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Old 10-29-2020, 10:42 PM   #21
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A Generac (or other brand) on natural gas is what people are installing here in south Texas.
I know 2 folks (back home) who have these. Their only disappointment has been that they've not really needed them. Power there is quite stable and black outs are only severe-weather related - uh, generation is primarily coal with a trace of wind No need to worry about endless supplies of NatGas, so virtually no time limit on backup availability. Not sure a Tesla Powerwall with or without solar would keep the power on for very long. With NatGas generator, you have uninterrupted power until you fail to pay your gas bill. I guess my only question would be which is cheaper to install/maintain/operate so YMMV.
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Old 10-29-2020, 10:45 PM   #22
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Originally Posted by NW-Bound View Post
On the Web, I found that some Californians do use their units to save money with the TOD differential.


Here in Phoenix, I chose a time-of-day rate structure that charges 24.09c/kWh during the peak summer hours of 2-8PM, and 7.3c/kWh outside that peak period. Or I could choose a fixed rate of 11.57c/kWh all day.

Even before I installed a DIY solar+storage, the TOD rate saved me a bit of money already, simply by programming my pool pump to avoid the peak period, plus installing a timer to cut out the water heater between 2-8PM (and avoiding using a lot of hot water during that period).

I looked on the Web and found the following rate by Southern Cal Edison: 41c/kWh for 4-9PM, and 26c/kWh for off peak. But for people with a residential energy storage system, the rates are 43c and 16c.

With an energy storage system, you want to arbitrage between the 2 rates, and that's 43c minus 16c, or 27c/kWh. But daily cycling of the battery will shorten its life, so that must be taken into consideration.

Now, Tesla guarantees that the Powerwall 2 will retain at least 70% of its initial storage capacity after 10 years or 37.8 MWh of throughput, whichever occurs first.

That 37.8 MWh or 37,800 kWh multiplied by $0.27 is $10,206. That's roughly the installed cost of a Powerwall 2 with 13.5-kWh capacity. The unit pays for itself after 10 years, and of course it will still has 70% of capacity left, so there's a significant residual value.

References:

1) https://www.sce.com/residential/rate...ial-Rate-Plans

2) https://www.tesla.com/sites/default/...nty_us_1-4.pdf
That’s interesting, thanks for posting. When I did the calculations for our system I think the payback rate was about 10 yrs, but I assumed pretty minimal price hikes in electricity, which hasn’t been the case. When we looked into the Tesla system, the cost to install was very expensive vs traditional batteries, but I’ll admit we just wanted to get our system in ASAP, so we didn’t spend as much time as I would have liked researching options.
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Old 10-30-2020, 05:27 AM   #23
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In some places, there may be enough time-of-day price differential to to offset the cost somewhat, or even be profitable if the delta is great enough.

Some people may want them just for black-outs, so if you can also make a little from TOD price deltas, it takes some of the sting out of the price, even if it doesn't pay for them outright.

That's just a theoretical, I don't know if many are actually using them in that way, but it would seem likely in CA?
That would work.

For several hours last night our price was less than 1c/kWh and between 4 and 7 this afternoon the prices will be between 25 and 30c/kWh. I have our batteries scheduled to charge at low rates so we never use any electricity during the peak period which is always between 4 and 7pm.
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Old 10-30-2020, 08:03 AM   #24
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I know 2 folks (back home) who have these. Their only disappointment has been that they've not really needed them. Power there is quite stable and black outs are only severe-weather related - uh, generation is primarily coal with a trace of wind No need to worry about endless supplies of NatGas, so virtually no time limit on backup availability. Not sure a Tesla Powerwall with or without solar would keep the power on for very long. With NatGas generator, you have uninterrupted power until you fail to pay your gas bill. I guess my only question would be which is cheaper to install/maintain/operate so YMMV.
An installation with 2 Powerwall units would probably keep our house going for 6 days, according to Tesla:
Quote:
6 Days Backup Duration
Includes plugs, lights, 120V appliances, and some 240V appliances
Even if you think that's overly optimistic, it would probably do for at least 2-3 with mostly normal usage, or maybe closer to 24 hours if it was ridiculously hot and we were running the whole house AC compressor. That's not too bad, IMO. As I said, a generator might be best for those who experience long outages, like those at the end of the infrastructure. A battery system would probably be optimal for those who have frequent but brief interruptions or dips in power.
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Old 10-30-2020, 01:05 PM   #25
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An installation with 2 Powerwall units would probably keep our house going for 6 days, according to Tesla:

