Looking into the sky on a sunny day, the notion that humans could have an "energy crisis" seems absurd. Each day, the earth receives 1.78 x 10¹⁴ kilowatts of energy, more than 10,000 times the amount needed by the whole world this year. All that is required is a way to collect and harness the energy of sunlight.

Humans have explored systems for the capture of solar energy for centuries. The Roman architect Vitruvius described a plan in the first century B.C. for building a bathhouse heated by sunlight. He explained that the building should "look toward the winter sunset" because that would make the bathhouse warmer in the late afternoon. More recently, water heaters operated by solar energy were built and widely sold in the early 1990s, especially in California and Florida.

Most historical examples illustrate the principles of passive solar heating, namely constructing a...