# Tesla House Battery / Utility Scale Battery



## jebatty (Apr 24, 2015)

The net is abuz about a battery announcement coming from Tesla on April 30. One post quoted a possible price for a 10kw house battery at $1.30/watt. Haven't seen a smart control system that would grid-tie this well to charge as the PV system had excess current available and discharge to the house when the PV system had insufficient energy, but it would seem this needs to be a part of the deal.


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## peakbagger (Apr 24, 2015)

I seriously doubt that Tesla will be selling these units to anyone. They will include it as an option to sell more Solar City leases. Selling a battery is one time profit. By using it as a cachet to lease more PV systems, there is ongoing revenue stream from the lease. There is also most likely some fine print that allows tesla to manage the battery pack. By communicating to the battery pack to sell power during high demand periods they most likely can get  additional long term intermittent revenue stream and most likely will be able to sell the capacity for short terms sales as another revenue stream. Folks don't realize that the Tesla cars are sold at a loss and the cost is made up by Tesla selling the zero emissions attributes to other car companies that aren't selling enough of their own.


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## billb3 (Apr 24, 2015)

Warren Buffet is helping to underwrite China's BYD foray into a 'Gigafactory' to rival and maybe even outclass the Tesla/Panasonic collaboration.
There's going to be a glut of  lithium-ion cells which ( the plan is) to lower costs and increase sales. The current solar/power industry will have to embrace this storage medium somehow. Either storing it themselves and maintaining SREC and net-metering or home-owners will embrace just one more investment themselves for the net savings.
It will be an interesting shake-out. However the shake-out proceeds, the poor will be the very last to benefit, if at all.


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## DougA (Apr 24, 2015)

Lower prices are not going to happen soon. Announcements are happening all the time but Tesla's factory is only partially built and it will be another 2 yrs before production is at levels to bring prices down to levels some of us might be able to stomach.

IMHO, power storage will be like PV & computers, what you are buying is older technology that they are getting rid of to bring in the better stuff.


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## jebatty (Apr 24, 2015)

> However the shake-out proceeds, the poor will be the very last to benefit, if at all.


This is open to discussion. Do the "poor" benefit from my solar? I would say yes: 

1) My excess kwh are daytime, times of load management of peak loads by the utility and service interruptions. I am adding capacity which will reduce the utility need for load management, which will result in less service interruptions and less need for the utility to buy expensive peak power, which should reduce rates for everyone.

2) My PV is adding efficiency to the grid. I doubt that my excess kwh even make it a mile down the road before they are used by other consumers. Line loss of such short distances is minimal, compared to 10-20% on grid supplied power. Increasing efficiency also translates to more kwh at reduced cost to the benefit of everyone. 

3) My PV is a capital investment in long term power, paid by me privately, thus relieving the utility of need to add generating capacity at huge cost with cost recover through rate increases. Once again, reducing utility costs and more kwh to everyone without additional capital cost and rate increases. 

4) This is nearly a ditto of (3). Distributed power means less need for long distance transmission lines, and avoidance of another large capital cost recovery by the utility through rate structure and rate increases. If distributed power is wisely planned, there also should be little need to add short distance transmission capacity which in any event is much less disruptive than long distance transmission lines. 

5) Hard to conclude that those installing PV are really benefiting directly. Rather, they are benefiting generally as are other rate payers and the public. They may be receiving a reduction in current charges at the cost of a substantial capital investment and cost recovery which, in my case, is nearly 20 years into the future. And I am bearing the future risk rather than the utility and its rate paying customers. Many including me would conclude that residential PV is really more costly than grid electricity, unless the other non-reimbursed indirect costs of grid electricity are paid to the PV investor. But may main reason for investing in PV was because "it is the right thing to do, something which my utility is not doing."

6) I will package the social and environmental benefits in one bundle. Estimates are that these costs likely are in the range of at least equal to or more than the current charges for electricity. Everyone benefits with clean, safe, power and a healthier environment, reduced illnesses, etc. 

PV, like most other innovations, is driven by the wealthy, the early adopters, those that set the future trends. Same with automobile, electronics, and the list goes on forever. In the long term costs drop to the great benefit of everyone; meanwhile some have also benefited hugely. PV is not unusual or an exception in this regard. It is capitalism and free enterprise at work. Let PV compete on a level playing field rather than continuing to give government sponsored and enforced monoply control to large utilities.

Lastly, most utilities are investor owned. Do you doubt for a moment that these investors are profiting at the expense of the poor from the current system?


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## woodgeek (Apr 24, 2015)

I still think when the dust on storage settles, the utilities will be owning nearly all the batteries.  

The utilities are getting scared re grid management and falling profits, and affordable grid storage with be a hallelujah.


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## jebatty (Apr 24, 2015)

I agree that utilities or utility scale batteries will be a major player. I also would not be surprised if there is more movement to off-grid with more affordable battery packs, more competition, even potentially less regulation.


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## woodgeek (Apr 24, 2015)

agreed.  But if I can buy RE off the grid for less than I can get it from my own off-grid system, I, like many will stay on grid.


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## jebatty (Apr 25, 2015)

Might a fit for the battery for those with PV, even with grid RE, be to supply electricity to the home/farm when solar is not producing or under producing and where full credit for excess kwh supplied to the grid is not compensated to the PV producer? For example, our general service electric on average is about 400 kwh/month, or about 13 kwh/day. Our PV roughly on average supplies 20% of that usage with 80% from the grid. Our heavy usage is during non-sun times. On average a 10 kwh battery, with direct use PV, would meet 100% of our general service home electric usage -- meaning now solar would be providing 100% of daily usage.

As to the remaining excess solar to grid, it would not take much load control to shift DHW heating from current timed service from the utility (between 11pm and 7am) to daytime periods when excess solar is being produced. On average that would be an additional 3 kwh/day. Similarly, during periods when we use electric supplemental heat in our lower level (Nov - Apr generally), rather than baseboard, we could use a ceramic electric storage unit to charge on excess solar and then provide the heat when needed. Electric heat from Nov - Apr averages 20-30 kwh/day. That still leaves May-Sept when there would be excess solar produced which I likely will not be able to capture, but on the other hand this is AC season and the utility may want the excess solar to meet demand for AC.

The point I am making is that PV with some home battery storage could substantially even out PV surges to the grid and provide a return to the PV homeowner that might not otherwise be available due to net metering restrictions, charges or unavailability, depending on the utility. Utility scale storage could offer the same benefits to the utility to even out PV supply, but there may be an advantage, cost or otherwise, to smaller scale storage as well.


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## jebatty (Apr 25, 2015)

Further as to home battery storage, might this be a market for the utility to lease the batteries to homeowners?


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## jebatty (Apr 25, 2015)

I see on Amazon 4 - 4ah 18650 li-ion batteries at $13.69, or $3.40 each. 2500 of these batteries would be 10 kwh of storage at a price of $8,500. A 10 kwh battery pack with charge/discharge control, and probably a higher quality battery, likely would cost more, but ballpark pricing could be in this range.


