Powewall battery by Tesla

[electro7]

Hi,

I was wondering if I could get some thoughts on the new Powerwall battery by Tesla?

I was wondering if anybody knew if the 10kwh rating means it can provide that without 100% discharge and damaging the battery? Ive heard people saying that it will be able to charge during the night and then discharge to meet the load during the day without receiving power from the grid. I am thinking that this type of control must be within the inverter and not the battery. Does anybody know?

Anybody know what model inverter is compatible with this battery yet?

 

[mkgrady]

It can output at a rate of 2kw based on what I read. So at best that would be for five hours and I would assume less. I would not expect that it would charge off the grid. Why would you want to charge a battery off the grid. Charging the battery from solar or wind makes more sense.

 

[winnie]

Charging off the grid at night makes sense if there is lots of underutilized base load capacity.

Charging off the grid also makes sense if you are using the batteries to support grid stability.

Of course this all depends on your grid being smart enough to tell the battery control system just when there is excess power and when there is excess demand.

-Jon

 

[electrofelon]

There has certainly been lots of buzz about this, but I really think much of it is nonsense - at least for residential use. I didnt read/hear the official announcement/press release so maybe Im off base in their claims, but most secondary sources are talking about this battery being in homes. I guess there are some markets that have time of use rates and demand charges for residential accounts (parts of California come to mind), but as far as I know that is the exception not the rule currently. I understand the need for grid stabilty, peak/off peak balancing etc, but without the utility offering an incentive for homeowners to buy batteries, I dont see any logical reason to buy one.

 

[jaggedben]

Details on the specs and features were lacking in the official announcement. I gather there's no inverter, so it is just a battery pack, perhaps with a built-in charge controller. If so there are other lithium battery packs and charge controllers on the market, so it's not clear what's new or special here. As I commented on Facebook where all my friends are 'liking' it, if you're not the sort of person who would buy a Tesla brand EV, you're probably not the sort of person who needs a Tesla brand home battery.

 

[ggunn]

Tesla batteries might be a good solution for folks who are already living off grid. I haven't seen any numbers yet comparing their price per Watt-hour with lead acid batteries or the number and depth of discharge they can handle.

For folks with a dependable grid connection at ~10 cents per kWh I don't see any reason yet to run out and buy one.

 

[ron]

In my home, I sell excess solar PV that I generate back to the utility at the same rate I buy it, and I pay the same ~15 cents per kWh, so it doesn't make sense in my application (and other similar).

The cost of the battery is exorbitant and then I would be charging from my same 0.15/kWh that I would sell back anyway, never mind the losses in the conversion from AC to DC for charging, than back to AC for use.

 

[jaggedben]

I believe in most places you'd have to either go off-grid and/or use this in combination with solar for it to be legal to sell back to the grid. Net metering laws are written for the purpose of generating energy, not storing it to take advantage of rates.

With that said, if utilities succeed in gutting net-metering while continuing to raise rates then lots of people in California will want this, as they will make solar+storage cheaper than their own rates for high usage consumers, at least for peak times. In Hawaii you would already save money by storing excess solar and trying to use as little utility energy as possible, even at off-peak times.

 

[Fulthrotl]

Tesla batteries might be a good solution for folks who are already living off grid. I haven't seen any numbers yet comparing their price per Watt-hour with lead acid batteries or the number and depth of discharge they can handle.

For folks with a dependable grid connection at ~10 cents per kWh I don't see any reason yet to run out and buy one.

there's a lot of fluff around this, it seems, and not much in the way of hard numbers.

in calif. there's a lot of people sticking up PV's on the roof.... used to be if you
generated more than you used, the poco sent you a check... that disappeared a
good while ago. so if this were smartly controlled, you could use it to add storage
capacity, but you still can't get your bill lower than zero, so without that incentive,
this isn't going to get legs and run anytime soon.

back in the late 80's all the schools around here with a full sized pool put in a
diesel genset designed to run on natural gas. the radiator was a heat exchanger
used to heat the pool off the combustion heat, and the load was a three phase
motor directly driven off the crankshaft, and hooked to the poco. to start the diesel,
you used the electric motor, and then firewalled the diesel to overspeed the
motor, and generate directly back into the grid. it was inherently synchronized,
required little in the way of controls, and ran the meter backwards.

