Plan: Off grid solar with a Model S battery pack at the heart

[Yoda101]

LOL - you are becoming as famous as EM.

 

[evp]

See, THIS is the PowerWall product that Tesla should be installing in homes -- something that can comfortably power the whole house for several days, not a couple of rooms for a few hours. Let's hope your pictures get Elon's attention.

 

[mitch672]

See, THIS is the PowerWall product that Tesla should be installing in homes -- something that can comfortably power the whole house for several days, not a couple of rooms for a few hours. Let's hope your pictures get Elon's attention.

They do, wk's 192KW is the equiviliant of (2) Tesla commercial Powerpacks (100KW each). They just won't fit INSIDE most homes.

 

[Cosmacelf]

Yeah, a setup like wk's is very adventurous indeed and even if you had off the shelf products, not many people would implement it. I believe a 100kW unit would weight about 2000 pounds? Try lifting that up and down the stairs

 

[wk057]

looks fantastic, wish I could do any solar on my condo.

here is some food for thought for you; you likely won't own this house/condo forever, so while it's fresh in your mind, make up some documentation, and perhaps contact a local electrical contractor, and get them familiar with your installation. The idea is, if someday you want to move, you'll have a local electrician that can be contacted.. Imagine a buyer walks into that electrical room for the first time, its a bit overwhelming. Not saying you are going to sell/move anytime soon, but it's something you have to think about. on the plus side, you're probably one of the few "netzero" houses in the neighborhood, and having small or no power bill is a huge selling point.

I actually have pretty much everything labeled and documented pretty well already. In any case, I plan on being here quite a while. Still have plenty of room to grow into this place and no foreseeable reasons to move.

LOL - you are becoming as famous as EM.

Woot! Me and my.... *checks*.... holy crap 8 followers! lol.

See, THIS is the PowerWall product that Tesla should be installing in homes -- something that can comfortably power the whole house for several days, not a couple of rooms for a few hours. Let's hope your pictures get Elon's attention.

They do, wk's 192KW is the equiviliant of (2) Tesla commercial Powerpacks (100KW each). They just won't fit INSIDE most homes.

Yeah, a setup like wk's is very adventurous indeed and even if you had off the shelf products, not many people would implement it. I believe a 100kW unit would weight about 2000 pounds? Try lifting that up and down the stairs

If you actually look at the space my project has taken up... it's actually not all that much. Most of it is wall mounted stuff except for the batteries which don't even take up much floor space. Presumably the things I have wall mounted could be condensed quite a bit using higher voltage DC. I bet my setup could be condensed into something not much larger than my battery rack if it were engineered properly. But the room this is all in is basically empty.

Also, think of all of the things that are large and installed in homes already. My entire 191kWh battery rack is ~2000 lbs, and is modular so no one had to lift/move 2000 lbs to install it. I think a similar setup could be done commercially. Basically buy a Tesla battery rack, add 5 kWh modules as desired. Would make a lot of sense I think.

I would be interested to see what response Elon would have to my project, however I don't really expect one.

 

[InTheShadows]

That's actually a minor bullet point on my todo list. Not visible in the photos (because I moved it) is one of those portable A/C units that vents out a window on the other side of the wall where the transfer switches are. It's doing the job for the moment, but I will be installing a more permanent solution to conditioning this space soon. A combination of a heat pump hot water heater ducted to this room, a mini split A/C unit, and an exhaust blower all on thermostats.

Believe it or not, under normal loads and PV regulation it doesn't get deathly hot in there. On Sunday I charged my Model S at 20kW while the A/C was running in the house and such (so about 25-27kW load), and I had the portable A/C unit off at the time. It got up to about 85F in there and held around there, most likely in a battle with the ground floor central air unit at that point. But it's good to know that it doesn't get to ridiculous temperatures even without special conditioning.

Awesome, you were only using 3.5 of those radians at that time. You did a really great job. Very professional looking.

You probably shared this earlier but this thread is so long I don't remember the reason. Why did you go with the MidNite Classics over the FlexMax80's?

Could you do some type of exhaust fan to vent the heat to the outside to save energy? Possibly even thermosyphioning? This might not be an option if you can't create an envelope around your utility room to create a seperate "conditioned space".. Dealing with BOS heat indoors is a pain.

 

[wk057]

Awesome, you were only using 3.5 of those radians at that time. You did a really great job. Very professional looking.

Thanks!

Actually, the Radians kick on in 4kW increments for efficiency purposes. So six of seven of the eight would be running at a 27kW load with about a 3.9kW-4.5kW load on each. I'm working on a script that works with the MATE3 USB connection that rotates out which inverters get utilized under load to balance the wear a bit, also. I'll have to physically change the master one occasionally to do the same since it's required to be on port 1 of the HUB10.

