Average Powerwall savings

[Debeucci]

Hello,

I'm thinking about adding two powerwalls to my 8.6 solar system. I have TOU with LADWP in SoCal. While it's great to have a backup in case of power outages, I'm more interested in trying to reduce my electricity bills. My system is slightly too small now that I'm charging an X and a 3.

So for everyone who got powerwalls, how much savings are you seeing managing your usage compared to before you installed energy storage?

Thanks!

 

[miimura]

My initial estimates for savings were too optimistic. Here are the two main factors that limit my savings.

1. Peak period energy consumption. You cannot arbitrage more than what you consume during the Peak rate period. Increasing consumption because it's available is not true savings. My home typically only consumes 10kWh between 2pm and 9pm. So, the savings is capped at the $/kWh difference between Peak and Part-Peak time 10kWh. If you use air conditioning in the Summer during the Peak period, your savings could be dramatically higher than mine.

2. Solar generation. You cannot arbitrage more than what your solar can generate. During the Winter, my solar generation dips below 10kWh/day. Even a day with full sun will only generate 5kWh in the depth of Winter. In addition, the rate difference between Peak and Part-Peak is smaller during the Winter (PG&E EV Rate). In the US, the Powerwalls can only charge from solar, hence this limitation. If you have a larger solar system, this limitation may not come into play for you.

 

[Jigglypuff]

For the year, I'm seeing about $1000 in savings with 4 powerwalls, 10kw of solar, and living in a canyon so I benefit extra from timeshifting.

 

[KSilver2000]

My initial estimates for savings were too optimistic. Here are the two main factors that limit my savings.

1. Peak period energy consumption. You cannot arbitrage more than what you consume during the Peak rate period. Increasing consumption because it's available is not true savings. My home typically only consumes 10kWh between 2pm and 9pm. So, the savings is capped at the $/kWh difference between Peak and Part-Peak time 10kWh. If you use air conditioning in the Summer during the Peak period, your savings could be dramatically higher than mine.

2. Solar generation. You cannot arbitrage more than what your solar can generate. During the Winter, my solar generation dips below 10kWh/day. Even a day with full sun will only generate 5kWh in the depth of Winter. In addition, the rate difference between Peak and Part-Peak is smaller during the Winter (PG&E EV Rate). In the US, the Powerwalls can only charge from solar, hence this limitation. If you have a larger solar system, this limitation may not come into play for you.

For the year, I'm seeing about $1000 in savings with 4 powerwalls, 10kw of solar, and living in a canyon so I benefit extra from timeshifting.

So, basically, the Powerwalls are not worth anywhere near their cost (w/ install). At least for those with TOU billing. And probably will not be for some time.

 

[miimura]

So, basically, the Powerwalls are not worth anywhere near their cost (w/ install). At least for those with TOU billing. And probably will not be for some time.

If you expect an investment return purely based on Net Metering TOU arbitrage, that is correct. In other places around the world with different utility rules (ie. no net metering), they can pay for themselves in a reasonable period just with avoided utility payments.

I got Powerwalls because I had already budgeted for a backup generator, I got a large SGIP rebate, and I am taking the tax credit. Absent any of those things, I probably would not have pulled the trigger when I did.

 

[cwied]

I'll add my +1 to that, with one addition. I also am participating in OhmConnect, which has the effect of giving me a couple of hours of super-off-peak rates in the evenings. Given that my cost for a two-Powerwall system after ITC and SGIP is about $4900, I think my break-even will end up only being about 6-7 years out.

 

[Jigglypuff]

The cost of a reliable backup generator, which I needed, makes PWs a good investment. Plus if there's a big quake and we lose power for a month, we're probably also going to have trouble getting propane. A generator is only going to last a week on a 500 gallon tank, and if I added a 1000 gallon tank, the price of a generator would meet or exceed the price of the Power Walls. Also propane is damn expensive in CA.

 

[miimura]

The cost of a reliable backup generator, which I needed, makes PWs a good investment. Plus if there's a big quake and we lose power for a month, we're probably also going to have trouble getting propane. A generator is only going to last a week on a 500 gallon tank, and if I added a 1000 gallon tank, the price of a generator would meet or exceed the price of the Power Walls. Also propane is damn expensive in CA.

When I had my house built, I had a natural gas line put in to where I thought I might put a backup generator. However, in an earthquake, there's no guarantee that the gas will continue to flow either. Glad I went with the Powerwalls instead. I think I'll use the gas line for a BBQ since it's right there on the back patio.

