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PowerWall technical discussion
- Thread starter lolachampcar
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- Powerwall Tesla Energy
SW2Fiddler
We Are Cognitive Dissidents
Well yeah, if you only consider Outdoors Installations.
But there are places that don't go to 110. Like every enclosed inhabited space (since this gadget won't kill you indoors like a Gasomoline Genset would).
I would think the smart inverter would basically feed your house with PV directing the excess to the battery while simultaneously isolating you from the grid. At night, it would draw from the battery until depleted. Once depleted by too much usage overnight or a rainy day, it would transfer seamlessly to the grid ala UPS style.
As you point out, this scenario precludes using micros...... Still, I'd change my system in a heartbeat if I could use a cost effective salvage MS battery (or Tesla's third generation cost effective PW) even if it does cause me to loose the efficiency of the micro inverters.
The spec on the teslaenergy page says no DC to AC inverter is included. That means the charging inverter/circuit is included but to get energy out, you need to determine if the units are going to be stacked or independent and determine the inverter need. What is interesting is how will the features like load shaving work based on time of day, whether you have solar or not and other factors.
It wasn't clear in my prior post, but the micro inverters are sort of a must-have for me. If I'm forced to pick PowerWall and switching to string inverters or sticking with my existing setup, the status quo wins.
That's because I have a multi-level roof, with a due southern exposure. My garage is on the east side of the house, and the family room on the west side. Both of these sit lower (maybe 6-8 feet; it's hard to tell from the ground) then the main roof. In the morning and evening, some of the panels on these lower side roofs are in shade. With micro inverters, I only lose those panels. With string inverters, I'm going to loose a lot more of my morning and evening production.
Maybe I can find a junkyard S charger? Hmmm...
roblab
Active Member
Regular panels are wired in strings. It is easy enough to figure out which areas will be shaded, and wire them together, so the shade only knocks out one section. Microinverters work well, too, but string inverters can work just fine if you are able to think a little bit about shading ahead of time.
Enphase is releasing a battery system later this year (AC Battery - Enphase Energy), that I would assume will play nice with their micro inverters (I have 8.3kw of microinverter based solar). Hopefully the PowerWall pricing will force Enphase keep the costs reasonable. The Enphases system is interesting, in that each modular pack has a bidirectional micro inverter, so it output AC directly. I as hoping Powerwall would do that.
In any case, I'm sure Radian or Magnum Energy will announce an integrated inverter/charging system that works with the Powerwall voltage levels and Enphase micro inverters (or any string inverter that outputs AC), and deals with decoupling you from the grid, and keeping the panels online when needed, and shutting them down when the batteries are full, etc.
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It depends quite a bit on your shading. The way the trees are near our house, shadows creep slowly from one end of the array starting mid afternoon. you can watch it taking out one panel after another on the panel monitor. Also, we have panels on three different area of our roof, with diffing orientations (south, mostly south and southwest), Micro inverter make that a non issue.
True, but that means a higher A/C load during most months, and it's not a small object either. It doesn't help that in my house none of the available walls are anywhere near the service panel.
harry
Member
Couldn't you use the Solar Edge system and get everything you need? That hybrid system has "optimizers" that manage each panel independently, and feed DC to a simple bulk inverter. Solar Edge partnered with Tesla on this stuff, so it looks like it would work well. How to supply power when the grid is down would still be an issue, tho.
Wouldn't work in my situation - say I break the system into 2 strings, 4.5kW each, and feed 2 5kw inverters. I still loose an entire string in early afternoon when one panel on the garage closest to the house goes into shade. The only way to stop that, and continue getting power out of the rest of the array is to put the shaded panel into a string of 1, ie, give it a micro inverter.
I agree, it would work if large sections transition into shade at the same time, but that's not what's happening here. Only 4 (morning) or 1 (evening) are shaded. It's hard to describe in words, and I don't have a picture handy.
The issue is that a shaded panel blocks the current flow through the string, cutting the output of the entire string. I quickly scanned a Solar Edge tech note that seems to imply the optimizers can deal with some amount of shading, but I couldn't tell how much/how well at first glance. But it is an interesting way to approach the problem.
What is powerwall round trip AC-DC-AC efficiency? Tesla says "92% round-trip DC efficiency". So this excludes at least DC-AC efficiency. But does it also exclude AC-DC efficiency? Is this 92% only round trip battery charging-discharging efficiency?
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A DC-DC converter is included with the powerwall. I do not see this in the tech specs, but Elon verbally mentioned it in the announcement. 92% efficiency presumedly includes both the battery and DC-DC round trip losses. If so, the DC-DC must be extraordinarily efficient. When used with PV panels, it probably only charges from their DC supply, so no loss converting grid AC to DC.
GSP
PS. Is there any info on the thermal management system? Liquid with pump, radiator an fan built into each 10 kWh unit? Air cooled with just a fan? What are the fan specs and how long will it live?
GSP
PS. Is there any info on the thermal management system? Liquid with pump, radiator an fan built into each 10 kWh unit? Air cooled with just a fan? What are the fan specs and how long will it live?
I wondered about that too. But given the PowerWall Specs show the storage and discharge operating temp ranges as being within the specs for a typical Li-ion chemistry, I wonder if it only has a heater in it to address the need for bringing the cells up to the warmer charging temp?
I haven't studied the Powerwall as much as I might have (it wouldn't do anything for my situation). Do we absolutely know that it uses the same cells as the car, or is this just an assumption?
If so, I guess I'm confused -- I thought a major contributor to the low production for the Model S was a shortage in the supply of batteries. Why find another product that uses up the same cells? I can understand if the Gigafactory is operational and there are batteries in abundance, but why use up the current supply even further? I've heard that home storage could be a use for used batteries, but I don't think that is happening here...
If so, I guess I'm confused -- I thought a major contributor to the low production for the Model S was a shortage in the supply of batteries. Why find another product that uses up the same cells? I can understand if the Gigafactory is operational and there are batteries in abundance, but why use up the current supply even further? I've heard that home storage could be a use for used batteries, but I don't think that is happening here...
No, Elon said in the press conference before the event that the cells are different, but he didn't elaborate.
Looking at the specs again I see "liquid thermal control" is mentioned. That would require a pump, but maybe only a resistive heater with no radiator or fan, for the reasons you mentioned. At 0.2C the cells should not heat up much past ambient.
GSP
Yeah curious on the scheduling capability. Ideally, you have the Powerwall charges at night when the rate is real low and then during the peak time it can power your house while your PV generates at the peak rate.
Also didn't see any mention but direct DC to DC fast charging to the car doesn't look possible?
