diy solar

diy solar

Has anyone designed and built an actual code compliant Powerwall system?

pgrovetom

New Member
Joined
Dec 20, 2019
Messages
4
Is anyone aware of any working DIY efforts to build a Powerwall for backup purposes now that PG&E will be shutting off power in California in the Autumn fire season regularly. It would be difficult to duplicate the fancy Powerwall software APP but it should be reasonable to build a straightforward power loss backup system controller using Python on a Raspberry Pi, a few Tesla $1000 5.2KWh batteries on Ebay, a commercial automatic transfer switch, a large frequency adjustable sine wave inverter and a battery BMS and solar charge controller. The tricky part is whether it can be done code compliant.

I have a Telecom Engineering background but the part that is daunting is whether it can be done code compliant. It would seem that duplicating Tesla's architecture with a commercial automatic transfer switch based disconnect gateway run by the Raspberry Pi communicating with battery modules built around the available 5.4KWh Tesla batteries on Ebay would make sense. The battery modules could be run by Raspberry Pi's all networked. Each battery module would require a commercial BMS, charge controller appropriate for the Tesla battery and frequency agile pure sine wave inverter. The frequency control over the inverters allows for shutting off the solar inverters when the batteries are fully charged. The UL1741 has a requirement that solar grid tie inverters shut down when the "grid" frequency drops below 59.3Hz. This can be used by the software to shut down the solar grid tie inverters once the batteries are charged and turn them back on when charging is needed.

I haven't given this much thought and was wondering if anyone had actually done a workable code compliant system. It seems feasible. It should be possible to build it cheaper than the $1100 gateway plus $6700 per 14KWh PW2 plus expensive installation. I see a 4 module 85KWh Tesla battery for $1250 on EBAY. If its accurate, just one of those 4 modules should exceed a 14KWh PW. Otherwise one could utilize 2-3 of the $1000 5.4KWh modules. I'm curious if anyone has actually built one or investigated the code issues and components. Hopefully a code compliant commercial automatic transfer switch would go a long way to meeting code requirements. It would disconnect the home and alert the software to bring up a battery powered master inverter in the 5-7KW range. It would bring up the house and prime the solar inverters to begin startup. The charge controller could be run off grid power or off backup mode solar power. The home would be powered by all the inverters slaved off the main frequency agile master inverter. When the software detected the batteries were fully charged, the frequency output of the voltage mode master inverter would be dropped to 59 Hz. That would cause the UL1741 current mode solar inverters to drop off. The Raspberry Pi's provide easy to use WiFi which could be used to monitor the system via a simple Web interface in the home on a PC. When the power came back on, the ATS would alert the software and the master and any slave system inverters would shut off till next time.

Thoughts? Ideas? Problems? Code issues?
 
Have you watched any jehugarcia videos?

With a properly set up mpp inverter, automatic transfer when power drops should be simple.
 
You said, Powerwalls... not PV. That is an entirely different scenario.
For rolling blackout protection, you only need battery backup. PV, gets you power company independence, PW gets you a power company cushion.
 
Ah, you're right, he's talking about a house backup system. Related but different animal. For the cost you'd be better off with a generator based system, a transfer switch, and a small battery bank and inverter/charger to tide you over until the genny gets up to speed. If you really want a large battery bank to minimize the times you have to run a genset to charge it up you might want to take a look at the used BYD batts at batteryclearinghouse. Dirt cheap vs the amount of power you get, but then you'll have to get smart on BMSs and such. If you use a outback or magnum inverter charger you pretty much cant go wrong.

Pick out your load, figure out how long you want to run it before genset charge-ups, and work backward from there to inverter size and battery bank size. Code in this case doesnt really apply. Edit: other than the interlock you'll need in your breaker panel.
 
Last edited:
For the cost you'd be better off with a generator based system, a transfer switch, and a small battery bank and inverter/charger to tide you over until the genny gets up to speed.

It amazes me that the generator vendors are not jumping on integrating UPS into their solutions.
 
I found an excellent forum post implementing a system very similar to my suggestions. Its quite thorough.


It would be nice to get his final design summarized rather than a running string of posts where he adjusts the design as he discovers issues.

I wouldn't want to use a generator setup as it needs propane or a fuel which might not be available in an earthquake scenario. I live 1/2 mile from the Rogers Creek Fault which is the most likely source of a Bay Area earthquake of 7.0. I suspect my solar and home will survive but infrastructure could be down for weeks. I prefer the Powerwall. I think I'll defer building my own for now and get a duel PW2.

