Tesla Powerwall: Engineering Analysis

[OmCheeto]

Did you post the Watts somewhere? Maybe I missed that info.

I just wanted to point out that the Powerwall is rated for 6 Amps. I was wondering if you refrigerator + dishwasher / dryer combined load would be able to stay within those Amps. I didn't think it would work.

I don't know how much you eat, or roll in the mud, but I only have only one appliance that runs 24/7 in the summer.
The others can wait for Sunday.

 

[rollingstein]

I don't know how much you eat, or roll in the mud, but I only have only one appliance that runs 24/7 in the summer.
The others can wait for Sunday.

At least on Sunday you need something rated for the combined Amps?

 

[OmCheeto]

At least on Sunday you need something rated for the combined Amps?

I don't understand what you are asking/saying.

Or perhaps you don't understand my pictograph?

Summer rates start on May 1 ____ Winter rates start on Nov 1

What it means is that I can get off-peak rates all day Sunday. So I can run everything in the house, which is about 20,000 watts.

One funny thing is, that the way I cook, is already optimal for "Time of Use" metering. Ha!
I cook about 5 lbs of meat overnight at fairly low temperatures, and then take it out in the morning.
Then I store this in the fridge for the week, and heat it up in the microwave.

5 minutes of microwave cooking/day @ 500 watts = 42 watt hours
16 hours of refrigeration/day @ 500 watts = 8,000 watt hours
total = 8,042 watt hours

I'm thinking I will only need one of these things.
But I'm still working on the maths on how to heat my house in the winter.
It's been 25 years since I've done some of these calculations.

This is the problem I'm working on:

Outside temperature is 43°F
Specific heat capacity of my house is 5000 Btu/°F
R-value is 13
Conductive surface area is 1900 ft²
If the house is heated to 75°F at 6 am, what will be the temperature in the house, 16 hours later?
And if it's less than 60°F after 16 hours, how much water, heated to 150°F would be required to maintain the minimum temperature at 60*F?​

I should have the solution by noon tomorrow.
But right now, my brain hurts, and I feel like watching some Hulu TV before bed.
Ciao!

 

[nitsuj]

They listed specs near the bottom of the page. I'll list the clues as to why I believe a 10 year lifespan is doable:

Specs
Technology
Wall mounted, rechargeable lithium ion battery with liquid thermal control.Models
10 kWhPower
2.0 kW continuous

How many Amps does your refrigerator pull? How many Amps will your Laundry / Dishwasher pull?

apparently 2,000 watts (household = 120 * 15 = 1800)

10,000 / 2,000 = 5 hours at 2000 watts

I'm more confused now...

 

[CWatters]

If you need more than 2KW...

The extra can be drawn from the grid.
or
If you are off grid multiple Powerwalls can be connected together.

 

[nitsuj]

If you need more than 2KW...

The extra can be drawn from the grid.
or
If you are off grid multiple Powerwalls can be connected together.

If it's seamless ( powerwall <-> grid) that's perfect, if not I think that's more math than most want to do in determining what to power with it to ensure all energy is used before night charging. I think this is a step towards higher production volume of batteries as opposed to a step towards convenience / energy cost savings / meeting market demands.

 

[OmCheeto]

If it's seamless ( powerwall <-> grid) that's perfect, if not I think that's more math than most want to do in determining what to power with it to ensure all energy is used before night charging. I think this is a step towards higher production volume of batteries as opposed to a step towards convenience / energy cost savings / meeting market demands.

I think you are correct, in that this is "more math than most want to do".
It's taken me an hour just to convert from imperial to SI units.
It may be 2 pm, before I have my answer.

...the problem I'm still working on:

Outside temperature is 43°F ( 6.11 °C )
Specific heat capacity of my house is 5000 Btu/°F ( 2.6 kwh / °C )
R-value is 13 ( (2.3 m² °C) / watt )
Conductive surface area is 1900 ft² ( 176 m² )
If the house is heated to 75°F ( 23.9°C ) at 6 am, what will be the temperature in the house, 16 hours later?
And if it's less than 60°F ( 15.6 °C ) after 16 hours, how much water, heated to 150°F ( 65.6°C )would be required to maintain the minimum temperature at 60*F?​

Thank god those silly Europeans haven't yet devised their own SI time unit...

 

[nitsuj]

apparently 2,000 watts (household = 120 * 15 = 1800)

10,000 / 2,000 = 5 hours at 2000 watts

I'm more confused now...

Ah I see now, it's 350-400 volts...presuming for efficiency & reliability reasons (not bad if a few cells are poor).

This unit is getting a bit more impressive...wish there was more info on the batts though.

 

[James Alton]

Ah I see now, it's 350-400 volts...presuming for efficiency & reliability reasons (not bad if a few cells are poor).

This unit is getting a bit more impressive...wish there was more info on the batts though.

7KW of energy storage could be very interesting to people that live in Northern Climates. That is enough power to run an oil furnace or perhaps a wood pellet stove for an extended period of time in case a power loss and make the difference between freezing and not! In the event of an extreme winter with an extended power loss could even save some lives. Generators are another option but the beauty of a charged battery is that you don't have to get it started for it to start producing power and gasoline units especially can be pretty unreliable. I could imagine powering my home for about 3 days using one of these batteries after removing loads that were not critical. Personally if I had to choose between relying on a generator or a charged lithium battery for backup, I would take the battery. And no, a bank of wet cell lead acids of the same capacity would not be a suitable replacement. Besides the corrosive/explosive gases, those batteries self discharge at an unacceptable rate IMO. I think that there will be a market for Elon's batteries, I might even help a little! James

 

[OmCheeto]

Ah I see now, it's 350-400 volts...presuming for efficiency & reliability reasons (not bad if a few cells are poor).

