Basic question about net metering..

[atlynch860]

PG&E (Silicon Valley) recently shifted the rate timings on EV2-A so that peak rates no longer overlap with peak production. it's $0.17 until 3PM, $0.27 until 4PM, then $0.46 until late. So I am generating and selling at $0.17 and buying back at $0.46. According to the PG&E estimation page my electric bill is going to triple, from about $500/year to about $1500/Year. There is a PGE utility app (3rd party) for the iPad which runs all available rates, estimates with Powerwalls, etc. It says that if I get 2 Powerwalls I will save about $1800/year. I assume that this is done by saving my off-peak production and using it on peak, instead of selling it to PGE and then buying it back at a higher rate.

-Drew

 

[plunk99]

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.

^^This^^

Definitely important in South Florida, where Hurricane Wilma in 2005 left my neighborhood without electricity for 2 1/2 weeks. I wouldn't want to have solar panels idle that long (or my Model 3) because I didn't have PWs.

Also good to note that PWs when installed with panels qualify for the 26% federal tax credit this year.

 

[cwied]

There is a PGE utility app (3rd party) for the iPad which runs all available rates, estimates with Powerwalls, etc. It says that if I get 2 Powerwalls I will save about $1800/year. I assume that this is done by saving my off-peak production and using it on peak, instead of selling it to PGE and then buying it back at a higher rate.

-Drew

Make sure you understand the way the app calculates the savings using the Powerwall. The last time I looked at it (admittedly quite a while ago, so it may have been updated since), it made the assumption that you could grid-charge the Powerwalls off-peak and discharge them fully on-peak. This is not currently allowed. With EV2-A, you would be able to charge the Powerwalls fully off-peak from solar, but your discharging would be limited to the amount of usage you have on-peak. Your savings would be roughly on-peak usage * (on-peak rate - off-peak rate * 1.1).

 

[miimura]

Your savings would be roughly on-peak usage * (on-peak rate - off-peak rate * 1.1).

I was wondering why you were multiplying by 1.1 but it appears this is how you are accounting for charge-discharge losses.

My savings are also limited by my Winter solar generation, since it's less than my Winter Peak usage for many weeks a year.

 

[Mr. Jim]

Having a battery gives me piece of mind. I can remove myself from the grid (or they from me) and I still have power in the house and the ability to drive my X. Living in the fire prone area of Santa Barbara it is only a matter of time before it is blackout time.

 

[kbaybob]

dortor4ev Is correct. The main value of the Powerwalls whether or not you have net metering is to keep your PV running when the grid is down and to provide backup power when the grid is down. Here in Hawaii we had (no longer do) net metering, and that was what our initial PV installation was for. It used the grid as a giant inexhaustible battery. Until there is a power outage. Then we had 104 pv panels sitting there doing nothing. We added Powerwalls to avoid that and to also carry us through night time outages when the PV would not produce enough power. We also added 14 more panels to slowly recharge the 7 Powerwalls, but they were primarily to add a bit to our total generation, because they take several days to fully recharge the Powerwalls. Under the NEM+ system in Hawaii, those panels qualified for a tax credit, but cannot feed directly to the grid. They do feed the house when the powerwalls are charged, though, so they augment the main PV system in that respect. When the grid goes down, ALL the PV panels are available for supplying the house and charging the Powerwalls. In theory we can go indefinitely with no grid power, though a long period of cloudy days might run us out of battery power if we did not reduce loads. Rules are different everywhere, but in all locations, your PV system will be forced to shut down in a grid outage so as to not back feed the grid and cause shock hazards on the grid. With a battery backup of any kind, your PV can continue to operate.

 

[leodoggie]

I have gone with a 3.5Kw grid tied system and a separate off grid system that has 12Kw of lifepo4 battery storage. I designed, built and installed both systems myself and after the 30% federal tax credit the total cost for me was $10,000.
I live in California so the roi for the grid tied system was roughly 3 years. I did not consider the battery back up as a roi proposition but I cycle it by charging my Bolt.
Since I put in my battery system in we have had two PG&E shut offs and one fire shut off. Those black outs lasted about six days total so well worth the effort, my friends and neighbors came over to charge up and use our WiFi.
If anyone is thinking of a battery back system insist on lifepo4 battery cells they are very safe. No thermal run away and if damaged no fire.
The biggest pain in the butt of doing things myself was getting permits from the city.
I have ordered a MY so we will soon be a two ev household, can’t wait.

 

[gpez]

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.

Totally disagree here.

My utility has no ToU charging and full net metering - what I produce over what I consume is banked through the year and I can use that banked production during low production times at 100% of retail pricing. It's the best net metering possible. My Powerwall is only for backup purposes.

I got a quotes for a home standby generator (11kw + ATS) which was nearly $1,000 more than my Powerwall quote before ITC. All in my Powerwall was actually $4,500 less expensive than the generator on install and since the Powerwall has zero maintenance and zero fuel costs in the long term it's the much more economical option.

 

[Ctein]

Drew Wrote: "There is a PGE utility app (3rd party) for the iPad which runs all available rates, estimates with Powerwalls, etc."

Hey, neighbor! (I live in Daly City.)

