Tesla announces "Powerwall" batteries

[Willy T]

Maybe people like Tesla will come up with something that is very cost effective on a much larger scale used by the POCO at specific grid points to smooth out the variable voltage fluctuations and outages caused by RE. .

They can, how much are you willing to pay ?? If RE is causing the problem then PV owners should be willing to pay for it, Right ?? They'll be glad to take your money.

[SunEagle]

They can, how much are you willing to pay ?? If RE is causing the problem then PV owners should be willing to pay for it, Right ?? They'll be glad to take your money.

If PV owners are part of the cause for grid power fluctuations or can benefit from POCO stored energy then they should take some responsibility for paying to have it place.

I am sure the POCO will raise their rates to cover the cost of a battery system due to weather the RE system belongs to them or private individuals.

I believe CA has already put through a mandate for certain POCO's to have XX MWatts of energy storage in place by 2020. So their customers will be paying for batteries even if they don't have PV systems.

Of course the amount of the tariff increase may be conditional by how much competition the POCO has from privately owned RE systems. They would like to have total control of all power generation. It is in their blood.

[Amy@altE]

First, I am a novice when it comes to designing solar systems and battery banks so please bear with me as I am in the initial phases of designing my totally off the grid home. Nonetheless from my understanding, basic electrical calculations are as follows:

Watts = Volts x Amps
Amps = Watts / Volts
kWh = (Amp x Volts) / 1000

Amps = Amount of current in a circuit
Volts = Strength of current flow
Watts = Total electrical power per second

For this post I'm going to make an assumption that I'll be using 20 kWh per day for calculations sake. From that I can calculate amp hours used per day per input volts.

20,000 / 120v = 167 Amps / day (Normal Utility Voltage)
20,000 / 48v = 417 Amps / day (48VDC Battery Bank)
20,000 / 350v = 57 Amps / day (PowerWall)

Obviously you're going to need an inverter capable of handling a 350V input voltage to use the PowerWall. I've seen them but their pricey (starting around 10K). In addition you'll need a charge controller capable of handling an input voltage of 350v as well - have not run across any of those for home use but I'm sure they're available. (i.e. I would think that utility scale solar farms have controllers capable of handling high voltages). I would also think that you would have to wire your solar array to provide the higher input voltage required of the PowerWall.

Another point of confusion (for me) is on the consumption side of things. I would think based on the calc's at the beginning of this post that amps used by a particular appliance falls as voltage increases.

For example, let's say you have an appliance rated at 1000 watts - that would seem to indicate the following:

Watts / Volts = Amps =

1000 / 48 = 20.8 amps with a 48V Battery bank
1000 / 120 = 8.3 amps at normal household voltage
1000 / 350 = 2.85 amps with a PowerWall

So based on my understanding you would need at least 3 PowerWalls to supply 20kWh per day and that's at almost 100% DOD (which I don't think is feasible even for a LiON battery). Additionally you have no days of autonomy with the scenario above and the real kicker is that I would think you're probably going to shell out close to 25K before you even get to the solar array side of things.

For the sake of comparison a conventional FLA or AGM 48V battery bank would cost about 9K for 1200 amp hours or roughly 58kWh (1200 x 48) / 1000 = 57.6). So if I have this correct, from just the battery bank perspective you're shelling out 9K for 58 kWh as opposed to 9K for three PowerWalls at 21kWh.

As I said above I'm still a novice so if anyone finds fault with my calc's and assumptions please feel free to reply.

Thanks in advance

You are making the common mistake of confusing watts and watt hours. So for your equations above, you need to add time into the math.
Watts = Volts x Amps
Amps = Watts / Volts
kW = (Amp x Volts) / 1000

Watt hours = Watts x hours
kWh = Wh x 1000


For your 1000W appliance; how long is it running? 1 hour a day?

Watts x hours / Volts = Amp hours =

1000Wh / 48V = 20.8 amp hours with a 48V Battery bank
1000Wh / 120V = 8.3 amp hours at normal household voltage
1000Wh / 350V = 2.85 amp hours with a PowerWall

But to normalize the voltage across the technologies, people have been using watt hours or kWh to describe the batteries, so voltage is irrelevant. Notice the watt hours in your examples are the same, all 1000Wh (or 1kWh). So to run that 1000W appliance for 1 hour, you need 1kWh, so you can run it for 10 hours with the 10kWh PowerWall (at 100% DoD, which you wouldn't do)

[Amy@altE]

Joe Homeowner should use the Grid as their battery.

Amen brother.

[RoadGlide]

You are making the common mistake of confusing watts and watt hours. So for your equations above, you need to add time into the math.

Thanks for the reply - and I completely understand the necessity of factoring in time of use. I just want to make sure my assumptions are correct - i.e. that amperage goes down as volts increase.

Also, that I would have to wire my solar array to output at least 350v to be able to charge a PowerWall if I chose to go that route.

Thanks again for the reply

[Amy@altE]

Thanks for the reply - and I completely understand the necessity of factoring in time of use. I just want to make sure my assumptions are correct - i.e. that amperage goes down as volts increase.