This unit is getting a bit more impressive...wish there was more info on the batts though.

I was assuming Tesla was going to use the same technology as their vehicles. I don't know about the battery, but the cells used are currently made by Panasonic. And they have 19 different versions!

http://na.industrial.panasonic.com/search/18650


ps. interrupting me will only delay the solution to my problem.
pps. and then there's lunch... I'm shooting for 4 pm at the moment.

 

[nitsuj]

7KW of energy storage could be very interesting to people that live in Northern Climates. That is enough power to run an oil furnace or perhaps a wood pellet stove for an extended period of time in case a power loss and make the difference between freezing and not! In the event of an extreme winter with an extended power loss could even save some lives. Generators are another option but the beauty of a charged battery is that you don't have to get it started for it to start producing power and gasoline units especially can be pretty unreliable. I could imagine powering my home for about 3 days using one of these batteries after removing loads that were not critical. Personally if I had to choose between relying on a generator or a charged lithium battery for backup, I would take the battery. And no, a bank of wet cell lead acids of the same capacity would not be a suitable replacement. Besides the corrosive/explosive gases, those batteries self discharge at an unacceptable rate IMO. I think that there will be a market for Elon's batteries, I might even help a little! James

Yea...it's good for down to -20c, I presume damage after that.

I am unsure of Li-ion, but know for certain that li-poly cannot be "stored" charged for any significant period of time (days). Hopefully Li-Ion doesn't have the same constraint.

Calling this unit a possible life-saver is a bit of a stretch no?

 

[James Alton]

Yea...it's good for down to -20c, I presume damage after that.

I am unsure of Li-ion, but know for certain that li-poly cannot be "stored" charged for any significant period of time (days). Hopefully Li-Ion doesn't have the same constraint.

Calling this unit a possible life-saver is a bit of a stretch no?

Li-Poly can be stored charged long term but the batteries I am familiar with will suffer some loss of capacity. With Li-Poly, the rule of thumb I have seen is to store at about 50% of charge to maximize the life expectancy. Interestingly, Li-poly is damaged by freezing temperatures mores when the battery is fully charged, at 50% charge the safe temperature is a lot lower. I am just guessing but am pretty sure that the Tesla battery is not Li-poly due to the cells being less stable. Li-Ion that I am familiar with is of a lower power density but likes being kept fully charged. I think that the self-discharge of Li-Ion is higher unfortunately but much less than wet cell lead acid.

Definitely not a stretch to say that having power available to keep your heating system going in event of a power loss could be a life saving system IMO. Not only do you tend to lose power in an extreme storm, you can also lose access to transportation. Combine this will someone that is elderly, and yes, backup power could be pretty important I think. James

 

[nitsuj]

Li-Poly can be stored charged long term but the batteries I am familiar with will suffer some loss of capacity. With Li-Poly, the rule of thumb I have seen is to store at about 50% of charge to maximize the life expectancy. Interestingly, Li-poly is damaged by freezing temperatures mores when the battery is fully charged, at 50% charge the safe temperature is a lot lower. I am just guessing but am pretty sure that the Tesla battery is not Li-poly due to the cells being less stable. Li-Ion that I am familiar with is of a lower power density but likes being kept fully charged. I think that the self-discharge of Li-Ion is higher unfortunately but much less than wet cell lead acid.

Definitely not a stretch to say that having power available to keep your heating system going in event of a power loss could be a life saving system IMO. Not only do you tend to lose power in an extreme storm, you can also lose access to transportation. Combine this will someone that is elderly, and yes, backup power could be pretty important I think. James

I'm trying to find data on storage voltage being nominal cell voltage and that degradation is inevitable when "stored" at those "max" cell voltages. I am of course presuming the pack charges the cell to near full.

Battery university (website) indicates the chemistry maybe nickle/cobalt!

Lithium Nickel Cobalt Aluminum Oxide2 (NCA) LiNiCoAlO2
(9% Co) N/A Electric powertrain (Tesla Model S), grid storageI agree having heat when it's cold could be a life saver, whatever the means.

I've only found this (assertion) which I experienced with my use of Li-Poly batt. Though I had not ever noticed the batteries at an "elevated" temperature.

Formation of the electrolyte oxidation at the cathode that may lead to a sudden capacity loss. Keeping the cells at a high voltage and at an elevated temperature promotes this phenomenon.

 

[James Alton]

I'm trying to find data on storage voltage being nominal cell voltage and that degradation is inevitable when "stored" at those "max" cell voltages. I am of course presuming the pack charges the cell to near full.

Battery university (website) indicates the chemistry maybe nickle/cobalt!

Lithium Nickel Cobalt Aluminum Oxide2 (NCA) LiNiCoAlO2
(9% Co) N/A Electric powertrain (Tesla Model S), grid storageI agree having heat when it's cold could be a life saver, whatever the means.

I've only found this (assertion) which I experienced with my use of Li-Poly batt. Though I had not ever noticed the batteries at an "elevated" temperature.

Formation of the electrolyte oxidation at the cathode that may lead to a sudden capacity loss. Keeping the cells at a high voltage and at an elevated temperature promotes this phenomenon.

