Powerwall 2 install.

[JSchnee21]

Wow, even at $5,320 (after rebates and tax credit) that's a great price! If the Panasonic lithium cells in the PowerWalls last anywhere near as long as the ones in Tesla cars, they seem to be surprisingly robust. Unlike the ones in my laptop and iPhone!

For comparison, when spec'ing a commercial UPS system from APC for example:

http://www.apc.com/shop/us/en/products/APC-Smart-UPS-RT-20kVA-RM-230V/P-SURT20KRMXLI

A unit's load capacity is generally spec'ed by it's Volt-Amp capacity -- For example, 20,000 VA = 240V * 83 Amps assuming a power factor of 1, and no reactive loads (aka motors). Often times the actual kW rating (depending on the MFG) will be a lot less as they play games with the power factor.

Generally you would for 60-80% (or less) to provide for growth and to prevent overload alarms during operation. If the UPS cannot handle the instantaneous load (of all your equipment turning on for example) it will drop the load,

Based on your actual load (for example my house runs about 1kW nominal, 6kW with AC running, and 8-9kW peak with AC, Microwave, Keurig, etc. From your observed loads you can estimate the maximal carrying and inrush currents that are needed to support these loads for comparison to the output specs of the UPS system. Generally there is a diversity calculation to estimate and allow for the fact that the UPS is generally not sized for 100% of the output wiring capacity. But in a home, the AC is the primary concern. Mine, for example, (older 4 ton) draws ~30amps @ 240 continuously, and has an inrush of 60-80 amps.

From there, once you have identified the kVA of the UPS, you can then scale the Amp-hours of the batteries to lengthen the kWh of the solution. Most UPS vendors have a modelling tool for this (see link above) where you supply the average continuous load in Watts, and based on the number of strings of batteries, it will tell you the run time.

I haven't tried to get technical punchouts for the Tesla PowerWalls, but they should be readily available. But, unless the PowerWall DC to AC inverter can put out 100amps or more at 240, I would seriously consider moving the circuit breaker for the HVAC condenser into a non-UPS panel. Is this new construction? Or are you setting this up in your basement or garage? That's a lot of wall space in your diagram.

Do you have any consumption data for your home? I would start by metering it and looking at the current/power specs for your HVAC. For comparison purposes, with the HVAC, I'm running an average of ~55 kWh per day with peaks up to 76kWh. So, I'd have to drop the HVAC from the equation to get any meaningful runtime from a 37kWh pack.

I agree the solar PV array is rather small, but remember, this is not an off-grid solution. Realistically, the PV array would never be able to charge the battery packs if they were discharged by more than 15-20% or so.

-Jonathan

[max2k]

Yes assumption is that the AC unit is not on. Which works for most of the year here. Mostly cloudless days and sunshine year around.

Bottom line there is no realworld data as these units are brand new. I'll get actuals in the next few months. Everything else is speculation.

Max load should be somewhere in the specs- how else did they pull permit without supplying those details? For one it would define size of the breaker ... Don't get me wrong, I wish this project complete success despite my reservations against Tesla practices in general, I'm just trying to paint more realistic picture.

[sriram97]

Fwiw Tesla has a 10 year warranty. But the warranty is vague in that it does not guarantee output rate.

[sriram97]

Yes assumption is that the AC unit is not on. Which works for most of the year here. Mostly cloudless days and sunshine year around.

Bottom line there is no realworld data as these units are brand new. I'll get actuals in the next few months. Everything else is speculation.

[cebury]

Since the CA SGIP is a rebate you need to do the calculation as:
( 17k - 9,400 ) x 0.7 = $5,320

I didnt think his math was right but suppose lots of folks did/do it that way and are fine until audited.

[ButchDeal]

The cost of the install was 17k just for the 2 powerwall installs. State of California sgip rebate was 9400 and with the federal credit of 30% the total out of.pocket is 17k - 5.1k - 9.4k = 2.5k.

Since the CA SGIP is a rebate you need to do the calculation as:
( 17k - 9,400 ) x 0.7 = $5,320

[max2k]

I dont have any actual numbers but from the calculations and assumptions we made, These 2 units put out enough to power my whole home for 15 hours. As such There's no separate subset of appliances and lights that are powered by these units. And assuming that the sun comes back in 15 hours which is a good bet ? here in norcal my PV system should kick back in power these units and my home. And if I cut my consumption in this scenario, which I don't but I can if needed, I can be off grid indefinitely if needed is the plan.