Quote:
6 Days Backup Duration
Includes plugs, lights, 120V appliances, and some 240V appliances
Even if you think that's overly optimistic, it would probably do for at least 2-3 with mostly normal usage, or maybe closer to 24 hours if it was ridiculously hot and we were running the whole house AC compressor. That's not too bad, IMO. As I said, a generator might be best for those who experience long outages, like those at the end of the infrastructure. A battery system would probably be optimal for those who have frequent but brief interruptions or dips in power.

It is best to know exactly how much energy you use.

My utility company has a Web site where I can look up my exact daily usage, going back 3 years. It even has the hourly usage, but going back only 1 year.

Prior to having my DIY solar+storage system, my minimal usage was 24 kWh/day, in fall and late spring when there was no need to run air conditioning nor heating. That seems high, but I have a large pool to filter, and two large fridges, and the house is all electric with cooking and water heating all done with electric.

In the summer when it gets to 120F, my highest daily usage was 100 KWh/day. Thanks goodness it got that high only about 10 days each summer. The average usage in August was about 90 kWh/day.

In comparison, 2 Powerwall units have the combined capacity of 27 kWh. They do not last long for me under the normal usage, although in the case of electric outage, I may cut back enough so they last 2 days. More on this later.
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Old 10-30-2020, 01:53 PM   #26
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As mentioned, it pays to know how much you use, in order to see how much you can cut back in the case of electric outage.

In my case, in the 30 years living at this address, I have had only one significant outage that lasted 4 hours, and it was due to a substation failure. I do not count short outages of a few seconds that were apparently caused when they were doing some power switching.

I was interested in the power usage when I was building and testing out my DIY solar system, and wanted to know how much of a dent it would make of my power bill.

And I found some interesting numbers, such as the 24-kWh/day minimum usage. I found that the main 32-c.f. fridge draws 4.8 kWh/day, while the smaller 26-c.f. fridge draws 1.6 kWh/day. The large fridge gets opened several times a day, and we use tons of ice out of it. The smaller fridge gets opened once or twice a day at most. I guess that just to keep the fridges going plus some minimal lighting plus the basic router+laptop usage will require 8-10 kWh/day.

My solar system has been cranking out 25 to 45 kWh/day, depending on the season. And I am still tweaking it.
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Old 10-30-2020, 03:49 PM   #27
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That’s interesting, thanks for posting. When I did the calculations for our system I think the payback rate was about 10 yrs, but I assumed pretty minimal price hikes in electricity, which hasn’t been the case. When we looked into the Tesla system, the cost to install was very expensive vs traditional batteries, but I’ll admit we just wanted to get our system in ASAP, so we didn’t spend as much time as I would have liked researching options.

Yes, Tesla system installation cost can be high, as I gather from the info found on the Web. They also have a backlog, and do not serve some areas at all.

I am not interested in having one installed, because I can DIY for cheaper and for fun. However, I am curious about this industry, and have been watching out for developments. I know that many other companies also offer competitive systems. However, they are not cheap either, and usually do not have the clean look of the Powerwalls.
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Old 10-30-2020, 05:15 PM   #28
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One more thing about the Tesla Powerwalls or any other battery storage systems: their power output can be more limited than you think.

Central ACs have a huge inrush current demand when they start. It is usually 5X the normal run-time current drawn. This means that my 5-ton central AC which draws 4-5 kW when running needs 20-25 kW to start.

A Powerwall 2 can handle the peak surge of 7 kW. Two of them combined will provide 14 kW of surge power. That's not enough for a central AC.

And even if you can start the AC, at 4 kW drain, each of the Powerwall will provide 3 hours of run time each. You would need a bank of them, maybe 10 in a row?

In the usual installation, the Powerwalls are wired such that they will not provide power to heavy appliances such as ACs, water heaters, cloth dryers, ovens, etc...

