Active and passive solar control

Solar control means using the sun's energy for heating in cold seasons and keeping it out in hot seasons.

Passive solar control

Uses only the building design and natural energy flows, with no mechanical parts.

• Orientation and layout: Main openings face south.
• Direct gain: South windows let in winter sun to heat the floor and walls (thermal mass).
• Trombe wall: A dark masonry wall behind glass absorbs heat and releases it into the room.
• Sunspace / greenhouse: an attached glazed space.
• Shading devices: chhajja, louvres, pergolas and trees, to block summer sun.
• Reflective roof colours, insulation and cavity walls to cut heat gain.
• Natural ventilation and evaporative cooling.

 Winter sun --> [glass] --> room, dark wall stores heat
 Summer sun --> blocked by overhang

Active solar control

Uses mechanical or electrical devices, with collectors and a pump or fan.

• Solar water heater (flat-plate collector with a circulating pump or a thermosyphon tank).
• Solar air heater with a fan to blow warm air into the rooms.
• Photovoltaic panels to give electricity for lights, fans and heat pumps.
• Motorised shades / louvres that follow the sun.
• Solar-powered absorption chillers for cooling.

Passive systems cost little and need almost no maintenance. Active systems give more control but cost more and need maintenance. The best design combines both.