Size of inverter needed

Get a Kill-a-Watt type meter... They should be pretty common now almost anywhere for your power needs (120/230/50hz/60hz).

http://www.solar-electric.com/kiacpomome.html

And you will want to conserve as much power as possible--Especially if you are looking at solar power.

However, that does raise the question--Is this going to be a UPS type system instead (AC mains -> battery bank -> AC inverter) used to provide power for ~4 hours per day during afternoon blackouts?

-Bill

In general, I would suggest that you look at a 5% minimum rate of charge for the battery bank (if using AGM or GEL).

And, you have to decide on the type of batteries you want to use... If your power outages are rare, then a "float service" battery type (used for UPS systems) would be a better choice... The downside that these batteries, if cycled deeply, will not have very good cycle life. From my limited experience, I would suggest replacing batteries of this type (typically GEL and AGM) every two years, or after a couple of deep cycle events.

Note, when designing a solar power system, we suggest using ~1/4 of the battery bank's power per day... For a UPS system, the banks are designed to support the systems for ~15 minutes, so the battery bank may have 30 minute capacity (C*2 discharge rate).

This keeps your battery bank "small" and relatively cheap to replace every 2 years (for reliability).

If, however, you have "scheduled" power failures every weekday afternoon, you are probably better off designing this as we would for an off grid system. Design the battery bank to meet both conditions:

1. 8-20 hour discharge rate (nominal battery bank current draw).
2. Maximum draw on battery bank 5 hour discharge rate (minutes to 1 hour). And 2.5 hour maximum draw rate for surge current (seconds, starting water pump, fans, etc.).
   
3. 25% to 50% draw of battery bank capacity for "afternoon power failure" (battery bank should be 2-4x daily use AH capacity).
4. Suggest 10% rate of charge--Deep cycle batteries may do better with >5% rate of charge.
   

If you are looking to "ride through" power outages... Make sure your Internet service is capable of doing that too (battery/generator backed ISP connection). In the US, is is really unclear if cable/DSL connections have battery bank up at all, or if the backup would last more than a few hours.

And there is always the question about long term power outages (days)--Solar/fuel based genset, etc...

-Bill