Basic question about net metering..

[solarAddict]

I hope I'm not kicking a dead horse with this question.

My coworker tried to talk me out of Power Wall claiming that grid is ultimate storage and with net metering and same rate 24x7 it makes no sense. His argument was "you are getting paid the same rate - so no reason to store it locally".

My understanding that net metering is only for "basic service" and not on "delivery services". Here in MA these two are pretty close, so my bill is double of what the "basic service" is. Meaning if I "export" to the grid i woudl get credit only for "basic service". Am I correct?

Besides, I see PW as a generator alternative as we don't have a natural gas line and I don't wanna deal with canisters or propane for the generator.

Thanks!

 

[dortor4ev]

net metering varies by region and I'm not personally familiar with MA enough to analyze the differences - but here is my take

1. your friend is right "the grid" is the best battery in the world
   1. it has unlimited capacity - it can accept _ALL_ the power you can throw at it
   2. there is no DC->AC->DC->AC losses - there are losses between Solar & the battery and back to the home
      1. you get less power "out" then you put "in" with PW's
   3. you can "draw" more kWh's than you "deposit" - kinda like a checking account where you can take out more money than you put in - if you add 10 kWh to the grid on Tuesday - you can withdrawn 20 kWh on Wed. when it's cloudy - best bank in the whole world!
   4. there is no overnight vampire loss (my PW's lose about 2% overnight even when they are not being used)
   5. there is a small chance of actual $$$ in your pocket if you overproduce - which in my case annually covers about 4-7 months of my Natural Gas bill as a $$$ credit on my monthly bill
2. There is NO ROI for Powerwalls that I've been able to find - there is simply no way they pay for themselves like solar - they are too expensive - and the margin on power isn't enough to make up the investment

But I got PW's not because of the ROI, but because my wife and I were tired of the frequent (but short duration - sometimes long) outages our particular region in CA suffers (38 outages covering 19 hours of "downtime" in the first 12 month we've had the PW's)

The Powerwalls are not an investment like the solar panels, they will not save you money - they are a home appliance like your HVAC, Oven, Water Heater - they are your whole home backup and if that is a valuable feature to you then the cost is a simple equation of do you want to have power when the grid is down?

so while your friend is right (in my opinion) it doesn't matter - Powerwalls aren't about ROI - they are about quality of life and of the best investments I've recently made...

in fact they are sooooo good, and our power outages are such a nuance that several of my neighbors got tired of seeing my home with lights on when the power went out - there are 6 PW systems being installed in various neighbor's homes over the next 3-4 months - and since I live in an HOA I've taken to having an "open house" once a month to answer questions for others who have yet to make the plunge - in the past 6 months I've had 4 "open houses" for sharing what PW"s are, how they work and what they look like - they have all been well attended - even though I don't offer coffee or donuts.

nothing in the world sells Powerwalls as well as a good night time power outage where you have the only home in the area with the lights on - and the neighbors wonder "why do they have power?". Many many knocks on my door the next day…

"Hi, I'm Bill, we're neighbors, we had an outage last night, and I'm wondering how you kept your lights on?"​

 

[morbidz]

while the grid IS the ultimate storage in a true 1 to 1 net metering, powerwall is the answer for the outage situation where you can ONLY power your house if you have it.
Otherwise solar and no powerwall would leave you without power when the grid is down.

 

[dortor4ev]

there is also a very very subtle "feature" of the Powerwalls that most people don't realize, and seem to have a hard time wrapping their heads around even when it's explained to them...

99% of residential solar installs are "grid tied" solar - which means you get power from the grid, and provide power to the grid, and the two systems are "interconnected" - but you have "generators" on your roof/ground, and during the day your panels generate power and your home gets it first and any excess goes to "the grid" - great - solar 101 - we all seem to understand that…

however what most people don't realize, is that with "grid tied" solar

if the grid is down - your personal solar is also down! yep , zip, zlinch, nada - you are not producing power today my friend! no grid = no solar power = no kWh's - fire up the generator! cause your panels are doing squat!​

whaaaaaaaaaaaaaaaaa? so even on a sunny day with 180,000 solar panels on you roof and you normally generate 457,523,982 kWh/day - _IF_ the grid is DOWN - you generate 0 (zero) kWh's while the grid is down - [insert Homer Simpson 'doh' here]