I don't know why Li-Polys suffer from being left fully charged but that position has been consistent over the years. I have probably used more than 500 Li- Poly batteries of various sizes, some with greater than 400 cycles and so far have never had one experience a sudden loss of capacity. The capacity loss seems to generally be age related and how many cycles the battery has on it. None of my experience may be applicable to the Tesla cells but I will say that I am a Lithium convert pretty much across the board. I can charge the Lithium batteries for instance for a tool and fully expect almost a full charge a year later when I use it. Or the fantastic lithium primary AA and AAA batteries with a 20 year shelf life and a much better power density than the alkalines…they also won't kill your electronic devices from leakage I am told..so far so good! They are also apparently environmentally friendly compared to most other chemistries I am told. James

 

[nitsuj]

I don't know why Li-Polys suffer from being left fully charged but that position has been consistent over the years. I have probably used more than 500 Li- Poly batteries of various sizes, some with greater than 400 cycles and so far have never had one experience a sudden loss of capacity. The capacity loss seems to generally be age related and how many cycles the battery has on it. None of my experience may be applicable to the Tesla cells but I will say that I am a Lithium convert pretty much across the board. I can charge the Lithium batteries for instance for a tool and fully expect almost a full charge a year later when I use it. Or the fantastic lithium primary AA and AAA batteries with a 20 year shelf life and a much better power density than the alkalines…they also won't kill your electronic devices from leakage I am told..so far so good! They are also apparently environmentally friendly compared to most other chemistries I am told. James

Hmm... I wonder why your experience with them is different. Mine is mostly with 5AH 11.1v (3 cell) simple "shrink wrap" type lipo. rated for 35-70c.

Worst treatment seemed to be from dropping the voltage to low during use. This continued into the most noticeable degradation of the batteries..."voltage sag". Powering "Off-road" type vehicles (bout 3.5kg) would draw over 1,000 watts, I think it's max is 12.6v * 35c * 5ah = 2,200w so less than 50% of an overstated "nominal" c value. That and would endure some heat (40c) and g-shock (crashes).

I've got one left of three, It has about 250 cycles I'd guess, and further guess its about 50-60% original capacity 'n holding voltage. That said it still charges to 4.18ish volts on all three cells which is surprising to me, the others had failures mostly attributable to dropping voltage too low during use (voltage sag) and in turn not "balancing" properly and having to "junk" it (I had luck removing the "bad" cell from one of the packs...the 2 cell pack was poor performing but lasted a while longer). With that dropping voltage low seems to heat the batteries more which I think indicates resistance increasing / cell damage??

The competitive advantage of a Powerwall maybe it's liquid cooling.

Oh and for the record I too have never had a "sudden lose of capacity". We'll outside of trying to "revive" a small 3 cell I had discharged to nill by accident. It's voltage never came back high enough for the charger to attempt a charge.

Oh and Power tools are generally iron type, it's safest (ask Apple about li-poly) and more important for our different experience is it's more reliable, though less capable of high amperage. I don't think Li-poly's are shipped air freight by most postal. I think currier's still do.

 

[James Alton]

Hmm... I wonder why your experience with them is different. Mine is mostly with 5AH 11.1v simple "shrink wrap" type lipo. rated for 35-70c.

Worst treatment seemed to be from dropping the voltage to low during use. This continued into the most noticeable degradation of the batteries..."voltage sag". Powering "Off-road" type vehicles (bout 3.5kg) would draw over 1,000 watts, I think it's max is 12.6v * 35c * 5ah = 2,200w so less than 50% of an overstated "nominal" c value. That and would endure some heat (40c) and g-shock (crashes).

I've got one left of three, It has about 250 cycles I'd guess, and further guess its about 50-60% original capacity 'n holding voltage. That said it still charges to 4.18ish volts on all three cells which is surprising to me, the others had failures mostly attributable to dropping voltage too low during use (voltage sag). With that dropping voltage low seems to heat the batteries more which I think indicates resistance increasing??

The competitive advantage of a Powerwall maybe it's liquid cooling.

Hello, My larger batteries are 8AH 6S being used in series giving 12S (around 50 volts) . I am not sure of the exact power since my tester pegs at 150 amps. I am very careful to avoid getting the cell voltage too low, normally finishing with at least 3.7volts per cell. I have some 5 year old Li-polys that are nearly as good as my new batteries in capacity that balance almost perfectly. I have had one pack get hot and puff up but 0 failures power failures to date. I think that you are right that dropping the cell voltage too low is probably the most damaging thing that you can do to these batteries. Even shorting them is apparently less of a problem since whatever contacts you had vaporize and the battery is still fine..don't ask me how I found that one out! (grin) I don't use multi cell batteries when any of the cells show voltages that are much lower. If I get a new battery and one cell won't balance properly I won't use it as is and sometimes remove the bad cell. I have found that generally the lower voltage in an unbalanced battery is due to a cell outgassing due to some rupture in the packaging so any attempt to rebalance does not help. If you open the outer packaging you can normally see a whitish powder where the leak is. Discharging to a low voltage also creates a lot of heating and if one cell is bad especially in the middle of the pack it's not good, especially if the pack is loaded heavily. My batteries normally finish even in the summer just slightly warm. James

Hmm... I wonder why your experience with them is different. Mine is mostly with 5AH 11.1v (3 cell) simple "shrink wrap" type lipo. rated for 35-70c.
In order to revive an overly discharged Li-poly, you have to use an alternate charging source ( I keep an old Triton for this purpose) to gently lift the voltage enough to reach the minimum cell voltage that the Lipo charger will begin charging at. I would always use the Lipo charger to do almost all of the recovery charging, it usually takes only a couple minutes on the Triton to get back up to minimum voltage. Needless to say, all overly discharged batteries should not be recharged and you need to be present to keep an eye on things. I have recovered the same TX battery that was run flat about 3X and while I am sure the capacity is down it still balances fine, no puffiness at all and it has been used for several additional years.

