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Discussion in 'Energy, Environment, and Policy' started by wk057, Aug 10, 2014.
What is your plan for the electricity being produced once the battery is full?
I'm sure that if you do detailed simulations you'll find that it is cheaper for you and better for society as a whole to just put in a 15 kW solar system and skip all of the batteries, but do as you please. It is, after all, a free country.
I'm all for staying on the grid but last month I paid $65 for the 'privilege' of being connected to the grid.... and I was out of town so I only used 79kWh. Yep, net export of 1495kWh and I was charged ~$15. I get charged more for producing electricity than I'm paid for exporting it; That.... is.... insane.... If I'm still here when my production credits expire I'm going off-grid out of spite unless Xcel gets their head out of their a$$. :cursing:
You need to calculate some value for the ability to have power when the grid power is interrupted. After all people pay thousands of dollars for backup generators.
I can pitch in the micro work for talking to the pack and managing the buck to maintain maximum power point of the string. What is needed is the coms protocol for the battery and that will require reversing Tesla's work (as I do not believe they will be telling us for fear we would set our houses on fire as we climbed the learning curve). The reverse engineering likely violates the agreement an owner (like me) signed. There was the rub for me.
Fortunately, with a pack from a salvage, I've signed no related agreement. The agreement I signed was for the Model S I just happen to have already purchased from Tesla directly.
If I start tinkering with my actual vehicle in some way (such as tapping battery<->ECU comms or something) then I would have crossed the line. But, the salvage pack is mine and I can and will do whatever I please with it. Such reverse engineering projects have been supported by case law for a while now. The salvage pack has no warranty and is no longer supported by Tesla.
I can almost understand them not helping me by selling parts or sharing any information. Their loss, in my opinion. I think it would be much safer to know how and be able to interface with the battery appropriately from the start than to have to do the tinkering myself to figure it out (which I will). If something crazy happens, like my house catches fire, because I used some inappropriate part for interface, sure, it's technically my fault. But we all know how the media would spin that if they got a hold of it. In this case I wouldn't feel too bad about it either if it is after I asked Tesla for parts related to this project and was refused, since that would force me to figure out my own way to make the connections and all.
I certainly will not be using my working Model S for anything with this project (aside from using generated power to charge it normally, of course) for fear of doing anything with it to put any part of my warranty in jeopardy.
A simple high voltage cutoff relay on the solar DC would be similar to what most people in the DIY community use to avoid overcharging the pack. Ideally the existing battery management system would also work at the cell level to keep the pack balanced. Presumably the BMS also has a high voltage cutoff as well.
Yeah, I plan to investigate a lot of this once I physically have a pack here to tinker with. The way I understand the setup from what I've read and seen so far is that the pack has no self balancing in place. Power flows into and out of the battery via a single set of high voltage/high current cables. Presumably the other connection on the pack is for the BMS and other electronics on the pack. I'm also figuring that there should be a main contactor inside the pack that is controlled somewhere from this other connector as well, since most of the safety documentation says that cutting the power to the contactor (near the 12V battery) "isolates the high voltage to the battery pack." It wouldn't make sense if it isolated it to the pack AND a few wires underneath the back seat...
So, I'll need to figure out how to control the main contactor assuming it is inside the pack.
As I mentioned a few posts back, I would like to setup the home's HVAC system with this project to allow some upward or downward deviation from the current setting (depending on season) to utilize some of the excess energy produced. This way the energy will be put into the home to cause slightly less usage later in the day/night at the expense of slight deviation from the set temperature during the day. I for one am fine with it being a little cooler on a summer day and a little warmer on a winter day any time.
The place I plan on doing this project also has a pool, so, I could have the system override some pool pump timers if possible. Perhaps dump the power into the pool for heating if it's needed.
Lots of places to put the potentially excess power. Worst case scenario it is just underutilized, in which case I should probably add battery capacity. Second Model S pack anyone?
In the following video JB Straubel from Tesla talks about storage packs. There is a picture of a residential pack. I watched the whole video some time ago and if I remember correctly he said there were 1000 domestic installations of that pack through Solar City. He also said the financing was integrated with the solar panels.
On Solar City website it is explained here:
Solar Energy Storage for Home Battery Backup System | SolarCity
Also you might want to check these two topics about the same subject:
Solar Power and Battery Backup: Tesla and SolarCity's Dream Home - Page 3
The Battery Solution - Home/Business Supercharger and Battery Backup/Energy Storage!!
SolarCity does all grid tie related things as far as I know. I also just don't like their pricing model, personally. I want to invest in my own power generation, not lease my roof space to a company AND pay them for it also, even if it is a net savings.
As I mentioned previously, I'm somewhat against grid tie solar due to all of the politics involved in keeping it useful. Nothing to stop the utilities/lawmakers/etc from changing things on their end to make it no longer profitable to use the grid as a battery like net metering works now. But I won't get into all of that. I try to avoid politics.
So, off-grid is what I plan to do. I think even if the cost is pretty great (with even a 15-20 year ROI at current electric prices) it will probably end up being worth it vs grid tie in the long run.
