Skystream wind turbines convert the kinetic energy in the wind into electricity.
If the wind speeds are below "cut-in speed" there will be no output from the generator and all of the needed power is purchased from your electricity company, as normal.
As wind speed increases, the Skystream's output increases and the amount of electricity purchased from your electricity company is proportionately decreased. This happens automatically - you will consume the electricity you are generating in preference to buying it from your supplier.
When the Skystream is producing more energy than you are using, the surplus electricity is automatically exported back onto the grid, thereby displacing other more polluting sources of electricity.
In very high winds the Skystream will start to use some of the electricity it is generating to control the rotational speed of the blades, thereby protecting the turbine in high winds and still being able to harness the energy therein.
A Skystream in a reasonable location should produce between 2,000 and 4,000 units (kWh) per year, depending on location and weather. To put that into context the average household in the UK consumes 4,700 units (kWh) per year.