Page 364 - Handbook of Energy Engineering Calculations

the rise in fuel prices, solar energy apparatus continues to fall in price while
its efficiency increases. Hence, the future of solar energy as a renewable
alternative energy source continues to improve.
More architects and building designers are situating and orienting
buildings to take advantage of solar energy. And the green building

movement enhances the attractiveness of solar energy.
Studies by private groups and government agencies continue to show that
the green building initiative is both economically and environmentally

attractive. A dollar spent in making a building green is rewarded by lifetime
savings of 2 or 3 times this amount.
Solar energy apparatus can be located on building roofs in otherwise
unutilized spaces. Energy delivered to the building cuts utility costs while
saving fuel. And with ice or other storage systems for air conditioning, solar

energy can become a major green contributor in many buildings, large and
small. Hence, mechanical engineers will find many more solar designs
crossing their desks in the years ahead.

DESIGNING SOLAR-POWERED PUMPING SYSTEMS

Devise a solar-powered alternative energy source for driving pumps for use
3
in irrigation to handle 10,000 gal/min (37.9 m /min) at peak output with an
input of 50 hp (37.3 kW). Show the elements of such a system and how they
might be interconnected to provide useful output.

Calculation Procedure:

1. Develop a suitable cycle for this application

Figure 20 shows a typical design of a closed-cycle solar-energy powered
system suitable for driving turbine-powered pumps. In this system a suitable
refrigerant is chosen to provide the maximum heat absorption possible from
the sun’s rays. Water is pumped under pressure to the solar collector, where it
is heated by the sun. The water then flows to a boiler where the heat in the

water turns the liquid refrigerant into a gas. This gas is used to drive a
Rankine-cycle turbine connected to an irrigation pump, Fig. 20.