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?
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?