This is a concept that @rolosrevenge presented at TMC Connect 2014; it's great to think that Tesla might pick it up and run with it. (There were at least two Tesla employees who heard the talk.)
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My utility has such a program already in place. If you participate in the program, every 15 minutes the utility will signal your EV if it should or shouldn't charge depending on spot electricity prices that night. Afterwards you get a rebate on your bill depending on how many 15 minutes intervals your car voluntarily didn't charge.
InTheShadows
Active Member
I'm pretty sure I saw a video or listened in on a call somewhere that Tesla said they would not be using recycled car batteries for stationary storage because they are a different form factor.
Johan
Ex got M3 in the divorce, waiting for EU Model Y!
Also it was stated by Elon (or was it JB?) that it won't be the same cells in stationary storage packs. They will have lower energy density and perhaps a different chemistry.
JRP3
Hyperactive Member
I suppose a box form factor is easier to install in most locations than the S battery "slab", but I'd think a used S pack on it's side along a wall, or tipped up on end against a wall, would work well in some situations.
jhm
Well-Known Member
I wonder if it really will use lower density cells. I'd like to see Tesla move forward with new higher density cells for auto packs. Would this leave capacity for cells currently used in autos? Think of autos always needing the very highest density and stationary as using the old capacity for the next to highest density. I don't quite see the point in rolling out new capacity for older technology. The key thing is to drive down the cost, and the only reason to use lower density is to save cost on retooling.
Batteries, solar cells and computer chips are different products. Like any other product, they are produced to a given specification and have to pass multiple stages of quality control. Hence the phrase 'they don't know what they are getting until it comes off the line and its performance is tested' does not apply.
I think what Theshadows is saying is that batteries may be "speed binned". When high-end computer chips are made they can be tested and binned as like 10% 3Ghz, 20% 2.8GHz and 70% 2.5GHz. Any product which has a natural distribution of its key spec can be binned in this way. I don't know the answer, but it is a valid question. Panasonic may be "capacity binning" for all we know.
glhs272
Unnamed plug faced villian
I really hope this is not all there is to this April 30th product reveal. We knew about this system a long time ago (referring to the Trip Chowdhry article). This picture highlights what is wrong with it, small battery and AC charging. It needs to be a DC system (for car charging). It needs to have much more capacity. Telsa needs to be thinking of the complete ecosystem, integrated solar, grid, and battery (car) charging. It needs to have capacity for my house and car. If it has those things, why not make it DC fast charge. I guess I have high expectations for this system. I also have a lot of confidence that Tesla gets it.
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JRP3
Hyperactive Member
It doesn't need to be anything. It will be what Tesla and SolarCity think they can sell in volume at a profit. Most people would not want a battery system that was large enough to provide DC fast charging.
InTheShadows
Active Member
That is what I am talking about. Solar cells are the same way. The solar cells for 250w 255w 260w panels and loose ebay cells all come off the same line. They are tested then sorted to their appropriate performance spec.
glhs272
Unnamed plug faced villian
Ok, I'll add "needs" to be in order to be useful for me. I do think that the DC fast charger feature might be more marketable than you might think. If it has that feature it may push electric car owners like myself to buy who might not be able to justify any battery system at all. If the battery system doesn't have the capacity to charge my car to it's daily usage, then it really reduces it's utility to me. If it does have the capacity to charge my car, then making a direct DC to DC connection will improve it's efficiency at charging my car, therefore requiring less battery capacity. If it has the DC charging capacity, why not make able to pull enough amps to qualify as fast (i.e 50kw or more). The experimental house that Honda built already had these features (from anti-EV Honda no less), so I have to think that Tesla is thinking of this. If this only about putting a small battery in the house to shave off a few peak kWh during the day then I don't see how it will be all that useful to folks like me in the Midwest where solar power is only marginably cost competitive.
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I like the idea of reducing charging losses by a direct DC-DC link. Some things to ponder:
- Because of high DC transmission losses, the stationary storage should be located near to the parking spot, as in the picture above. That may not be a suitable location for many customers.
- To get a high charging rate, you must either have a large battery or discharge the battery at a high rate. The former is expensive, the latter contributes to cell degradation. If we cap the continuous draw from the battery at 1.5 C (about the same rate as 120 kW supercharging on an 85 kW battery), the battery would have to be 33 kWh to support 50 kW charging. That's about twice as much battery as typically needed to manage peak/off-peak power shifting and solar integration.
glhs272
Unnamed plug faced villian
Ok running with that... I imagine this system would incorporate 1 main battery bank 30 to 50kwh in size, 1 main inverter, 1 DC to DC controller for controlling solar to batteries, 1 DC to DC controller for charging external batteries (such as an electric car). The goal is to have as few DC to AC and back type power changes in order to maximize efficiency.
