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Tesla launches line of Li-ion stationary storage systems for homes and businesses: POWERWALL and POWERPACK

Multiple POWERWALL units may be combined. Click to enlarge.

As widely expected, Tesla CEO Elon Musk unveiled the company’s new product line: scalable stationary battery systems for homes, businesses and beyond. Available for immediate order on the Tesla Web site ( or is the modular wall-mounted POWERWALL system, which is targeted at homes and perhaps some small commercial applications, Musk said. Delivery is projected for sometime later this summer (3-4 months from now.)

The sleek, sculpture-like Li-ion packs come in 7 kWh ($3,000) and 10 kWh ($3,500) configurations. Both are guaranteed for 10 years (with an optional 10-year extension), and can be combined to up to 9 units—i.e., up to 90 kWh of storage. The packs contain all the integrated safety systems, the liquid thermal control and the DC/DC converter, and work with solar systems straight out of the box, Musk said.

Tesla POWERWALL unit. Click to enlarge.

Round-trip DC efficiency is 92%, power output is 2 kW continuous, 3.3 kW peak. Voltage is 250-450 volts, with 5 amp nominal current, 8.5 amp peak output. The POWERWALL units are rated for indoor or outdoor installation, and operate in the range of -4°F to 110°F / -20°C to 43°C. The POWERWALL requires installation by a trained electrician; the AC-DC inverter is not included.

The 220 lb (100 kg) unit measures 52.1" x 33.9" x 7.1" (130 cm x 86 cm x 18 cm), and comes, noted Musk, in different colors.

The fact that it is wall-mounted is vital. You don’t need a battery room filled with nasty batteries. A normal household can mount these in the garage or outside the house.

—Elon Musk

The POWERWALL units will initially be assembled at the Fremont plant, Musk said, and the ramp will be slow. a plans to transition production to the GigaFactory in Nevada next year, resulting in a higher ramp.

For larger scale systems, Tesla is proposing the industrial POWERPACK, which, Musk said, is “designed to scale infinitely. This could be a GWh solution.” Musk said that a Tesla is already working with a utility that wants to do a 250 MWh pilot. (The entire evening livestream event was powered by POWERPACKs.)

At the conclusion of the streamed announcement, Musk said that solar panels and batteries represented “the only path I know” that could transition the world to sustainable energy. He suggested that 2 billion POWERPACKs could fully transition the world to a solar/battery future, and observed that it is “within the power of humanity to do so.


Account Deleted

A found a link to a news peace confirming that the batery chemistry used in Tesla's powerwalls and powerpacks is not the same as the one used in the Model S. However, no specifics about what type of chemistry and who delivers them. I can only speculate that Tesla sticks with the 18650 form factor and perhaps is still using Panasonic for those other types of cells. The prices that Tesla charges for the batteries is the best evidence yet that Tesla's costs at the cell level must be in the 200 to 250 USD range per kwh which is much better than all of Tesla's potential competitors for energy backup.

Teslas backup batteries are already sound economic business in places where electricity prices are high or where there are large fluctuations in prices from peak to non-peak demand such as Hawaii, Califormia, Italy and Germany. As renewable energy is expanding further globally there will be even more daily fluctuations in elctricity prices on the grid in more places and this will drive the sales of Teslas backup batteries.

This year 50 GW of solar power will come online globally costing 150 billion USD or 3 USD per installed watt. Practically none of this capacity is delivered with energy storage which would add about 1 USD per Watt to the cost of solar power. By 2030 we can expect solar and battery backup to cost 50% less so about 2 USD for solarpower and daily battery backup per installed watt and therefore a total cost of residential electricity at about 10 cents per kWh (as each installed watt delivers about 20kWh during its 20 year life). In 2030 I expect the global solarpower and battery backup business to be a 500Gw per year business or 1000 billion USD per year. For comparison the global oil industry at 90 million barrels per day at 55 USD per berrel is a 1800 billion USD per year industry. However, in 2030 I expect this oil industry to be in rapid decline as self-driving battery electric taxis and trucks are at full speed replacing the globel fleet of vehicles that operate on gasoline and diesel. We simply do not need to burn fossils in the future.


