We have an aging UPS, a 15 KVA Eaton 9155 that we are thinking of replacing as its 10 years old this year. It has a 3 phase inverter to DC which charges the batteries and drives an output inverter all the time. If the power goes off there is a zero off time as the batteries are on the input of the always on inverter, there is a bypass to one phase if there is an inverter failure but that has never happened. Its been a very reliable peice of kit but I don't want to push my luck due to the age.
When I first got the UPS it was running at around 70% of capacity but over the years the servers and switches have become more power efficient and its currenlty running at 27% of capacity. The real power used is just under 4KW.
Solar technology has come a long way and in Australia many homes have solar panels with passively cooled grid tied...