Two Large Transformers. 20kVa and 15kVa (Athens)
I have two brand new transformers, never used, never installed. One is 20kVa (about 15,000 watts) and also 15kVa (about 12,000 watts). The primary (or input) is 120VAC and the secondary (or output) is 240VAC.
These are ideal for buildings where you have a large array of computers. On average, a computers power supply is Protected content . With the larger of the transformers (the 20kVa) you can supply power during a blackout or power failure to approximately 37 machines (personal desktops or printers). The smaller transformer of the two will supply 30 machines (personal desktops or printers that also have an average of Protected content per unit)
From my research, you take 10 automotive car batteries or gel cells and connect them together. Each battery is 12V DC. Ten of them connected to each other will become 120V DC. You run this through an inverter which converts DC to AC and you supply it to your grid. Talk to an electrician. See if will work for your business or environment.
Email and we can discuss specifics and I can send you some pictures. They each weigh about 120kilos. They are loaded in my truck as it is, I can deliver them locally but not excessively far. If you buy both, I'll give you a better deal on the pair.