There are many types of renewable energy systems available, and which one you opt for will depend on your individual needs, where you live, and how much power you're looking to generate.
The Energy Saving Trust lists carbon savings for different renewable energy systems:
Biomass boiler - 840 kg CO2
Air source heat pump - 830 kg CO2 (if replacing a gas system, up to 6 tonnes for electricity)
Ground source heat pump - 830 kg CO2 (up to 7 tonnes for electricity, interpolated for gas as on par with air source heat pumps)
Solar PV systems (for generating electricity) - 1200 kg CO2
Solar hot water systems - 325 kg CO2 (if replacing a gas system)
(Wind turbine figures are not included as there is not yet enough data)
Taking an average of these savings:
= 805 kg CO2 saved per year