The early Lipos were pretty volatile but things seem to have changed a lot. Li-polys are now being used inside the cockpit of some manned aircraft. Would make me a little nervous but I have not yet heard of any disasters. I guess anything that has a high energy density can be somewhat risky...

Yes, I knew that the tool batteries were of the iron phosphate (A123 if I am not mistaken) type chemistry. Still good batteries. I really like the stable voltage they hold during discharge. I am wondering how the Lithium primaries such as the energizer provide 1.5v when Lithium cell voltages are higher. Are they actually putting a voltage regulator into the battery itself?

I hope that the Tesla Powerall concept does well. I glad to see the discussion and hope to learn more about them.

James

Worst treatment seemed to be from dropping the voltage to low during use. This continued into the most noticeable degradation of the batteries..."voltage sag". Powering "Off-road" type vehicles (bout 3.5kg) would draw over 1,000 watts, I think it's max is 12.6v * 35c * 5ah = 2,200w so less than 50% of an overstated "nominal" c value. That and would endure some heat (40c) and g-shock (crashes).

I've got one left of three, It has about 250 cycles I'd guess, and further guess its about 50-60% original capacity 'n holding voltage. That said it still charges to 4.18ish volts on all three cells which is surprising to me, the others had failures mostly attributable to dropping voltage too low during use (voltage sag) and in turn not "balancing" properly and having to "junk" it (I had luck removing the "bad" cell from one of the packs...the 2 cell pack was poor performing but lasted a while longer). With that dropping voltage low seems to heat the batteries more which I think indicates resistance increasing / cell damage??

The competitive advantage of a Powerwall maybe it's liquid cooling.

Oh and for the record I too have never had a "sudden lose of capacity". We'll outside of trying to "revive" a small 3 cell I had discharged to nill by accident. It's voltage never came back high enough for the charger to attempt a charge.

Oh and Power tools are generally iron type, it's safest (ask Apple about li-poly) and more important for our different experience is it's more reliable, though less capable of high amperage. I don't think Li-poly's are shipped air freight by most postal. I think currier's still do.

 

[nitsuj]

Hello, My larger batteries are 8AH 6S being used in series giving 12S (around 50 volts) . I am not sure of the exact power since my tester pegs at 150 amps. I am very careful to avoid getting the cell voltage too low, normally finishing with at least 3.7volts per cell. I have some 5 year old Li-polys that are nearly as good as my new batteries in capacity that balance almost perfectly. Discharging to a low voltage also creates a lot of heating and if one cell is bad especially in the middle of the pack it's not good, especially if the pack is loaded heavily. My batteries normally finish even in the summer just slightly warm. James

Oh wow those are some big cells! 50v 8ah in li-poly could produced mad power!

I've used the same cut off of 3.7-3.8v (rest) which apparently is rather kind to the batts. But during use have likely dipped bellow 3v at times. Sounds like you treat yours well, what are they powering?

I agree lipos were bad at first, and perhaps a bit had to do with the vastly different charging requirements to nicad and even nimh or whatever. i.e. most failures where likely over charging.

 

[James Alton]

Oh wow those are some big cells! 50v 8ah in li-poly could produced mad power!

I've used the same cut of of 3.7v (rest) which apparently is rather kind to the batts. But during use have likely dipped bellow 3v at times. Sounds like you treat yours well, what are they powering?

I hope that it is ok here to post a link? I did static tests at high power settings for pretty extended periods and my voltage held quite well on the cells I tested. It would probably be good to do some inflight monitoring to catch any packs with a weak cell early in the game.

Does anyone know if the Tesla powerall has any venting for cooling?

James

 

[nitsuj]

Does anyone know if the Tesla powerall has any venting for cooling?

James

Says "liquid thermal management" or something like that.

I cracked out laughing when you blipped the "throttle" at take off...WOW! Surprised the rest of the plane followed the motor lol Great Video

Have you measured the thrust of your set up? Yea if I had a rig like that you could bet there would be telemetry on pretty much everything.

 

[OmCheeto]

...
Outside temperature is 43°F ( 6.11 °C )
Specific heat capacity of my house is 5000 Btu/°F ( 2.6 kwh / °C )
R-value is 13 ( (2.3 m² °C) / watt )
Conductive surface area is 1900 ft² ( 176 m² )
If the house is heated to 75°F ( 23.9°C ) at 6 am, what will be the temperature in the house, 16 hours later?

And the answer is: 62.8 °F ( 17.1°C )
So one Powerwall unit will work for me.
Though, I'm retired, and don't get out much in the winter.
2 years ago, I would have laughed at heating my house to such a ridiculous temperature while I was at work all day.

I think I'll work on the heat capacity of an auxiliary water heater next.
I found one for $1,107.59 with a 105 gallon capacity. It has a 150°F maximum temperature.
Since it won't be hooked to the water mains, the associated plumbing shouldn't be too complicated, nor spendy.

I generally keep my house around 65°F in the winter.

And if it's less than 60°F ( 15.6 °C ) after 16 hours, how much water, heated to 150°F ( 65.6°C )would be required to maintain the minimum temperature at 60*F?

This shouldn't take too long to figure out.