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## peakbagger (Apr 25, 2015)

Lithium chemistry is the wrong choice for a home battery system. Lithium's big benefit is watts/pound and fast charge and discharge capacity. It also uses a lot of high value materials. A household battery does not need to be particularly lightweight so other battery chemistry's are more appropriate. The deal for a home battery is $/watt. Tesla has made a huge bet on Lithium technology and the only way they can win it is to mass produce the batterys to drive the cost down. If they can have multiple channels to sell (or lease) them, its a way of ensuring that they hit the volume they need.

There are couple of other reasons to sell lithium house batteries.  When lithium batteries are made there are inevitably going to be some low grade cells. Many of the cells for sale on Ebay and Amazon are "seconds", generally there is nothing wrong with them except that their charge density (watts per pound) is low so they are not great for a car. Tesla can sort the batteries at the plant and divert the seconds to the home battery line. Lithium batteries also wear out due the hard demands placed on them in automotive application. At some point the battery pack loses charge density. Its still a good battery pack but not good for an auto. Rather than scrap the batteries, they can get several more years of life by reconfiguring them as house batteries. This delays the inevitable costs to recycle the batteries as I expect that the government is to force recycling of dead batteries rather than generating a new toxic waste stream.

Some of the battery technologies currently better suited for house use are the Aquion batteries, GE Durathon batteries, good old lead acid, and possibly some new variation of Edison's favorite nickel/iron. They all have their pluses and minuses but they are lower cost per watt. This battery battle has been going on for years in the off grid community and to date lead acid seems to be the winner. Sure folks try other battery chemistry's but when they have to write the check to replace a battery bank they usually write it for lead acid.


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## jebatty (Apr 25, 2015)

Not promoting li-ion, but the idea of house batteries seems to be very feasible, practical, and in the end competitive.


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## woodgeek (Apr 25, 2015)

Let's crunch some numbers....  

Let's say you can get your home battery for $200/kWh, just a quarter of what you are supposing.  If I can only get 1000 cycles out of them (full capacity cycles, or equivalently 2000 50% DOD cycles, 5000 20% cycles, etc), then my cost of energy from the batteries is $200/1000 = 20 cents/kWh.  If the battery engineers can get the cycle costs to 2000 cycles, its still a 10 cent per kWh up charge for storage, which is pretty steep.

For Li-ion, I think the (closely guarded) numbers for EV batteries are closer to $250-300/kWh in 2015, and the cycle numbers are in the 1000-1500 range.  

E.g. my LEAF can do 85 miles on a charge, and the battery will be pretty beat by the time the car gets to 85,000 miles (1000 cycles).  If a replacement/trade-in battery is $5500 for 24 kWh, that is 5500/24*1000 = $0.23/kWh for the privilege of having the juice in a moving vehicle!

Some off-grid folks could estimate better, but it seems cheap Lead-acid batteries are ~$100/kWh (to 80% DOD).  I think nice AGW batts are $200-300/kWh, and can do ~1000 cycles (2000 = 7 years at 50% DOD), corresponding to a $0.25-$0.30/kWh battery premium for off-grid applications.

The real action as peakbagger noted is in batteries with other chemistries, like the Aquion battery. http://www.aquionenergy.com/
These need to get the cost down below 5-10 cents per kWh delivered, and both Li-ion and Lead acid are still 4-5x that today.

It'll happen and be huge, but not at scale on April 30th.


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## begreen (Apr 26, 2015)

jebatty said:


> The net is abuz about a battery announcement coming from Tesla on April 30. One post quoted a possible price for a 10kw house battery at $1.30/watt. Haven't seen a smart control system that would grid-tie this well to charge as the PV system had excess current available and discharge to the house when the PV system had insufficient energy, but it would seem this needs to be a part of the deal.


That seems expensive. 10Kw is fairly small for average house usage without a lot of energy management say for a week long cloudy spell. Used lithium car batteries still have a lot of life left, especially for this application. A new 16Kw Volt battery is about $4500 I think. Used are less than half that.
http://www.extremetech.com/extreme/...old-chevy-volt-battery-into-a-whole-house-ups


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## Cynnergy (May 1, 2015)

Tesla just announced 10kWh for $3500.  www.teslaenergy.com


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## begreen (May 1, 2015)

http://www.businessinsider.com/here-comes-teslas-missing-piece-battery-announcement-2015-4

Lots of details still missing. In particular I want to know how it is proposed to backup grid-tied solar.


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## Jeepman401 (May 1, 2015)

begreen said:


> http://www.businessinsider.com/here-comes-teslas-missing-piece-battery-announcement-2015-4
> 
> Lots of details still missing. In particular I want to know how it is proposed to backup grid-tied solar.



http://www.teslamotors.com/powerwall

Sounds like it would act like a battery back-up, when the power goes out it would power the home. Details will be coming. But the few times some people lose power it would be better used to size a solar system smaller and charge the battery during the day and use it at night to power the home...if you didn't get enough sun and the battery got low you could draw from the grid. This is a game changer if people could use their imagination and aren't limited by Krouch Brothers $$'s and regulations. 
Personally I will be thinking of going completely off grid in 5 years or so if the price drops a little more and or how my system actually produces just because I could. Although, the current draw specs make me wonder if you could power a welder with this while off grid completely.

I love the times we live in now, so many advancement's in technology!


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## jebatty (May 1, 2015)

> It will be sold to installers for $3,500 for 10kWh, and $3,000 for 7kWh. Deliveries will begin in late Summer.


 The controller technology could be as simple as a timer, if the battery is used for night charging at low utility rates and then supplying electricity to the home for the morning coffee and evening dinner, and maybe some AC during the day. Or with a sensor monitoring PV output and house demand, when PV exceeds demand, charge the battery. In my case, typical daily kwh usage is 10-15 kwh total (not including electric heat). A photocell sunlight sensor could switch charging on and off during the day from PV, and except for densely cloudy days, my system produces enough kwh to meet daytime demand and/or charge the battery and the battery would meet demand from sunset to sunrise.

Not to get bogged down on the details of the controller possibilities, the real big thing is an inexpensive battery that combined either with charging from low rate utility supply or PV, or both, real economies may be on the doorstep, including fully off grid for many more PV users.


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## JP11 (May 1, 2015)

At current rates.. I don't believe there's a battery system out there that can be maintained for 10 dollars a month.  That's what my utility is charging me to be my 'battery'  This battery lasts 12 months on a charge (I must use excess credits within a rolling 12 month calendar)

Now, eventually they might try to discriminate against solar powered homes and make different 'minimum connect fees'  but for now.. I won't be interested in battery tech.

JP


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## EatenByLimestone (May 1, 2015)

I wonder how useful it would be as a stand alone for people on a smart meter.  You could draw all your energy from the grid at the low evening rates and then use that power during the day. 

