How a Grid Feed Solar System Works
A grid feed solar system works by producing electricity from sunlight via a solar array (more correctly a photovoltaic array). The electricity produced by this solar array is fed to a device called a grid feed inverter. The grid feed inverter converts the DC electricity produced by the solar array into AC electricity suitable for household consumption.
In most instances the connection from the inverter is made on the house side of the electricity meter as opposed to the grid side of the electricity meter. Electricity produced on the house side of the meter will supply your house first and the grid only if any is left over.
Let's say we have fitted a simple solar array of 1kW. In full sun it will theoretically supply around 1 kW of energy into a house. If; inside this house there are no appliances switched on whatsoever all of this 1 kW of electricity will feed back through the meter and into the grid. In reality though most houses seldom have a load of less than 1 kW. If we go from having nothing on at all to switching on say a 2 kW kettle to make a coffee then the grid feed system will provide 1 kW into the kettle and the grid will provide the other kW needed to get the water to the boil.
Please note: Very very few houses ever have zero consumption of electricity. A few simple little things like a computer plugged in, the clock on a DVD player or microwave or the fridge making your food cold will bring your electricity load away from zero. In most houses with grid feed solar systems very little power ever gets into the grid.
When the solar array is connected to the house on the house side of the meter it is called net metering. If you are one of the few that have net metering and any of your electricity actually makes it into the grid, this power will be metered by your electricity provider. You won't receive cash for this power but you should receive a credit. This is usually 1:1. If you feed a kWh or unit into the grid you should be entitled to take one unit back without charge. In effect you are lending your power out then taking it back.
If you are one of the few that have a grid feed system that is connected on the grid side of your electricity meter then you will feed all of your solar into the grid. How you get it back depends on where you live and the deal your electricity provider gives you.
What happens if the power goes off?
Unless you have a battery backup then you will still have no power. If the grid goes off your grid feed inverter must stop working. Otherwise it may send power down the street and try to "island" or provide power for everyone. Obviously this would not be possible!. another reason is that if anyone is performing electrical work on your house they may get an electric shock even when the power to the house was disconnected.
some grid feed systems have battery backup and specific blackout protection to some lights and power points but the battery option adds considerable expense to a grid feed system and makes something that is not economically sound into a complete waste of money. See economic info here:
How can the power company give me a 1:1 credit (or better) and will they continue to do so?
In a business world buying power from you at the sell price makes no sense business sense at all. The only reason this can happen is that everyone that uses electricity from the grid is subsidising grid feed solar power systems. This includes the owners of grid feed systems as well as folk who choose not to fit them.
What has happened is that the Federal Government of Australia has mandated that the power companies pay you the buy price for power (give a 1:1 credit or better). As a sweetener to the power companies who obviously would not want to do this, the Government has allowed them to increase the price of electricity for everyone to cover this legislated imposition.
Make no mistake about it, grid feed power systems have been profitable for power companies! None of them are complaining!
Unfortunately the above was written in the "good old days". What is happening now is the power companies are reneging on the 1:1 credit system and wanting to pay a reduced price for power fed into the grid. The business of power is all about profit after all. At the time of writing figures from 20% - 50% return are being proposed around Australia. Unfortunately this is leaving a few people in both the solar industry and the government a bit red faced. For the last decade grid feed solar power systems have been sold with the promise of a 1:1 credit system. Sadly this may not be the case for much longer.
Know what deal you are getting!
The important thing here is to understand what deal you are going to get from your power company before fitting a grid feed solar system. When you connect your grid feed system into the grid it will be a prerequisite that a contract is in place with the power company you are providing power to. Your system supplier or power company should be able to provide you with a copy prior to getting your system installed.