I cannot power the central AC with my DIY solar either. I installed 2 minisplits, so that I can make use of my off-grid solar system. The minisplits are of the DC inverter type, and they start up gently under electronic control.
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Old 10-30-2020, 10:30 PM   #29
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An installation with 2 Powerwall units would probably keep our house going for 6 days, according to Tesla:Even if you think that's overly optimistic, it would probably do for at least 2-3 with mostly normal usage, or maybe closer to 24 hours if it was ridiculously hot and we were running the whole house AC compressor. That's not too bad, IMO. As I said, a generator might be best for those who experience long outages, like those at the end of the infrastructure. A battery system would probably be optimal for those who have frequent but brief interruptions or dips in power.
In my mom's case, I'm sure she would have been more than satisfied with just running the forced-air furnace and the fridge plus a lamp or two. Of course, about 10 days is a long time. So Powerwall might have worked but no idea of the cost. A small Generac IS affordable though I don't have the numbers (just going by the couple of folks I know that have one.) YMMV
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Old 10-31-2020, 04:38 AM   #30
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One more thing about the Tesla Powerwalls or any other battery storage systems: their power output can be more limited than you think.

Central ACs have a huge inrush current demand when they start. It is usually 5X the normal run-time current drawn. This means that my 5-ton central AC which draws 4-5 kW when running needs 20-25 kW to start.

A Powerwall 2 can handle the peak surge of 7 kW. Two of them combined will provide 14 kW of surge power. That's not enough for a central AC.

And even if you can start the AC, at 4 kW drain, each of the Powerwall will provide 3 hours of run time each. You would need a bank of them, maybe 10 in a row?

In the usual installation, the Powerwalls are wired such that they will not provide power to heavy appliances such as ACs, water heaters, cloth dryers, ovens, etc...

I cannot power the central AC with my DIY solar either. I installed 2 minisplits, so that I can make use of my off-grid solar system. The minisplits are of the DC inverter type, and they start up gently under electronic control.
When I built my house, I designed it so the guest quarters are on one side with it's own AC system. There are two AC units each are rated at 2 tons each. Do you think 2 Powerwalls could handle a single 2 ton unit with the other phantom powers? My typical phantom power is around 300 watts and when I run my generator, that has a watt load meter on it, it reads right around 3000 watts, maybe a little more. If I kick on both AC units it reads a little over 5000watts load. Also, I set up the AC this way because all 'portable' generators are limited to 30amps due to their built in breakers and wire gauge. A 4 ton and higher unit uses more than 30amps so a full sized home generator, along with it's cost, would be needed. I got away with a 7kw Honda inverter generator I bought used for $1,500, converted it to propane and plumbed the house's 500 gallon propane tank to it's location.
BTW, I'm getting the 2 Tesla power walls via 'Grid Resiliency' program funded by the California PUC and based on Medical Base Line utility rate and located in an area where power shut offs due to high fire danger are common. Cost is $26,400 installed. I have to fund to get the install, but am rebated the full amount after permission to operate is granted by the utility company, usually about 3 months to obtain.
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Old 10-31-2020, 06:45 AM   #31
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Every home in my township has at least one generator.

It is common to see two generators. One large unit and one small unit.

The small generators can power lighting and PCs. The small unit sips a gallon of fuel every 8 hours.

The big generators allow you to flush toilets, run laundry, and refrigerators & freezers, and to take showers. Those big units guzzle a gallon of fuel an hour.

Those homes run the big unit for one-hour each day, as they do laundry, take showers flush toilets, and bring the temps of freezers back down to appropriate temps.

In this manner, you consume the least amount of fuel. One hour each day running a big generator and 23 hours of running a small generator, means that you only consume 11 gallons each day tops. If you shut down the small one when you sleep, you can consume even less.

Nobody here has A/C, and most homes here burn firewood for heating.

One of our neighbors is a gunsmith. His insurance company insisted that he install a big generac to power his machine shop and security system. He regularly goes through $150 in fuel each month.

I have lived here for 15 years so far. During the past 15 years, our power company has never been capable of providing power for one-month continuously. Every month our power will go out at least once.

