Page 304 - Applied Photovoltaics

Appendix

G

STAND-ALONE

PHOTOVOLTAIC

SYSTEM DESIGN

G.1 INTRODUCTION
The following material outlines two approaches used when designing photovoltaic
stand-alone systems. Australian Standard AS4509.2, discussed in Chapter 7, is more
recent than either and is normally the method to be used by accredited installers in
Australia. The first method detailed here was used extensively by Telecom in
Australia during its early days of photovoltaics application and represents a very
conservative approach in which array size is optimised as a function of battery
capacity. The second was developed by Sandia National Laboratories in the USA and
is considerably more sophisticated, automatically incorporating many years of
accumulated insolation data. Examples of both approaches are provided.

G.2 STAND-ALONE SYSTEM DESIGN PROCEDURE
The following example deals with the design of a stand-alone PV system for
powering a microwave repeater station (based on Mack, 1979).
Step 1—Load determination. A microwave repeater station typically draws 100 W
on average and requires voltages in the range 24 ± 5 V. The corresponding average
current is therefore 4.17 A.