The document discusses using passive solar gain and indirect solar gain for heating. Passive solar gain uses large south-facing windows and thermal mass materials in floors, walls and ceilings to trap heat inside during the day and release it at night. Indirect solar gain uses thermal storage materials placed between the sun and interior space and vents in walls to circulate heated air. The document also discusses using magneto hydrodynamics to directly convert solar energy to electricity using concentrated solar power to heat an ionized gas channel containing caesium to induce electric current from the gas flow through a magnetic field. Improving solar air heaters can be done by enhancing heat transfer using different artificial surface roughnesses to create turbulence without excess fan power.