What is the name of this app?

Just got a Model X and changed my PGE account to EV2-A, which I *think* works out as a win for me, as I'm self-employed and work from home, so it's not hard to avoid charging during the peak hours. Several years back, when we installed solar and I didn't have an EV, a PowerWall made no sense economically-- the installed cost per kWh was higher than PGE's highest tier. Now? I dunno. I'd love to be able to do a new analysis.

Thanks!

pax / Ctein

 

[Anubis]

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

Is it possible to just purchase the Powerwall GATEWAY Module only, that is, WITHOUT batteries?
Your summary above seems to suggest the Gateway is the brain of coordinating the grid, solar and home.
I'd love to have my solar continue to work when there is a grid outage, but I'm not ready to purchase a full battery system just yet.

 

[dortor4ev]

you still need a battery - the batteries are “clever addition” in that they provide a buffer that can accept excess solar power and fill in power when the solar can’t meet the home’s demand - solar production can’t be precisely controlled and there are things like ‘clouds’ that will drop production in an instant.

I don’t see running a gateway without a battery system in order to smooth out the demand/unflow/overflow issues that can occur with solar…

the batteries for example shut down the solar when they are more than 95% full because there is no place for the excess solar to go if the home isn’t consuming all the available solar…

my limited understanding of this sort of system is that the batteries are key part of the solution - they meet demand when solar can’t, and provide a place for the solar to go when it’s over producing - and the gateway can shut down the solar completely when the batteries are nearly full knowing that the batteries can “match” the home’s demand - and start the solar back up again when it can know it’s production can be consumed.

 

[jjrandorin]

Is it possible to just purchase the Powerwall GATEWAY Module only, that is, WITHOUT batteries?
Your summary above seems to suggest the Gateway is the brain of coordinating the grid, solar and home.
I'd love to have my solar continue to work when there is a grid outage, but I'm not ready to purchase a full battery system just yet.

Not and have it do anything, no.

 

[WattBeatsGas]

Who’d have thought the house would need 3 PowerWalls!?

Here’s why 3 are necessary.

1. We really like our house/home/neighborhood, so we don’t want to move.

2. It’s a three-story house, so what if we get incapacitated and need wheelchairs? How to move between floors (a stair-climbing, sit-down apparatus wouldn’t work in this house)?

3. Answer: Put in an elevator. OK, did that.

4. But the grid electric power goes out sporadically, leaving the elevator useless and leaving a wheel chair user stranded. Now what?

5. Answer: Get solar panels and 2 Power Walls.

6. But Tesla designers say the elevator motor draws too many amps (65) briefly at motor startup. So, need three PWs to supply that millisecond-long, high-power draw. (Once the motor is turning, it only draws 17 amps, well within the capability of 2 PWs.)

7. No way to beat it … it’s either pay for a third PW or give up on some of the other requirements/constraints.

8. And I used to think, as a kid, that life would be simpler when I grew up and had the freedom of an adult!

 

[cwied]

What is the name of this app?

Thanks!

pax / Ctein

The one I have is called PG&E Toolkit.

 

[Sunshine Speed]

City of Los Angeles DWP generates its own power and sells it to surrounding areas. My house in city of LA has never had any power outages the whole seven years I've lived here. I'm getting the Solarglass roof with no powerwalls to save 14 Grand.

 

[Vapourick]

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.

Can you elaborate on exactly what are the preconfiguration costs?

 

[trevorlane]

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.

I'm new to solar and in MA. The reduction in Kwh from power that's generated from your solar system, is that reflected in your bill? I've had a system that's been online since November, but I haven't seen any reductions in my monthly bill. Comparing it to historic consumption, I've been generating roughly half my normal monthly consumption, but National Grid is still reporting and charging about the same before I had the system installed.

 

[jjrandorin]

I'm new to solar and in MA. The reduction in Kwh from power that's generated from your solar system, is that reflected in your bill? I've had a system that's been online since November, but I haven't seen any reductions in my monthly bill. Comparing it to historic consumption, I've been generating roughly half my normal monthly consumption, but National Grid is still reporting and charging about the same before I had the system installed.

If your electricity plan does not have net metering, and you are not home to use power during the day, you may be generating all your power and sending it to the grid with no credit for it, and then using your regular amount of power you consume when you come home.

If your solar monitoring shows you are generating solar, then look at your electricity plan and see if you have net metering or can sign up for it. If you dont have net metering, and cant switch to one, and are not home to consume solar, then you either need to buy powerwalls (or some other battery solution) to consume your own power at night when there is no sun, or you wasted money getting solar (again, if you cant do net metering where you are).

I suspect its what I said though, that you are not on a net metering plan, and are not home to use the solar power you are generating.

 

[jrielley]

One more thing to think about: net metering isn't forever. It's an unsustainable business model for the utilities. Sooner or later, it's going away. YMMV.

 

[jrweiss98020]

Check your state laws. In WA the sunset is July 2029, or when total private production hits 4% of the utility's 1996 peak demand. However, installations completed before that time will be grandfathered and continue to sell to the grid.

Also, it is NOT an "unsustainable" practice as long as the utilities are struggling to meet demand...