Page 125 - Solar Power in Building Design The Engineer's Complete Design Resource

4

INTRODUCTION TO SOLAR POWER

SYSTEM DESIGN

Essential steps required for solar power systems engineering design include site eval-
uation, feasibility study, site shading analysis, photovoltaic mapping or configuration
analysis, dc-to-ac power conversion calculations, PV module and inverter system
selection, and total solar power array electric power calculations.
In previous chapters we reviewed the physics, manufacturing technologies, and
design considerations applied to photovoltaic solar power cogeneration systems. This
chapter is intended to provide a pragmatic approach for designing solar power systems.
In order to have a holistic understanding of solar power cogeneration systems,
designers must have a basic appreciation of insolation concepts, shading analysis, and
various design parameters that affect the output performance and efficiency of the
overall system. In view of the California Solar Initiative (CSI) and other state rebate
programs, which will be discussed in future chapters, the importance of system
performance and efficiency form the foundation that determines whether a project
becomes financially viable.

Insolation

The amount of energy that is received from the sun rays that strike the surface of our
planet is referred to as insolation (I). The amount of energy that reaches the surface of
Earth is by and large subject to climatic conditions such as seasonal temperature
changes, cloudy conditions, and the angle at which solar rays strike the ground.
Because our planet revolves around the sun in an oval-shaped orbit with its axis
tilted at approximately 23.5 degrees, the solar declination angle (i) (shown in
Figure 4.1) constantly varies throughout the revolution, gradually changing from
+23.5 degrees on June 21–22, when Earth’s axis is tilted toward the sun, to −23.5
degrees by December 21–22, when Earth’s axis is tilted away from the sun. Earth’s

95
Copyright © 2008 by The McGraw-Hill Companies, Inc. Click here for terms of use.