Jan 9, 2006

Q & A: Solar Energy Strategy

Question:
We are planning to build a home in Northern Thailand in next few years. Are there some solar energy ideas which we can consider - ideas which are cost effective ways to harness all this sun in Southeast Asia?

Answer:
It depends on what you want to do with the energy - if you're thinking of climate control in your new house then you should consider a range of cooling strategies. If you're going to use the energy to generate electricity for other uses, your options are fewer.

Hours of sunshine is just one variable in the solar energy equation; it's raw energy. If you're trying to cool your house you can deal with it in several ways - either collect it to power cooling devices, or block it from overheating your house.

Another nearly as important variable is humidity. The climate in that part of the world is extremely humid - cities like Chiang Mai get almost 10" of rain a month in the fall and nearly 50" a year. If you want to cool your house you MUST deal with the humidity first - it's virtually impossible to cool air without removing the water from it. Once the air is dry, it's easy to cool it - although you'll find that hot, dry air is far more comfortable than hot, humid air (think of Palm Springs, CA in the summer - it's hot, but it's a dry heat).

But you may find that trying to effectively dehumidify indoor air in that part of the world is an expensive, energy-intensive losing battle. After all, you're not building there so that you can seal yourself in the house - you want to be able to enjoy the outside. A common indigenous strategy is to open the house up and encourage cooling breezes with deep overhangs and porches (screened, I assume).

Back to your question - solar energy strategies come in two forms - active and passive. Active strategies are things like solar voltaic panels that collect sunshine and convert it to electricity. Solar panels are often mounted on the rooftop and may be connected to a bank of batteries for storage. Active systems are expensive and maintenance-intensive. They're good for generating electricity to power electrical and mechanical systems. If your location in Thailand isn't serviced by a reliable electrical utility then an active system might be worthwhile.

"Passive" is a much broader category of solar energy utilization. It's part of the architecture of the house. If your goal is an energy-efficient, comfortable house then you ought to look beyond simply adding an active system to a house design. A properly-designed passive-solar home in that climate could have a very small energy footprint; it could be very comfortable to live in; it could be low-maintenance; and it could be a very interesting and beautiful building. Locals have been building climate-responsive homes that use very little or no energy in Southeast Asia for generations - there's something to be learned from them.

Simple passive strategies include such things as wrap-around porches that block direct sunlight from entering the house and allow cooling breezes to flow through; "convection towers" that create an air current that carries heated air out of the house and drawing cooler air in (sometimes these are combined with subgrade tubes that create a reservoir of cool air); and careful orientation of the house to take advantage of the sun angles throughout the day.

Allow the climate to take the leading role in the design of the home, rather than adding solar strategies to an existing plan. You'll end up with a much better house - and the money you spend on design fees will come back to you in a lower house cost and lower energy bills. Each situation is unique, resulting in a unique design - but that's what good house design is all about!

Richard Taylor, AIA