A SMA system that includes a Sunny Island inverter and a traditional SMA string inverter, along with a battery bank, will also continue to allow the PV to charge the battery. The SI will "fool" the grid tied inverter into continuing to produce AC power even when the grid is not available by simulating the 120V/60 Hz signal that the inverter must sense to stay in operation. As long as the sun is shining the PV array will work normally and [hopefully] keep the battery charged enough that all your backup loads will operate. The SMA Sunny Islands are only rated for 120 VAC each and have been around since about 2005.

Jim Duncan
Solar Acres Farm
817.917.0527
solarguy2004@...

On 7/4/2020 8:11 PM, thewineprince via groups.io wrote:

When the grid is down and the batteries are full the microgrid turns off and the house runs off the batteries. When the batteries have drained to a certain level the microgrid turns on to top off the batteries from the solar panels. That’s how my powerwalls work with my Enphase microinverters.

 

Kind Regards,

Michael Schwartz

 

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On Sat, Jul 4, 2020 at 6:14 PM, Robert <robert@...> wrote:

This is an attempt for me to get some more information in the subject and hopefully others are interested as well.

I'm currently looking at adding a 10kW panel array and would like to add batteries to maintain power when the grid is down. We will go with an AC coupled system, microinverters and some type of battery that fits in. The target has been Enphase IQ8 that is still not on the market. Thus we might  go with something else, skip the batteries or wait. Meanwhile it would be good to learn a little bit more about what it means to run a micro grid and how it is designed. This topic is not solely for AC coupled systems and input related to pros and cons related different system designs are also welcome.

My initial questions are.

• What happens with a small microgrid in local mode (off main grid) when the solar power is more than the current load and the batteries are full?
• What are the general design criteria to balance solar panels, load and battery size?

Robert L.