Tesla Powerwall, The Specs, Numbers, and Implementation Absolutely Brilliant

[bberry]

Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.

With new construction you will be able to do a very nice solar install. Storage choices really are not relevant at your stage of planning, except to get a rough estimate of cost. In a new house I would do a budget set of batteries for the initial purchase. That would have you making the choice of a better battery system after 2020. If utility scale storage does "take off", there will be some really nice choices for off grid storage in five years.

[Sunking]

A 9 KW array capable of generating 1200+ kWh per month (40kWh per day) with a 1200 amp hour battery bank will set me back about 35k before tax credits.

I can only assume you are thinking 48 volt battery with two 80 amp charge controllers. A 1200 AH battery is a bit to small with 9000 watt panel. You would be adding water weekly and splashing electrolyte everywhere. You cannot replace electrolyte and that destroys the battery. Minimum size required is 1500 AH, and that only gives you 14 Kwh per day usable.

[Sunking]

A 9 KW array capable of generating 1200+ kWh per month (40kWh per day) with a 1200 amp hour battery bank will set me back about 35k before tax credits. Another 5k for a generator and I won't have to worry about cloudy days. In other words I could install an off grid system w/ generator backup for about 30k after tax credits i.e. half of what the utility company wants just to bring power to my house.

What tax credit?

[RoadGlide]

Do you understand what off grid life style is?

Most think of off grid as a direct replacement for grid connect, its not really,

Grid connect gives you as much as you need whenever you want it unless there is a power failure,

Off grid gives you some of the power some of the time, you stress over what you can use when.

Off grid you generally dont have electric kettles, toaster and cant just light up the workshop and do a bit of welding or run a compressor anytime.

Think carefully about the lifestyle you want to lead then way up the pros and cons of grid or offgrid.

Have thought carefully about going totally off the grid. Right now I use about 23 kWh per day in a house that is not nearly as efficient ( all electric appliances etc.) as the one I am designing which will incorporate gas fired appliances (dryer, oven, water heater, radiant heat, etc.)

A 9 KW array capable of generating 1200+ kWh per month (40kWh per day) with a 1200 amp hour battery bank will set me back about 35k before tax credits. Another 5k for a generator and I won't have to worry about cloudy days. In other words I could install an off grid system w/ generator backup for about 30k after tax credits i.e. half of what the utility company wants just to bring power to my house.

Of course I won't be able to fire up a tig welder in the middle of the night (If I needed to I could always fire up the generator). However I don't see any issue with using it during the day as the above array should be able to provide the necessary power while at the same time still charging my battery bank.

[silverhorsefarm]

used with GTI

I think I know the answer, but will this battery with an inverter allow GTI to stay on in the event of a power outage?

[organic farmer]

Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.

When we were shopping for land, most properties I looked at were like that.

In the end we decided to live 'in-town', so hooking up to the grid was cheap. Now we wish we could go more than a week at a time with continuous power.

[Bala]

Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.

Do you understand what off grid life style is?

Most think of off grid as a direct replacement for grid connect, its not really,

Grid connect gives you as much as you need whenever you want it unless there is a power failure,

Off grid gives you some of the power some of the time, you stress over what you can use when.

Off grid you generally dont have electric kettles, toaster and cant just light up the workshop and do a bit of welding or run a compressor anytime.

Think carefully about the lifestyle you want to lead then way up the pros and cons of grid or offgrid.

[RoadGlide]

Once you understand the economics and what you are asking for you might care, and care a lot.

Buying power from the utility toady's average is about 12 cents for all you can possible waste and want. In TX the more you use, the less expensive it gets down to 6-cents per Kwh.

You wanna go-off-grid with batteries? Nothing will make your battery supplier happier. For Pb (lead acid) batteries just in battery cost alone, no equipment, you are looking at 55 to 75 cents per Kwh in a very limited daily supply.

Want the convenience of lithium? You battery man is really going to fall in love with you. You now get to pay $1 to $2 per Kwh.