Since I do not live in America I was not about to get involved in the arcanae of investigating peak and off peak rates in various regions of the US, and left it to those who claim cost savings to show them, which you have not done so far.

However, here is some analysis from someone who is, presumably, American:

'The tiered system that California uses - and that you describe above as the basis for your argument, makes it impossible to significantly arbitrage rate differences using batteries. If you're in tier 1 then you pay $0.15/kWh to charge a battery, then save $0.15/kWh when the battery discharges. If you're in tier 4 you pay $0.31 to charge and save the same on the discharge. There's no immediate benefit at all. And of course there is charging inefficiency and battery cost that actually produce a significant penalty for the poor saps who buy these things.

Note that HI uses a tiered system similar to CA:

No incentive for batteries there either.

There are places where the rate difference between peak and super-off-peak approaches $0.1/kWh. But assuming the 7 kWh battery (the one rated for daily use) actually delivers 5 kWh/day (15% - 85% charge/discharge range) at a savings of $0.1/kWh, the annual savings is a whopping $180 excluding cost and maintenance of the ~$7000 battery. Not financially viable. Not even close.

Simple fact: There is no legitimate business case for batteries in residential use based on storing electricity.'

So I await your detailed costings to show where the error is in the above if you wish to claim financial viability.


Link here, if I have managed to make it work properly:

Davemart, I've shown my numbers clearly enough. The example you posted shows that the original author either wildly misunderstands the proposition or is simply spreading disinformation.

Correct, there is no cost savings under a tiered rate plan. That's not the application.

The opportunity for arbitrage is under a Time of Use rate plan. The delta is not $0.1, it is $0.31-$0.34 in the high rate utility areas I am familiar with, California and Hawaii.

Whether buying off-peak grid power or using your own generated solar power after the sun goes down, these systems are cost effective.

As Henrik points out, they will become even more cost effective over time as battery prices come down 8% per year, and utility rates go up 5% or more per year.

A lot of companies are going to make these systems, not just Tesla. But whoever makes them competitively is going to need a very large battery factory.


Here are the calculations for I live in Melbourne, Australia.

Cost to install 5 KW solar power system = AUD$ 6700.00
(Full quote from reputable dealer who has been in business for over 5 years).

Melbourne has 4.24 KWHr/m^2/day
Generation per year = 5*4.24 = 21 KWHr/day = 7700 KWHr/year

Average residential cost for electricity = $0.25/KWHr

My annual cost per year for electricity consumption = $2000.00

Cost of 3* 7 KWHr systems = 3*4000/0.8 = $AUD 15,000
(This assumes a significant break in installation charges since I'm doing 3 module install and I.m building my new home)

Total cost = $AUD 21,500

Annual electricity savings of ~$1,600 (unavoidable charges with spikey demand and connection costs to the grid)

So overall a payback period of ~15 years. On the other hand I get totally reliable power 24/7 plus the feel-good fuzzies of avoiding brown-coal generated electricity and keeping windmills off our beautiful coastline :-)

A factor-of-2 reduction in cost would make it a complete no-brainer here.


Mahonj, this sort of battery storage system should work in emergency grid failure, with or without a rooftop solar array. Households may not be able to power all appliances, nor continue routine long-distance driving, but a limited backup power system would save lives.

Let's say a grid failure continues for weeks/months. Households with a plug-in hybrid also have the option of burning any available fuel to recharge both the stationary battery pack and the similarly small (5kwh) pack in the car. The wise household uses electricity frugally.


Some have questioned the lack of an inverter. I think this is meant to be used with a PV system, which will have its own inverter (those with micro-inverters are out of luck).

The economics of this using PG&E E-6 TOU rates would be: charge 7 kWh at 90% AC-DC conversion efficiency and 92% battery efficiency is 8.5 kWh x 13.1¢/kWh = $1.11. Return power to grid at 95% DC-AC inverter efficiency = 6.65 kWh x 13.1¢/kWh = $2.15. Profit is then $1.04/d. Breakeven is then 2885 days (again not counting time value of money), or 7.9 years.

These things are no where near big enough to provide backup power for a house (a few lighting circuits and a refrigerator could be powered in a blackout if your home were wired just right), or to enable off-grid operation, which is why I calculated its utility for load-shifting, but it doesn't appear to be that cost-effective at that either (especially if you were to include the time value of money).

