Mechanical Shades for Solar Homes

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One of the aspects of passive solar house design that surprises many people is the need for shade. If your heating depends on sunlight, why would you block it? Because not all sunlight is beneficial to a passive solar home – the high summer sun, in particular, can produce far too much heat, requiring some kind of shade to stop your home turning into an oven.

The sunnier your location, the more likely it is that you will need window shades. There are many types of shade, each of which has its uses, but external choices are generally more effective than internal options. They stop the sun ever hitting the glass, rather than trying to cope with solar gain after the fact.

Let's start with the external options:

  • Awnings are a simple, cheap option. They are usually made of a light-colored fabric, to reflect the sun's light away from the house, and are easy to deploy. They may block views, but also remove up to 65% of sunlight on a south-facing surface. Always leave a space between the top edge of the awning and the house, so heat trapped underneath can escape.
  • Shutters are external window covers. They block the sun's light completely, and block the view. Some shutters are insulated to improve heat retention in winter.
  • External louvers (adjustable slats) give more control over how much sun gets through. They can be mounted with vertical or horizontal slats and adjusted from inside the home.
  • Roller shutters or shades are the most expensive option. They are horizontal slats which run along a track beside the window, unraveling into place or being rolled up out of the way of the window. They are usually made of sun-resistant materials and controlled from inside the home. A security version of these shutters is made of metal slats and locks into place when deployed.
  • Solar screens look just like regular window screens, but are designed to reduce sun penetration and glare without affecting the view.

If you prefer an internal shading device, there are still several options:

  • Drapes and curtains work well at blocking sunlight. The best are tightly-woven, light-colored fabrics which are opaque, as they reflect sunlight rather than just blocking it. Double-layered drapes and curtains work even better, and can provide insulation value in winter. The closer the drapes are to the window, the better they work.
  • Window shades work very well and are available in many formats. Some are light-colored to reflect the sun, others are dark to block incoming light, and yet others are cellular, with two or three layers to provide more R-value (useful in summer and winter).
  • Venetian blinds do not work as well as the other types of internal shade. The advantage is that they let a certain amount of light through and some models are coated in reflective material to improve effectiveness.

Most internal options are more convenient than their exterior counterparts, because they are operated from indoors and are cheaper. However, they are less efficient, as sunlight still warms the air between the barrier and window.