the high schools using them got a check mailed back from the poco for the excess
electricity, as they ran tied to the poco demand loads, so they weren't generating off peak.

it was a simple system, and iirc remember correctly, worked pretty well, and continues to
do so.

and it didn't need a media bling worthy of an apple product roll out to function. :-/

 

[jaggedben]

there's a lot of fluff around this, it seems, and not much in the way of hard numbers.
in calif. there's a lot of people sticking up PV's on the roof.... used to be if you
generated more than you used, the poco sent you a check... that disappeared a
good while ago. so if this were smartly controlled, you could use it to add storage
capacity, but you still can't get your bill lower than zero, so without that incentive,
this isn't going to get legs and run anytime soon.

You've got this a bit wrong. They didn't used to pay you for excess generation, but now they do. Thing is, the rate is a wholesale rate well below the levelized cost of solar energy, so it would be dumb (financiall) to generate more than your annual use.

What did disappear a while ago were the cash rebates that the state paid you simply for installing the equipment. Although the federal tax credit still exists.

 

[don_resqcapt19]

It can output at a rate of 2kw based on what I read. So at best that would be for five hours and I would assume less. I would not expect that it would charge off the grid. Why would you want to charge a battery off the grid. Charging the battery from solar or wind makes more sense.

Charging off the grid may work if you have a real time rate structure (rates change every 15 minutes or so), where you can charge the battery when the utility rates are low and discharge it when the rates are at their peak.
However given the cost of the equipment, I am not sure there would ever by an economic payback...at least not in the lifetime of the battery.

 

[don_resqcapt19]

Hi,
...
I was wondering if anybody knew if the 10kwh rating means it can provide that without 100% discharge and damaging the battery? ...

It looks to me that the 10kwh rating is for a "stand by" system, and expect that would be close to 100% discharge. It specifies 7kwh for daily use.

 

[ron]

Charging off the grid may work if you have a real time rate structure (rates change every 15 minutes or so), where you can charge the battery when the utility rates are low and discharge it when the rates are at their peak.
However given the cost of the equipment, I am not sure there would ever by an economic payback...at least not in the lifetime of the battery.

I was surprised when I learned that Niagara Falls was primarily generating power during the day (high priced) based on the water they pumped up the falls at night (low price). I guess that is pumped water storage (energy) and this is a similar concept, but in chemistry.

 

[electro7]

One thing that really catches my attention with this battery is that it has a 10 year warranty. As far as I know the lead acid and newer AGM batteries have a 1 year warranty and only will last around 5 years. Any thoughts?

 

[electro7]

Am I calculating right that if I have a 1000 Ah battery bank of AGM batteries at 48 volts, I will have a 48kwh capacity?

 

[gadfly56]

Am I calculating right that if I have a 1000 Ah battery bank of AGM batteries at 48 volts, I will have a 48kwh capacity?

Yes, but understand that's your "nameplate" capacity. If you sucked every last erg out of the batteries on the first go, you'd destroy them. Effective capacity also depends on how fast you pull energy out. IIRC, in the end your 48kwh storage unit can probably deliver a total of 24kwh, and limited to about 500 watts. That's ball park, someone here may be a real battery guru and put some more solid numbers on it.

 

[BillK-AZ]

The Powerwall battery system is more of a load management tool rather than simply a photovoltaic system component.

Many aspects need to be considered. Some simple math using a cost of $3500 (w/o inverter, etc.), a daily 7 KWH stored, and a life of 10 years (3652 cycles) gives a cost of $0.137 per KWH processed without considering the cost of energy lost due to inefficiency (no data released). Hard to justify, but there is also the possible savings as part of load management.

Demand charges can be rather high. In Arizona the Salt River Project now requires new residential PV systems to be on their new E-27 solar tariff with a summer peak season demand charge for 30-minute demand over 10 KW of $34.19 (reducing to $27.77summer/$9.74winter) per KW. If one could reliably reduce peak demand by 2 KW (one Powerwall battery system) the savings are significant.

But the practical side is "How can one do this with a Powerwall battery system?". There are many challenges.

