set them to Backup Mode which means they will only get use during an outage.
Set it to Self Powered and they will be used to power the house, and charge via solar. Excessive solar generation will be sent to the grid.
Advance Cost Savings is what I use, so that it charge some of the batter for all time period except for peak, but net meters during peak. While net meter it is running the house from the battery.

I also set my reserve to 50%, so one battery is use for house consumption, and one for backup.

Note: If you do plan on selling them, how much for the set?

 

[nyprepper]

I'll share some of my observations. I have 2 PW's and a 6.5kw solar array. I leave my Powerwalls set to backup-only mode for grid outages. The Powerwall's will expend about 2% of their capacity daily in backup mode (e.g. about .6kwh). When they get down to 96% they will re-charge from solar and it takes about 2KWH to bring the PW's back up to full charge. This seems to be very inefficient but it only amounts to about 30KWH per month used to maintain the two PW's in backup-only mode.

 

[cwied]

Something doesn't sound right with your setup. What rate plan are you on, and what mode do you have your Powerwalls in? 70% sounds low for total round-trip efficiency. The only way I could imagine your average being 70% is if you aren't discharging much and the vampire drain is significant compared to your usage.

If you have a time-of-use plan, the difference in rates between peak and off-peak should be able to overcome any efficiency. This is the main way you can realize a financial benefit from using the Powerwalls.

 

[miimura]

I have a two Powerwall system and I have been shallow cycling them due to the my limited solar output in the Winter. Since my solar only generates about 5kWh/day this time of year, I raised the Reserve to 75% on Time Based Control Balanced. With those settings, it was charging from solar, then during the Peak rate period, was draining to the Reserve every day. The system never reached 100% SOC. So, I was able to see that day after day I was putting 1kWh extra into the system than what I was getting out. I would post the screen shots but I just reduced the Reserve to 70% yesterday because the generation has increased to ~7kWh and it was approaching 100%. This caused the data to show more discharge energy than charging because of the lower Reserve.

My Part-Peak Winter rate is $0.205/kWh so the extra energy "wasted" by the Powerwalls only costs me about $6/mo. In December, the system discharged 67kWh during the peak hours. That avoided buying power from the electric company at the Peak Winter rate of $0.338/kWh for a savings of $22.65 and a net savings of $16.65 versus solar without Powerwalls.

I don't know what's going on with the OP's system, but it should be investigated further because it doesn't seem right.

 

[Az_Rael]

We had a solar panel system installed september last year (2018) and it's not acting like we wanted. First off, the saleslady seriously mislead us. We told her we wanted a 13.KwH system, and instead of giving us that much in panels, she gave us 8.5Kw panels and TWO Tesla Powerwalls. She is no longer working there.

Did your contract show the 13KwH in solar? If so, I would go after them for that. That would give you an avenue to make them take the powerwalls back and install the solar you wanted.

 

[Electric700]

SolarInAZ, congrats on going solar! If you leave the Powerwalls on with the app set to Self-Powered at 45% reserve (for outages), can they power your home for most of the night when sufficiently charged?

Any time you use electricity during the day (solar generating hours), that is power that won't be used to charge the Powerwalls.

This might help you too:
https://www.tesla.com/ns_videos/pw_walkthrough_TB.mp4

Perhaps you'll want to add more solar or even wind capacity at a future point, so I'd give it some more thought and try out some settings changes for at least a few more weeks.

You should try to target an 80 - 90% maximum daily Powerwall charge state for better battery health. This is from the same learning we've seen with the lithium-ion car batteries (e.g. for the Model S).

Lastly, the battery is 92% efficient. More here:
Should You Get a Tesla Home Battery? Let Physics Explain

 

[SolarInAZ]

Note: If you do plan on selling them, how much for the set?

I have no idea right now. I'd like to figure out how to make them save me money, not cost me money. If that's possible, I'll keep them. Otherwise, I'd like a fair price for them. They're installed in my garage, and were switched off for two months, since I wasn't figuring it out.

Something doesn't sound right with your setup. What rate plan are you on, and what mode do you have your Powerwalls in?

It's a peak hour plan. Peak hours are from 10am to 3pm.

I've have it on backup only right now. I had it on the peak hours setup in the phone app.

Did your contract show the 13KwH in solar? If so, I would go after them for that. That would give you an avenue to make them take the powerwalls back and install the solar you wanted.

I thought it did, but it shows 8.5KwH solar. She told us that it was actually 13K, or 125% of our usage, which is what we wanted.

 

[zanary]

Perhaps you'll want to add more solar or even wind capacity at a future point, so I'd give it some more thought and try out some settings changes for at least a few more weeks.

We've all been waiting for the Powerwall gateway to support wind... Tesla still have this comment on their page

Source URL = Powerwall & Backup Generator Connection | Tesla Support

"
I have a wind turbine/hydro turbine. Can I charge Powerwall with it?​

Powerwall does not currently integrate with other renewable generation equipment. Please stay tuned for future updates.
"

 

[SolarInAZ]

That's a good video, btw. So I changed to advanced, balanced, 50% reserved. I had 10% reserved.

I guess I'll see what happens in a couple days like this.

 

[NuShrike]

Talking to Tesla for months about this, I've been told, that's because when you are running them as a backup, the house is drawing its energy from the batteries constantly. And they are less than 70% efficient. Meaning I will use 130% of my normal power consumption.

power -> batteries -> Home use.