My house is arranged with an outside service entrance with underground conduit to the house about 75 away and my garage is also underground with a 50A breaker hung off a 100A panel in my house. My 3 solar systems are located ground mounted another 75-150 feet west of my sevice entrance. My inverters are colocated with my service entrance. That makes a garage system almost impossible with only a 50A backfeed with the ATS 200 feet away at the service entrance. Yuk! This means the system needs to installed fully outdoors. A DIY system would want to be installed in a garage or similar building so its easy to build, tweak and monitor while avoiding freezing the Lithium batteries and hot days. That means I would need to build a small building which is more cost and effort and a permit. The PW2 is the only clean installation approach fully outdoor proof so I'll bite the bullet and go with Tesla.
 
Last edited:
"Have you watched any jehugarcia videos?

With a properly set up mpp inverter, automatic transfer when power drops should be simple. "

This guy on the Tesla Forum did a very detailed design and getting it right is not terribly easy, but its feasible. I've watched Will's videos and he does a nice job of detailing a complete system that is well thought out. He is very good at assembling off the shelf components into a well thought out system. He has done a nice job in detailing how to properly build the EBAY Tesla battery based storage system with well thought out Lithium battery management for life and safety in his RV application.

Its the next level of complexity to add and manage a UL1741 Grid Tie PV system, a commercial ATS, a custom SBC controller such as an arduino or a Raspberry Pi, etc... And possibly demonstrate a complete whole home backup as I describe. Every year in the fall, many people in California will be facing days without power. Anybody who experienced it this last year will appreciate why this may become a necessity in many homes in California. Tesla will sell and install a complex 2 PW2 for about $18,000.

see - https://teslamotorsclub.com/tmc/threads/building-my-own-pseudo-powerwall.154473/

It would be nice to have a nice video by someone like Will that tackles this bigger application.

I've not seen any truly detailed videos which implement a full "PowerWall like" system in a real existing Grid-Tie arrangement that provides full or "near-full" of a home like the PW2 when its in the backup mode. The purpose is not to timeshift or arbitrage PV power but to provide a home UPS that carries the home load overnight from batteries and is charged each day by my Grid-Tie Sunny Boy and Enphase based 16KW ground mount solar system. So when there is a power failure or PG&E shuts the power off to reduce fire risk, my PV system can carry me through the outage. The exception would be rainy days but it rarely rains here from August to November. Since I have 16KW of PV, I would not want to use a propane generator for a variety of reasons. I designed and built my own PV system in 2008 and want to use it. My PV system cost me about $30k to build the original 12.6KW and it paid off at almost $10,000 per year. It was paid off by 2010 and has made me $10k/yr for the last 9 years. So I want to use it.

It would be truly cool to detail out a system with a vidoe, schematics, BOM with all components ( batteries, ATS, BMS, Inverter(s) Charge controller and various protection devices) , design description documents, Raspberry Pi code, of something similar to what is descibed in the Tesla Forum Post " https://teslamotorsclub.com/tmc/threads/building-my-own-pseudo-powerwall.154473/ " . If anyone has seen anything as good as this I would love to know. If my home power wasn't laid out so poorly with my garage 200 feet from my PG&E service entrance with no possible way to run wires, I would tackle it and base it on the Tesla Forum approach. Or I would need to construct a small shed or building near my service entrance and PV systems. I have a little time before I commit to the Tesla PW2s.

.
 
I found an excellent forum post implementing a system very similar to my suggestions. Its quite thorough.


It would be nice to get his final design summarized rather than a running string of posts where he adjusts the design as he discovers issues.

I wouldn't want to use a generator setup as it needs propane or a fuel which might not be available in an earthquake scenario. I live 1/2 mile from the Rogers Creek Fault which is the most likely source of a Bay Area earthquake of 7.0. I suspect my solar and home will survive but infrastructure could be down for weeks. I prefer the Powerwall. I think I'll defer building my own for now and get a duel PW2.

My house is arranged with an outside service entrance with underground conduit to the house about 75 away and my garage is also underground with a 50A breaker hung off a 100A panel in my house. My 3 solar systems are located ground mounted another 75-150 feet west of my sevice entrance. My inverters are colocated with my service entrance. That makes a garage system almost impossible with only a 50A backfeed with the ATS 200 feet away at the service entrance. Yuk! This means the system needs to installed fully outdoors. A DIY system would want to be installed in a garage or similar building so its easy to build, tweak and monitor while avoiding freezing the Lithium batteries and hot days. That means I would need to build a small building which is more cost and effort and a permit. The PW2 is the only clean installation approach fully outdoor proof so I'll bite the bullet and go with Tesla.

That's my system. it's a build thread so that's why it is chronological. What do you want to know?
 
Back
Top