Biomass fuel systems.
Wood fueled heating systems generally burn wood logs, chips or "pellets" to power central heating and hot water boilers or to provide warmth in single area.
Unlike many other renewable energy technologies, burning wood does release carbon dioxide(CO2) but this will only be the same amount that was absorbed by the tree when it was growing. There are obviously other emissions associated with the logistics of production of the wood fuel and the transportation to site but these should still be significantly lower than those created by burning fossil fuels.
Biomass technology can be linked with other fuel sources to create a large thermal store which collects and stores energy from biomass, plus solar thermal, oil, gas and electric, then into your heating system.