105 gal * 8.34 lb / gal = 876 lb
1 btu = 1°F lb
ΔT water tank = 150°F - 65°F = 85°F
x btu = 876 lb * 85°F = 74,400 btu / 3400 btu/kwh = 21.8 kwh
ΔT interior exterior = 65°F - 43°F = 22°F
power loss at 22°F = 940 watts
21.8 kwh / .94 kw = 23.2 hours
required hours (off-peak): 16
7.8 hour surplus

hmmm...
That sounds ridiculously wrong.
Though, a 22°F ΔT isn't that much.

Reality check:
Ave temp for Dec 2014: 43°F
days measured: 34
actual kwh heating used: 1170 kwh
theoretical calculated: 770 kwh ( 0.94 kw * 24 hr/day * 34 days )

Not quite off by a factor of two. I'm guessing my R-value must be too high.

Anyways, this Powerwall thing should work for me.

Perhaps tomorrow I'll figure out the ROI on this new system.

 

[nitsuj]

I'm looking for HVAC related math for you to include in the analysis required for answering "Is a Powerwall right for me?"

 

[WhatIsGravity]

Apologies for intruding on the discussion, and I haven't read this entire thread, but the basic idea of this product, with our energy sources and efficiencies, makes me think of the quote, 'you're either crazy, or an economist.' With a really good marketing department... and hoping for investors.

 

[OmCheeto]

I'm looking for HVAC related math for you to include in the analysis required for answering "Is a Powerwall right for me?"

There's not much to it for most people.
Mine is more complicated, as I heat primarily with baseboard electric.
I have a woodstove for emergencies, and hyper-cold snaps.

Step 1:
Determine if your utility offers "Time of Use" metering.
If they don't, then there's no use in even calculating it.

If they do
Step 2:
Simply determine your mandatory hourly electrical loads for each hour of the day.
If the mandatory hourly electrical loads are less than 10 kwh, then the system will probably pay for itself, in a period determined by your electrical rates.

I probably didn't have to do all of my thermodynamicky stuff, as my energy use can be interpolated pretty easily from my monthly utility bill.

For fun over the last few months, I've been transcribing my old electrical bills.
Between 1989 and 1995 you can see my winter energy use dropping every year.
This is because I discovered my first winter, that the house had virtually no insulation.
So each year, for 5 years, I removed the sheetrock from a single room, rewired, and insulated the exterior walls.
I also added insulation in the attic and crawlspace.
The jump in 1997 and 1998 were due to me taking in a roommate.
Some people like the house warm, when they're not the one paying the bill.
I kicked him out.

 

[nitsuj]

Apologies for intruding on the discussion, and I haven't read this entire thread, but the basic idea of this product, with our energy sources and efficiencies, makes me think of the quote, 'you're either crazy, or an economist.' With a really good marketing department... and hoping for investors.

I think a product that can "pay for it self" has the potential to save money and in turn is a "smart buy", more so if it can be financed and still be a positive ROI...that said I do agree with you. In that this isn't some great leap in tech.

Side note, we know the cost and used that as basis for payback, but the unit also requires installation & I believe most municipalities would have it so only licensed electrician can do electrical work. So there is that additional cost of Professional installation.

I watched the product presentation and it's context is "environmental concerns"...my concern is with the battery manufacturing...in particular if the "dirty work" is done in China due to low cost, in part due to little to no regulations with respect to the environment. I see this product as a net "drain" on resources holistically. That said it maybe a required step to get that battery production up to a point that cost is low enough that Tesla can compete with "median" priced cars.

 

[OmCheeto]

I think a product that can "pay for it self" has the potential to save money and in turn is a "smart buy", more so if it can be financed and still be a positive ROI...that said I do agree with you. In that this isn't some great leap in tech.

Not everything has to be a "leap". This is merely a transition from one energy source to another: Carbon to Sun

$3500: Powerwall unit
$_600: 6000 watt power inverter
$_500: installation
$1600: Water heating installation
---------------
$6200: Total​

My usage:
1000 kwh/month average = $126/month on-peak & $42/month off-peak = $84/month savings
$84/mo * 12mo/yr = $1000

So I estimate my ROI at about 6 years. Still not great, but better than nothing.
But it also means I get a $1000 savings per year for the last 4 years. Which, to me, corresponds to a $400 savings per year, over 10 years.
By the time the first unit is worn out, in the guaranteed first 10 years, I'll have to replace it.
But then you can subtract the costs of the inverter, installation, and water heating device.
So the ROI on the second unit drops back to the original 3.5 years, which corresponds, to my situation, to an extra $650 per year.
And then I will be dead, of old age. or

But the kids who buy my house can look forward to cheaper energy, because I decided to do it.
Kind of like my dad, buying all those solar electric panels back in the 90's, dropping dead, and leaving me with 4 of them.
You can learn a lot, by having a solar panel.

Side note, we know the cost and used that as basis for payback, but the unit also requires installation & I believe most municipalities would have it so only licensed electrician can do electrical work. So there is that additional cost of Professional installation.

When I rewired my house, back in the early 90's, homeowners were allowed to do their own wiring, provided that they lived in their amateurishly wired, dead traps. Fortunately for me, I was an electrician in the USN for 4 years, and didn't wire a death trap. (knocks on head)
If you can't afford the rates of a licensed electrician, you can always seek out someone like myself, to supervise everything.
I'm pretty sure, the installation rate will be much cheaper, if there are a pair of wires hanging out of the wall.

Silly safety side note: A friend of mine, about 30 years ago, asked me to install a 220 volt outlet, at his parents house, so he could make beer.
Upon inspection of the existing wiring, I started cursing, at the amateurish (ie: Om; "I'm surprised that your house didn't burn down years ago! Holy ****! ... ") job someone had done when wiring their electric range.
I discovered later, that my friend's father, who was standing there, when I blurted that out, was the one who had done the wiring.

