In a carbon neutral building, energy efficiency is paramount. Architects and engineers use principles such as passive solar design, natural ventilation and high-efficiency insulation. In addition to energy-efficient design, carbon-neutral buildings also use renewable energy technologies to generate electricity. This can include solar panels, wind turbines and in some cases geothermal systems. The electricity generated by these systems can be used to power the building's lighting, heating and cooling systems, as well as any appliances or equipment in the building.