You probably shared this earlier but this thread is so long I don't remember the reason. Why did you go with the MidNite Classics over the FlexMax80's?

The panels I have are huge. They have a VoC of ~86V each, even higher in the winter. If I were to use the FlexMax units I'd have to run at half of the voltage since they only support up to 150V VoC. With the Classic 200s I can do up to 200V VoC which will cover me for strings of two panels + three sets in parallel even on the coldest days. I bugged Outback about this particular issue with their units not supporting higher input voltages, but they said I'd have to run at lower voltage/higher amperage to make them work. Overall, the MidNite Classics worked for a more efficient install.

Could you do some type of exhaust fan to vent the heat to the outside to save energy? Possibly even thermosyphioning? This might not be an option if you can't create an envelope around your utility room to create a seperate "conditioned space".. Dealing with BOS heat indoors is a pain.

Yeah, that's one of the options. To exhaust I need to replace that air, so I'd have to have a fresh air vent. I want to make sure I'm not pulling in air that is hotter than what I'm exhausting, so I'll have the mini split A/C unit there for days when it's hotter outside. I'll also be having a heat pump hot water heater in a nearby room with a duct kit sourcing/venting from/to this room. I also plan on insulating this room a little better against the rest of the house so that I can keep it a little warmer when needed for energy savings (exhaust vs running mini AC unit).

Should be fun.

 

[InTheShadows]

Thanks!

Actually, the Radians kick on in 4kW increments for efficiency purposes. So six of seven of the eight would be running at a 27kW load with about a 3.9kW-4.5kW load on each. I'm working on a script that works with the MATE3 USB connection that rotates out which inverters get utilized under load to balance the wear a bit, also. I'll have to physically change the master one occasionally to do the same since it's required to be on port 1 of the HUB10.

Oh, I miss understood how they came in then. I thought inverter one would bring up 4kw, then the other 4kw in that unit then inverter 2 would bring on the first 4kw. Allowing the rest to fully sleep. So with two inverters and a 7kw load each inverter would be providing 4kw

We have a big Outback Power training session tomorrow. I'll talk to one of the engineers about rotation of inverters to balance their usage. This would even be good in a single unit to go back and forth between the two units.

Another question. Are you noticing any voltage sag when big loads come on? Like if you plug your car in, how well do the inverters prevent and react to the sudden load. This would be in mini grid mode.

I have seen magnum 4448pae inverters sag enough when a well pump kicks in to cause tv's to turn off.

 

[pgiralt]

ike if you plug your car in, how well do the inverters prevent and react to the sudden load.

Plugging the car in is not a good example because the car ramps up its current draw slowly. Things like AC Compressors turning on are more likely to cause a sag.

 

[InTheShadows]

Plugging the car in is not a good example because the car ramps up its current draw slowly. Things like AC Compressors turning on are more likely to cause a sag.

Oh yea good point. I forgot about that. I was just thinking 20kw at the flip of a switch.

So I guess it could be done by throwing the main off and setting all the big loads to come on when it's reenergized.

 

[wk057]

Oh, I miss understood how they came in then. I thought inverter one would bring up 4kw, then the other 4kw in that unit then inverter 2 would bring on the first 4kw. Allowing the rest to fully sleep. So with two inverters and a 7kw load each inverter would be providing 4kw

We have a big Outback Power training session tomorrow. I'll talk to one of the engineers about rotation of inverters to balance their usage. This would even be good in a single unit to go back and forth between the two units.

Another question. Are you noticing any voltage sag when big loads come on? Like if you plug your car in, how well do the inverters prevent and react to the sudden load. This would be in mini grid mode.

I have seen magnum 4448pae inverters sag enough when a well pump kicks in to cause tv's to turn off.

I'm in MiniGrid mode, yeah.

Well, the car isn't actually a sudden load. It ramps up over about 30 seconds, and the inverters come on perfectly in response.

My one large A/C unit is another story, though. I actually changed the power save settings to keep two inverters (4 modules) out of power save to compensate. When that unit kicks on lights flicker as the other Radians come out of power save to handle the surge, sometimes six of them even though it's only a 3kW compressor (which probably needs replacing given this surge power). Works a little better with master power save set to 3 (4 modules/16kW capacity on all the time) at the expense of higher idle load. I may bump it up to 4 or 5 if it doesn't solve the surge issue. Only things in the house that react to it are some LED lights and a couple of UPS's. Aside from that it seems OK, but would be nice if they handled that particular surge a little cleaner, though.