That alone could save a bundle.  10 year warranty...  maybe good for 15?


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## peakbagger (May 1, 2015)

I have been paying a monthly fee to be hooked to the grid for about 4 years and run a net credit on my power usage.  There is no off peak sell back program with my utility. My utility has no current interest in energy storage. The utility charges another monthly fee for off peak power and since I don't buy power, I don't see why I would voluntarily pay my utility even more.  My backup generator has never been used since if was purchased in the year 2000. So what rational justification would I have to buy a battery bank? There is the geek factor, the keeping up with the Jones factor but I drive cheap econo boxes into the ground and have never owned anything made by Apple, so neither one really applies. On the other hand there are plenty of lemmings that could care less about reality and get on the wait list. I will be curious how much the homeowners coverage goes up in a few years.   

I expect a lot of folks will be upset when they find out that the pricing is based on subsidies that may not exist with their utility.


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## EatenByLimestone (May 1, 2015)

How useful is a 10kw battery?   How do I calculate how long that will run, a 60 watt light bulb?  Is it as simple as a kilowatt is 1000 watts so you are looking at 10,000 watts?  10000/60=166 hours?  Obviously if the battery has limitations such as don't discharge below xx% that would shorten the amount of hours.


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## jebatty (May 1, 2015)

Local utility rates will vary, individual motivations will vary, available incentives will vary, and state laws will vary. If an analysis is made on kwh usage and having a battery that can charge when PV is available or when the grid has excess capacity, then a much different picture of energy supply and cost starts to form, as well as a much different picture of environmental impact of energy usage. Imagine most houses having a 10kw battery and businesses larger kwh batteries, grid tied to draw from and possibly even supply to the grid - micro distributed power which would even out grid supply/demand, possibly eliminate or greatly reduce the need for peak generating capacity, and add a level of emergency energy security. Imagine greatly reduced carbon emissions, cleaner and healthier air, water and soil - an environment that sustains rather than depletes life.

I give great credit to people like Elon Musk and Tesla. People like him in various areas imagine a better world while most of us barely can get past a cup of morning coffee and the last installment of Survivor. We need more of and need to celebrate the great thinkers, great entrepreneurs, and great risk takers. Without those that came before we still would be wearing loin cloths and using a rock for a hammer. 

As to the reality of the geek factor related to PV and battery storage, so what? My neighbor drives a big honker pickup truck ($40,000), one person in the vehicle, rarely hauls anything in the bed -- just because he can. Another neighbor has a 6000 sq ft home -- just because he can. Another neighbor is a bejeweled fashionista -- just because he can. Not one of these has any payback, let alone an economic payback. So what? Our lives are full of geek factors, culturally induced behaviors, and shaped by big bucks media advertising. PV has real value beyond the geek factor.


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## jharkin (May 1, 2015)

First off, whomever found an 18650 LiIon cell with a 4Ah capacity - give me a link Most of the ones Ive seen (we use them in hobby applications) are 2.6Ah... sometimes 3.

But that doesn't matter, since 18650 are very small format cells - they are laptop battery cells.  For a large off grid battery it would be better to use larger format individual cells so you dont have to string as many of them together. Trying to make a many kilowatt pack out of little cells you end up having a large % of the mass, volume and cost of it go to the metal in the cell cans , packaging and interconnect wiring... a waste.


Furthermore, as folks have mentioned, Lithium Ion in general is a waste for fixed applications.  Its big benefit is energy density by mass meaning its great for vehicles, but there are so many cheaper options for a battery that wont move. Like mentioned above lead acid.  Which also is currently more recyclable and made with materials that are far more abundant in nature than any lithium technology.  Off grid folks use lead batteries for that reason.  And they dont put 10,000 little flashlight batteries together, they use a few big ones like so 






(these cells are made up to 2000+Ah per)

As far as cycle lives go, I'd be really impressed with a LiIon that actually manages 1000+ cycles.  When used hard, LiIon is more like a couple hundred until noticeable capacity loss is evident - Im sure we have all experienced laptops and cell phones that wont hold a charge in as little as 1-2 years.  A123 Lithium Iron Phosphate's are probably the leader in this regard, doing an honest 1000+ at very hard discharge rates, but they are very expensive, even compared to already expensive LiIon.  Again, Lead Acid is still the value leader here, good cells can manage close to 1000 cycles but it comes at the cost of low discharges  -even for good flooded deep cycle off grid batteries like the Rolls Surette pictured above reaching those numbers means limiting to 40% discharge depth.  If you go for 80% the life cuts in half.


As regards nickel iron... yes Ive heard some discussion to bring them back but I dont see it ever getting big.  They have one large benefit - a lifespan measure in decades unaffected by discharge depth... Telco's like them for phone backups for that reason. OTOH, they have lower recharge efficiency than most other types, even lower energy density than lead acid, and they tend to self discharge like all nickel chemistries.


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## woodgeek (May 1, 2015)

Here's another link, with the fun 18 minute presentation embedded.

http://insideevs.com/tesla-reveals-battery-storage-solution-missing-piece/

I recommend the video.  Elon is a bit of a nerd, but solving climate change just became sexy, fun, and an excellent investment opportunity. 

Its clear that the two products...7 kWh and 10 kWh have the same footprint, and IMO likely the same physical battery.  The 7 kWh is intended for daily cycling, and prob only charges the cells from 10% to 80% SOC (thus 70% of nominal capacity), but with (low charge discharge rates, below C/5) the hopes of getting say 2000-3000 cycles (i.e. 10 years on a daily cycle).  The other unit, intended for backup, allows you to use the full SOC, but limits you to a 'weekly'/backup cycle application, or about 500 nominal full cycles in 10+ years.

So, if you were going off grid, you would have to go with the 7 kWh version, gang them together until you got the bank size you wanted, and then have a zero-maintenance, XXX year warranty system in place.

If we figure the 7 kWh system is good for 3650 cycles (10 years, diurnal) and ran the full 7 kWh delivery, that is *13.7 cents/kWh* upcharge to store your power in an off-grid system.  I think this (if it comes with a 10 year warranty/ performance guarantee) is competitive on price with existing solar off-grid applications, and is VERY competitive on space/maintenance ground, and hopefully on reliability as well.

The 13.7 cents/kWh rate will be competitive in Hawaii today, and that market could presumably absorb a lot of the first year 'ramp' of production.

As for profits?  If Tesla is currently costing ~$250-300 /kWh for its cells, then the 7 kWh system (10 kWh actual) costs $2500-3000 for the cells. Not leaving much for the balance of system inverter, controller, housing etc.  I don't see a huge profit margin here...but they could be close/negative on costs today, and still project a decent profit when they open the spigot in a year or two (with $150-$200/kWh cells).


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## JP11 (May 1, 2015)

I can't quite wrap my head around the differential. but let me try.

