Aloha all, Here in the State of Aloha we’re leading the way as far as being the first PV peeps to add AC-coupled storage to existing grid-tie NEM systems with the benefit to the homeowner being having back-up power if/when the grid goes down.
During a grid outage the AC-coupled battery storage system effectively provides a micro grid for the existing PV inverter(s) and allows the PV array to power house loads and charge the battery. So what happens when the sun is out, the loads are all being met and the battery is fully charged? Some AC-coupled back-up systems shift the AC frequency higher to push the power quality out of the inverters’ specs range thereby causing the PV to curtail its output. If the PV potential goes down or the loads go up or the battery drops below 100 percent state of charge, the frequency drops and the PV output goes up again. Makes sense so far. What I am concerned about is the fact that there are hundreds of thousands of grid-tie inverters across our state dating back to 2001 when NEM first came into being here. Over the past 16 years there have been many different models and vintages with different operating parameters put into service. Adding AC-coupled back-up power to existing systems with all these varieties of inverters has me wondering how reliably and effectively all these systems are going to work in the real world during a grid outage period? Below are some of the questions I've come up with. * Will the existing PV inverters be able to effectively charge the battery storage during grid outages? * Will the battery storage be able to reliably and effectively curtail the output of the PV inverters during a grid outage by frequency shifting alone? * Just how high can the frequency be pushed up during a grid outage? Is it dependent on time of day? Solar irradiation? Loads on or off in the home? * Will that curtailment of the PV inverters be gradual or all on or off? * Will that high frequency shift during grid outages have the potential to damage the PV inverters? * Will that high frequency shift jeopardize the warranty coverage of the PV inverters? * Beyond potentially causing clocks and electronic equipment in the home to behave abnormally during periods of high frequency shifting, will that high frequency have the potential to actually damage loads in the home? For example, the newer Enphase IQ micros now have a high frequency tolerance as high as 68 hz. Whoa. Which means that the battery storage system would need to push the frequency to above that to get them to curtail. Any insight into this stuff would be appreciated. Mahalo, marco _______________________________________________ List sponsored by Redwood Alliance List Address: [email protected] Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