The inverter would be much like what is already in the model S that can Pull or Push power between the battery and the AC side (grid), just locked at 60hz. That inverter would be sized appropriately to manage loads that a typical house might have (HVAC and such). In the model S this inverter can run over 240kw at peak and over 30kw sustained (I don't know the real specs). In my case 20Kw (80amps @240V) of power would be sufficient to run all my house loads at peak (not including car charging). This allows efficient on the fly power flow between battery, grid and loads. The system would also have a DC to DC controller to take DC power from the solar array and directly charge the house battery. Solar power would always be used to charge the batteries or get split between charging the batteries and maintaining the AC loads (via inverter). If AC loads and battery charging loads are less than what is being provided by solar, the extra power can be pushed into the grid. All programmable to sort out what is the best use of power, incorporating factor such as TOU, battery state, expected loads (predictive), actual loads, and even maybe using weather forecasts predict solar power availability.
Lastly would be the focus on the DC to DC controller for charging external batteries (home supercharger if you will). I envision a few scenarios:
-In scenario 1
The home owner may only want to "slow" charge their electric car at the end of a day. In this case they want to charge efficiently as possible with the least amount of power purchased from the grid. Time is not an issue so it can take a while. If solar power is available it would mix that into the DC charging. If the house battery falls below certain level, it could stop charging the car until more favorable TOU.
-In scenario 2
The home owner wants to recharge his car now, costs be damned I need to get somewhere type thing. In this scenario all of the systems resources can be brought online simultaneously. The inverter can be pulling from the grid to dump power onto the DC side. The solar panels can be brought into the mix as well if available. Such that the max power available from the battery + max power available from solar + max power available from grid - AC loads from the house such that the total power available from the system can be brought online to charge the car as fast as possible.
I am thinking about these things because it seems like all of these things are possible. Most of the hardware is out there and are already in use in these systems as stand alone parts. It's just that no one has a combined complete solution that brings it all together both hardware and software. If any company would be capable of doing this it would be Tesla. Solar city can install it for me. I am trying to come up with a more broadly focused product, not something niche for only certain customers in high utility rate zones.
Am I missing something fundamental here?
glhs272
Unnamed plug faced villian
Ok, clearing away my ideas on what this system should be to me.... What is the ROI for what we are guessing this system to be? Or rather what should I be taking into consideration to calculate a ROI for myself. Talking strictly the residential system here, maybe just modeling what Tesla has already done with the 5kW/10kWh system. I am trying to understand why the average home owner would buy this system or who Tesla would try to market this system to. Is this a global solution or just useful in high utility rate areas with lots of sun. Perhaps this has been done already on this site, any links?
A DC FC system running off inversion from the grid which has massive power on the wire is still incredibly more efficient than storing the charge first in a local battery bank and then pushing it into the cars. The reason is the energy lost during the Grid -> battery storage charging. Let's say a supercharger site has 8 stalls and needs up to 480 KW+ off the grid when all the stalls are busy. What size battery will really help here? If it is attached as a hybrid battery store from a local Solar PV array, that can help cut peak load for the main meter at the site. But only is a benefit when the peak load is occurring, perhaps afternoons during a commute. How many discharges will it need to pay for itself - depends on the peak rate versus and how many kWh can be saved using the batteries. I can imagine in California, these charges can be substantial. In other states, not so much.
I'm pretty sure @gls272 is thinking about residential battery storage, not Supercharger. While the technical losses added by putting storage into the system are clearly high, as much as 25% round-trip if AC-DC-AC-DC conversions are required, the hard-edged rules of retail electricity tariffs can nonetheless make storage an economically sensible investment--not from a societal POV, perhaps, but from a pocketbook POV.
dhanson865
Well-Known Member
I think you and others are overly demanding to look at 50KW charging or better at home. The home standard is the HPWC. 10KW for a single charger model S, 20KW for a dual charger model S. Any improvement on that is a plus.
I'm thinking even a 10 kWh system allows you to do DC to DC charging in theory faster than a HPWC. Maybe it needs to be 15 kWh to be enough to bother. But I don't see the need for massive home packs before we do some sort of HPWC replacing / supplementing system.
Looking at P85D 691HP should have an asterisk * next to it.. there seem to be plenty of posts showing an 85kWh battery can do bursts well above 85KW. Take for example
Seems to me that means you can get some output above 2C even short bursts at 3C. So you have a charge / discharge curve and a small home system can still give you a quicker charge than your HPWC at least for the few minutes it can sustain that.
glhs272
Unnamed plug faced villian
I guess even if it is not fast charger, just being a DC to DC charger is significant in my opinion. I "burn" about 20kwh each day with my car alone. That may be a bit above average, but I would think most people would use at least 10kwh per day in their cars. So the way I see it, there does need to be some significance to the size of the home battery to really be useful in the fully electrified world that Elon is trying to make a reality.
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