If I went to 'time of use' billing on my house.  and I use 1000kwh in my house (that's a close average back when I was using oil heat, big house,and an attached business)

so.   that's 150 dollars of power at my 'standard rate'

If I went to time of use..  and got ALL of my power off peak.. that's 97 dollars.  Peak rate it would be 183.

So I've saved 53 dollars per month.  636 per year.

That's 5.5 years to pay off the 3500, not including install.  How many years do you say it would last?

Not all decisions are dollars and cents.. but this one seems just a bit out of reach FOR ME.

JP


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## woodgeek (May 1, 2015)

jharkin said:


> First off, whomever found an 18650 LiIon cell with a 4Ah capacity - give me a link Most of the ones Ive seen (we use them in hobby applications) are 2.6Ah... sometimes 3.
> 
> But that doesn't matter, since 18650 are very small format cells - they are laptop battery cells.  For a large off grid battery it would be better to use larger format individual cells so you dont have to string as many of them together. Trying to make a many kilowatt pack out of little cells you end up having a large % of the mass, volume and cost of it go to the metal in the cell cans , packaging and interconnect wiring... a waste.
> 
> As far as cycle lives go, I'd be really impressed with a LiIon that actually manages 1000+ cycles.  When used hard, LiIon is more like a couple hundred until noticeable capacity loss is evident - Im sure we have all experienced laptops and cell phones that wont hold a charge in as little as 1-2 years.  A123 Lithium Iron Phosphate's are probably the leader in this regard, doing an honest 1000+ at very hard discharge rates, but they are very expensive, even compared to already expensive LiIon.  Again, Lead Acid is still the value leader here, good cells can manage close to 1000 cycles but it comes at the cost of low discharges  -even for good flooded deep cycle off grid batteries like the Rolls Surette pictured above reaching those numbers means limiting to 40% discharge depth.  If you go for 80% the life cuts in half.



Great info, Jeremy.

The bigger 18650 cells if I recall are a 'special product' made by Panasonic for Tesla.  Tesla _claims_ that the cylindrical form factor is cost optimal, since the fabrication is readily mechanized.  They also claim that in EV apps, the small cells facilitate thermal management in high charge/discharge rate.  The assembly of cells into banks is also robotized if I recall.  They also put a fusible link on each cell, which makes the bank fail-safe if one cell should come up with a short.  (Too bad Boeing is not buying these for APUs).

As for Li-ion cycles, it comes down to the charge controller.  Certainly a lot of cheaper electronics have bad controllers and short battery lifetimes (do you need a windows laptop to run longer than 3 years?).  Case in point, all my Apple laptops have managed >1500 cycles (counted on a full discharge basis) with only a negligible capacity loss, including the ones made 10 years ago.  If Elon thinks he can baby his cells (C/5 or lower, 10-80%SOC) and get 2500-3500 useful cycles (as implied by the calcs above), then I believe it.


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## woodgeek (May 1, 2015)

JP11 said:


> I can't quite wrap my head around the differential. but let me try.
> 
> If I went to 'time of use' billing on my house.  and I use 1000kwh in my house (that's a close average back when I was using oil heat, big house,and an attached business)
> 
> ...



Your numbers make sense.

1. I do not think this product makes sense in 99% of US applications.  But I think for 1% of customers, most of whom have solar already, there can be a good value proposition.

2. It also puts a 'cap' on grid energy costs before you would 'defect'.  If the current PV off-grid electricity costs are seen as $0.50-0.75/kWh, depending on seasonal needs for battery storage (less needed in HI or CO than ME), Elon just dropped the cost of going off-grid in the more favorable locations by 20 cents/kWh or more, and made it 'effortless' and sexy.

3. In my HCOL area, folks are happy to pay $20k for an automatic backup genny.  How many would rather pay $10-13k for a 30-40 kWh bank of 'powerwalls' that can run their house for a day or two (if they have fossil heat), and the difference in cost pays for a lot of hotel rooms for longer outages.  IMO, the 'backup market' could be as big as the 'off-grid solar' market.


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## JP11 (May 1, 2015)

I agree.. in a remote setting this could be a great part of your system..

solar
battery
genset

when you're forced to run your generator, you can store your excess production.  I imagine that SOME that are off grid have already come up with a solution like this.  If elon can make this an 'iPhone' simple system.. more power to him.  I think it would be very cool, and could be the beginnings of a 'smart grid' for remote areas.

as this tech is adopted though, lets say in a mythical island.  Those that are disconnecting from the grid will only make costs higher (economy of scale in reverse) for those remaining connected.  This will make this tech even more appealing as prices per Kwh rise.

JP


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## woodgeek (May 1, 2015)

To folks in Maine, Hawaii might seem mythical, but its a real place!


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## DougA (May 1, 2015)

Musk reminds me of Steve Jobs. A whole lot of fanfare & hype to show off something that is a snazzy version of stuff we can already buy cheaper. I've done the math multiple times and I cannot justify the cost of this or any other battery system to untie me from the grid.  The payback is far too long, even calculating in the future increases in hydro rates. In my case, you are either on the grid or not. Reducing power usage does have some effect but our hydro rate is one half of the total bill and the 'extra surcharges' are what is the killer.  Today, I'll be using $25. in energy coupons to buy more LED lights to replace the last of my old bulbs. That $25. is not free, someone else on the power grid will pay for my savings. Tomorrow, I'll have to pay for someone else's. Coupons like that are BS and I hate that.  

The one good thing about this announcement is that it takes all of us one step closer to power independence. Not close enough for 99% of us, but it will come eventually.


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## woodgeek (May 1, 2015)

DougA said:


> Musk reminds me of Steve Jobs. A whole lot of fanfare & hype to show off something that is a snazzy version of stuff we can already buy cheaper.



Sorry, where now would you buy a cheaper 10 kWh Li battery bank for residential backup use?  I don't even know of any 'turn key' lead-acid systems that size.


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## jharkin (May 1, 2015)

JP11 said:


> I agree.. in a remote setting this could be a great part of your system..
> 
> solar
> battery
> ...



Thats exactly how off grid folks build their systems. 

First they size their battery back. Knowing that there is always going to be cloudy days they figure the average ratio of sunny to cloudy days and size the bank for a reserve to run when the cells are not producing. This varies but I think 2-3 days is typical.  The cells are sized to cover that many days to 50% DoD.

Then they size their panels to be able to recharge the bank at 50% DoD in a reasonable time span. I think 1 day of good full sun is used.  (this means that the panels end up sized to produce more than the house uses per day when its sunny)

Then they add a small generator for backup for the occasional long stretches of bad weather.  The generator is used to charge the batteries, not power the house directly - so it can run at full load max efficiency.  Often diesel or natgas generators are used to avoid fuel storage concerns.


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## DougA (May 1, 2015)

Who says you need turn key?  How much effort is involved in wiring together some lead acid batteries?  Gee, sounds just like Apple that wants to charge twice the price for 'packaging' a sexy looking system.