Robert Haylar

As earlier stated by another poster, the matter does not concern home storage and generation in general, nor inverter costs, but just the Powerwall's contribution towards the aim.

The Powerwall's storage is too low, and so is its power output. Figures are amusing. Taking the given dimensions, the energy density is 50Whr/litre. Power density is a laughable 10W/litre.

Those results are, in part, due to the use of a large number of small cells. Tesla were by no means the first to see the cost advantages of using bulk commercial cells to make packs - but that approach has its limits. Cost of assembly and battery volume are large. In the car, that worked out because a very expensive and high performance vehicle was wrapped around the battery.

The employed NCA cells have both high power and high energy density, but one can't be divorced from the other, and that can lead to unhappy combinations of storage capacity and power output. Cells must be arranged in series and parallel strings, dictated by the 18650 format.
NCA is great for a performance car, but not storage.
18650 is great for portable applications, but otherwise, a millstone.

Telsa need that specific NCA cell, or they have nothing, and new cells are becoming a threat.

But, is the Powerwall useful? I doubt it. Volume sales are necessary to success, so one should use general numbers, and not those that flatter. The US is the current market.

Average household consumption: 900kWhr/month.
Average tariff: $0.12kWhr
Average monthly bill: $108

Battery capacity: 7KWhr.
Maximum storage over 1 month ( 100% daily cycling); 7kWhr*30days = 210kWhr

Percentage of total household consumption; 210kWhr/900kWhr = 23.3%

Monthly bill reduction assuming the 210KWhr is free;
$108*.233 = $24

It would take a long time to get the $3000 battery cost back, even if the energy supplied to it were entirely free and without additional capital expenditure.

Robert Haylar

By the way, I realise that the average tariff does not fully reflect the difference between high and low tariffs which the battery is said to exploit.

As far as I can ascertain, other than exceptional cases such as Hawaii, the night tariff is typically 2/3 of the daily tariff. I doubt that difference would better my assumption that the stored 7kWhr were free.

In most of California, the peak/off peak delta is between $0.31-$0.34 kWh.

This appliance won't make sense for everyone day one.

Follow the trend line for utility rates. Then for solar and batteries.

One goes up. The other goes down.

Handwriting is on the Powerwall.

Robert Haylar

Well, the above says nothing about how the Powerwall suddenly makes the difference. But...

From the E.I.A:
Avearge monthy household consumption: 557/Kwhr
Average tariff: 0.1619/kWhr
Average month bill: $90.19

From Southern California Edison;
Lowest tariff; $0.11/kWhr
Highest tariff: $0.46/Kwhr ( summer only)

It's worth noting that the average price paid is closer to the lowest tarrif, that the highest.

Remember that the battery's sticker capacity is 7kWhr, but in the interest of cell life, depth of discharge will be 80% ( battery software will ensure that it is)
Then, there are battery,charger and inverter losses. Say,10%

Practically, the battery will output around 5kWhr - at least some of its claimed 10 year life.

I will leave it to you to show how you can make a return on the $6000 investment made in the battery
and inverter.

I calculate that you can save no more than $500 per annum, even in this case where the tariff differential is large.

Some advice: Don't go on vacation in the summer (or any other time), or you will miss the opportunity to 'save'. Also, ensure that you don't demand more than 2kW from the battery, and be at home during the day so that you can discharge the battery when the tariff is highest. Elron Musk will thank you for that.

Robert Haylar

For those still following:

Answering a question about a SolarCity spokesperson saying that the Powerwall doesn’t really make sense for most homeowners yet, Musk stated:

“For the specific case of SolarCity, what they’re referring to is that, there’s two version of the Powerwall — there’s the daily cycling version, and there’s the Powerpack version. One’s energy optimized and one’s daily cycling optimized. For the daily-cycling-optimized one, the economics is true in the US, with rare exception, are more expensive than utility.

So, if somebody wants to do daily cycling — basically, go off grid — it’s going to be more expensive than being on grid.

“This doesn’t mean that people won’t buy it, cause there are people who want to go off grid on principle, or they just want to be independent. That’s what the SolarCity comment is about."

I am not any happier about that, than those who believed.

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