When I run them for cost savings, there isn't any. Again, that power efficiency problem. You get less out than you put in. I guess I didn't understand that initially. I thought you get out what you put in.

So if I charge them during the morning it costs me 130% of the energy I will get from them during peak hours. So much for saving money.

Some of what you're sharing is weird. In backup mode, the PWs charge up, and then DO NOTHING unless you have an outage. So once charge, they effectively go "offline" until needed. Your home is NOT drawing energy from them constantly.

Cost savings/advanced etc/self-powered: do you have TOU (time-of-use) rates? The PWs time-shift cheaper electricity rates from off-peak/solar to get used during your peak times. You will get savings even though it's only 90% efficient -- as long as your off-peak rates * loss% still costs less than peak rates.

You can try -- don't tell Telsa and if you're not taking the ITC rebate -- to redo the installation wizard and set it up as standalone battery (no solar). Then it would charge entirely from the grid and make it more worthwhile? Has anybody else successfully done this?

 

[Dave EV]

I thought it did, but it shows 8.5KwH solar. She told us that it was actually 13K, or 125% of our usage, which is what we wanted.

Maybe if we can start by getting units correct, that will help us figure out what's going on. Let's start with the basics:

M = mega = 1,000,000
k = kilo = 1,000
W = Watt
h = hour

A Watt is a measure of power. A Watt-hour is a measure of power over one hour, or energy. Your PV system generates power and over time, energy.

Because of context, I have to assume what you call a 8.5 KwH system is actually a 8500 W or 8.5 kW PV system, which in Arizona is probably going to generate at least 13,000 kWh a year (or 13 MWh). Depending on the install, it might generate up to 15 MWh a year.

Saying you have a 8.5 kWh system or a 13 kWh system only leads to confusion. I myself have a 3.2 kW STC rated system it also generated 8.5 kWh yesterday. It also generates around 5 MWh a year.

You can see how easy it is to get confused when the wrong units are used.

It sounds to me that you were sold a PV system that has a rating of 8.5 kW, but is projected to generate around 13 MWh a year.

 

[Cycle11111]

To Dave EVs point and for OP. We have a 7.3kw system installed in Truckee CA and it generates up to 50kwh per day during the summer - on the inverter screen max power I see at about 2pm is 6.5kw. During the winter with the panels not covered in snow I get about 31kwh.

If you want to sell the powerwalls I would also be interested. We average 30-40kwh hours of usage per day.

 

[Electric700]

That's a good video, btw. So I changed to advanced, balanced, 50% reserved. I had 10% reserved.

I guess I'll see what happens in a couple days like this.

Glad to help! In a few days you may want to try Self-Powered mode to see if that gives you better results.

 

[cwied]

You might also want to look into other rate plans. In particular, since your Powerwall can easily guarantee 0 usage during your peak hours, the plans that have demand charges for those hours might save you some money (provided the Powerwalls will be able to satisfy your summer usage during those hours - I don't know how high your AC load is).

 

[bonaire]

Hi, new to forum, here in Cornville, AZ, where it's almost always sunny.

We had a solar panel system installed september last year (2018) and it's not acting like we wanted. First off, the saleslady seriously mislead us. We told her we wanted a 13.KwH system, and instead of giving us that much in panels, she gave us 8.5Kw panels and TWO Tesla Powerwalls. She is no longer working there.

So here's what happens: When I turn them on, I send less power to APS, and I use more power.

It's really that simple.

Talking to Tesla for months about this, I've been told, that's because when you are running them as a backup, the house is drawing its energy from the batteries constantly. And they are less than 70% efficient. Meaning I will use 130% of my normal power consumption.

power -> batteries -> Home use.

When I run them for cost savings, there isn't any. Again, that power efficiency problem. You get less out than you put in. I guess I didn't understand that initially. I thought you get out what you put in.

So if I charge them during the morning it costs me 130% of the energy I will get from them during peak hours. So much for saving money.

End result: I turned them off, and had a power bill credit of $65 in December. I turn them on, and it's $31 for January. I do not have electric heating (well, I do, but I didn't use it, since that can vary, I used my gas furnace for both months.

We bought them, and they've told us, "It's too late to return them". So here I am with TWO powerwalls turned off in my Garage.

My wife keeps telling me to have an electrician come out and disconnect them, then sell them on Ebay. I'm hoping there is some other solution.

Batteries are net power consumers.

If your Solar PV put out 50kWh on a good solar day, if you put them through batteries, the result is usable maybe 45kWh. you spend kWh by storing them. It's well know and sales should always be telling this. Batteries do not store the input electrons, they undergo a chemical reaction causing the electrons to move between Cathode and Anode. So, there are charging losses. Also, EVs undergo similar losses during charge. You may use 80kWh to charge a car and only be able to use 72kWh out of those.

If you charge batteries from the grid or solar PV all the time and they are used only for backup, you will spend a little money keeping them topped up, but not that much (they should not cycle much, they are Li-Ion and not Lead Acid which need topping up).

I think the only reason to use PowerWalls is if you really MUST have standby power and make sure you don't spend kWh doing so. And also if you are in CA and arbitraging the peak power load prices of a variable rate plan with super-peak prices in the afternoons.

Solar and batteries are a solution, but not an economic one.

 

[SolarInAZ]

Thank you for that information. That's what I have come to believe as well.

What's a fair selling price for them, anybody? And I imagine I need a good solar electric company to come out to disconnect them, right?

If I can sell them, I want to get more panels.