Just how it works here in rural areas of the East Coast.
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Old 10-31-2020, 10:36 AM   #32
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I see no real reason to have one without solar. There are a lot more efficient emergency power supplies. The savings in off-peak electricity would also be very hard to justify.

The one interesting capability that this potentially offers is the ability of the power grid to store energy offline and pull from the batteries if needed; thus avoiding the need for costly and polluting backup generation. It would require everyone to have one though... Eventually it might even make sense for the power company to provide subsidized units to each user to be used as a redundant piece of the smart energy grid.
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Old 10-31-2020, 11:08 AM   #33
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When I built my house, I designed it so the guest quarters are on one side with it's own AC system. There are two AC units each are rated at 2 tons each. Do you think 2 Powerwalls could handle a single 2 ton unit with the other phantom powers? My typical phantom power is around 300 watts and when I run my generator, that has a watt load meter on it, it reads right around 3000 watts, maybe a little more. If I kick on both AC units it reads a little over 5000watts load. Also, I set up the AC this way because all 'portable' generators are limited to 30amps due to their built in breakers and wire gauge. A 4 ton and higher unit uses more than 30amps so a full sized home generator, along with it's cost, would be needed. I got away with a 7kw Honda inverter generator I bought used for $1,500, converted it to propane and plumbed the house's 500 gallon propane tank to it's location.
BTW, I'm getting the 2 Tesla power walls via 'Grid Resiliency' program funded by the California PUC and based on Medical Base Line utility rate and located in an area where power shut offs due to high fire danger are common. Cost is $26,400 installed. I have to fund to get the install, but am rebated the full amount after permission to operate is granted by the utility company, usually about 3 months to obtain.

I think two Powerwall together can start up a 2-ton AC, although I suspect that Tesla will discourage you from doing this. The run time is another matter though. If you do not want a minisplit just for the bedroom, perhaps a window AC or a free-standing one can get you comfortable with a longer run time.

Please keep us posted on the installation. It's a heck of a deal to get two free Powerwalls.
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Old 10-31-2020, 11:16 AM   #34
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... The savings in off-peak electricity would also be very hard to justify.
I thought when they first announced the powerwall, the whole purpose was to charge them up using off-peak power and to use them during peak power.

How much difference is there between those two extremes?
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Old 10-31-2020, 04:03 PM   #35
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Every home in my township has at least one generator.

It is common to see two generators. One large unit and one small unit.

The small generators can power lighting and PCs. The small unit sips a gallon of fuel every 8 hours.

The big generators allow you to flush toilets, run laundry, and refrigerators & freezers, and to take showers. Those big units guzzle a gallon of fuel an hour.

Those homes run the big unit for one-hour each day, as they do laundry, take showers flush toilets, and bring the temps of freezers back down to appropriate temps.

In this manner, you consume the least amount of fuel. One hour each day running a big generator and 23 hours of running a small generator, means that you only consume 11 gallons each day tops. If you shut down the small one when you sleep, you can consume even less.

Nobody here has A/C, and most homes here burn firewood for heating.

One of our neighbors is a gunsmith. His insurance company insisted that he install a big generac to power his machine shop and security system. He regularly goes through $150 in fuel each month.

I have lived here for 15 years so far. During the past 15 years, our power company has never been capable of providing power for one-month continuously. Every month our power will go out at least once.

Just how it works here in rural areas of the East Coast.
Whoa! I thought we had it bad. Our outages are usually (fortunately) relatively brief. They range from a flicker - whereupon, we start resetting all the clocks to 2 or 3 minutes. SWAG is one power fail/month of the flicker variety. The 2 minute variety once or twice a year, but there is the occasionally 30 minute one. We did have the 18 hour one, but only once in 13 years.

Most power fails are due to wind. Just strong trades are enough to kill our power for a few minutes.

The good news is our condo has a large diesel generator that runs the elevators and walk-way lights as well as security cameras. Of course, we in our egg crate apartments are without power. I keep several battery powered lights around for the inevitable. Just don't think I could live where I had to depend (very often) on my own generator. Of course, YMMV.
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Old 10-31-2020, 05:34 PM   #36
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Whoa! I thought we had it bad. Our outages are usually (fortunately) relatively brief. They range from a flicker - whereupon, we start resetting all the clocks to 2 or 3 minutes. SWAG is one power fail/month of the flicker variety. The 2 minute variety once or twice a year, but there is the occasionally 30 minute one. We did have the 18 hour one, but only once in 13 years.