DOH!​

your solar panels are "inert" while the grid is down - this is the rule, and is a condition set by the power companies and the physics of electricity - that your solar panels will not produce _ANY_ power while there is "NO" grid…ostensibly the most important reason for this is safety - since your home is connected to "the grid" - if you were generating power - your home would be electrifying the grid while workers are trying to work on the lines - and they need/expect there to be no power while they are working on the outage - if your panels and your neighbors panels were generating power, the grid would be "powered" and add complexity and safety issues to restoration issues…

the physics of the issue are - even if your panels were allowed to produce power while the grid was down - it's highly unlikely your panels and your neighbor's panels could meet the demand of the entire neighborhood, so while you would be producing power - the ongoing demand of all your neighbor's power usage would essentially suck your panels "dry" because they simply can't meet demand for an entire neighborhood - think sucking on a straw from an empty container…unless your solar system is big enough to meet the entire neighborhoods demands - the grid would be unstable, and a brownout would occur, and the power quality wouldn't be standard, and cats, and dogs, and the end of the world, and the wrong political party in the White House, and your wife has left you, your dog has died…it just won't work…

so grid tied solar produces zero kWh's when there is _NO_ grid.

however if you can temporarily "disconnect" your home from the grid - you could have your solar generate power while the grid was down - powering your home during the day time - even though there is no grid…

if only there was some device that would monitor 'the grid' - say 1000 times a second - or a millisecond - and when "the grid" goes down - cut over a disconnect switch in less than 10 milliseconds - taking your home off the grid temporarily and then allowing your solar panels to continue to produce power…if only.....

wait that device exists! it's the Powerwall Gateway Module - and that is exactly what it does!

1. it monitors the grid
2. it connects and disconnects from the grid as necessary
3. it coordinates power to/from PW/Solar/Home/Grid
4. it "lies" to the Solar panels during an outage and "pretends" to be the grid so that they continue to produce power

my home solar system in summer produces 40-60 kWhs/day - without the PW's you lose that daily production - with the PW's during the day it's very likely your solar system can power the home leaving the batteries untouched...

it's a very very powerful but subtle feature once you understand it - PW's keep your solar producing during a grid outage - without PW's you lose all your potential solar production - which once you understand it is very frustrating…

when PG&E turned off my power last year for 36 hours at my home without Powerwalls - it was quite frustrating to me personally to go a day and a 1/2 with no power, knowing I had 30-40 kWh sitting on my roof "idle"…I ordered PW's the next day - not for whole home backup - but because I was tired of listening to the generator, and dealing with the propane tanks.

Powerwalls keep your solar online while the grid is down - this means you still have access to your normal daily production - and can recharge the PW's during the day - meaning not only do the PW's provide power to the house, they can sit idle saving their power, when your solar can pick up the load - this is a powerful powerful feature - but difficult to wrap your head around until you really understand it....

ohhhhh - you mean I get to power my home with the 30-40 kWh/day I normally produce, only using my batteries at night! Wow that's kinda cool.

 

[Merrill]

I agree, 2 most important things about the Powerwalls, I do not have to shower in the pool and I can still generate solar power. I do not care about ROI and having a hot shower, we are on a well is the best.

 

[gpez]

net metering varies by region and I'm not personally familiar with MA enough to analyze the differences - but here is my take

1. your friend is right "the grid" is the best battery in the world
   1. it has unlimited capacity - it can accept _ALL_ the power you can throw at it
   2. there is no DC->AC->DC->AC losses - there are losses between Solar & the battery and back to the home
      1. you get less power "out" then you put "in" with PW's
   3. you can "draw" more kWh's than you "deposit" - kinda like a checking account where you can take out more money than you put in - if you add 10 kWh to the grid on Tuesday - you can withdrawn 20 kWh on Wed. when it's cloudy - best bank in the whole world!
   4. there is no overnight vampire loss (my PW's lose about 2% overnight even when they are not being used)
   5. there is a small chance of actual $$$ in your pocket if you overproduce - which in my case annually covers about 4-7 months of my Natural Gas bill as a $$$ credit on my monthly bill
2. There is NO ROI for Powerwalls that I've been able to find - there is simply no way they pay for themselves like solar - they are too expensive - and the margin on power isn't enough to make up the investment

But I got PW's not because of the ROI, but because my wife and I were tired of the frequent (but short duration - sometimes long) outages our particular region in CA suffers (38 outages covering 19 hours of "downtime" in the first 12 month we've had the PW's)

The Powerwalls are not an investment like the solar panels, they will not save you money - they are a home appliance like your HVAC, Oven, Water Heater - they are your whole home backup and if that is a valuable feature to you then the cost is a simple equation of do you want to have power when the grid is down?