During the day, the PV inverter may already be at maximum from the PV system. PV systems could be designed with higher power inverters than the PV array would ordinarily require, then the question of just how does this connect to a PV system comes up. Waiting to see the list of compatible inverters mentioned in some articles.

Beginning to look like the only way to do this is with a very smart demand controller along with a way to actually control operation with an inverter.

Then think about the NEC and other code requirements. So far, no evidence of a UL Listing, but likely being worked on.

It is going to be a long path to a mass market.

 

[electrofelon]

I was surprised when I learned that Niagara Falls was primarily generating power during the day (high priced) based on the water they pumped up the falls at night (low price). I guess that is pumped water storage (energy) and this is a similar concept, but in chemistry.

It just so happens i was reading about this recently. I think using hydro plants as storage is used on other plants as well. Grand coulee does it i know

 

[CA Contractor & Builder]

there's a lot of fluff around this, it seems, and not much in the way of hard numbers.

in calif. there's a lot of people sticking up PV's on the roof.... used to be if you
generated more than you used, the poco sent you a check... that disappeared a
good while ago. so if this were smartly controlled, you could use it to add storage
capacity, but you still can't get your bill lower than zero, so without that incentive,
this isn't going to get legs and run anytime soon.

back in the late 80's all the schools around here with a full sized pool put in a
diesel genset designed to run on natural gas. the radiator was a heat exchanger
used to heat the pool off the combustion heat, and the load was a three phase
motor directly driven off the crankshaft, and hooked to the poco. to start the diesel,
you used the electric motor, and then firewalled the diesel to overspeed the
motor, and generate directly back into the grid. it was inherently synchronized,
required little in the way of controls, and ran the meter backwards.

the high schools using them got a check mailed back from the poco for the excess
electricity, as they ran tied to the poco demand loads, so they weren't generating off peak.

it was a simple system, and iirc remember correctly, worked pretty well, and continues to
do so.

and it didn't need a media bling worthy of an apple product roll out to function. :-/

Ditto that about the necessity of a media bling worthy of an apple product.

 

[PVfarmer]

wow. check out this link.

wow. check out this link.

Hi, I'm new here. I just stumbled across this link at the end below while looking for transformer info.
I am also pretty into batteries, and know a guy (over the phone) who will talk you HEAD OFF about them.
We agreed- the PowerWall is cool, but a lot of $$ for the storage capacity. It is smaller than other options, so there's that.
They (Tesla) are also kind of cagey about what it is and does.
You can do the same thing with the right kind of (Concorde/Lifeline/SunXtender...) AGM batteries, in fact you can really do more for less $$.
But nobody really wants to stick 4 or 8 or 12 golf cart sized batteries in a metal box on the side of their house...
However, if there's room in the basement...

The life of the batteries depends mostly on how deeply you discharge them, and therefore the draw and size of bank.
If you only take them down 10% a day, they will (or are supposed to) last for 10+ years like the Tesla. But you might need 600 or 900 or 1200 amps of storage, 4 or 6 or 8 batteries, depending on how much electricity is used.
For instance, electric water heaters...I might just run mine off a separate PV system and take it off the grid completely. It'll only run once or twice at night. If it uses 100 amps, 900A of AGM batteries would last quite a while. And keep the bill at zero (or below!)

Lithium can take more discharging, so the batteries smaller and lighter.
Concorde makes these and SunXtender. Not really sure about the difference exactly. But check out the Word doc specs for the "discharge curve".
http://www.lifelinebatteries.com/rvflyer.php?id=14

I'd never even heard of these VRB batteries before today. Neat.

"This situation becomes more complex if the introduction of an energy storage system is considered."
Yes. It certainly does. :huh: This is some heavy stuff. 180 PowerWalls. No big deal.hmy:
Of course, residential is a totally different thing, but some of this might apply. If you can decipher it!

However, decreasing the grid stability margins, PV plants with ESS perform better.
Specifically, over an expected global duration of shutdowns larger than 140 hours per year, the PV plant with
a 600 kVA transformer and a 1800 kWh VRB ESS is progressively more advantageous.
http://www.wseas.org/multimedia/journals/power/2013/035702-208.pdf