New books focus on a place in the sun; Sun Rhythm Form, by Ralph L. Knowles. Cambridge, Mass.: The MIT Press. 289 pp. $ 25. Solar Architecture: The Direct Gain Approach, by Timothy E. Johnson. New York: McGraw-Hill Book Company. 218 pp. $21.50. Passive Solar Homes: 91 New Award-Winning, Energy-Conserving Single-Family Homes with Specific Suggestions for Design and Construction, by the US Department of Housing and Urban Development in cooperation with the US Department of Energy. New York: Facts on File. 284 pp. $19.95 in hard cover. New York: Everest House. 284 pp. $12.95 in paperback.

The principles of passive solar energy are so simple: like the little girl in the comics who sits in a pool of sunlight, carrying on a conversation with the sunbeam. Passive solar energy is like that; a continuing discourse with nature.

We all know it's warmer to walk on the sunny side of the street on a crisp spring morning, just as in the hot summer we seek the breezeway or the cellar. Without much thought, we adjust our daily movement to natural rhythms. We are our own passive solar energy systems.

Buildings designed from a passive solar perspective have that same quality of moderation and movement. Like a choreographed dance, the building and its users move to these natural rhythms.

The sun rises, and up come the shades and night curtains that kept the evening chill away. Slowly the warmth of the day seeps into the floors, the walls, soaking in to be stored there, until night, with its chill, brings down the curtains. The dance repeats itself.

''Sun Rhythm Form'' explores the relationships of man, habitat, and environment, showing us the architectural form that results from an understanding of the natural rhythm of the sun.

Ralph L. Knowles, an early proponent of design that allows access to sunlight , is the first to develop ways to predict the invisible envelope into which a building must fit in order to guarantee solar access to all adjacent buildings.

While developing land with consideration for the three-dimensional properties of its buildings is not new (most zoning regulates height and setback), doing so to protect solar access is quite new.

As local planning and zoning authorities adopt the principles of solar access , it will become less common for huge, out-of-scale buildings and the shade they create to invade areas that have sunny gardens to protect.

A whole new architectural context arises from the ideas Knowles presents here , one which frees the designer to employ energy-saving techniques safeguarded against the intrusions of future development.

The historical and legal background Knowles includes here gives a good foundation for readers who want to spearhead a solar policy in their own localities. The designs shown in the book illustrate the effect of such policy on single-family homes as well as large urban design projects. Quality of life, a concept often discussed but seldom pursued, becomes through Knowles's writings a working strategy for the future of solar energy.

In ''Solar Architecture'' Timothy Johnson teaches the ''direct gain'' approach to passive solar design. Direct gain refers to the energy that enters the living spaces of a home and is then absorbed directly by the building materials, to be reradiated as surrounding air cools down. Getting the most from direct gain demands a sensitive balance of materials and building organization with climate. (''Indirect gain,'' not discussed in this book, refers to the energy absorbed by a building's exterior shell, which does not pass directly into the living spaces.)

Johnson's book is a comprehensive guide that will interest the professional and the student of solar energy. It is indispensable to architects who may have missed a thorough training in environmental studies, so necessary to good design. It brings together reference materials and formulas in a step-by-step calculation to test the effectiveness of one building material over another, one design solution against its alternative. The inclusion of climatic data and programmable calculator codes simplifies the work.

The textbook-like approach lacks some of the spirit of other books on solar energy. However, the technically comprehensive information, once understood, helps give the designer a residual, intuitive feeling for solar design. If all buildings were designed with this intuitive, knowing response, not only would the world's energy requirements be greatly reduced, but our homes and workplaces would give us greater comfort.

''Passive Solar Homes'' is a compilation of 91 award-winning designs. It illustrates in a simple, clear way the basics of houses that soak up sunlight - what they can look like and how they work.

The range of homes is diverse. Many are quite conventional in appearance, and yet very special in their solar design. Several are complex and costly. These do not gain significantly from their complexity.

Good passive solar homes embrace a life style. The best exhibit careful concern for the way activities are related to spaces. Service spaces, kitchens, baths, and closets are placed as buffers to deter undesired temperature changes. Living spaces are placed to take advantage of energy gains as well as views.

''Passive Solar Homes'' is part of the continuing effort of the US Department of Housing and Urban Development and the Department of Energy. This collection chronicles the use of solar energy technology in the marketplace. It proves that many home buyers do want to own a solar home. It is a tribute to the builders and developers willing to go forward - the beginnings of a movement.