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RegGuheert
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Re: Tesla Powerwall [Cost Advantage?]

Sat May 02, 2015 10:53 am

JimSouCal wrote:I remember it being announced. Is the Enphase AC battery out for sale in the marketplace and considered back behind leading bleeding edge? I am game to try..
No. I believe it is scheduled for the 2nd half of 2015 in the U.S. I've seen anticipated pricing (a guess) around $800.

I think it will be the easiest choice available for homeowners wanting to do some TOU shifting. The new S275 microinverter which is included apparently has power factor correction capabilities. Who knows how much the new Envoy will run to control these things. IMO, the software will be very important and likely will take a few iterations to get working correctly. (And, yes, the software can destroy or severely shorten the life of the batteries if done improperly.)
DanDietrich wrote:I have a 9kw grid tied solar array and a Leaf.
9kW of PV in NJ? Do you make a fortune from SRECs or has that boat sailed?
DanDietrich wrote:I use enphase microinverters on my system, and the tech sheet for the Tesla battery shows a 94% efficiency, so converting my ac to dc and back again costs me another 6% of my power if I use the battery.
I'm all for this stuff, and I don't mind that Tesla gets all of the attention while Nissan sells more electric cars, but this unit isn't really practical or cost effective in many situations. No one in this thread yet had mentioned the power loss due to conversion, and I think that is fairly important to keep in mind as a recurring expense.
The Tesla battery does not include an inverter, so you need to add another few percent loss for that (each way unless you are charging directly from DC PV).
RegGuheert
2011 Leaf SL Demo vehicle
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AndyH
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Re: Tesla Powerwall

Sat May 02, 2015 11:36 am

TimLee wrote:Pretty costly to be off grid :o
It always has cost more to be off grid when one uses a ton of electricity. That's why step one, two, and three is efficiency, efficiency, efficiency before step four: solar.
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dhanson865
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Re: Tesla Powerwall

Sat May 02, 2015 1:17 pm

evnow wrote:The rated power of 2 kW is almost useless for any home.

I'd been researching backup generators - minimum that would work in our house is about 7/8 kW.
Powerwall is modular. You can connect up to 9 of them side by side if you have the wall space. So line up 3 or 4 of them if you need that much power.

Also it is 2 kW continuous / 3 kW peak. So you can burst up to 50% over the continuous.
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dhanson865
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Re: Tesla Powerwall

Sat May 02, 2015 1:22 pm

TimLee wrote:
SmartElectric wrote:...
Can be combined up to 9 modules, 2x9=18kW of output power and 7x9=63kWh of storage
Better, but still maximum of 75 amps 240V service.
It's 2 kW continuous / 3 kW max. I haven't seen how long a burst it can do at 50% over but it might affect your math.

Hmm, I have a 200amp master breaker in my main panel. I wonder if I turned everything in my house on if I could come close to tripping it?

The heat pump is on a 40a circuit and it'd only max out when the resistant heating comes on in the worst case scenario on the coldest day.

I have another sub panel with 110a of breakers going to a 100a breaker in the main panel if I'm reading it all right.

I'm sure I have more than 200a of breakers total but I'm also sure I've never tripped an individual circuit in the last 5 years and I'm sure moving to more efficient lighting and appliances are part of that.
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LTLFTcomposite
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Re: Tesla Powerwall

Sat May 02, 2015 6:07 pm

FPL has smart meters and you can go on line and see your usage on an hour by hour basis.

I can't paste images here but our average monthly usage is 1349 kwh, which wouldn't be considered excessive for our area. Looking at a typical day last month our usage was 45 kwh, BUT roughly 36.5 of that was between the hours of 6pm and 10am, and the other 8.5 was between 10am and 6pm. Of course about 10kwh of that is for the Volt. Still, this isn't for a huge house by any means.

So we'd need 4 of these units to go off grid (or to zero out the push-pull). Considering our bill is running about $120/month I'm not seeing how this makes any sense whatsoever in our situation. I don't even see how net metering with a grid tied system would pay off.
LTL
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Slow1
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Re: Tesla Powerwall

Sat May 02, 2015 6:15 pm

evnow wrote:
Slow1 wrote:In any case if you assume remaining grid-tied then you can pull those peak loads off the grid and simply time shift whatever capacity you have. Still a potentially useful product I'm sure - fully off-grid is another story as you need several days supply etc, just not something most of us can justify from a cost perspective eh?
As a backup - one would need the ability to run the fridge, some lights, range, the heater / AC ... most "whole house" generators start around 10 kW.
Sure - and couple it with a good generator and you can re-charge it periodically (run the generator for a couple hours at near peak load and benefit from that efficiency) and you wouldn't have to listen to constant hum of said generator. Get really smart about it and one could have control circuits to turn the generator on and off using the battery to buffer the power.

Lots of applications that could be done - whether any are worth the cost/complexity is up to individuals I'm sure.

