All very useful comments.
But I wonder if it is effective to feed excess power in the net.
Consider the following option:
Since 15 years, we have our own, independent system.
I started similar as described above, inverters & batteries, but over the past years, I gravitated to another system and within a year, I will pull out the old system and replace it completely with a 12 & 24 V system.
Where to start? Simple: Throw out all high consumers and replace them with low consumption units. This is really the most important first step and I cannot stress it's importance enough. I don't need a 54" TV or a 3kW sound system or a huge American 4-door fridge or 2 kW lighting or floodlights in the garden.
Also ensure users requiring battery power are limited:
- All lighting 12 or 24 V LED. Be careful with the voltage. I put a voltage stabiliser on the lighting group.
- 12 or 24V ventilators, where needed. Construct the house such that air con is not required. It can be done.
- The fridge/freezer has a 24V compressor unit and is insulated with a 15 cm thick insulation. I can therefore switch off the unit at night and use only direct feed during the day and do not need big batteries for my fridge.
- my computers run either on 12V direct feed or 19V with a DC DC converter.
- I fill my overhead watertank during the daytime with a 24V pump, using excess power.
- if I would frequently need a heavy duty sewing machine, I would replace the motor with a 24V motor, otherwise have a small individual inverter for this machine.
- My stereo, television, satellite etc all run on 12Volt directly,
- only my washing machine needs 220V, but then we run the backup generator for this and I am now constructing a windmill so we can do the laundry when there is wind.
So since 15 years, we do not have a connection to the electrical mains and even my wife is very happy with it.
As your power bill is 50% transport / connection charges only, it hardly will be worthwhile trying to feed back excess power into the grid.
In my opinion, it is more energy efficient (Your Energy, Your sanity, Your patience) to spend your effort in becoming independent of the grid. And it is very rewarding to be the only house with light & television when there is a brownout and your neighbours 54" TV is dead while my wife continues her series on our 24" unit.
Why pay the highest electrical rate in the world and subsidise a highly inefficient system when you can be independent?.