On analysis of the relationship between the incidence of a solar water heater and the calorific efficiency,the optimum incidenceof a solar water heater is devised with the law of optics and the knowledge of geometry.

Based on the machining principle analysis of the nature ruled surfaces, the technologies of NC programming for intricate nature ruled surfaces by wire-EDM were studied, including the profile marking standard, the algorithm of seeking corresponding points, equal-error synchro-linear approximation of profiles and the method to calculate the maximum inclining angle of ruling.

In this paper, by the motion analysis of four-axis wire-Electric Discharge Machining (WEDM) machine tools, it is concluded that, during the machining of intricate ruled surfaces only with linear boundary curves, the maximum inclining angle of the wire and the maximum displacements of the machining table and the wire guiding head occur on the vertices of the boundary lines.

Research shows capacity of photovoltaic array can be confirmed,if generic program of optimum sizing stand-alone photovoltaic systems is adopted,and using days of storage of batteries equal to zero,at the same time the tilted angle with yields of the highest value of radiation in the month with the lowest radiation is considered as the optimum tilted angle.

The optimum tilted angle of fixed photovoltaic array toward the equator depends on the nature of loads besides the meteorological and geographical features,the characteristics of the three loads,balanced,seasonal and provisional,were studied.

In determining the optimum tilted angle of fixed arrays for a stand-alone photovoltaic power system with steady load throughout a year, the continuity, uniformity and maximum of solar radiation on the surface should be considered comprehensively.

According to the anisotropic Hay s model of the sky-diffuse radiation and the calculation of solar radiation of tilted surface, a mathematical equation for explicit calculation of the optimum tilt angle on a tilted surface toward the equator during heating season was developed.

A method of determining the optimum tilt angle of fixed PV arrays based on CAD method is presented.

It is found that the output power of the PV panel with a seasonal optimum tilt angle is increased by 12% in comparison with that of a horizontal panel,and the output power is decreased by about 5% when the temperature of the panel .

The optimum design was studied and calculation of the optimum slope were presented.

Tow parts are included in the paper: The study on the single crystalline silicon selective emitter solar cell and study on optimum slope design in PV engineering.