I'm honestly not doing it for the money savings or ROI anyway. Honestly, it'd probably be cheaper and less effort for me to just use the grid indefinitely. I like the idea of the project and the savings and environmental impacts are just a bonus to the experience of actually doing the project itself.
There are some things we nerds just have to do even if it does not really make sense to do it Hopefully you will share your BMS communication learning curve as that is where my curiosity points me.
Not sure where you live but in NE Tennessee battery backup is costly. While I am balanced for the year, during the 3 months of winter with higher heat loads and short cloudy days I ran a 1700 KWH deficit. I made up for it in the spring early summer when I did not need HVAC and we had longer, sunnier days. So I would need 20 Model S packs to fully go off grid and/or add additional panels for more winter generation that would be wasted during the spring and fall.
Now we do not have to pay for back up generation. We have a $7.21 connection fee which I consider quite reasonable for what is effectively a 1700 KWh battery. So your situation is different.
Was going through more photos from around the interwebs (mostly here) again to get some more ideas on how to proceed with this project.
Just going to use one pic I found (with some captioning by yours truly) to reassure my original assumption that the main contactor is located inside the pack itself.
(This image is NOT of my Model S and was NOT taken by me)
The HV output from the battery (right side) appears to be directly and permanently connected to the drive inverter input (left side) inside the charging related junction box. Connected at the same junction would be the input from the charger(s). The wiring from the charge port comes down on the far right (where the person in the picture has their finger pointing). This box also appears to contain the contactor needed to make supercharging possible by connecting the battery directly to the charge port.
That said, it only makes sense that the main contactor is inside the battery pack itself, allowing the cable on the right to be cut from power. Otherwise there would always be high voltage power present under the rear seats.
So, when I get my salvaged pack I'll probably have to open it up to figure out how to close that contactor.
Been doing a bit more research and it seems that I still can not find any commercial off-grid inverter that will accept a high input voltage in the range of the Tesla pack.
The range of voltages I've seen while supercharging is as low as 340V (4 RM) to as high as 403V (265 RM). So, I would need an inverter that could handle that input if I wanted to leave the pack intact.
Unfortunately the lack of a commercially available off-the-shelf solution is probably going to lead me to dismantling the pack into its 16 modules and rewiring them for a lower voltage. This would have the added benefit of easy transport later, also, since each module should be under 100 lbs...
Broken down into modules gives me the following possible configurations:
in seriesModules per group
in parallelVoltage ChargedVoltage Discharged16140334082201.517044100.75852850.37542.511625.187521.25
Configurations in red are not utilizing one or two modules, so, unlikely candidates.
Given this info, an off grid inverter rated for 48VDC input should probably be able to function in the 2 modules in series 8 in parallel configuration. Most I've found seem to accept a voltage range from about 40VDC to 60VDC, which this configuration would fall under easily.
I'm definitely not going to break them down into sub-module portions for sure. Honestly, I'm still hoping to find a high voltage solution, however I'd prefer not to have to build an inverter from scratch...
Many grid-tied inverters would accept the full high input voltage. However, I'm not 100% sure how this could be made useful.
Lets say I make a micro-grid that has nothing connected to the utility. Lets say I have and use something like a 5000W off-grid pure sine-wave split-phase inverter running continuously to get a phase, voltage, and frequency for the base of this micro grid. What happens if I put something like a 20,000 watt grid-tied inverter feeding my micro-grid powered by the HV battery pack (and solar charging). What does the grid-tie inverter do when there is less than 20,000 watts demanded on the A/C side? Does it adjust it's output accordingly? I'm thinking not, since it wasn't designed for this. My guess is it would bump the A/C line voltage up (trying to force it's power on to the underutilized micro grid) until it reached a cutoff, then just shutdown completely. Just a guess though.
Anyone have any suggestions on this? I'd prefer to keep the pack as intact as possible, honestly.
I'd bet there are some industrial inverters that can take a higher input voltage.
The other thing you need to consider is how much peak power you need to deliver. You will probably need more than one inverter, so breaking apart the pack to match the 48VDC nominal would also allow you to divide the pack among the inverters. Solar inverters try to do MPPT tracking - would it be confused by a battery that doesn't significantly change voltage when the current is modulated? You also need to think about what kind of charge management the the charger portion of the off-grid system has and how configurable it is. The residential grid storage display in the lobby of the Tesla factory in Fremont has a Schneider (formerly Xantrex) unit (presumably XW series) on display. So, that unit is definitely a good candidate.
So... got my 85kWh pack to my garage this afternoon.
Couldn't glean any information by probing the connectors on the exterior of the pack. So, after an hour or so of messing with it, decided to just start the tear down.
Got the top cover off 100+ screws and 3 hours of labor with 3 men working on it. Was a ton of work. Pack is built like a bomb shelter. The top cover was pretty much destroyed in the process. The top cover is thin steel.