I watched the product presentation and it's context is "environmental concerns"...my concern is with the battery manufacturing...in particular if the "dirty work" is done in China due to low cost, in part due to little to no regulations with respect to the environment. I see this product as a net "drain" on resources holistically. That said it maybe a required step to get that battery production up to a point that cost is low enough that Tesla can compete with "median" priced cars.

Um... Tesla is building their first battery factory in Nevada, and the second is planned for Japan. And lithium comes predominately from South America. Where are you coming up with China?

 

[nitsuj]

Um... Tesla is building their first battery factory in Nevada, and the second is planned for Japan. And lithium comes predominately from South America. Where are you coming up with China?

I did say "if they are made in China..." referring to the batteries themselves, not just the source of an input. The Tesla factory is still being built.

This link talks about China's growth in Lithium battery supply. I'd haven't found a source showing which country manufactures what % of total production. I'd venture a guess it's China. Though am unsure where Tesla batteries are made...again hopefully not China.

I am looking forward to see what impact the new plant has on lithium battery market. And props for having it the US!. Hmmm. I hope this means battery cells from scratch and not just "pack assembly".

That same site had this important piece of info I was missing "The mainstream Japanese energy storage systems cost approximately US$600 per kWh. Tesla’s batteries cost almost 60% lower than usual products, making them extremely price competitive in the battery market."

That is quite a price difference from competitors...I don't see how they'll actually beat China in that respect though, must be quite a factory their building in Nevada lol.

 

[OmCheeto]

...Though am unsure where Tesla batteries are made...

According to Elon Musk, in a video I'm currently watching, the Powerwall is being manufactured in their Fremont California plant, and the first packs are to be shipped in the next 3 to 4 months. These comments were made starting at 11:10.

I am looking forward to see what impact the new plant has on lithium battery market. And props for having it the US!. Hmmm. I hope this means battery cells from scratch and not just "pack assembly".

That same site had this important piece of info I was missing "The mainstream Japanese energy storage systems cost approximately US$600 per kWh. Tesla’s batteries cost almost 60% lower than usual products, making them extremely price competitive in the battery market."

That is quite a price difference from competitors...I don't see how they'll actually beat China in that respect though, must be quite a factory their building in Nevada lol.

Some interesting comments from the video starting at 16:15:

There will need to be many gigafactories in the future.
I do want to emphasize that this is not something that we think Tesla is going to do alone.
We think that there's going to be a need for many other companies building Gigafactory class operations of their own, and we hope they do.
And the Tesla policy of open sourcing patents will continue for the Gigafactory, and for the Powerpack, and for all these other things.

It sounds to me as though Elon thinks the market is big enough for more players than just Tesla.
So, just like you can choose between buying a Mercedes or Ford automobile, you'll be able to pick between a Bosch or Tesla battery.

All This Battery Hype Should Make Tesla Investors Nervous (Forbes)
5/12/2015
...
There’s competition for devices like the Powerwall, too. It didn’t get much attention, but a few weeks ago LG Chem also announced its entry into the home battery market, through a JV with Eguana Technologies. LG says it has sold 4,000 grid-tied battery systems into the European market over the past 18 months.

And several years ago German appliances giant Bosch started offering homeowners an integrated solar storage device combining lithium-ion batteries and a DC-AC inverter. It’s an attractive looking box the size of a refrigerator. As best as I can tell it costs upwards of $20,000 for a roughly 7 kwh system — before tax incentives.
...

 

[Highspeed]

The cars look good and perform well, the batteries are interesting, but are we really taking the numbers seriously from a company that has never made a dime in profit? Or did that change?

 

[nitsuj]

The cars look good and perform well, the batteries are interesting, but are we really taking the numbers seriously from a company that has never made a dime in profit? Or did that change?

I don't think it has, I am so confused and interested in this company. How can he give away patents? Those are assets; presumably valuable. I don't even know Musk's position in the company. I just don't get it. Is his particular talent "vision" or "dreaming"?

Ah he is CEO, but more inportantly when it comes to deciding open source patents (giving away assets)...he's the chairperson.

Anyways there goes hope of Tesla being an "OEM" supplier of patented parts to other companies for electric cars.

Heard Musk say "quarter million vehicles is about what is needed for economies of scale."

 

[nitsuj]

According to Elon Musk, in a video I'm currently watching, the Powerwall is being manufactured in their Fremont California plant, and the first packs are to be shipped in the next 3 to 4 months. These comments were made starting at 11:10.

Yea I saw that part, and looked up the Fremont plant. The Energy Trend website made a clear distinction in pack assembly (multiple cells) and cell manufacturing. Single cell is often a direct sale (electronic devices like phones) and often for multiple cells it is a different company that assembles the pack. So for me that raised the question about Fremont, if cells are made there, or are the packs just assembled there.

Some interesting comments from the video starting at 16:15:

It was interesting, so is Musk! "This is something Humanity is capable of doing." (2 billion "powerwall" type packs for renewable energy) That sounds like a pretty long term goal! lol

It sounds to me as though Elon thinks the market is big enough for more players than just Tesla.
So, just like you can choose between buying a Mercedes or Ford automobile, you'll be able to pick between a Bosch or Tesla battery.

That makes sense to me!

 

[OmCheeto]

Sometimes, I get this paranoid feeling, that smart people, steal ideas from our forum:

Electric power is almost worthless unless you can turn it on and off at will.