Looks like total capacity is 27 kWh so if discharge time is 15 hrs it can handle 1.8 kW which is less than 1 outlet at full power continuously. What is important is the peak power those can produce so even if time is shorter they still can handle something like AC turning on and off during night. At 1.8 kW these won't be able to handle single AC unit, especially its startup current. Hope the peak is at least x5 higher. Another more serious problem as I see it is significant undersize of the PV array- how 7.4 kW number came about? Was it just calculated based on available roof area? These 2 components (array & battery) need to match to provide best performance. Array of that size will produce 6 kW tops under best conditions during 4 hr period. It would be barely enough to charge the battery but then nothing will be left for the house.

Do you have any clouds in San Ramon? Those can easily stretch longer than 15 hrs so I think fully off the grid is still not realistic here but these should help to mitigate TOU rates differences. I'm not sure though if that will worth $2.5k spent on the system which would supposedly need replacement in 5(?) years.

[sriram97]

I dont have any actual numbers but from the calculations and assumptions we made, These 2 units put out enough to power my whole home for 15 hours. As such There's no separate subset of appliances and lights that are powered by these units. And assuming that the sun comes back in 15 hours which is a good bet ? here in norcal my PV system should kick back in power these units and my home. And if I cut my consumption in this scenario, which I don't but I can if needed, I can be off grid indefinitely if needed is the plan.

[sriram97]

And the install is in San Ramon California.

[sriram97]

Here's another picture with the wiring diagram. I'll get the additional detail and post. This is the AC powerwall with the built in inverter. One of the first units shipped from the gigafactory in sparks NV.

[sriram97]

The cost of the install was 17k just for the 2 powerwall installs. State of California sgip rebate was 9400 and with the federal credit of 30% the total out of.pocket is 17k - 5.1k - 9.4k = 2.5k.

[SunEagle]

Just completing my powerwall 2 install along with my 7.4kw PC system. Here are some.pictures of the powerwall install. No data yet as it will be a few weeks before the inspections are completed and the system becomes functional and I can keep you all posted

Sounds like you have a plan. Please let us know roughly where you live and about what the cost was to install that system. I appreciate you sharing your information.

[JSchnee21]

Could you also share the goal of your energy storage solution? Is it primarily time shifting your consumption to work around your PoCo's TOU plans? What's net metering like in your area? Does the system provide backup power in the event of a PoCo outage? If so, how do you manage load shedding? Did you have to install a second panel board and move circuits into / out of the battery protected load center?

It appears you have two Powerwall batteries. What size is the battery's DC to AC inverter? How many continuous amps can it supply at 240 VAC? for how long?

Thank you! Just curious. I have a lot of experience with large commercial UPS systems (208V & 480V 3-phase, 20kW-250kW) . The UPS systems themselves are generally not too expensive ($20K-$200K) but properly wiring the feeders and loads can be very expensive.

In a residential setting, you'd want to minimize the wiring cost (and the space it takes up) as much as possible. But unlike whole house natural gas generators which are cost effective and large enough (usu 10kW-22kW) to pickup the entire panel board using a simple manual or automatic transfer switch

For example this 22kW 1800-rpm natural gas unit from Generac -- $8800 -- will put out 92 amps @ 240VAC continuously

https://www.electricgeneratorsdirect.com/Generac-Protector-RG02224ANAX-Standby-Generator/p15945.html

https://www.electricgeneratorsdirect.com/manuals/generac-protector-d836ab0ec1c0c1f65ec336b8c980b1c8.pdf

None of the Solar PV / Storage solutions I've seen have been very large. Meaning that a lot of additional wiring would be necessary to separate out the protected vs non-protected circuits. And run times would be only a few hours -- aka good for a blip and maybe a downed pole. But not for a hurricane, ice storm, etc.

But, if all you want to do is shift your usage later in the evening to work around a TOU plan, then this wouldn't be necessary. Though, at least in the US, I haven't yet seen evidence that using storage for time shifting was cost effective, yet.

[max2k]

Just completing my powerwall 2 install along with my 7.4kw PC system. Here are some.pictures of the powerwall install. No data yet as it will be a few weeks before the inspections are completed and the system becomes functional and I can keep you all posted

Would you share costs/performance numbers? What are those batteries part #, capacity, voltage, charge controller, dimensions? It's hard to make anything from the pic itself. The wires look like they belong to some comm equipment instead of 7.4 kW power plant.

[sriram97]

Some pictures