Actually, solar cells are perfectly fine if you don't connect the outputs. Your inverter has to handle the float/no-load voltage (20~50% higher than at peak pow

Actually, solar cells are perfectly fine if you don't connect the outputs. Your inverter has to handle the float/no-load voltage (20~50% higher than at peak power), but that's it. Now, the inverter in this case has to be throttled by the secondary, instead of just blasting as much amps as it can with the solar power. You might want to have a nice-ish clock reference for the phase of your micro-grid, if you care about mains-phase-locked clocks keeping their accuracy. You'd want to count cycles and compare against those in the main grid, as well as adjust the frequency (much stronger than the large grid, as there won't be anything that initiates an emergency shutdown at the odd frequencies you might need to catch up/slow down to the main grid phase) so that the cycle count matches up when you sync back to the grid. If your inverter is sufficiently fast, and your transfer switch can at least disconnect external power from the internal system within less than half a period, you might be able to keep the internal power stable without any hickup at all. And it's not like the required control logic for the inverter is too hard to integrate nowadays with microcontrollers having WiFi etc.