There is great emphasis on natural methods, alternative technology and egalitarian engineering. Household energy is acuired via alternative energy sources. These include energy from wood in the form of fuel wood from sustainable tree plantations where tree spacing and high wood yield or wood growth rate are achieved, and other sustainable woodland and sustainable forest. Other sources are biomass energy. Solar energy is also acquired directly from solar radiation and indirectly from wind generators and via such things as heat engines like the linear Stirling engine alternator and water cooled photovoltaic arrays which also provide solar heating. These all provide clean energy.