gavine
Petrol Head turned EV Enthusiast
There was so much talking in the background, I had to really focus to make-out what they were saying. I guess I'm easily distracted by external noise. Did they do the conference call from the cafeteria?
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Elon, I love you... but the PowerWall isn't that great...... yet.
- Thread starter wk057
- Start date
There was so much talking in the background, I had to really focus to make-out what they were saying. I guess I'm easily distracted by external noise. Did they do the conference call from the cafeteria?
DC-DC inverter doesn't make much sense. An inverter would be DC-AC by definition.
I just listened for the second time to Elon's presentation and I heard him say "DC to DC inverter". It sounds odd to me but I am not an electrical engineer. If the proper word is "converter" that doesn't make sense to me either. What DC to DC "conversion" would be needed?
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Two places for DC-DC conversion:
1. The input. The varying voltages from the solar panels needs to be boosted/dropped to match the best voltage at which to charge the batteries.
2. The output. The battery voltage may needed to be boosted/dropped to best match the external DC-AC inverter depending on it's specifications.
Johan
Ex got M3 in the divorce, waiting for EU Model Y!
Yeah not an engineer either but DC-DC inverter sounds strange. Converter seems much more natural. Or transformer (the term we use for AC). Basically what we're discussing is an apparatus which takes electrical current and changes its voltage up or down (with a corresponding change in amperage of course). So yeah, converter seems good. Inverter seems appropriate for DC to AC. I believe the correct term for AC to DC is rectifier?
Yes but then these numbers are wildly inaccurate undermining the underlying argument. Inflation alone is around 3%, relatively predictable. Utility taxes add anywhere between 3-10% depending on the jurisdiction, and he KWH base cost varies wildly depending on where you are. There simply isn't enough data considered to make these estimates worth much. The one thing we should assume is with the Tesla power wall, these costs get flattened significantly.
As an example. LADWP Rates run from .14 - .21 per KWH depending on the amt of power used per month. Rates have climbed steadily every year or so. City utility tax is 10%. When looking at that, this seems like a good way to bring predictability to the cost of energy over the long term.
There is a lot in this thread and I was late too it. I would like to say that for a backup power option this works for my family better than a store bought generator ever would due to my wife's terrible asthma. It is very severe to the point that water vapor causes her lungs to seize up. While we are in the small minority here there are many other small minorities out there. The initial demand is mostly just Tesla Fans but over time I think there will be a lot more demand than most people realize. They don't need everyone to need this. They cant make one for everybody.
FWIW, residential power rates here in Maine have been flat in inflation-adjusted $, compared to 1999. I always run financial analyses in inflation-adjusted numbers because real interest rates tend to be more stable than nominal interest rates, and in theory nominal interest rates = real interest rates + expected inflation rate.
The bigger risk re electricity tariffs is whether the basic rate design is going to remain stable. E.g., here in Maine the governor has introduced a bill to replace net metering with a design that would pay distributed resources a separately determined rate, based on the adjudged value distributed resources bring to the system. Depending on who's doing the judging, that could be a big shift in the economics of residential PV. In most areas, I think that there are more "tariff surprises" that could hurt the value of PowerWall than help.
jgs
Active Member
I've been simplistically conceptualizing it this way: the utility is one potential buyer for your surplus PV energy. You yourself, through the agency of time-shifting, are another. If the utility's offer is the most attractive, great. If not, and your costs to time-shift your surplus energy are better than what your utility is offering you, then you go purchase a PowerWall. When you say "'tariff surprises' that could hurt the value of PowerWall", in my simple mental model that means a pleasant surprise, one where the utility is giving you such an attractive offer for your surplus power that hoarding it for yourself makes no sense. Is that what you meant?
The utility isn't forced to keep a given tariff for a long time, it may change when it wants (more or less.)
Say for example, you calculated the ROI for your PW to be 6 years. You buy one, get it installed and the month after that the utility changes its pricing to discourage home storage and solar (ex. :less difference between peak and off peak, low price for each kWh you put back in the grid.) Suddenly, your ROI get to 20+ years, but have already bought your PW and installed it.
Edit: the example about the low price per kWh bought by the utility is actually a good incentive for the PW, not against it. I'm leaving it because someone has quoted me.
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jgs
Active Member
I don't think this is strictly true where I live, depending on what you mean by "more or less". I believe the utility has to have tariffs approved by the PSC, they can't just set them arbitrarily.
I guess so, but given that this "harm" is caused by a competitor (the utility) reducing their rates to make them more attractive, I'm a lot more inclined to say "yeah! Free market at work!" than I am to complain. It's also instructive to remember that this imagined improvement in utility rates doesn't take a cent out of my pocket – my cost for the PowerWall installation is exactly the same before, and after, the rate change.
It's true I am assuming here that the PowerWall is being used for storage of self-generated PV electricity, not arbitrage between two different utility rates. Yes, arbitrage is vulnerable to rate changes. This is true regardless of the commodity in question. So don't do that.
jgs
Active Member
Very true, I was reading quickly and didn't pick up on that earlier. Actually I think the last few messages illustrate one of the benefits of increasing availability of home battery storage even if you never use it yourself – its very existence allows market forces to operate in the market for home-generated PV. (Although a possible second-order negative is that I would imagine a utility could use this to argue in court that they are not the sole outlet for purchase of home-generated PV and therefore their net metering tariff shouldn't be subject to regulation.)
lolachampcar
Well-Known Member
It is truly sad all of this is not being done at the utility level as they are best positioned to manage storage across a group of users instead of driving storage to the homeowner level.
schueppert
Member
The total electricity storage currently available to utilities is huge and growing. It dwarfs the in-home market. There are many technical solutions other than batteries that work at a utility level: gravity-based solutions, compressed air, flywheels etc.. And I suspect Tesla will sell more into this market than they do into the home.
That said, in-home storage does provide a key benefit that utility based storage cannot: backup.
That said, in-home storage does provide a key benefit that utility based storage cannot: backup.
The main problem I see with other types of energy storage that involve a mechanical aspect is the huge round trip efficiency loss. Such storage mechanisms could never compete with a more solid state approach such as batteries.
jgs
Active Member
"Never compete"? I would imagine that in many deployments a more important metric than round-trip efficiency would be cost per kilowatt hour, something it's easy to imagine a mechanical storage system doing well at.
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glhs272
Unnamed plug faced villian
JGS, I respectfully but vehemently disagree. In states like mine, the public service commission (PSC) is chaired by politically appointed members by the governor. Such that when a change in government happens, saying going from Democratic to Republican or vise versa, the public commission is going to represent the interests of the party in power. By that statement all that I mean is that what your calculated ROI is today with a 6 year return on investment may no longer be valid after the next election. You may say "yeah free market wins" but not necessarily. Such as in the case of Wisconsin, PSC specifically both raised the grid connection fee (the amount you pay regardless of how much power you use) and lowered the delta between on and off peak kWh usage. This drastically changed the ROI on solar. They did this specifically to make sure that solar is non-competitive, they even said as much. And the net result is they raised the fees ON EVERYONE. The only way in which this made solar more competitive is if you were completely off grid. Which is very expensive to do and in no way competitive to a standard grid connection when you look at todays cost of a complete off grid solution (the amount of solar and storage need for year round consumption in a northern state). Thus in one fell swoop they turned a 6 year ROI into a 20+ year ROI AND RAISED FEES ON EVERYONE ELSE!