So tell me which price would you pay for a Kwh?

12-cent
55 to 75-cents
$1 to $2


Does it matter what it cost now?

Understand exactly what you're saying Sunking, however understand that I own 10 acres in northern California and the utility company wants close to 60K just to bring power to the house I have planned. That makes solar and commensurate battery's much more attractive not even considering tax credits.

[Sunking]

However if money was not necessarily the object I'd rather hang 6 of these units (which from my understanding are basically maintenance free) as opposed to having a huge bank of FLA's and the commensurate maintenance.

Once you understand the economics and what you are asking for you might care, and care a lot.

Buying power from the utility toady's average is about 12 cents for all you can possible waste and want. In TX the more you use, the less expensive it gets down to 6-cents per Kwh.

You wanna go-off-grid with batteries? Nothing will make your battery supplier happier. For Pb (lead acid) batteries just in battery cost alone, no equipment, you are looking at 55 to 75 cents per Kwh in a very limited daily supply.

Want the convenience of lithium? You battery man is really going to fall in love with you. You now get to pay $1 to $2 per Kwh.

So tell me which price would you pay for a Kwh?

12-cent
55 to 75-cents
$1 to $2


Does it matter what it cost now?

[RoadGlide]

Almost any grid tied inverter is capable of 350 V. The SolarEdge inverters that will be used with the Powerwall (per press reports) actually run at 350 V nominal. A 3 kW SolarEdge inverter costs a bit over $1k. The inverter will probably handle the charge controller function, or it will be built into the Powerwall itself. No reason to believe a standalone controller will be required.

Off-grid is not the target market for this.

That much I understand, and I know the PowerWall is not necessarily intended for "off the grid". However if money was not necessarily the object I'd rather hang 6 of these units (which from my understanding are basically maintenance free) as opposed to having a huge bank of FLA's and the commensurate maintenance.

Like I said, I'm still learning.

Thanks for pointing me at grid tied inverters. I hadn't even thought of that. I'll have to research that approach as I have seen grid tied systems with battery backup so I would think that you could use such an inverter off grid as well

[sensij]

Completely understand that I've got a lot to learn, however I would think that I would need an inverter capable of handling 350v input voltage as well as a charge controller capable of handling a solar array wired to push out at least 350v

Almost any grid tied inverter is capable of 350 V. The SolarEdge inverters that will be used with the Powerwall (per press reports) actually run at 350 V nominal. A 3 kW SolarEdge inverter costs a bit over $1k. The inverter will probably handle the charge controller function, or it will be built into the Powerwall itself. No reason to believe a standalone controller will be required.

Off-grid is not the target market for this.

[RoadGlide]

You've got some more to learn about charge controllers and inverters. That aside, your basic conclusion is correct. There are much less expensive options than the Powerwall for someone who wants to take 20 kWh daily off grid.

Completely understand that I've got a lot to learn, however I would think that I would need an inverter capable of handling 350v input voltage as well as a charge controller capable of handling a solar array wired to push out at least 350v

[sensij]

You've got some more to learn about charge controllers and inverters. That aside, your basic conclusion is correct. There are much less expensive options than the Powerwall for someone who wants to take 20 kWh daily off grid.

[RoadGlide]

First, I am a novice when it comes to designing solar systems and battery banks so please bear with me. 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 a "totally off the grid" user uses 20 kWh per day for calculations sake. From that you 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 rewire (and or augment) your existing 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 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 so please feel free to reply.

Thanks in advance

[donald]

As far as the $7000 price, consider the install on a typical existing system. There needs to be a grid disconnect, and also branch circuit control. Either an ethernet cable needs to be run, or a wireless adapter installed. Most people should probably add a generator connection too. So I can see $7K, especially at first when there is no direct competition. Early adopters are going to pay full retail on all the work and parts involved in a complete installation. That is just how it is when demand exceeds supply.
Simply installing powerwalls for California Tesla owners should keep solarcity electricians busy for a year.
Each additional Powerwall should cost considerably less than $7K.