I do believe that Elon is on a mission here - not just to make money. Load balancing for utilities is indeed an important part of a long term strategy I'm sure. I'm not sure that there are enough individuals willing to foot the bill to help make it happen on their own.

When talking full off-grid I think we're a good ways away from that at the moment. With net metering the value proposition just isn't there.. yet. Now, I've read a few proposals out there intended to 'let PV owners pay their fair share' of infrastructure. IF regulators/utilities were to remove net metering and/or disadvantage things sufficiently then the incentive (financial) could be created to make full off-grid solutions viable (even if they included a generator as part of the solution for multiple-cloudy day situations). Personally I think that would be a shame - as I project it could lead to a muliti-class power distribution with only the wealthy being able to afford reliable power.. Of course all this is an extreme (and highly unlikely) scenario... and I've rambled :)
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Slow1
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Re: Tesla Powerwall

Sat May 02, 2015 6:25 pm

LTLFTcomposite wrote: So we'd need 4 of these units to go off grid (or to zero out the push-pull). Considering our bill is running about $120/month I'm not seeing how this makes any sense whatsoever in our situation. I don't even see how net metering with a grid tied system would pay off.
1349kWh/month for $120 is very inexpensive IMO - about $0.09/kWh. I bet it is hard to sell PV systems in your area at those rates. To put things into perspective - we pay about $0.26/kWh (and a bit more over 500kWh/mo but I don't know the rate) putting your bill here at about $350/mo. That gives a bit more play to work with eh?

Our monthly usage here (before PV) was just under 500kWh/mo. Different climate (we only run our A/C a few weeks a year and heat with wood which requires no electricity). We also have economized quite a bit - rarely use electric clothes dryer (have indoor and outdoor clothes lines) and LED lighting throughout. Conservation is where it is at. Our net metering PV system (at 6.5kW dc rating) is enough to cover our household electric on annual basis and leaves a bit more for the car but not enough to fully cover it. I imagine that if we had TOU netmetering (i.e. got paid higher daytime rates for our excess and had lower cost at night when charging car) we could benefit quite a bit.
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minispeed
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Re: Tesla Powerwall

Sat May 02, 2015 6:39 pm

BrockWI wrote:For home installations I can't imagine it competing with lead acid for cost per watt. We have 18 kwh of lead acid that was $1800, its not that large of floor space, but weighs a couple of tons, but it does require some periodic maintenance, I miss our AGM's :)
If you're not sure you will be staying in your home a few tons of batteries isn't something you'd want to think about moving and something that may deter buyers if you include it. The powerwall is small enough to take with you good looking enough that people probably won't mind if you leave it.
Slow1 wrote:
I wonder what the utility companies think of the idea of folks time-shifting loads via the charge/discharge cycle... Seems that it would be good for their grid stability as a whole and thus a good thing, but I wonder if the delta in rates between peak and off-peak will reduce over time (and thus reduce incentive to invest in the battery).
I imagine that they would offer some sort of incentive as a rebate to tie into the control of the unit to allow them to control the load. If all you want is to save money through TOU they utility could control what time you charge during the cheaper times or at what speed depending on the local load. All the end user really cares about is being at 100% when the rates go higher.

I just got $175 back for signing my nest up with the hydro company. They will either durn up my AC a few degrees during peak load (which I can then turn back if I want) or pre cool my house if I have an AC schedule set to a lower temp during an anticipated higher load time.

I wonder what it would be worth to them to be able to provide me most power (AC excluded) during off peak times instead of on peak.
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LTLFTcomposite
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Re: Tesla Powerwall

Sat May 02, 2015 6:46 pm

My numbers are a little skewed as the monthly is based on level pay, we're more like 11 cents/kWh. Also we have the thermostat programmed to go up to 81 during the day while we're gone. With solar panels it would probably make more sense to get the house cooled down as much as reasonable in the afternoon. So maybe I could get by with three units :-)
Minimal AC usage climates are likely where this works best. Of course then you probably have more co2 emissions from oil or nat gas heating.
LTL
White 2012 SV delivered 10 Dec 2011 returned 25 Nov 2014 replaced with stopgap ICE Sentra
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LeftieBiker
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Re: Tesla Powerwall

Sun May 03, 2015 2:23 am

I started skimming during the Car Fires Argument... This is close enough to being affordable for us (for backup and peak reduction use) that it's a shame that with installation and charger/inverter it's probably way too expensive for our budget. I'd love to ditch or at least mothball our little 3.5/4.0 kw backup generator. I have it connected (as needed) through a RV type outlet, to a panel interlock (prevents both grid and generator from being connected at once) to our 200 amp panel, and do load balancing by turning off breakers when we use it. Since a gen that size, even a quiet one like ours, makes a lot of noise under full load, and drinks a relative lot of fuel, I'm used to working with about 2kw.
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