EDIT: for got to add that AFAIK, this unit is not turn key. It still needs an inverter to run appliances - at least according to news reports and that will up the price A LOT.


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## JP11 (May 1, 2015)

There's always someone willing to pay for 'plug and play'


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## jharkin (May 1, 2015)

woodgeek said:


> Sorry, where now would you buy a cheaper 10 kWh Li battery bank for residential backup use?  I don't even know of any 'turn key' lead-acid systems that size.



10KWh is not that big to do with lead.. You could get away with just 2 of these   But the 4 volt series voltage would be to low to be practical.

http://www.solar-electric.com/batte...s/suprdecyba/2voltbatteries1/suba2vo24am.html


Better option would be 4 of these 6 volt batteries for 10,300 watt hours @ 24 volt series voltage.  $1200 for the batteries plus wiring and charge controllers. That's 11.7 *cents* per watt-hour   maybe 20-25 cents once you add in all the wiring, charger controller, inverter and installation.

http://www.solar-electric.com/batte.../rolls-surrette-s-550-deep-cycle-battery.html


EDIT - Big goof, for lead you only use 50% DoD so this owuld be doubled to give 10KWh usable. Making the figure more like 25-50 cents per W-h installed.


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## woodgeek (May 1, 2015)

DougA said:


> Who says you need turn key?  How much effort is involved in wiring together some lead acid batteries?  Gee, sounds just like Apple that wants to charge twice the price for 'packaging' a sexy looking system.
> 
> EDIT: for got to add that AFAIK, this unit is not turn key. It still needs an inverter to run appliances - at least according to news reports and that will up the price A LOT.



Time will tell.  I thought the inverter was built in (and only 2 kW_peak per module), crazy not to since its part of battery management...a bad inverter could kill the thing.

Re price.  I agree that good AGW batteries are easy to wire and maintenance free...and cost the same or more per kWh*cycles as this thing.  You can beat the price on flooded cells (I think, more like $100-$150/kWh), but then you have a lot of acid slinging maintenance.  There is a reason most off-gridders go for warrantied AGW...but I think Tesla has clearly beaten the AGW on 'lifecycle' cost per kWh stored.

If Tesla only has a 2 yr limited warranty, then I'm with you Doug!  I expect it will be more like 7-10.


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## woodgeek (May 1, 2015)

Jeremy, what is the cycle rating/warranty on the surrettes?  And converted to a 100% SOC basis...as in *rated kWh out* over the life of the battery?  Converted to a $/kWh_delivered??


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## jharkin (May 1, 2015)

woodgeek said:


> Jeremy, what is the cycle rating/warranty on the surrettes?  And converted to a 100% SOC basis...as in *rated kWh out* over the life of the battery?  Converted to a $/kWh_delivered??




good question.. I looked it up, they warranty for 5 years pro-rated, 2 years full replacement on batteries used in off grid.

Oh and I knew I must have made a mistake.  In my calcs above to get 10KWh of usable capacity the lead bank would be sized to 20KWh.  So my example above would actually be 25 cents/watt for the batteries.  Probably 50 cents per watt instaleld with wiring, chargers, inverters.  Still seems a lot cheaper than the $1.30 a watt quoted at the top of thread.

disclaimer - Ive never done one of these, just getting my info from solar forums and the battery MFG webpage.


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## begreen (May 1, 2015)

jharkin said:


> As far as cycle lives go, I'd be really impressed with a LiIon that actually manages 1000+ cycles.  When used hard, LiIon is more like a couple hundred until noticeable capacity loss is evident -


 The key here seems to be to control the rate of depletion and limit it to avoid full depletion. Electric car LiIon batteries do this with maybe an average of 300 charge cycles a year, or more for a daily driver like a Prius taxi cab. Our 7 yr old Prius battery was showing no sign of exhaustion when we sold the car. The Volt and Leaf batteries are warranted for several (8 and 6) yrs..


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## Clarke (May 1, 2015)

This looks like a great unit, but how would I install a 300V battery into an existing 12, 24, or 48V system?


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## begreen (May 1, 2015)

I am wondering how they do the grid-tie interface too. My guess is that it is post solar inverter. If so I would suspect it to be managed as a feed to the battery pack charger.


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## Clarke (May 1, 2015)

That sounds right, but it would make for a very complicated retrofit for those of us who run DC charge controllers (solar, hydro, wind) and have no grid to tie into.


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## jharkin (May 1, 2015)

Regardless of the difference in voltage, the LiIon cells also have a different charging profile than an existing 12/24/48v lead acid system so there would have to be a separate charger  fed by the output of the solar cells.


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## DougA (May 1, 2015)

Not to go too far off topic, but I'm way more interested in finding a way to convert heat from my wood stove into usable electricity.  The Thermoelectric effect (Seebeck/Peltier) has far more potential for us wood stove users.  I've got a fan that sits on my stove that gets all of it's power from the heat so why can't this be ramped up to charging a battery at night and using solar during the day?  Both are free - at least for us stove/furnace people.


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## Clarke (May 1, 2015)

Luckily, all of my charge controllers, and my inverter/charger are configurable for the LiIon charge profile.  Maybe I could find a massive buck converter. Joking. Unless Tesla has some further ideas, or models in the works???


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## Clarke (May 1, 2015)

Check out e-bay. there is quite a selection.


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## JP11 (May 1, 2015)

Here it is.. Stirling Engine.  BIG money.

http://www.energymanagertoday.com/b...g-engine-heats-water-generates-power-0109653/

I found one in MI I believe it was.  Natural Gas input.  Power and heat output.  Something like 50k BTU and 5kw energy.  40 grand!


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## jharkin (May 1, 2015)

TEG's have been discussed before.. They are expensive to make and the efficiency is so (5% ish) low taht even if you could build one to capture a majority of the heat output from your woodstove the electric output would be tiny.

For example, say your stove is outputting 30,00 BTU/hr
Thats 9500 watts of heat energy.

If you can capture all of it with a TEG you would get an electric output of under 500 watts.


And thats best case, assuming the stove is cranking full blast all the time and the TEG is very large.


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## begreen (May 1, 2015)

Clarke said:


> That sounds right, but it would make for a very complicated retrofit for those of us who run DC charge controllers (solar, hydro, wind) and have no grid to tie into.


In that case I might consider getting a used Prius battery and tying it into a 240v inverter/charger.


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## begreen (May 1, 2015)

DougA said:


> Not to go too far off topic, but I'm way more interested in finding a way to convert heat from my wood stove into usable electricity.  The Thermoelectric effect (Seebeck/Peltier) has far more potential for us wood stove users.  I've got a fan that sits on my stove that gets all of it's power from the heat so why can't this be ramped up to charging a battery at night and using solar during the day?  Both are free - at least for us stove/furnace people.


Yes, off topic. Do a search on TEG in this forum. There are lots of threads here on the topic.