As for voltage sag, under 55kW load (highest I've been able to put on the inverters) I see about 1.3V sag on the DC side (MATE3 is only good in 0.4V increments and shows a 1.6V sag). Not bad considering that's about a 1400A load. And that comes out to only about 1A draw per cell... still a pretty light load by LiIon 18650 standards.

If Outback could add in some automatic wear rotation that would be totally awesome. I like my master inverter being the one closest to the batteries, since it has the shortest cable run, but I would like to rotate out the slaves for sure.

And actually, I was accidentally a little misleading on power save. The inverters power on the modules in 2kW increments, so it works out to 4kW per inverter. When the load disappears they slowly go back into power save starting at the end (can hear the relays) on something like a 15 second delay. So in my case with my current settings, any load over 8kW causes more slave modules to start coming online.

Overall though, I love the Radians. Best inverters I've ever messed with. I have a few gripes, which I've spoken to Outback about, mainly revolving around cut out/cut in voltages. For example, in MiniGrid mode the inverter wants to switch back to the utility when the voltage gets to a set point. That's fine, and that's what I want to happen. However, the lowest that set point can be set to is 44V..... which is like 60% charge on my batteries and isn't all that useful. So, I have the AC input manually dropped which will let the inverters run all the way down to 36V if I wanted (I have it set to 38.2V I believe), then I have a script running on my monitoring PC using the MATE3 USB that enables the AC input near that cut off voltage. Not ideal, since the Radians/MATE3 should be able to set this to a voltage below 44V since the inverters themselves work down to as low as 36V.

 

[Dave EV]

My one large A/C unit is another story, though.

I wonder if the startup capacitor on it is wearing out or failed?
Something like this may help:
Compressor Saver Hard Start Capacitor Model CSR U2 - Hvac Controls - Amazon.com

 

[wk057]

I wonder if the startup capacitor on it is wearing out or failed?
Something like this may help:
Compressor Saver Hard Start Capacitor Model CSR U2 - Hvac Controls - Amazon.com

Yeah, I actually have a new capacitor and a hard start kit that I plan on putting on it as a short term potential fix. In the long term I plan on replacing it entirely with something that has a much higher SEER rating.

I also have an appropriately sized power factor correction capacitor I want to add to my pool pump to see if it lowers amperage any (PF looks like about 80-85% on it), which would have a minor efficiency gain/power reduction over the life run time.

 

[schueppert]

"As for voltage sag, under 55kW load (highest I've been able to put on the inverters) I see about 1.3V sag on the DC side (MATE3 is only good in 0.4V increments and shows a 1.6V sag). Not bad considering that's about a 1400A load."

I think that's the best you could have done in the circumstances, but it's still burning up 2kW! I totally understand that low voltage was the only option open to you with currently available equipment, but it does show the wisdom of Tesla/SolarEdge moving to high voltage for Powerwall.

Regarding the AC, have you thought about trying to run 3 of the Outbacks as 3 phase and investing in a 3 phase compressor? You would get much higher efficiency and lower startup current.

 

[wk057]

"As for voltage sag, under 55kW load (highest I've been able to put on the inverters) I see about 1.3V sag on the DC side (MATE3 is only good in 0.4V increments and shows a 1.6V sag). Not bad considering that's about a 1400A load."

I think that's the best you could have done in the circumstances, but it's still burning up 2kW! I totally understand that low voltage was the only option open to you with currently available equipment, but it does show the wisdom of Tesla/SolarEdge moving to high voltage for Powerwall.

Regarding the AC, have you thought about trying to run 3 of the Outbacks as 3 phase and investing in a 3 phase compressor? You would get much higher efficiency and lower startup current.

It would take a major rework of a lot of my setup to do any 3-phase, and wouldn't be worth it. Three 8kW units (24kW) to run maybe 7kW-8kW max worth of compressors total wouldn't make much sense.

As for low voltage vs high voltage, keep in mind that Tesla hasn't actually done anything at all to solve this particular issue. I could have easily wired my battery bank to be high voltage. However, there still exists no readily available off-the-shelf off-grid inverter capable of accepting high input voltages. If SolarEdge comes out with an off-grid capable one, that'd be great. But as of now nothing exists that fits the bill. Sure Tesla's PowerWall will provide HVDC, but the only things currently capable of using that are grid-tied string inverters.

Also! Let's say I had enough PowerWalls to put out 55kW (would take ~28 of them). They're only 92% efficient not even counting inverter inefficiency due to their DC-DC converter. So that's nearly 5kW wasted right off the top. Assuming an inverter efficiency of 95%, PowerWall efficiency of 92%, at 55kW load that would be about 8kW wasted. My setup loses ~2kW in wiring due to the lower voltage and about 4kW to inverter efficiency for about 6kW losses at that load.

