Electronic – My Solar PV system correctly shuts off power during a blackout – I want to safely override that

solar cell

For obvious safety reasons my residential PV system disconnects from the grid if it notes the grid is down. The thing is it also shuts itself off so that during a grid blackout rather than providing me power but detaching from the grid the inverter disconnects itself from both the grid and the panels leaving me without power. I want to safely defeat this safety feature that is to say I want to be able to use solar power when the grid is down without frying the guy in the cherry-picker working on the lines to fix them.

Edit to add: I was hoping I could do something more clever along the lines of : 1) manually throw knife switch to disconnect grid from my home. 2) turn on little liar circuit that puts out a drip of 240vac (powered by say a motor cycle batter) to make my inverter think the grid is live and then uses the inverter power feed to keep the 240vac liar circuit powered (as well as the battery charger for the motorcycle battery). Seems safe for the line workers and simple enough to build assuming the inverter will be fooled.

Note that SolarCity now sells a battery pack along with the switch setup I was looking for.

Best Answer

All grid tie inverters MUST disconnect the A/C supply when the grid is lost. This is a safety measure to prevent injuring hydro employees when they isolate systems to work on them. It should be noted that standard procedures require the linesmen to ground the secondary of transformers they have isolated so your inverter will most likely be shorted out if the hydro company is working on your system, maybe damaging your inverter. When hydro finds out you have defeated the safety feature without informing themyou will be immediately disconnected from the grid and it will cost a bundle to get back on, not withstanding any fines you will incur from ESA. However there are grid tie inverters that provide a separate A/C supply that you can power up a few appliances. This is a separate system and is always powered through the inverter. For significant loads you will need batteries to act as buffers to absorb extra power and provide sufficient power for startup, motors typically require 5 times the current to start as they need while operating. So starting your fridge on solar alone will probably not work, it will need a battery to get it going, after its running the current drops back down and the extra power goes into the battery. You can purchase a grid tie/islanding system. It will include the system you have plus a battery bank and an automatic transfer switch(ATS). The setup will insure that when the grid is lost your house is disconnected from the grid and transfered to the inverter. The inverter will then startup in 5 minutes and will run until the ATS detects the grid. At which point the inverter will shutdown and transfer your house back to the grid and startup in 5 minutes. This system insures that the inverter is NEVER connected to the grid when the grid is down. You will need the system properly engineered, inspected and tested before hydro will allow you to connect it. Keep in mind that a backfed pole transformer will provide 13,000 Volts to the primary if you make a mistake, and easily kill your local linesmen. Steve