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## DougA (May 1, 2015)

jharkin said:


> For example, say your stove is outputting 30,00 BTU/hr
> Thats 9500 watts of heat energy.  If you can capture all of it with a TEG you would get an electric output of under 500 watts.





jharkin said:


> TEG's have been discussed before


Thanks.  Didn't realize it had been discussed. I guess I have to search now that I know it's called TEG. 



jharkin said:


> For example, say your stove is outputting 30,00 BTU/hr
> Thats 9500 watts of heat energy.  If you can capture all of it with a TEG you would get an electric output of under 500 watts.



OK, but my stove is over 100,000 BTU at max and I do not need all the heat and have plenty of free wood.  So 1500 watts would power one normal house circuit for free (once you've paid for the equip.) that's not bad.  Just found Tegmart - thanks.


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## Jeepman401 (May 1, 2015)

Thinking about this, if you could now meet 100% of you electric use with Tesla's battery could this work to your advantage under the Value of Solar Austin TX uses (and MN has modeled theirs upon) should the utility decide Solar Value is lower than Grid power?

As I read/understand the Value of Solar is set by the Utility(and approved by the PUC) you get 2 meters, one all the power you use and the other all the power you produce. The 'catch' is both can have different rates, at some point the value of solar could be set lower than grid power, thus after leaving you with a bill even though you met your power demand.
If you could store excess power for use over night, drawing from the battery until sun up your power use meter wouldn't move and you would recharge the battery for the next night. Cloudy days after your battery went dead and solar wasn't producing enough you would then start to turn your power use meter. By the end of the month your grid use could be zero and your power produced would be at zero or little more in a properly designed system. The utility would get very little power from you as you recharge the battery. I believe they limit paying for over production by a set % of use all year and you lose any credits. There would be no need to over size your solar system, lowering PV costs. The utilities ownership of your REC's credits are now not worth them anything because with neither meter turning now no power is "produced" for the Utility to claim and their meter has not turned so they can't bill you for power usd at night either.

This could leave the utilities no choice other than to come up with some sort of other way to get money out of a solar user. Back to higher base fees, at that point you would see droves of rooftop solar owners cutting the cord I believe.

The Tesla battery is suppose to connect with Solar Edge systems, which have their own central inverter with power Opimizers at the panel. So if you have this system you could potentialy already own the inverter making the Tesla battery even more attractive. My system came with a 6KW grid tie inverter.

Very exciting times to be alive now.


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## begreen (May 1, 2015)

You would need several of these packs in our house to meet the demands of 240v loads like hot water, oven, heat pump, etc.. And it's unlikely you would have enough solar gain to recharge well in the heart of winter here. A single pack would be good for some lighting, maybe a stove fan or pellet stove, tv and computer during an outage.


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## Jeepman401 (May 1, 2015)

begreen said:


> You would need several of these packs in our house to meet the demands of 240v loads like hot water, oven, heat pump, etc.. And it's unlikely you would have enough solar gain to recharge well in the heart of winter here. A single pack would be good for some lighting, maybe a stove fan or pellet stove, tv and computer during an outage.



Southern climates? 
If used for a back-up, would you really worry about everyone getting 30 min showers a day and 3 meals out of the oven during the black out or would you like to keep the food in the fridg/freezer from spoiling?

No one said it would work for everyone, why is that always the deciding factor about renewables?


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## woodgeek (May 1, 2015)

Re this discussion and solar....I suspect they are trying to capture FUTURE solar customers in new installs, no luck for retrofits.  At current growth rates, 80% of systems installed in 2020 will have been installed after 2016.

And again, given their volume limitations before the gigafactory is done AND ramped up, if they have good customer interest from solar customers in HI and SoCal, they will be sold out for the next 2-3 years.

Those will be the beta testers, the rest of you might be interested in the next gen of this tech that costs a little less and stores 1.5-2x the energy per unit.  Maybe when your inverter quits 4-7 years from now.  Short Xantrex.

I had not thought of selling cheaper/greener backup to the $$rich$$ folks living in my neighborhood, instead of $20k natgas gennies.  3 units gets me 6kW sustained power output, 30 kWh energy output (fine for a day on average if fossil heat, limited AC) and 'only' costs $12k + installation.  As a pure backup, the batteries will last their shelf life, easily 8-10 years in most climates. Fully automatic, wifi linked, silent, no pollution, indoors (garage). Nice. Install has to be cheaper than an upsized gas connection.  No more LOUD 30 minute monthly test fires to annoy me or my neighbors.

Maybe I should go door to door and sell them on commission.


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## woodgeek (May 1, 2015)

jharkin said:


> good question.. I looked it up, they warranty for 5 years pro-rated, 2 years full replacement on batteries used in off grid.
> 
> Oh and I knew I must have made a mistake.  In my calcs above to get 10KWh of usable capacity the lead bank would be sized to 20KWh.  So my example above would actually be 25 cents/watt for the batteries.  Probably 50 cents per watt instaleld with wiring, chargers, inverters.  Still seems a lot cheaper than the $1.30 a watt quoted at the top of thread.
> 
> disclaimer - Ive never done one of these, just getting my info from solar forums and the battery MFG webpage.



Ok.  lets say 30 cents per (usable) watt-hour capacity from the Surrettes (being generaous relative to your 50 cent figure including wiring), and 6 years of diurnal cycles = 2200 cycles.  30 cents/Wh stored = $300/kWh *1/2200 cycles = 13.6 cents/kWh_delivered, for the battery and charge controller.

This is bang on the previously estimated cost of the Tesla 7 kWh 'daily cycle' unit, which I think includes charge controller and inverter, assuming a (generous?) 10 year cycle life.  

So, this Tesla unit compares roughly to 6 of the 6V Surrettes, that cost $2k total just for the cells (but **may** have shorter service life) and that weigh 750 lbs.

--------------------------------------

The flip side, of course, is that it will not really pay to store off-peak power for peak usage, unless the differential is > > 13 cents/kWh.

I doubt these units will be marketed for that anytime soon. Leaves that sector to the utilities and Aquion (and teslas other storage product, price not revealed).


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## begreen (May 1, 2015)

Jeepman401 said:


> Southern climates?
> If used for a back-up, would you really worry about everyone getting 30 min showers a day and 3 meals out of the oven during the black out or would you like to keep the food in the fridg/freezer from spoiling?
> 
> No one said it would work for everyone, why is that always the deciding factor about renewables?


The deciding factor is that load size is limited to about 2.2Kw per pack. I just gave a couple examples of 240v loads that would exceed 2.2Kw. How one manages their house during an extended outage is their business. We run a generator twice a day to keep refrigeration going.


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## woodgeek (May 1, 2015)

Here is a thread from he NAWS solar forum:

http://forum.solar-electric.com/forum/discussion-forums-café/new-battery-technologies/338077-tesla-powerwall

Apparently the unit DOES have a 10 year warranty, and you can buy a 10 year extension.