 

[schueppert]

I sort of assumed the reason you had 8 inverters in the first place was to provide startup overhead for the AC. Do you actually have 55kW of load?

It was sort of my point that you had to go low voltage because that's what the currently available off-grid inverters support. But SolarEdge and Fronius already make on-gird inverters that support high voltage and clearly they will make these off-grid capable in order to support Powerwall. In SolarEdge's case, they have stated their solution is compatible with their existing inverters; it's not completely clear what this means, but I suspect it means all they need is a software update to the inverter and a replacement unit for the AC/DC disconnect that adds a relay controlled by the inverter to isolate the grid.

I would be interested in seeing end-to-end efficiency numbers for your storage solution.

Your system will always win for awesomeness and being first!:smile:

 

[wk057]

I sort of assumed the reason you had 8 inverters in the first place was to provide startup overhead for the AC. Do you actually have 55kW of load?

Yeah, I can fully load the inverters under some circumstances. I can get 40kW of load just from the two HPWCs in the garage. ~8kW for HVAC and outside heat pump/AC units, about 25kW worth of auxiliary electric heating (should never all be in use at once, but can be), electric hot water heater (5kW), electric range (? kW... varies), pool pump @ 1.7kW, etc etc etc. Basically a 100% electric household.

It was sort of my point that you had to go low voltage because that's what the currently available off-grid inverters support. But SolarEdge and Fronius already make on-gird inverters that support high voltage and clearly they will make these off-grid capable in order to support Powerwall. In SolarEdge's case, they have stated their solution is compatible with their existing inverters; it's not completely clear what this means, but I suspect it means all they need is a software update to the inverter and a replacement unit for the AC/DC disconnect that adds a relay controlled by the inverter to isolate the grid.

I would be interested in seeing end-to-end efficiency numbers for your storage solution.

Your system will always win for awesomeness and being first!:smile:

I should have some decent efficiency numbers once I gather up some more data. So far looking pretty good. The batteries themselves, at the load/charge levels I'm using, are almost indistinguishable from 100% efficiency so far. Going to take more data to dial that in a bit more. The inverters appear to be at least 90% efficient, peaking as high as 95% so far. The charge controllers appear be 97-99% efficient.

And thanks everyone for the enthusiasm and support.

 

[InTheShadows]

I sort of assumed the reason you had 8 inverters in the first place was to provide startup overhead for the AC. Do you actually have 55kW of load?

It was sort of my point that you had to go low voltage because that's what the currently available off-grid inverters support. But SolarEdge and Fronius already make on-gird inverters that support high voltage and clearly they will make these off-grid capable in order to support Powerwall. In SolarEdge's case, they have stated their solution is compatible with their existing inverters; it's not completely clear what this means, but I suspect it means all they need is a software update to the inverter and a replacement unit for the AC/DC disconnect that adds a relay controlled by the inverter to isolate the grid.

I would be interested in seeing end-to-end efficiency numbers for your storage solution.

Your system will always win for awesomeness and being first!:smile:

SolrEdge will not be able to do a software only fix. There will be hardware necessary. For mini grid mode the inverters have to disconnect from the grid. This would require a transfer switch added at the very least. I also think there will need to be something else added to handle startup surges. A 7.7kw solaredge inverter is max 7.7kw. The 8kw radian can handle 16kw surges.

 

[schueppert]

Cleary it needs new hardware, but from the horse's mouth:

"Designed to manage both functions with just one SolarEdge DC optimized inverter, the solution will allow for outdoor installation and will include remote monitoring and troubleshooting to keep operations and maintenance costs low. The solution will also support upgrading existing SolarEdge systems with the storage solution."

The SolarEdge unit has a separate DC/AC disconnect and I'm sort of interpreting their comment as meaning that is all that will need replacing.

 

[AntronX]

My one large A/C unit is another story, though. I actually changed the power save settings to keep two inverters (4 modules) out of power save to compensate. When that unit kicks on lights flicker as the other Radians come out of power save to handle the surge, sometimes six of them even though it's only a 3kW compressor (which probably needs replacing given this surge power). Works a little better with master power save set to 3 (4 modules/16kW capacity on all the time) at the expense of higher idle load. I may bump it up to 4 or 5 if it doesn't solve the surge issue. Only things in the house that react to it are some LED lights and a couple of UPS's. Aside from that it seems OK, but would be nice if they handled that particular surge a little cleaner, though.

How about some inrush current limiters? I don't know which amperage rating would work, but maybe start with 15A ones and just parallel them for more current. bigAMP - Inrush Current Limiters | Ametherm