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.
Insulation is the number one thing to get right. A poorly-insulated home loses massive amounts of heat to the atmosphere and is uncomfortable to live in. This is doubly true if you are planning a passive solar home.
- The building standard minimum is often inadequate: try to exceed it.
- The International Energy Conservation Code minimum (or ASHRAE 90.2 for commercial buildings) is a better standard to achieve.
- Exceeding both standards is the ideal goal.
Insulation always has an R-value, which defines how resistant it is to heat movement. Most solar experts choose insulation in the R-22 to R-30 range for walls and R-40 to R-50 for ceilings, though sometimes they will go for even higher values.
Don't forget natural insulation, which can be surprisingly effective. For example, two-string straw bales laid flat inside a wall can achieve around R-32 insulation.
It is important to insulate in both cool and warm climates. Insulation retains cool air as much as it does warm air, so proper insulation will reduce your summer cooling energy costs in hot regions. In warmer climates, the lower end of the range of R-values is more appropriate; in colder climates, target the top end.
How much installation should I use?
The easy answer to this question is "as much as possible". It is not really possible to over-insulate a building. With that in mind, there is definitely a point of diminishing returns, where the insulation you add costs far too much for the extra heat retention it provides. As always, the best bet is to aim for the "sweet spot" where the insulation is efficient and the cost is within your budget.
There is some benefit to over-insulating, though. Over time, almost all commonly-used cellulose and fiberglass insulation decreases in R-rating as it settles and accumulates moisture. There is nothing you can do about this, so adding extra insulation to compensate means that you will always have a properly heat-sealed home.
Make sure it's installed properly
It is extremely important to ensure that your insulation is installed by competent, experienced professionals. Badly-installed insulation which is crammed in too tight, has gaps or gets wet will do little to protect your home, even if it's material with very high R-values.
The walls and roof spaces also need to be constructed properly, using appropriate framing techniques, radiant barriers and other approaches to reducing heat transfer. Don't forget to insulate the foundations, basement walls and slabs, especially in colder climates.
Should I cover my windows?
Windows are often the Achilles' heel of good insulation. Glass is a terrible insulator and enormous amounts of energy can be lost through large, poor-quality windows. This is especially true in homes with lots