are discussed in the following sections. In addition, the underlying
economic and technical assumptions are discussed.

 Energy Requirement and Array Design Component

 The primary function of this component is to determine the pump
motor power requirements for a specific type of irrigation system and then
determine the size (m 2) of the photovoltaic array necessary to power the
system. The input variables for this component include acre inches of
water per application (gross), total acres irrigated, hours per day
irrigating, days to complete one irrigation and total dynamic head. Values
for these variables depend on the type of irrigation system, irrigation
strategy and geographic locations which can be obtained from Harrison
[1978] and Stanley et al. [1980].
 Given values for these variables, simple engineering equations
[Harrison and Choate, 1969] are utilized to calculate the necessary
pumping rate (GPM) and the continuous brake horsepower (BHPC) required
at the pump shaft. These calculations assume a pump efficiency of 75
percent and a motor efficiency of 88 percent [Pair et al., 1975]. The
estimated BHPC is then converted to a continuous kilowatts (1KW) per hour
electrical demand using standard conversion values. Because the electri-
cal demand of the pump motor is uniform over time, this value provides an
estimate of continuous kilowatt hours (KWH) per hour required to power
the system. This estimate is utilized in obtaining the necessary size
of the photovoltaic array.
 The present model does not provide for battery storage of electri-
city produced by the photovoltaic system. Given the variation in solar
insolation level during the course of each day (see Appendix A) it is
not reasonable (in terms of cost) to design a system which could hypo-
thetically provide full power to the system during all sunlight hours.
Thus, the design rule used in the simulation model is that the average
hourly output of this photovoltaic array equals the continuous KWH
per hour demand of the pump motor.
 Using the Orlando/Herndon Solmet data [U.S. National Climatic
Center, 1980], a mean hourly solar insolation profile was estimated.0

10The Solmet data contains hourly surfact meteorological readings on a