While one module has a 2.0kW continuous rating, it has a 3.3 kW surge rating.  Sounds to me like it has an inverter built in.

And I am sure folks who want more power/energy will just buy more modules.

EDIT: they will be selling the inverters separately....


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## begreen (May 1, 2015)

Waiting for literature to see how it is wired to grid and solar input and what the options are.


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## Laszlo (May 2, 2015)

Looks like an attractive, no-maintenance solution for some specific situations. Should prove popular now for those living off-grid, or solar owners who aren't being fairly compensated for excess/anachronous  production by their utility. These groups may be tiny market segments currently, but the appeal will widen with lower costs later on (perhaps with the completion of Tesla's Gigafactory, next year...).

But even on-grid, without solar, I'd likely install a system within a few years to act as a whole-house UPS. PECO has the annoying habit of fixing the lines to our street last in any power outage, and aside from the hours-long power losses, we'll have glitches roughly monthly that reset the clocks and computers. Instead of spending thousands on an automatic backup generator like most of our neighbors already have, we could ride out most disruptions with a quiet, fuel-free battery.

For the users mainly keeping the batteries around as emergency backup power, I bet utilities would be interested in partially controlling the flow of energy to and from the grid. Musk _did_ say they'd be internet connected, and utilities have programs in place already like PECO's Smart A/C Saver, which allow them to reduce residential usage during times of peak demand. For a monthly discount (or a large utility rebate), I'd be willing to give up some capacity for PECO to tinker with and smooth out demand. With enough battery owners, utilities could retire their peaker plants and save a bundle--_without_ having to purchase and house megawatts of batteries for themselves.


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## jebatty (May 2, 2015)

> I bet utilities would be interested in partially controlling the flow of energy to and from the grid.


 Micro-distributed power through House/Business Batteries could be a win-win for utilities and for households and businesses with PV. This type of battery offers the opportunity for micro-distributed power which can be very effective and efficient, thus being a profit opportunity for the utility. It also can be very effective and efficient for homes and businesses seeking a cost competitive way to be free of the monopolistic utility. On the one hand, a means for utilities to sustain their monopolies and on the other hand a means for aggressive competition for monopolistic utilities. Some of both probably would make a better world than we now have.


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## Laszlo (May 2, 2015)

jebatty said:


> Micro-distributed power through House/Business Batteries could be a win-win for utilities and for households and businesses with PV.



For businesses, even those with no PV installed could save money. Besides avoiding any downtime (which can be extremely costly, depending on the business) there are also "Demand Charges" to contend with. As this Floridian dentist's story illustrates, the peak electric usage from a business can result in hundreds or thousands of dollars in surcharges, even if the surge only lasts 15 or 30 minutes in an otherwise quiet month. Additionally, even a once-a-year spike in usage could be enough to designate you as a Demand Charge customer for the next 12 months. With that sort of incentive, many commercial or industrial users will be interested in Tesla Power. Their battery storage could be set to recharge slowly during off-peak hours, then kick in at times of high usage and significantly reduce (if not eliminate) Demand Charges.


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## DougA (May 2, 2015)

Laszlo said:


> I'd likely install a system within a few years to act as a whole-house UPS.


You would have to install multiple units. 2 KW is what my Honda generator produces and it is barely enough to power my fridge, very small freezer and a few lights IF I am careful on hooking them up correctly.  It covers very basic needs in a power outage. 1.8 KW is one standard (bedroom - not kitchen) 120v circuit in a normal house. A 20 amp 120 v circuit (kitchen) is 2.4 KW.  The thought of utilities tapping in to the unit to help with power grid usage is a complete joke.


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## begreen (May 2, 2015)

Agreed. I suspect the average household would need 2-3 packs to assure backup power during a multi-day outage that also was during a cloudy or stormy period of no sunshine. And that still would require turning off heavy load breakers to assure adequate power for the essentials. Wondering if there is a provision for generator charging of the packs as well as solar and grid charging.

The amount of packs needed would also be determined by the location. After a big storm a 3-5 day outage is not uncommon for us due to our rural location and lots of trees + overhead wires. Where we lived in Seattle a 2-8 hr outage every 3-5 yrs. might be more usual if that.


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## Laszlo (May 2, 2015)

DougA said:


> You would have to install multiple units. 2 KW is what my Honda generator produces and it is barely enough to power my fridge, very small freezer and a few lights IF I am careful on hooking them up correctly.



Yeah, I don't envision roasting a turkey while running laundry with the house air on high. The published specs show the continuous power is 2.0 kW, with peak of 3.3 kW, so it basically fills in the role of my gas generator. Enough juice for phones, laptops, LED lights, the fridge, and a simple rice-cooker dinner. And presumably, if the Powerwall can store up solar output, it could also be charged by generator. Then no power goes to waste if you're forced to run one during a longer outage.

With the modular design, hopefully the delivered power can scale up with more units. It obviously must for the Powerpack batteries offered to utilities that can be linked up into Gigawatt-hour storage arrays. If thousands of homes within a utility's service area buy them and allow remote management, I don't see why the size of the individual cells matters. In aggregate they'd function like a utility-scale battery bank.


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## jebatty (May 2, 2015)

This discussion is informative and illustrates those who try to find reasons the Powerpack won't work and those who see how it can work. Agreed, many different situations for many different people. A person might assume correctly that Tesla put a lot of research in developing and sizing the Powerpack and believes that there will be a strong market with great potential. It would be very interesting to see that market research. As the Powerpack becomes available, it should become clear as to the niche that the Powerpack will fill, and who are the early adopters.


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## begreen (May 2, 2015)

I've already got a spot picked out for mounting one .


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## DougA (May 2, 2015)

Put me on the list of those who are highly skeptical of anything that is promoted with great fanfare.  I actually like Musk in that he has the guts to push ahead with things others won't.  However, the Tesla car has not been the success he envisioned, the stock is inflated with a lot of hot air and the battery factory and solarcity are built on huge gov't subsidies.  

I'd absolutely LOVE to cut my hydro line and be self sufficient but I will sit on the sidelines for this one until there is a solution that makes sense to me.


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## woodgeek (May 2, 2015)

You are welcome to your skepticism...I think this world could do with more of it.  I also get that a lot of people find Mr. Musk or hype not to their taste.  That seems to be business culture these days in the US/Si Valley. I agree that Tesla valuation is high, and completely speculative (based on very optimistic projected sales for the still just drawings Model 3).

l alternate between being a shameless fanboi and a critic (I think the IP thing is a stupid stunt, and their unique technology is BS).

As for govt subsidies....Tesla's original DOE loan was paid off in full, with interest in 2013.  The fed rebate on the Model S amounts to a 7% discount to buyers, which is a good bit less than Tesla's profit margin.  You could argue that the other EV makers are worse offenders re govt subsidy (on a $$ and %% basis). 