 

[TapHabit]

I use a boatload of power at night, off peak. My EV rates are significantly lowered during that time. I use next to no power during the day, during high peak. The 20kwh system with 2 power walls covers 60% of my overall home usage. I save 100’s every month between this.

 

[SDRick]

My initial estimates for savings were too optimistic. Here are the two main factors that limit my savings.

In the US, the Powerwalls can only charge from solar, hence this limitation. If you have a larger solar system, this limitation may not into play for you.

I was not aware of this. Why can't the batteries be charged from the grid? Why can I charge the batteries in the car but not the batteries in the Powerwall?

 

[cwied]

I was not aware of this. Why can't the batteries be charged from the grid? Why can I charge the batteries in the car but not the batteries in the Powerwall?

It's because to qualify for the 30% federal tax credit energy storage systems must be charged only from on-site renewable energy sources. Tesla decided to restrict all Powerwalls installed in the US to charging only from solar for this reason. I'm assuming it makes their lives easier when trying to prove that Powerwalls meet the requirements.

 

[zanary]

It's because to qualify for the 30% federal tax credit energy storage systems must be charged only from on-site renewable energy sources. Tesla decided to restrict all Powerwalls installed in the US to charging only from solar for this reason. I'm assuming it makes their lives easier when trying to prove that Powerwalls meet the requirements.

In my case I had my Powerwalls installed in 2017 by itself because I got SGIP. I could not claim 30% ITC for the cost of the Powerwall project.

In 2018 I added 10 panels to my system. I get to claim ITC only on the cost of this solar project and not the storage as that was a year earlier, however my Powerwalls will only charge from solar...

I'm guessing is not just claiming ITC of 30% on the Powerwalls+Solar, but if you have solar with ITC 30% after the Powerwall install then you can't charge powerwalls from grid, period!

 

[Shygar]

Unless Stormwatch is active, then it will charge from the grid.

Aside from SGIP (which should be soon but haven't got the check yet, 1.5 years after install) and ITC, the main benefits for me are like @miimura said with shifting 5-10kW during my peak with part peak cost and also having solar available in an outage. I've had it happen twice now with outages where it was a sunny day and I still had power because my powerwall allowed my solar to keep functioning in an outage.

 

[cwied]

I'm guessing is not just claiming ITC of 30% on the Powerwalls+Solar, but if you have solar with ITC 30% after the Powerwall install then you can't charge powerwalls from grid, period!

Exactly. Tesla restricts any Powerwall installed with solar to charging only from solar. This means that when they are asked to prove that an installation that claimed the ITC was charged only from solar they can just say that all Powerwalls are programmed that way rather than having to keep data for each site.

 

[markus478]

I had a 5KW PV and tesla battery installed a week ago. So far, i am able to use mostly from the battery; about 95% self sufficient without needing the grid. Only use grid when i use the big reverse cycle A/C which draws 7KW at times.

 

[SDRick]

Exactly. Tesla restricts any Powerwall installed with solar to charging only from solar. This means that when they are asked to prove that an installation that claimed the ITC was charged only from solar they can just say that all Powerwalls are programmed that way rather than having to keep data for each site.

Is charging batteries only from renewable sources a limitation unique to the Powerwall or all battery backup systems?

 

[miimura]

Is charging batteries only from renewable sources a limitation unique to the Powerwall or all battery backup systems?

If you don't have solar, the Powerwall can charge from the grid during off-peak and discharge during peak. You can even get the SGIP rebate for that kind of installation. The only SGIP requirement is that you have to do at least one full discharge equivalent per week. Basically, you can't just let it sit in backup waiting for an outage if you get the rebate.
Other battery systems have their own configuration options. If you take the ITC, you can only charge from on-site renewable energy. If you get audited, then you may have to prove it.

 

[SDRick]

If you have solar do other battery backup systems allow charging the battery from the grid when rates are low?

 

[Shygar]

It's not a technical limitation, it's a government tax credit limitation. They should all behave the same way to be compliant with the ITC (assuming you're taking the ITC, if not you can charge from grid if you don't have solar).

 

[SDRick]

It's not a technical limitation, it's a government tax credit limitation. They should all behave the same way to be compliant with the ITC (assuming you're taking the ITC, if not you can charge from grid if you don't have solar).

Let's put the tax credit aside for a moment. As I understand it, the Powerwall is designed to be unable to charge from the grid if there are solar panels connected. Does the same hold true for other battery systems?