so while your friend is right (in my opinion) it doesn't matter - Powerwalls aren't about ROI - they are about quality of life and of the best investments I've recently made...

in fact they are sooooo good, and our power outages are such a nuance that several of my neighbors got tired of seeing my home with lights on when the power went out - there are 6 PW systems being installed in various neighbor's homes over the next 3-4 months - and since I live in an HOA I've taken to having an "open house" once a month to answer questions for others who have yet to make the plunge - in the past 6 months I've had 4 "open houses" for sharing what PW"s are, how they work and what they look like - they have all been well attended - even though I don't offer coffee or donuts.

nothing in the world sells Powerwalls as well as a good night time power outage where you have the only home in the area with the lights on - and the neighbors wonder "why do they have power?". Many many knocks on my door the next day…

"Hi, I'm Bill, we're neighbors, we had an outage last night, and I'm wondering how you kept your lights on?"​

This is a really great post!

I only very slightly disagree with the "Powerwalls aren't about ROI". In my area we have full net metering and no ToU charges so my Powerwall is 100% backup. For me, the return on my Powerwall investment is insurance and like anything else insurance at the right price provides great returns.

The return (R) that a backup-only Powerwall provides is:

1) The actual value of having backup power. Ask yourself, as I did, how much you'd pay to have power for an hour during a grid outage. Multiply that by your expected number of outage hours and compare to the Powerwall price. That's your direct dollar ROI. Of course that number is a bit tricky because I imagine you probably wouldn't pay that much for an hour long outage but 24+ hours is well worth a few hundred dollars to prevent food from spoiling, be comfortable, and stay safe!

2) The peace of mind you have knowing that even during extended outages you'll have power. This is tougher to quantify but think of it like insurance as I mentioned above. I have a lot of peace of mind knowing that if I get in to a car accident I have good insurance coverage and I'm willing to pay for that. Similarly I have a lot of peace of mind knowing that during a grid outage I pretty much won't care. That's worth something.

Now, all of that said you personally may find that ROI calculation to not make sense. For me it did.

@dortor4ev you should start charging for your tours! That would really give you a return on your investment

 

[cwied]

I hope I'm not kicking a dead horse with this question.

My coworker tried to talk me out of Power Wall claiming that grid is ultimate storage and with net metering and same rate 24x7 it makes no sense. His argument was "you are getting paid the same rate - so no reason to store it locally".

My understanding that net metering is only for "basic service" and not on "delivery services". Here in MA these two are pretty close, so my bill is double of what the "basic service" is. Meaning if I "export" to the grid i woudl get credit only for "basic service". Am I correct?

Besides, I see PW as a generator alternative as we don't have a natural gas line and I don't wanna deal with canisters or propane for the generator.

Thanks!

Net metering rules vary a lot depending on the rules applicable in your state and the utility you use. However, if you get your energy from Eversource, it looks like your understanding may be incorrect (see https://www.eversource.com/content/...a-electric/68-tariff-ma.pdf?sfvrsn=ff21c062_8):

(i) The Standard Net Metering Credit shall be calculated for each Billing
Period as the product of:
(1) 100% of the excess kWh, by time-of-use if applicable; and
(2) the sum of the following Distribution Company kWh charges
applicable to the rate class under which the Host Customer takes
service:
a. the basic service charge (in the ISO-NE load zone where the
Host Customer is located);
b. the distribution charge;
c. the transmission charge; and
d. the transition charge.

 

[eml2]

As other have said, the feed-in tariffs rate depends on the utility. For me, I have municipal utility. They pay me back the average wholesale generation rate for my export, which is usually around 3 cents / kwh, compared to retail (generation + distribution + transmission) off-peak rate of 10 cents / kwh that they charge me for usage. Peak and shoulder rates are higher.

 

[jboy210]

I agree, 2 most important things about the Powerwalls, I do not have to shower in the pool and I can still generate solar power. I do not care about ROI and having a hot shower, we are on a well is the best.

Ha! Glad I am not the only one.

The one thing I powered during a power outage with my gas generator (vintage Y2K) was my tankless water heater. I can get by without lights, but not having hot water for showers is way too primitive.

 

[jjrandorin]

@dortor4ev

Fantastic summary and posts!

Hopefully all those neighbors are using you as referrals at the very least. When you go on tesla's website to look at powerwall propaganda, one of the things I remember them showing in the video was a home (with a lot of windows) and a nearby lightning strike, and homes around our "target" home with all the windows going dark, while every light is still on in the target home (which has powerwalls).