The Model S has been backordered for months or years since launch, as has been the Model X.  They are literally selling them faster than they can make them.  The car got award after award and high marks from customers and the ultimate in customer service. How is that not a 'success' by any measure??  They know how to find a niche and exploit it to make a profit.

The two powerwall products are targeting currently rather small and narrow niches....but I suspect they figure to make a profit at it.


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## DBoon (May 3, 2015)

The financial aspects have been discussed well by others, both pro and con.  $3500 for 7kW storage with a 10 year warranty is a pretty good deal, I would say.  It has good merits as an alternative to a generator for backup, and conceivably is at a price point that could permit far more people to decoupage from the power grid.  Having lived through two extended grid blackouts, seen firsthand what a crazy mess Hurricane Sandy created in the NY metro area, and routinely see power interruptions in my upstate NY home, I can say that I do not have much faith in the electric utilities to deliver what I would consider to be reliable service.  Alternatives (a reasonably efficient generator set with decent power quality) are expensive also, with their own disadvantages.  

Given that I have solar PV now, and will likely add another 4kW system in the future, this is pretty compelling for me to consider.   The next 4kW system could have an inverter that supported battery storage and inversion from DC to AC to power loads.  

However, realistically I would not consider this battery to be the "same" as installing your own battery backup.  I have read that Tesla will retain control over the storage.  Tesla expects to make money on these products not in the gross profit on the hardware, but the retention of the rights by Tesla to control the Powerwall to optimize aggregate storage capacity.  California has mandates to add huge amounts of storage to the grid, and various products and industries are vying to supply that storage now.  These mandates will likely increase and expand into Hawaii (high solar penetration) and New York (grid reformation initiatives).  Tesla could conceivably make far more money supplying and controlling storage in the electricity market than they can by selling hardware. 

So this is pretty cool, a good step in the right direction, and good for some people.  Personally, by the time I expect to take the plunge on an additional 4kW array and battery storage (4-5 years out), I expect more choice and the ability to retain the rights to use my storage as I see fit.


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## begreen (May 3, 2015)

Minor correction. The 7KW pack= $3000, 10KW pack=$3500. Besides the questions asked about how it interconnects with existing inverters and aux generator charging option, it would be helpful to understand the circuitry that lets it island the house from the grid. I also want to know how it would affect existing grid-tie contracts. This is bound to vary from state to state. In the event of a power outage is the transfer to the battery pack instant and automatic? What if there are high loads running at the time of outage like a range, hw, etc.? My guess is that one would want some sort of sub-panel to tie in and route the emergency power required loads. Not sure.

At $3500 + some wiring rework costs this could be interesting if it not only provided some nighttime power, but also provided several day power outage insurance for refrigeration. We store a lot of food in a freezer and have two refrigs going as well so that would be our primary need.

FYI, rereading the specs and I see they say: "DC-AC inverter not included." If so this sounds more like it sits on the solar panel side before the inverter. It sounds like one would still need a 3d party solution like a Sunny Island inverter/charger for robust power backup. Not sure how they plan to defeat the grid voltage sensing though. That should shut the system down instantly if there is a power outage which would defeat its value for us. What I want is a solution that allows the system to automatically disconnect from the grid during an outage, but continue on battery power with solar charging during the day. This system may not do that without at least doubling the cost. The more I look into this the more I am starting to side with the skeptics.


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## woodgeek (May 3, 2015)

My guess is that the two products will have different interconnect architectures to your panel.  Maybe the 10 kWh unit(s) act like an automatic backup genny (and have its own inverter), and would be wired in the same way with an interlock, and the 7 kWh system would steal/donate DC to the solar side (before the current inverter) and have a DC-DC converter to allow usage with a wide variety of PV string voltages (but not microinverters).

This would be contra DBoon's idea.  If the above were true, the 10 kWh unit could be set up to do demand shaving (and has cycles to spare, so to speak), while the 7 kWh system would be dedicated to solar buffering (i.e. not connecting to grid AC directly)???


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## Jeepman401 (May 3, 2015)

As I suspected... It sounds if you have a SolarEdge system, you may in fact already own the inverter. SolarEdge inverters already meets NEC Rapid Shutdown and is IEEE1547 & UL1741 approved. I am hoping they have a simple wire kit and software upgrade that will allow the Tesla battery to operate with Solar Edge...one reason I went with SolarEdge instead of Enphase.

*SolarEdge*
SolarEdge, a leader in the global PV inverter market, and Tesla partnered for the joint development of a PV storage and backup power solution for the worldwide residential solar market. Building on SolarEdge’s proven DC optimized inverter proven and Tesla's leading automotive-grade battery technology, the solution will require only a single SolarEdge inverter to manage both PV and storage functions. The system is designed for efficient, outdoor installation and includes remote monitoring and troubleshooting to keep operations and maintenance costs low.

Founded in 2006, SolarEdge provides an intelligent inverter solution that has changed the way power is harvested and managed in solar photovoltaic systems. The SolarEdge DC optimized inverter system maximizes power generation at the individual PV module-level while lowering the cost of energy produced by the solar PV system. Since beginning commercial shipments in 2010, SolarEdge has shipped more than 1.3 Gigawatt (‘‘GW’’) of its DC optimized inverter systems, including over 220,000 inverters, its products have been installed in PV systems in more than 73 countries, and more than 100,000 systems are monitored in its cloud-based monitoring portal.


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## Jeepman401 (May 4, 2015)

http://www.aurora-energy.com/solar-edge-optimized-battery-backup-solution/


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## woodgeek (May 6, 2015)

Well, some more news re the PowerWall....

1. SolarCity has stated that it will not be installing the 7kWh system, but will instead offer its own off-grid system in the near future.  Snub!

2. SolarCity will install the 10 kWh backup system to interested customers for a $7100 installed, or leased for $5k.

http://www.bloomberg.com/news/artic...new-battery-doesn-t-work-that-well-with-solar

3. The backup unit and the 100 kWh PowerStack grid storage system (for $25k) are 'sold out' through next year, anticipated production is already booked.


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## Cynnergy (May 6, 2015)

100 kWh for $25k is interesting to me!  Wonder what that is in Cdn$.  Much more no doubt.


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## DBoon (May 8, 2015)

Yep - the Bloomberg article says that Tesla is selling batteries at a loss, and they won't sell the 7kWh battery at all.  No doubt, the 7 kWh and 10 kWh battery are just the same battery but with different ratings for discharge rate and number of cycles.  Therefore, they make $500 more on the 10kWh battery.  But that doesn't even allow them to turn a profit, so the real price is $7140 purchase or $5000 lease.  Why the discount on the lease?  Likely so that they can retain the rights to control the storage capability and make money off of that. 

Yawn.  I'll check back in 3-4 years.


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## woodgeek (May 9, 2015)

DBoon said:


> so the real price is $7140 purchase or $5000 lease.



That price is with installation and inverters, and not a direct reflection of Tesla's loss.


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