Also, that I would have to wire my solar array to output at least 350v to be able to charge a PowerWall if I chose to go that route.

Thanks again for the reply

The inverter manufacturers who are working with Tesla are making the inverter/charger one component. Currently, SolarEdge has you use their optimizers to input 350V from the array to the inverter. StorEdge (as it will be called) will treat the battery bank as an optimized PV string.

I'm not sure of the details of how Frounius will be handling it.

[SunEagle]

The inverter manufacturers who are working with Tesla are making the inverter/charger one component. Currently, SolarEdge has you use their optimizers to input 350V from the array to the inverter. StorEdge (as it will be called) will treat the battery bank as an optimized PV string.

I'm not sure of the details of how Frounius will be handling it.

They will probably call it StorFroun.

[RoadGlide]

The inverter manufacturers who are working with Tesla are making the inverter/charger one component. Currently, SolarEdge has you use their optimizers to input 350V from the array to the inverter. StorEdge (as it will be called) will treat the battery bank as an optimized PV string.

I'm not sure of the details of how Frounius will be handling it.

I understand that as well - however when I visited SolarEdge's website couldn't find any meaningful info. Perhaps it's still a bit early in the process as Tesla just announced the PowerWall.

I appreciate your help - thank you

[Sunking]

The $7000 includes the inverter, obviously you'd need one regardless of which type of battery, and installation and maintenance. Figure at least $2k for the inverter, probably closer to $3k, and I can see where the $7k comes from. But I did the math, the price per watt for just the 7kWh battery is about the same as Aquion's stack, and 2X as much as the Trojan Industrial line and some AGM batteries.

Amy you need to read the latest from the shyster. You can buy the battery outright for $7000.

[Amy@altE]

Amy you need to read the latest from the shyster. You can buy the battery outright for $7000.

Right, my point, “For a 10 kilowatt-hour system, customers can prepay $5,000 for a nine-year lease, which includes installation, a maintenance agreement, the electrical inverter and control systems. Customers can also buy the same system outright for $7,140, Bass said.”

So $3500 for the battery + $2000 for the inverter = $5500, leaves $1640 for installation and maintenance agreement.

[Amy@altE]

They will probably call it StorFroun.

I wish! It's the Fronius Symo Hybrid. Doesn't quite roll off the tongue.

[Sunking]

http://www.teslamotors.com/powerwall just says "10 years". Since they haven't claimed DoD yet, people are making guesses (I've seen 70%, 80%, and "it's really a 12 kWh battery

Wrong it is 400 volt @ 25 AH.

If used off grid to be equal with a FLA you only discharge 33% per day vs 20% per day with FLA. Tesla claimed warranty is undefined. Its talk, no teeth, and absolutely no third party test data. Very few Lithium batteries have passed the IEC 61427 test protocol. Very few even dare to submit.

Find the manufactures who subscribe to 3rd party testing, use IEC 61427 like Trojan and a few others have. IEC 61427 is a brutal test protocol using real life parameters for Solar Deep Cycling., The test results strongly indicate the Trojan Industrial line are good for 15 years operating to 80% DOD daily cycling. Not many in that price range can touch those results. Even Trojans lower Premium Line test results indicate 8 to 9 year battery. Tesla would not dare dare to submit to the testing.

But if you really want to see who the Big Bad Boys are in battery long life look no further than Sandia National Lab Testing using IEC 61427. No Tesla to be found. On the Pb side you have East Penn Ultrabattery, Furukawa Ultrabattery pushing 15,000 cycles. On the Lithium side you have Altairnano Titinate at 40K, and International at 20K cycles.

Show me the test data and I will believe Tesla and that ain't going to happen. Until than forget it. Panasonic who makes Tesla batteries will not submit to the test. You can believe BS talk, not me it walks.

[Amy@altE]

Just found this for the Euro version of the Fronius Symo Hybrid. http://www.fronius.com/cps/rde/xbcr/...1_snapshot.pdf

[Sunking]

Thanks for the reply - and I completely understand the necessity of factoring in time of use. I just want to make sure my assumptions are correct - i.e. that amperage goes down as volts increase.

Also, that I would have to wire my solar array to output at least 350v to be able to charge a PowerWall if I chose to go that route.

Not gong to happen. Tesla battery uses standard 240 VAC @ 50 or 60 Hz to charge the battery. That does not come from solar panels directly. That comes from the utility or in a round about way a grid tied system for which you have no use for a battery. FWIW it takes a 450 volt source to charge a 400 volt battery.

[bberry]

Not gong to happen. Tesla battery uses standard 240 VAC @ 50 or 60 Hz to charge the battery. That does not come from solar panels directly. That comes from the utility or in a round about way a grid tied system for which you have no use for a battery. FWIW it takes a 450 volt source to charge a 400 volt battery.

I bet they are more clever than to only allow AC charging. Perhaps reconfiguring the pack in solar charge mode to halve the needed DC voltage.