This is true. I once traded one of my 50 watt solar panels for a friend's surplus air conditioner. Although I've been using the air conditioner for 3 years, I've yet to deliver the solar panel. I told them it would be useless unless they purchased a deep cycle battery, as the panel would just be a silly wall ornament without one.

...

...
To be more precise, the sun does not shine on photovoltaic cells at night (local night for the photovoltaics). At least not in any relevant amount. And clouds give a similar problem.

Hence the deep cycle battery sitting in my living room.

ps. It's really only there to keep the crack heads from stealing it out of my boat. I cycle it lightly through the winter month by powering my xmas lights.

Yup. I've had a mini-me, DIY Powerwall, in my living room, for I don't know how many years. Maybe 10.
It's only a 1 kwh unit, and I can't remember the last time I actually needed it.
The electrical grid never went down for more than a few seconds at my house this last winter, even though we had some very nasty wind storms.

And the power to keep the battery alive comes from the grid, and not my solar panels, as, well, you know, the neighbors tall trees...

 

[OmCheeto]

There's not much to it for most people.
Mine is more complicated, as I heat primarily with baseboard electric.
...

On the other hand, for other people, it's just as complicated, only in a different way.
My current situation, retired, does not require me to know the specific heat capacity of my house.
Though two years ago, and for working class people, it does.

Unfortunately, all of the thermodynamic testing I did was 25 years ago, on an ancient PC, which is now dead.
hmmm...
I think I'll redo all the tests today.
My notes suck.

Anyways, while you are waiting:

I'm looking for HVAC related math for you to include in the analysis required for answering "Is a Powerwall right for me?"

maths
R = ΔT / Q dot_________________(thermal resistance)
U = 1/R =(Q dot)/ΔT____________(thermal conductivity)
Q dot = U ΔT___________________(heat loss)
C_house = Q delta T______________(house heat capacity)

It's best to do these thermodynamics experiments in the winter, and to check the weather report before you do them.
The maths is more accurate when you have a higher delta T.
Unfortunately for me, although the outside temperature is 52°F, it's supposed to reach 70° by 2 pm. (currently 10:46 am here)
This may be a "bust" experiment, and I'm already into it for 50 cents worth of electricity!

Argh!

 

[nitsuj]

... I'm already into it for 50 cents worth of electricity!

Argh!

Worse yet, that 0.50$ of electricity is or will be heat, that escapes and may contribute to evaporation, and rain down somewhere over Ontario/Quebec Canada,.And eventually the gravitational potential of that evaporated water will be converted back to electricity hydro-electrically...and do you think you're gunna get your share of that pie? No way hosay.

 

[OmCheeto]

Worse yet, that 0.50$ of electricity is or will be heat, that escapes and may contribute to evaporation, and rain down somewhere over Ontario/Quebec Canada,.And eventually the gravitational potential of that evaporated water will be converted back to electricity hydro-electrically...and do you think you're gunna get your share of that pie? No way hosay.

I knew I should have terminated the experiment after I checked the weather report.
The sun burst through the clouds only an hour after I started... Stupid Sun!

Though I was able to get a new, very approximate, heat capacity number: 7000 btu/°F (minus the cumulative heat loss. see below)
I suspected I'd collected too much junk in my house over the last 26 years...
I dumped about 52,000 btus into my house from T=0 to T=3 hours, raising the temperature from 61.4° to a maximum of 71.8°F, which stabilized at 68.7°F @ T=5.5 hours.
Hence, my new heat capacity.

Inside and outside temperatures ended up being the same at T=7 hours, @ 68.7°F
Attic and crawl space temperatures were both around 57.5°F at the beginning of the experiment. I didn't bother checking them after that.

edited for new experiment:

Outside temperature is 50.7°F ( 10.4 °C )
Specific heat capacity of my house is 5000 Btu/°F ( 2.6 kwh / °C )
R-value is 13 [edit: °F ft^2 hr / BTU] ( (2.3 m^2 °C) / watt )
Conductive surface area is 1900 ft^2 ( 176 m^2 ) [edit: I left out the floor area for some reason. It should be 2760 ft^2 (256 m^2). Probably because, thermodynamically, the crawl space is weird.]
...

Total thermal loss from T=0 to T=7 hours (equilibrium) = 2.4 kwh = 8200 btu

Reinserting that into my first equation:

43,000 btu
61.4 Tc
68.7 Th
7.3 delta T
yields: 5890 btu/°F (heat capacity of one OmCheeto house)

Good grief! I'm less than 10% off, after 25 years! Yay!

ps. This experiment cost me around $1.40, and took about a day. I had nothing better to do. Well, ok, I did have something better to do, but I was able to do it whilst experimenting.
pps. As to what this has to do with the Tesla Powerwall? hmmm... I would explain, but it's time for my nap.

edit: I forgot my obligatory nerdly graph...

Data was collected every 30 minutes, from 9:40 am to 7:40 pm.
Raw data available upon request.

 

[insightful]

Just to be a nag, ROI is percent return. Payback period is in years:

http://en.wikipedia.org/wiki/Payback_period

 

[nitsuj]

Just to be a nag, ROI is percent return. Payback period is in years:

http://en.wikipedia.org/wiki/Payback_period

Thanks! I didn't know there was a term for it.

 

[OmCheeto]

Just to be a nag, ROI is percent return. Payback period is in years:

http://en.wikipedia.org/wiki/Payback_period

Thanks! That might explain why I'm broke. I don't know anything about finance.

And I just realized, that I have two systems I'm working with.
The Powerwall, and the hot water system.
The hot water system could actually be implemented without a Powerwall, so that should be calculated separately.

