The best advice is often the advice you hear every time you ask a question. In the case of solar energy, the best advice is always "fix everything you can fix before you start planning your project". If you plug all your leaks, improve your energy efficiency, and insulate your home properly, your solar energy installation can be smaller and will cost you less.
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As with all forms of solar power – solar thermal, PV panels, solar chimneys and others – the amount and quality of sunlight to which a home is exposed is extremely important in holistic home design. Thankfully, again in common with many other forms of solar power, even areas that might appear at first sight to be far too gloomy can, in fact, provide enough energy to reduce heating bills by 50% or more.
When you read about solar systems, especially solar thermal and passive systems, you may come across the "10-Degree Rule". The rule states that, wherever possible, a building should be constructed with the long axis facing within 10 degrees of true south (not magnetic south).
The reason for this rule is very simple: south-facing walls get the most sun (in the northern hemisphere). You want as much of a building as possible facing that way to gather as much heat and energy as possible.
One of the most infuriating aspects of passive solar design is that one size never fits all. A design that works perfectly on your site may be ineffective two miles away on the other side of a hill, on higher ground, or in a rural area.
With that in mind, regional adjustments are not too difficult. The basic design can stay much the same in areas with similar climate, but you will have to adjust four factors:
One of the aspects of passive solar house design that surprised 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.
Direct gain passive solar homes have many advantages and disadvantages compared to other approaches. Historically, the first direct gain homes were often a complete mess, because the designers had little understanding of the need to balance things like solar glazing and thermal mass. Modern designs are much better, especially since analysis software is now available to help make the tough decisions.
Thankfully, the days of cookie-cutter houses built quickly to exactly the same design are on their way out. Even in places where the homes are all based on the same floor plan, individual home owners add and change things to suit themselves. One of the easiest things to change in any home is the color of the exterior walls.
In most cases, we talk about thermal mass as something that absorbs and stores useful heat from the sun's light, releasing it when your home gets colder to maintain a comfortable indoor temperature. However, it is possible to use thermal mass as an effective cooling mechanism.