It sounds a bit like fear mongering, but the point you make that, if you have solar, it is EXTREMELY frustrating to be in an outage situation, know your solar can power your home, but it isnt, due to the excellent reasons you laid out.

I just got 2 powerwalls installed as well, and I am on NEM 1.0 where I am paid 1:1 for solar, so there isnt really a "real" ROI for me either, other than the piece of mind / knowledge that "I will have power". From Mid february through late november, I could probably power my home on just solar + powerwalls every day there is sun, and live fairly normally without much change. If I went into "curtail" mode, I could probably go through december and January as well (curtail = only using power for necessary things, washing clothes in the middle of bright sunny days, etc).

Its incredibly satisfying to know that, never again will I lose hundreds of dollars of food in my freezer and fridge due to spoilage from a power outage, and with our "new normal" of safety shut offs here in california (northern and southern), its even more satisfying.

 

[jboy210]

...

Its incredibly satisfying to know that, never again will I lose hundreds of dollars of food in my freezer and fridge due to spoilage from a power outage, and with our "new normal" of safety shut offs here in california (northern and southern), its even more satisfying.

A conspiracy theorist might think Elon engineered those power shutoffs to sell more solar power systems and Powerwalls. Hmm.

 

[gpez]

Ha! Glad I am not the only one.

The one thing I powered during a power outage with my gas generator (vintage Y2K) was my tankless water heater. I can get by without lights, but not having hot water for showers is way too primitive.

Funny related story - pre solar install and pre Powerwall for about 4 months my street (literally only my street) would experience weekly 2-4 hour outages due to a dying underground cable. Water or bugs or something would fault the cable connecting the two ground level transformers feeding the 18 homes on the street, tripping them both and causing the street to go dark. Took a couple of hours for a truck to come, diagnose the problem, reset what needed to be reset, and move on to the next call. Got annoying fast.

One day my wife and I were at the gym and I got a notification from my home automation (which was backed up on UPS) that the power was out. When I got home I texted my wife that she probably wanted to shower there since everything was our at home, including the tankless gas water heater. She was already almost home by the time she saw my message so now both of us were home and really just wanted a warm shower. So I had the brilliant idea to take that UPS and plug the tankless hot water heater in. Worked like a charm since it only needed power for the blower and control electronics. The UPS, which was of medium size and already at about 50% since it was being used, said it could run the heater for about an hour straight.

We had nice, hot showers during the outage and now with the Powerwall I never have to move my UPS!

 

[DrGene]

I wish we had a way to take grid tied panels with inverters on each panel that make AC and be able to plug them into a box that would allow us to plug those panels into the Tesla EV even if we do not own a power wall. This would be a way to extract energy into the car off grid or when the grid is down. With the power wall you run into the problem of discharging the small power wall battery. Omit that system and run the solar panels directly to the car through a small box would be preferable. We could then use our cars as a sort of tiny microgrid when the big grid is down for a long time. The cost savings to the EV owner could be significant.

 

[Heltont]

What others above have said is true; without some sort of local storage you don’t get anything from your solar panels. Ask the people in California that had solar and when they shut the grid down they had nada. So, I’ll relate our experiences as to our solar and PW installation. 1) we love where we live and have no interest in moving; 2) we’ve had our solar panels for close to 18 months and PW’s for 12; 3) during that time we we’ve had our PW’s we have had 30 power outages, with no loss of power to the home; 4) many were 5 to 20 minutes but some were for 4 hours or more.

Lastly, a short story. The first major power outage of over 4 hours after having PW’s our neighbor came over and rang our doorbell. My wife answered the door and our neighbor said “you have power? My wife replied, you don’t. We never noticed the outage and switch over. Totally seamless. When we went outside the entire neighbor hood was black, except for our house. It was summer and our air conditioner was running and we were cool and fine.

With the PW’s we just never notice a power outage unless someone else mentions it or I look at the statistics in the Tesla app.

SOLAR IS FANTASTIC!!! The PW’s are the icing on the cake that closes the loop for a happy solar experience.

 

[Heltont]

Want to add one more thing. Having the PW’s means you can avoid resetting the electronic clocks we have everywhere. Even our stove, microwave, refrigerator, and all the various other clocks don’t have to be reset. You don’t realize how many you have until you have to reset them all, multiple times. Sure, not a reason by itself but it’s just another small benefit...

 

[Raechris]

I hope I'm not kicking a dead horse with this question.

