Just to note: from your prior note, your "generator" appears to be homemade, an alternator attached to a gas engine. I would not expect this to be even close to good enough in terms of power quality. I expect a fairly high-end generator with sophisticated power quality controls to be required, quite likely (as some have mentioned) an inverter-linked generator. Of course, that's sort of what you're building when you then rectify your AC "generator" to DC, and then run it through your solar inverter. You are playing with a lot of variables here though: I'm a risk taker, but I'm not sure I'd be quite so cavalier with such expensive equipment (the PW and Inverter specifically). But inverters are comparatively cheap these days, maybe cooking a $1000 inverter wouldn't bother you.
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PowerWall 2 Interface with a Generator
- Thread starter shs1
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Just to note: from your prior note, your "generator" appears to be homemade, an alternator attached to a gas engine. I would not expect this to be even close to good enough in terms of power quality. I expect a fairly high-end generator with sophisticated power quality controls to be required, quite likely (as some have mentioned) an inverter-linked generator. Of course, that's sort of what you're building when you then rectify your AC "generator" to DC, and then run it through your solar inverter. You are playing with a lot of variables here though: I'm a risk taker, but I'm not sure I'd be quite so cavalier with such expensive equipment (the PW and Inverter specifically). But inverters are comparatively cheap these days, maybe cooking a $1000 inverter wouldn't bother you.
Sorry, when I was explaining my generator, I sort of simplified it. Its actually a Dunlite DGUH6S-2. I'm definitely one for pushing the boundaries! I was under the impression a good rectifier would really clean up the output anyway. I was planning to buy a <$500 second hand inverter because it is never going to be grid connected it doesn't need to follow the latest rules.
Well, I'm intrigued in any case. With the limitation of not being able to solar charge and generator charge at the same time, which might be addressed by getting your PI controller to access weather API's (for predicted solar output), NEST or equivalent API's or at least your historical usage patterns, you might swap smartly between the two and lose little or no solar contribution, depending to some degree on how your total storage capacity compares to the corresponding use rate. I will be very interested in hearing if you move forward on this, I'm trying to solve this problem for a project, though I think I can't afford to get this creative for a client...
So how is the MPP algorithm of the solar inverter going to interact with the voltage regulator of the generator? I don't see how you can get such a setup to present a constant load to the generator.
Cheers, Wayne
That is the next problem to be solved Wayne. It is going to be an interesting one! The generator should present a current at idle which the MPP should pick up. I assume as the MPP starts to draw that current the generator will generate more (due to the load of the current actually flowing) and it will be a feedback cycle until the inverter is maxing out. Otherwise I will have to find another way to force the current to flow just like a solar panel
That should work, I think. Not sure how fussy solar string inverters are about the ripple current must rectifiers put out. You also need a easy to disable the maximum power point tracking on the inverter, or one that's old enough not to have it (might be a simple configuration setting at installation.)
I'm thinking you set the power delivery on the inverter, too. How much the generator produces would normally be based on the load placed on it, and neither the generator nor the rectifier can easily control that.
I don't see why the you couldn't do solar and generator at the same time with the described approach and both sets of inverters permanently wired in parallel to the Powerwall solar connection.
If the Powerwall has a config parameter about how much solar output is possible it might freak out, or if the combined output exceeds its charge rate, but otherwise it should be fine.
As long as the generator's continuous power rating is larger than the max output of the repurposed solar inverter, I don't think anything weird will happen with the MPPT. That function is just balancing the voltage and current to get the maximum power. Since the rectified voltage probably won't drop much as the current draw is increased, it will just hit up against the max inverter current and the generator will throttle up to maintain its frequency under the new load. This could actually be an interesting and workable solution. I would suggest that you wire it so that the PowerWall thinks it is solar generation and only run the generator while you're supervising the system.
I was planning use a large capacitor in parallel with the solar inverter to eliminate as much ripple as possible. If I can get as close to true DC as possible the whole system should have a much better chance of working. As for MPPT I think most inverters allow them to be paralleled (for single direction panel orientation installs) and I'm hoping the MPPT will work like miimura explains as my generator can output 5.5kW continuously.
Yeah, that's the plan! I'm going to either buy another clamp (does anyone know where neurio clamps are sold individually?) Or wire the generator solar through the solar clamp with my actual solar.
Just an update
I have managed to make my generator start and stop automatically based on the powerwall charge level.
Next step is to create a rectifier for the generator and feed the DC to a grid tie solar inverter.
I have managed to make my generator start and stop automatically based on the powerwall charge level.
Next step is to create a rectifier for the generator and feed the DC to a grid tie solar inverter.
This is an interesting. My main problem with the way Tesla engineered the powerwall setup is that when the PW reaches 0 charge, the solar can't charge the battery anymore, because the inverter needs line power for the inverters to turn on. Even if you were feeding DC power from a generator to the solar inverters, they will not turn on unless they see a line source, and once the PW has drained, it can't provide that signal to the inverters, regardless of where the DC is coming from.
Also, does the REST interface that talks to the PW need connectivity to the Internet to work? In most cases, an extended power outage is likely to take out the cable HFC network that most people in the US for connectivity.
What I would really like is the Tesla gateway box to not have a switch in it at all, but control an off the shelf transfer switch between the line side and the genset. Once the line power failed, the ATS switches to the genset, but the PW can simply not turn the generator on. If the PW goes too low, it can turn the genset on, which should cause the inverters to shut down. The PW can charge from the genset and then switch the generator off.
