Hello everyone. We are in the process of building a large home (9000 sq ft) in a PGE area with poor power reliability. That means high cost (esp in band 5 usage which a home like this one would definitely hit), and dealing with reliability means a generator (since I travel a lot and I want my wife and kids to not have to be improvising if I am not here when the power fails). I have been looking at these forums and talking to solar contractors, but still can't quite understand how the Powerwall wiring is supposed to work and what the control mechanism is. I am an engineer so this is rather frustrating for me.
So far, I think I can get about 21 kW of solar array capacity put into place on the roof. Hooking that into a few grid tie inverters and doing net metering is pretty straight forward. There is the question about microinveters, vs SolarEdge, vs string inverters, and I am trying to understand what makes the most sense for maximum kWH production, but there are lots of choices that should work and get me out of the most expensive usage bands from PGE. Installing a solar roof is an option, but I am about 6 months away from having to make that call, though right now it doesn't look like Tesla will be ready by then.
The house will have a 400A panel, and for backup I plan to install a generator that can handle the whole house load with a conventional transfer switch. I am also using a Mitusbushi VRF type system for HVAC, so that actually avoids the high startup current that many normal HVAC systems create on the power system, as it starts up slow and ramps up with demand.
Now, I'd rather avoid generating the pollution the generators use, and if for some reason the power were to go out for an extended period of time, having the ability to operate on solar alone would be nice. Also, if I could do some TOU shifting, I could probably zero out my power bill completely.
If the Powerwall were still being made in a DC version, the path forward would be easy. There many solutions (Fronius, SMA, SolarEdge) that have hybrid systems, including generator support my configuration. But an AC Powerwall is not supported officially by any of them as far as I can tell. And I'd rather not go down the lead-acid battery path, since it's much more expensive and I don't like the environmentals of those batteries.
So setting aside how the genset support would work for now, is there a Powerwall 2 configuration that would work with some set of multiple inverters that would work in my my situation? No matter which inverter type and vendor I would use, I'd have to have multiple of them. Does the Powerwall work with only some of them, or does it use it's frequency management to enable any old inverter to island properly?
I am confused about the "gateway" and what it does. It appears you have to have one to shut off the AC feed to prevent feeding the grid in an outage, but I can't find any info about what exactly the specs for these are in terms of amperage and how they are controlled. I assume it doesn't talk via the cloud because if there was an internet outage at the same time nothing would happen.
If the purpose of the gateway was just isolating the house, a generator automatic transfer switch would seem to be a better choice, as the controls could be set to isolate the house from the grid, but not turn the genset on unless there was a power deficit that needed making up, presumably only at night when the panels were not generating any power. A 3 pole transfer switch could also support disconnection from the grid as well as the genset.
Because of the lack of any reasonable documentation from Tesla, solar contractors and electricians can't tell me if a powerwall 2 could or couldn't work in this setup. They seem as clueless as I am. Even if the powerwall 2 for backup couldn't work now, but could in the future, I'd like to wire things in a way that would allow then to be retrofitted in, but again, we don't really know how to do that now.
Do you all have any documentation that would help with these decisions (types of inverters, transfer switch choices or wiring, etc...) that would help at least with being able to use one in the future if not when the house is completed (likely end of next summer)? I'd sure be obliged.
Thanks!
mike
So far, I think I can get about 21 kW of solar array capacity put into place on the roof. Hooking that into a few grid tie inverters and doing net metering is pretty straight forward. There is the question about microinveters, vs SolarEdge, vs string inverters, and I am trying to understand what makes the most sense for maximum kWH production, but there are lots of choices that should work and get me out of the most expensive usage bands from PGE. Installing a solar roof is an option, but I am about 6 months away from having to make that call, though right now it doesn't look like Tesla will be ready by then.
The house will have a 400A panel, and for backup I plan to install a generator that can handle the whole house load with a conventional transfer switch. I am also using a Mitusbushi VRF type system for HVAC, so that actually avoids the high startup current that many normal HVAC systems create on the power system, as it starts up slow and ramps up with demand.
Now, I'd rather avoid generating the pollution the generators use, and if for some reason the power were to go out for an extended period of time, having the ability to operate on solar alone would be nice. Also, if I could do some TOU shifting, I could probably zero out my power bill completely.
If the Powerwall were still being made in a DC version, the path forward would be easy. There many solutions (Fronius, SMA, SolarEdge) that have hybrid systems, including generator support my configuration. But an AC Powerwall is not supported officially by any of them as far as I can tell. And I'd rather not go down the lead-acid battery path, since it's much more expensive and I don't like the environmentals of those batteries.
So setting aside how the genset support would work for now, is there a Powerwall 2 configuration that would work with some set of multiple inverters that would work in my my situation? No matter which inverter type and vendor I would use, I'd have to have multiple of them. Does the Powerwall work with only some of them, or does it use it's frequency management to enable any old inverter to island properly?
I am confused about the "gateway" and what it does. It appears you have to have one to shut off the AC feed to prevent feeding the grid in an outage, but I can't find any info about what exactly the specs for these are in terms of amperage and how they are controlled. I assume it doesn't talk via the cloud because if there was an internet outage at the same time nothing would happen.
If the purpose of the gateway was just isolating the house, a generator automatic transfer switch would seem to be a better choice, as the controls could be set to isolate the house from the grid, but not turn the genset on unless there was a power deficit that needed making up, presumably only at night when the panels were not generating any power. A 3 pole transfer switch could also support disconnection from the grid as well as the genset.
Because of the lack of any reasonable documentation from Tesla, solar contractors and electricians can't tell me if a powerwall 2 could or couldn't work in this setup. They seem as clueless as I am. Even if the powerwall 2 for backup couldn't work now, but could in the future, I'd like to wire things in a way that would allow then to be retrofitted in, but again, we don't really know how to do that now.
Do you all have any documentation that would help with these decisions (types of inverters, transfer switch choices or wiring, etc...) that would help at least with being able to use one in the future if not when the house is completed (likely end of next summer)? I'd sure be obliged.
Thanks!
mike