My coworker tried to talk me out of Power Wall claiming that grid is ultimate storage and with net metering and same rate 24x7 it makes no sense. His argument was "you are getting paid the same rate - so no reason to store it locally".

My understanding that net metering is only for "basic service" and not on "delivery services". Here in MA these two are pretty close, so my bill is double of what the "basic service" is. Meaning if I "export" to the grid i woudl get credit only for "basic service". Am I correct?

Besides, I see PW as a generator alternative as we don't have a natural gas line and I don't wanna deal with canisters or propane for the generator.

Thanks!

Hi, I am in MA with solar and PW. I understand where you are coming from with the delivery vs. power, but the answer to your question is No. MA systems are designed to be net grid consumers, so every Kwh you generate reduces the Kwh you are billed for one to one.

Your coworker has a point compared to other states that do not have full net metering, but that is not the whole story since PV Solar cannot operate when the grid is down without Powerwall.

If you export more to the grid than consume, the credit is carried month to month and paid out at the end of the year. The calculation of a net credit is not 1:1 because a couple of the delivery line items don't apply as previous poster mentioned.

 

[Yermell]

I hope I'm not kicking a dead horse with this question.

My coworker tried to talk me out of Power Wall claiming that grid is ultimate storage and with net metering and same rate 24x7 it makes no sense. His argument was "you are getting paid the same rate - so no reason to store it locally".

My understanding that net metering is only for "basic service" and not on "delivery services". Here in MA these two are pretty close, so my bill is double of what the "basic service" is. Meaning if I "export" to the grid i woudl get credit only for "basic service". Am I correct?

Besides, I see PW as a generator alternative as we don't have a natural gas line and I don't wanna deal with canisters or propane for the generator.

Thanks!

I don’t know if you are familiar with the Connected Solutions program that the State of MA is developing with Eversource. National Grid already put it in place this past year. Powerwall purchase if tied to PV is eligible for a 0% HEAT Loan. Also the utility will pay you $225/avg. kW for peak power from your PW during summer peak periods. You can find out more from MassSave, MassCEC, Tesla and utility. Eversource is very poor at responding however, I’ve had my PW interconnection application in since early December and have no feed back from Eversource yet.

 

[jmcr]

Once Power Wall batteries are charged, you are back to where you are. Since they hold a couple days charge in a power outage, if you have net metering, they are a too expensive option for a generator. If you have net metering, which does vary by state, then it seems doubtful they will do much for you. The market for Power Wall is in a few states that do not allow net metering or severely limit it and a few people living off the grid. States that do not allow Net Metering or severely limit it generally happen to be desert and some other states usually where solar power makes the best sense. Sunny all year round compared to us back east. Nevada for one. California has a funky formula that has something to do with peak production -- the point is net metering is severely restricted. I don't remember all the states, Hawaii is another. On the east coast, Georgia, either Alabama or Mississippi. Point is a Power Wall typically makes sense only were people are off the grid entirely or for most of them, where net metering is not allowed.

 

[dswansonsb]

Solar + Powerwall + Electric Car + Net Metering + Time Of Use billing = Big Savings (at least with Southern California Edison).

Last year was my first full year with my 2 Powerwalls on SCE's TOU tariff. Having the powerwalls allow us to run on battery power during peak rate hours while generating electricity at peak rates. Most of our usage is at night to charge my Model 3 at super off peak rates. By the end of the year we consumed more electricity than we generated and yet still got a check from SCE. My "credit" at year end was about $330 which translated into a check for about $65. We should be able to charge an additional EV for "free". A caveat: we're on grandfathered NEM 1.0 and TOU-D-A.

 

[diyguy]

I agree with all the “power during a blackout” comments, which in my mind is itself a conclusive argument for a Powerwall. Operating it so that it helps shave down its own cost is icing on the cake. If you’re on a Time Of Use billing plan where the peak rate is more than 10% of off-peak (preferably a lot more) then charging off-peak and discharging on-peak is a savings (not taking into account accelerating wear and tear on the battery). If you have PV and only use it to charge the battery, you can take the federal tax credit. If your utility (or other power provider) can control the discharge, they may pay you something for each use. California also has the SGIP program where they will reimburse part of the installation if you agree to discharge a certain amount annually. You can also save on Tesla labor costs by having everything already configured for installation. I did this and my Tesla final cost with installation was about $7000 (about $6500 Powerwall and $500 installation). Preconfiguration costs of course will vary widely depending on your situation.