After finally getting the modules exposed I was able to test the pack voltage. The full pack is sitting at 313.8 VDC. This works out to 19.61V per module, or 3.27V per cell. Definitely below 0 rated miles, since at 11 rated miles my pack had 345 VDC (21.56V per module, 3.59V per cell). So, it definitely is dead, but not really irrecoverable from a normal use point of view. 3.2 seems to be the low voltage usage point for other projects I've tinkered with, so, I'm confident that given a good slow charge that it will charge up just fine. It hasn't been sitting all that long from what I understand. Most likely this is drain from the BMS system. From what I can tell there appears to be a very small DC-DC built in to the main BMS board, which I assume is used to power itself and the BMS on the modules. I could be wrong.
I may remove the main fuse (located under the black plastic cover at the front of the pack) and put a meter on it to test that theory.
The modules appear to be balanced decently with the largest deviation from average being about 0.14V at the module level.
I took tons of pics, but I'm debating on posting them. I don't think there is any harm at this point, but, it is interesting to see how some of the battery is setup when examining it closely.
More to come...
I for one am very interested in seeing what you are willing to share. I've been following this thread and it sounds like a cool project.
Now that's what I like to hear!
Every automaker has already broken down its Model S battery, so there's probably no harm in posting your pics.
Well, I'm not particularly concerned about the automakers, really. Anyone who wants the info badly enough will pay to get it themselves. I just don't want to do legwork for anyone who could be opposed to Tesla or who would somehow use the info to their detriment. While I doubt this will happen, the last thing I want is for someone to notice something about the pack that could be given a negative spin somehow and for something like that to be blown out of proportion. I think the chances of this are pretty low, however.
On that note:
Images I post in this thread and my related commentary are posted and published by me, the original photographer. All copyrights and all other rights reserved. These images may not be copied or otherwise distributed outside of this forum without my express permission.
All of that said, here are some images with the hopes that people find them informative:
Pack right after it came off of the truck.
85 kWh "D" Pack
Plastic cover which I later discover has the pack main fuse under it.
Label on the center of the pack.
Top view of the high voltage connector
Pack after removing the plastic cover which what appears to be some type of fireproofing material under it (between the plastic and pack).
The two dents were where some hooks on chains were when the pack was being lowered to the ground by the transport truck. The actual modules are further down under this piece and not affected.
Removed all screws from the top of the pack and starting to peel away the top cover. The thing is held on with so much adhesive/sealant that it took us nearly 40 minutes to get to this point.
Making progress opening the pack, first couple of modules now visible. I popped a few of the orange HV caps from the one module because I was anxious to get an idea of the pack voltage and module voltage since the pack had been sitting for a while.
Top view of the one module.
Put a volt meter on the hot side of the main contactors to read the full pack voltage. 313.8V. So, not toast but definitely dead. (No comments about my cavalier method for testing this please, I know what I'm doing... most of the time)
Close up of the pack's main fuse.
Got the security screws out of the front portion of the pack and removed the metal cover finally, revealing the two front modules which are stacked.
View of the front two modules showing the coolant loop quick disconnects. Those are spring loaded and the coolant actually seems to be under pressure. I may work on a way to connect to that to hook up a small radiator and pump later.
Pack with the entire top cover removed safely, over 2 hours after starting. (Yes, I bolted some wheels to the sides of the pack, and they work...)
Close up of some of the cell level fusing. Awesome safety feature here.
Another shot of the coolant loop connections and front modules.
View of most of the pack.
Main contactors. One is for positive and one is for negative. They are connected with bus bars to the pack and to the external connector. There are also small leads (visible on the top) from both sides of the contactors that go to what I would call the main BMS board.
View of part of the high voltage bus bars.
External low voltage connectors, presumable for BMS communication and pack control.
Close up view of the external HV connector showing part of the actual connection that makes contact with the large male blade connector on the car. This configuration would likely have very low resistance since it would make uniform contact across the entire connection.
That's it for pics. I decided to not post the closeups I took of the BMS board(s) however. Some of the chips are easily identified, but I also doubt they would be very informative. I will say that all PCBs inside the pack seem to be sealed with some kind of resin or epoxy, which makes them pretty much shock and vibration proof... probably reasonably indestructible.
I'm reconsidering breaking down the pack. The configuration is so nice that I just don't know if I'll be able to bring myself to break it down into the modules... we'll see, I'm continuing my hunt for a useful off-grid/non-grid-tie inverter with HV input capability.
Enjoy the pics!
[I][B]Images I post in this thread and my related commentary are posted and published by me, the original photographer. All copyrights and all other rights reserved. These images may not be copied or otherwise distributed outside of this forum without my express permission.[/B][/I]
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Note: click images for higher resolution
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Some other notes:
The dang thing is HEAVY. We used several dollies with high weight ratings, chains, rope, a winch, and a few other crazy things to move it, and it took the three of us pushing in unison to get the thing to budge. I did mount some wheels to the sides to try and move it that way, and it worked OK, but I need a way to mount them better.
Also... don't try this yourself if you have never done anything with high voltage. It's definitely dangerous and I do not suggest it.
This project is not endorsed or condoned by Tesla. Everything I'm doing I'm sure is frowned upon by them and I am doing so at my own risk and hold Tesla harmless with regard to this project. If something bad happens as a result of me messing with this battery pack it has nothing to do with Tesla.[/URL][/URL]