When the sun starts shining the solar can charge the PW more, and the genset only runs when the PW can't handle the load or is too low on power.
If they could just control an existing ATS, we wouldn't have this 200A limitation, or all the complexity of genset wiring, etc...
thx
mike
Also, does the REST interface that talks to the PW need connectivity to the Internet to work? In most cases, an extended power outage is likely to take out the cable HFC network that most people in the US for connectivity.
What I would really like is the Tesla gateway box to not have a switch in it at all, but control an off the shelf transfer switch between the line side and the genset. Once the line power failed, the ATS switches to the genset, but the PW can simply not turn the generator on. If the PW goes too low, it can turn the genset on, which should cause the inverters to shut down. The PW can charge from the genset and then switch the generator off.
When the sun starts shining the solar can charge the PW more, and the genset only runs when the PW can't handle the load or is too low on power.
If they could just control an existing ATS, we wouldn't have this 200A limitation, or all the complexity of genset wiring, etc...
thx
mike
The way @technerdx6000 is planning to do it, he would have to start up his generator and simulated solar before the Powerwalls shut down.
This whole discussion made me think of a contorted way to get a few hundred watts into my PowerWalls from my EV. It's easy to hook up a 1,000W inverter to the 12V battery and just leave the EV on so it's continuously charging the 12V from the traction battery. However, that kind of inverter will not synchronize to the Powerwall like a solar inverter. Proper on/off grid hybrid inverters start at $2,000 and 2,000W and would still need an autotransformer to get from 120VAC to 240VAC.
So, here's my crazy contorted solution to keep the house going with 500W through the overnight hours during rainy winter days when the solar is not producing enough.
EV 12V aux battery -> 1000W 120VAC inverter -> 600W 48VDC power supply -> 2 each 250W solar micro-inverter -> NEMA 6-20 socket wired to PowerWall Generation Panel & looped through the PowerWall solar CTs.
The total cost of those parts is less than $600. Can anybody think of why this wouldn't work?
So, here's my crazy contorted solution to keep the house going with 500W through the overnight hours during rainy winter days when the solar is not producing enough.
EV 12V aux battery -> 1000W 120VAC inverter -> 600W 48VDC power supply -> 2 each 250W solar micro-inverter -> NEMA 6-20 socket wired to PowerWall Generation Panel & looped through the PowerWall solar CTs.
The total cost of those parts is less than $600. Can anybody think of why this wouldn't work?
I think you're almost as crazy as I am. I don't see why it shouldn't work though!
Right now I am tackling the issue of ripple in the DC output from my rectifier because I doubt the solar inverter will be too pleased about it. I've found I need some serious capacitance to reduce this ripple (greater than 1 Farad). I can't believe how difficult it is to find a 400V 1 Farad capacitor. They all seem to top out at 5V. At the moment the plan is to wire 150 2.7V 500 Farad capacitors in series which will give me a 3.3 Farad capacitor at 405V.
Your idea might work, but I think the efficiency of those conversions will be terrible, and the warranty for your solar inverters will almost certainly be voided by feeding it DC from a generator. I would also worry about how you deal with grounding, as those small generators are really not designed to be coupled in to a power system like this, though maybe the rectification will isolate things enough. Going through isolation transformer would probably fix that though.
Part of me is just frustrated that Tesla has such a lame solution for generator support. Maybe I should just spend the money on a big genset instead of powerwalls and be done with it. At least that is something that works with no manual intervention and my wife will not need a textbook to work make it all work if I'm not there during a power failure.
Part of me is just frustrated that Tesla has such a lame solution for generator support. Maybe I should just spend the money on a big genset instead of powerwalls and be done with it. At least that is something that works with no manual intervention and my wife will not need a textbook to work make it all work if I'm not there during a power failure.
Here's a 5.3F 160V super-capacitor. You'll probably have to shop around some more to find one in stock:
BMOD0006 E160 B02 Maxwell Technologies Inc. | Capacitors | DigiKey
Looks like Mouser has some in stock:
BMOD0006 E160 B02 Maxwell Technologies | Mouser
Cheers for checking that out for me!
150 500 farad caps were gonna cost $450 off ebay, but I did some calculations and I think I will need much less than that for the solar inverter to be happy.
I ended up buying a $250 400V 18000uf capacitor.
I have wired up all my gear now and I did a test run this evening after work.
Initially the inverter powered up fine from the generator DC output and started looking for grid sync.
However it made some loud bangs and switched off before turning back on again.
Not sure what caused that, but I am going to take another look tomorrow.
Attached a pic of the current setup. Sorry its a bit of a mess, but I was too excited to clean up as I went
I have simplified the parts list to eliminate the first AC inverter and use a cheaper micro-inverter. This is the new chain of parts:
EV 12V aux battery -> 720W DC-DC Step Up Converter 24VDC 30A -> 600W Solar Grid-Tie 120VAC micro-inverter -> 120V/240V 1000W step up transformer -> NEMA 6-20 socket wired to PowerWall Generation Panel & looped through the PowerWall solar CTs.
I will probably get around to trying this out sometime this summer because the BOM is now less than $300. I was worried about not having an auto-transformer with a neutral tap, but the existing micro-inverters don't connect to the neutral at all, so this shouldn't need to either.
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