Microgrid at home with Powerwalls - crazy?

[mspohr]

OK, I had this wild idea and I need you to tell me all the things wrong with it.

We are planning to build a second house (small cottage) on our property for just the two of us so our daughter, son-in-law, two kids and large dog can move into the main house.
Main house has 200 amp service, 9.5 kW solar pv. Electrical usage peaks up to 10 - 15 kW.
I want to avoid adding an additional service entrance feed to the cottage.
I was thinking of running a 50 amp service to the cottage (about 100 feet from the service entrance). This would fit in the current service entrance panel and would provide about 10 kW. Of course, the cottage will have peak power draw of more than 10 kW so I was thinking that I would install a Powerwall at the cottage to provide extra power when needed. The cottage will also have additional solar PV and meet California new building requirements.
Would probably also have Powerwall(s) at the main house.

The advantages of this is that I could avoid additional power company service connection cost and monthly fees, take advantage of net metering and TOU as well as have battery backup for power outage (which are more likely with California wildfire danger as well as Winter storm power outages).

OK, I know this is unconventional, but would it work? (Have to consider building codes, etc.)
Tell me everything wrong with this idea.

 

[miimura]

Powerwalls don't have an operating mode designed to limit the grid draw to a specific value. Other battery inverters like ones from Outback Power can do this. Your idea is sound but you can't use Tesla Powerwall to solve your problem at the cottage. Since you only need to handle intermittent loads at the cottage, you won't need that many kWh of batteries. You can use Tesla Powerwalls at the main house.

 

[mspohr]

Powerwalls don't have an operating mode designed to limit the grid draw to a specific value. Other battery inverters like ones from Outback Power can do this. Your idea is sound but you can't use Tesla Powerwall to solve your problem at the cottage. Since you only need to handle intermittent loads at the cottage, you won't need that many kWh of batteries. You can use Tesla Powerwalls at the main house.

I was thinking that might be a problem. I need a battery/inverter that can supplement the 10kW utility feed to cover peaks. I guess the Tesla Powerwall can't do that. I'll look into other inverters.

 

[mspohr]

Powerwalls don't have an operating mode designed to limit the grid draw to a specific value. Other battery inverters like ones from Outback Power can do this. Your idea is sound but you can't use Tesla Powerwall to solve your problem at the cottage. Since you only need to handle intermittent loads at the cottage, you won't need that many kWh of batteries. You can use Tesla Powerwalls at the main house.

Looks like the Outback Grid/Hybrid Inverter-Charger and batteries might work.

 

[miimura]

This is the relevant function description for the Outback Radian.

This image is Page 13 of the manual here:
http://www.outbackpower.com/downloa...adian_8048a_4048a/gs_8048a_4048a_operator.pdf

 

[mspohr]

This is the relevant function description for the Outback Radian.
View attachment 383659

This image is Page 13 of the manual here:
http://www.outbackpower.com/downloa...adian_8048a_4048a/gs_8048a_4048a_operator.pdf

That is exactly what I need!
Thanks so much!

 

[NuShrike]

Powerwalls don't have an operating mode designed to limit the grid draw to a specific value. Other battery inverters like ones from Outback Power can do this. Your idea is sound but you can't use Tesla Powerwall to solve your problem at the cottage. Since you only need to handle intermittent loads at the cottage, you won't need that many kWh of batteries. You can use Tesla Powerwalls at the main house.

That's really weird, as they basically limit it to Zero. All. The. Time. -- when supplying.

You would think it should be reasonably easy to make it configurable to target something else than zero.

 

[mspohr]

That's really weird, as they basically limit it to Zero. All. The. Time. -- when supplying.

You would think it should be reasonably easy to make it configurable to target something else than zero.

It's just software.

 

[miimura]

That's really weird, as they basically limit it to Zero. All. The. Time. -- when supplying.

You would think it should be reasonably easy to make it configurable to target something else than zero.

This is a special case that I don't expect Tesla to address. However, you're right, it's just one more operating mode that could be implemented in software.

The only problem I see is that Tesla cannot prevent an overload condition when the battery runs down while the Radian can just shut down and it will automatically drop all the loads. That's the difference between a grid interactive inverter and an off-grid inverter charging from a limited grid connection (or generator).