The present invention relates to a conveying apparatus run by electric power from an unstable electric power supply and, more particularly, to a conveying apparatus for conveying liquid, such as water, and fine powder by using electric power supplied from an unstable electric power supply, such as a solar cell and a wind power generator, which generates variable electric power, as a power source.
Recently, anathermal of the earth, exhaustion of fossil fuels, and radioactive contamination caused by accidents in nuclear power plants and radioactive wastes have become social issues, and the issues on the terrestrial environment and energy are rapidly collecting interests of many people. Under this situation, a solar cell, for example, which generates electric power from the solar ray that is an inexhaustible clean energy source, is anticipated as the energy source of tomorrow.
There are various sizes of systems the solar cell, and the electric power required by those systems ranges from several watts to thousands of watts. Further, there are many types of systems: a system which directly uses electric power generated by the solar cell; a system which charges electric power generated by the solar cell to a storage battery; and a system which uses electric power generated by the solar cell along with commercial electric power, for example. Among these systems using the solar cell, a system suggested as a solar pump system for drawing water from the source, such as a well and a river, for irrigation and drinking is very useful especially in some geographic regions, such as tropical regions, where the amount of insolation is large, and in unelectrified regions, because the running cost of the system and the load of transportation of fuels for running the system can be saved. Further, it is also advantageous for highly electrified cities to own a solar pump system as measures to cope with a natural disaster, such as an earthquake, since it is possible to supply water relatively easily by using the solar pump system in a case where the supply of electric power and water stops.
FIG. 12 is a diagram illustrating a configuration of a water supply apparatus employing a solar pump system. In FIG. 12, direct current electric power obtained from a solar panel 12, i.e., an unstable electric power source, is provided to a pump 5 via an electric power regulator 14 whose output is controlled by a controller 13. The water in a well 15 is taken through the intake 7 of a water supply pipe 1 and drawn through the water supply pipe 2 up to the discharge opening 20 by the pump 5, then stored in a water tank 19. Note, in the water supply pipe 1, a foot valve 81 for preventing backflow of the water is provided near the intake 7 and a valve 8 which is closed for preventing backflow of the water when the pump 5 stops operating is provided.
However, the water supply apparatus as shown in FIG. 12 may not be able to draw water in the mornings and evenings when an amount of insolation is small and on cloudy days, since the electric power generated by the solar panel 12 becomes small, and although the pump 5 operates, the water does not reach the discharge opening 20.
In order not to waste the electric power generated by the solar cell when the amount of insolation is small, methods of using a plurality of low output pumps, as disclosed in Japanese Patent Application Laid-Open Nos. 56-132125 and 57-153531, are suggested. As shown in FIG. 2, however, the higher the output of a pump is, the better in efficiency. Therefore, by using a plurality of low output pumps to obtain a predetermined output, and using a part of the pumps to supply water when the amount of insolation is small, less energy is wasted, however, the efficiency is not good, as can be seen from FIG. 2. Furthermore, the initial cost of the apparatus is high since a plurality of pumps are necessary.
Further, there is method of temporary storing electric power generated by the solar cell in a storage battery. However, the cost of the storage battery is considerably high and load of maintenance of the storage battery is not ignorable. In addition, it is necessary to control charging and discharging of the storage battery, which makes the system complicated.