Most power fails are due to wind. Just strong trades are enough to kill our power for a few minutes.

The good news is our condo has a large diesel generator that runs the elevators and walk-way lights as well as security cameras. Of course, we in our egg crate apartments are without power. I keep several battery powered lights around for the inevitable. Just don't think I could live where I had to depend (very often) on my own generator. Of course, YMMV.
Maine is over 92% forest. Whenever there is a wind storm somewhere trees blow down. When trees blow down on power lines, from that spot going down line the next 20 townships will all lose power.

Maybe once a year our town loses power for a week.

Most power outages here are between 6 hours and 3 days.
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Old 10-31-2020, 06:59 PM   #37
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I think two Powerwall together can start up a 2-ton AC, although I suspect that Tesla will discourage you from doing this. The run time is another matter though. If you do not want a minisplit just for the bedroom, perhaps a window AC or a free-standing one can get you comfortable with a longer run time.

Please keep us posted on the installation. It's a heck of a deal to get two free Powerwalls.
I think with my solar still at work, charging the batteries with about 7kw of solar, I'd be good to go at least running the AC during peak solar generation.

The reason they are funding the batteries is because the CPUC is trying to eliminate peaking power generation as well as harden the grid. By focusing on micro generation, they figure they can draw down my batteries when I'm not expecting an outage for their own peaking needs. That's the deal; I have to agree on an equivalant draw down of 80% capacity 52 times a year or, once a week drain. The electric company uses this to keep from firing up peaking generators which are usually very environmentally unfriendly.
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Old 10-31-2020, 07:28 PM   #38
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I thought when they first announced the powerwall, the whole purpose was to charge them up using off-peak power and to use them during peak power.

How much difference is there between those two extremes?

As I mentioned in the earlier post at #19:

My Time-of-Day (TOD) rate in Phoenix: 24.09c/kWh during the peak summer hours of 2-8PM, and 7.3c/kWh outside that peak period.

Southern Cal Edison TOD rate: 43c/kWh for 4-9PM and 16c/kWh for off peak, for people with battery storage.
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Old 10-31-2020, 07:34 PM   #39
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I think with my solar still at work, charging the batteries with about 7kw of solar, I'd be good to go at least running the AC during peak solar generation.

The reason they are funding the batteries is because the CPUC is trying to eliminate peaking power generation as well as harden the grid. By focusing on micro generation, they figure they can draw down my batteries when I'm not expecting an outage for their own peaking needs. That's the deal; I have to agree on an equivalant draw down of 80% capacity 52 times a year or, once a week drain. The electric company uses this to keep from firing up peaking generators which are usually very environmentally unfriendly.

If you have 7 kW of solar, that's plenty good to run the 2-ton AC right there.

I did not know about the arrangement the utility has with you about tapping into your batteries. That's interesting. They have to work with Tesla in order to gain control of the Powerwalls in order to program the Powerwall operation. That's neat.

Of course when the grid goes down due to PSPS, you are disconnected from the grid because of the power cut-off, will be on your own and do not have to share the Powerwalls and your solar generation with anybody. It should work out great.
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Old 10-31-2020, 10:14 PM   #40
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As I mentioned in the earlier post at #19:

My Time-of-Day (TOD) rate in Phoenix: 24.09c/kWh during the peak summer hours of 2-8PM, and 7.3c/kWh outside that peak period.

Southern Cal Edison TOD rate: 43c/kWh for 4-9PM and 16c/kWh for off peak, for people with battery storage.
If your TOD system is more-or-less the way it's going to be, I'm wondering why someone hasn't come out with a cooling system that uses ice which is frozen when it's cheap and melted in a blower system when rates are high. Early car "air conditioning" used ice in the trunk with blowers to circulate air over the ice and into the cabin.

I'm not an engineer, but I think the only real trick would be sizing - but YMMV.
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