Starting from scratch:

Powerwall               
cost (c)       $4,600       
On peak rate   $0.12581        $/kwh
Off peak rate  $0.04195        $/kwh
Difference     $0.08386        $/kwh
use                10         kwh/day
time             3,652         days
gain (g)        $3,063       
ROI = (g-c)/c   -33.4%

hmmm... Did I do something wrong? Why would anyone buy one of these Powerwalls?
In my defense, for being so far off previously, I did mention that this was worse than figuring out taxes.

pps. As to what this has to do with the Tesla Powerwall?

Obviously it shows that a single Powerwall can't heat my house, as the peak heating power use was 5.6 kw. A single unit is limited to 2 kw.
Though that was for heating it up, at an average temperature (inside vs outside) differential of 12°F (6.7°C).
Were I just trying to maintain such a differential, I would only require 500 watts.
In the winter, with an inside temperature of 65°F (18.3°C) and 32°F (0°C) outside, it jumps to 1400 watts.

But it's somewhat a mute point, as no matter how many of these things I have, they will always lose money.

On a happy side-note though, my thermal system has an ROI of 380%, over 10 years.

But this all brings up an interesting question, given that I haven't boogered my maths again.
Why were $800 million dollars of these ordered in the first week?

Is it viable for people with solar panels? Do Peak vs Off-Peak rates vary more elsewhere?
I'll have to spend some more time on this.

 

[Meloetta]

idk if you guys are aware of this, the output is actually 2 kw, and as for the 800m$ in sales, lot of good marketing, personal brand goes a long way

 

[OmCheeto]

...
But this all brings up an interesting question, given that I haven't boogered my maths again.
Why were $800 million dollars of these ordered in the first week?

Is it viable for people with solar panels? Do Peak vs Off-Peak rates vary more elsewhere?
I'll have to spend some more time on this.

Apparently it is viable.

Why this winery is using a bunch of Tesla batteries (Fortune)
by Katie Fehrenbacher JUNE 26, 2015, 4:29 PM EDT
...
Across the Jackson family wineries, solar panels and Tesla batteries are expected to lower the company’s electricity bill by nearly 40% in 2016, which is a savings of about $2 million.
...

$2,000,000 will buy a nice little yacht.

The Jackson family spent about $10 million installing a collective 6.5 megawatts of solar panels across their wineries...

I wonder if this included tax incentives. That is freaking dirt cheap.

Tesla’s algorithms use data like historical temperatures, energy use, time of day, electricity rates, and many other factors. Over time, Tesla’s algorithms learn what the winery’s power needs are and figures out the best way to use the storage to save energy and money.

Sweet! I love algorithms. And a "learning" algorithm? I've never heard of such a thing. Double sweet!

 

[Kafzilla]

A side question, could one hook one of these up with a generator and charge with the unused power?

 

[anorlunda]

A side question, could one hook one of these up with a generator and charge with the unused power?

Sure. I imagine that batteries in combination with on site generation are very attractive.

Remember that not all locations have net metering where you sell excess power back to the utility, nor are all users on the grid. On-site energy storsge is most attractive to those users.

I think the solar/storage combination is attractive. Once you have a solar installation, you already bought the inverter, mandatory grid interface (if any), and installation labor. The incremental cost to add additional panels is small. Combine that with the cost of adding battery storage, and the economics are compelling.

Where net metering is available, the grid acts as your storage battery at no charge. That is why I think net metering is not sustainable.

 

[shanaya]

i have question that how can we increase the output voltage 90vdc to 200v if we are having the input voltage 220v ac?

 

[anorlunda]

The DC to AC inverter will boost the voltage. It has an internal transformer.

 

[mheslep]

By the way, the world's biggest utility battery installation is in Fairbanks Alaska.

That facility was build with Ni-Cads in 2006 (45 MW, 4 MWh). The new largest in N. America is li-ion based and eight times larger, http://www.greentechmedia.com/articles/read/The-Biggest-Battery-in-North-America-Gets-Unveiled-By-SCE-Today in California.

 

[mheslep]

They are required to pay whatever it takes to buy all the energy needed to satisfy the demand, not matter what the price.

Also, in many places utilities are required by the state to buy a quota of certain types of power, specifically renewable power (aka RPS).

 

[anorlunda]

That facility was build with Ni-Cads in 2006 (45 MW, 4 MWh). The new largest in N. America is li-ion based and eight times larger, 32 MWh, in California.

Thank you mheslep, I was not aware of the California installation. In another recent thread, Batteries for utility storage, I found news of a battery facility under construction in Austrailia with 50 MW. 300 MWh . Maybe we'll see more wide spread use of utility batteries in the future.

I'm curious about choice of chemistry. For utility applicaitons, volumetric or mass energy density sounds unimportant. Their lifetime measured in cycles may be similar. Is it simply $/MWH that determines the choice?

Also, in many places utilities are required by the state to buy a quota of certain types of power, specifically renewable power (aka RPS).

But batteries are not an energy source, just energy storage. Do purchases of battery power count as renewable? It sounds complex, because you have to figure the source of energy used to charge the battery.

I would also add, that the location of the generation is sometimes also a requirement. For example, Manhattan Island in NYC, where some fraction of reserves must be on-island.

 

[mheslep]

Is it simply $/MWH that determines the choice?

amortized capital cost of storage $/MWh, efficiency, and $/MW, i.e. cost for storage, cost of wasted generated energy, and cost of rate of charge/discharge. The last may or may not add to the total cost.