A big part of the passive solar home equation resides in cutting down on how much heating and cooling you need. The lower your demands, the bigger the percentage you can cover with renewable solar energy. There are two main culprits of internal heat gain in the average home:

Appliance heat gain

With the average home containing more and more heat-generating appliances, your winter heating bills will fall. But you'll pay the price in summer cooling. In general, you want to use any heat-generating appliances (which is pretty much all of them, though some are worse than others) in the early morning and late evening, when the heat they generate will be less noticeable in summer and more useful in winter.

Moving heat-generating activities outdoors also helps. The easiest of these is often to line-dry laundry instead of running the dryer. Outdoor barbecues can also reduce indoor heat in summer months, as well as creating a family or neighborhood event. Designing these outdoor areas into a home – decking and patios with vegetation, shade, and perhaps a small fountain – can really help reduce your summer cooling bills, expand the usable footage of the home, and encourage you to get some fresh air.

Picking the right appliances also helps. For example, using a microwave oven to reheat food generates a lot less indoor heat than lighting and using a gas stove. Energy-efficient choices are, of course, fundamental to reducing not only indoor heat gain but also electricity use.

Finally, it is worth considering isolating very hot appliances. For example, putting the clothes washer and dryer into a nook with a separating door and a small, openable window allows you to choose between winter and summer options. You can close the window and open the door in winter, to allow the heat into the home, or close the door and open the window in summer, venting the heat externally.

Lighting heat gain

If you're still using old-fashioned incandescent light bulbs, you may be surprised by how much heat they generate. These bulbs use between 5% and 10% of the electricity they consume to generate light – everything else gets turned into heat.

Switching to CFLs ( compact fluorescent lights ), which are available in almost every traditional size and screw into most standard light fittings, reduces heat enormously. These bulbs use about 75% less energy to produce the same amount of light and emit around 90% less heat. They last longer, too.

You can also combine more efficient light bulbs with task-lighting. This is a different approach to traditional lighting: instead of having one powerful fixture (or more) in the middle of the room, lighting everything, you install several smaller fixtures in specific task locations. For example, you can put a lower-output bulb in the television corner, a high-intensity LED spot-lamp over your workspace, and a reading lamp by your favorite chair. Lighting all three lamps may use more electricity and generate more heat than a single, central fixture, but you're unlikely to use all three at once!

Finally, you can use passive solar