Dating adding machines
In the end, successful selection depends on the choice of the best trade-off between the availability of finance, the capability of maintaining and financing the recurrent costs of the system and the performance or productivity that is expected. 81 Linkages between energy resources and appropriate prime movers "Attendance" implies level of human intervention needed.It is possible that potentially useful systems are usually not considered simply because, not being conventionally used at present, they are unfamiliar and therefore are not known or understood well enough by potential buyers; this is where it is hoped that publications such as this may encourage some attempts to try new methods, preferably by institutions or individuals with the resources to underwrite the risks inherent in experimenting with new or unfamiliar technologies.To this end, some of the cost attributes of different prime-mover options are compared in Table 9 .Here the main categories of irrigation pumping system are reviewed in terms of first costs, recurrent costs and then in terms of two factors relating more to their "effectiveness" (i.e.
It shows how all energy sources of relevance to small or medium scale irrigation pumping originate from renewable energy resources or from fossil fuels; the arrows then show all the routes that can apply from an energy resource to produce pumped water.In reality, the selection decision is usually limited to what is known to be available and affordable and yet is capable of the required pumping duty.The selection process is discussed in more detail in the next section, but certain considerations inherent in the economics and hence in the relative cost-effectiveness of different system choices are important in relation to any discussion of linking components to make up pumping systems.In some cases similar components can be used within systems energized in completely different ways; for example electric motors are necessary either with a solar photovoltaic pumping system or with a mains electrical system, so the motor-pump sub-systems of both types of system can have a lot in common. 81 are discussed through the following section, but it is first worth reviewing a few generalities relating to the combination of prime movers and pumps.Almost every aspect of an irrigation pumping system consists of compromises, or trade-offs, between the capital (or first) cost of the system and the running (or recurrent) costs.
In the example motor "A" has a best efficiency of 58% while motor "B" achieves 66%, yet, because the optimum efficiency of motor "A" occurs at a speed which coincides well with the optimum efficiency of the pump, the combined efficiency of that combination is better if the motor is direct-coupled to the pump; (motor "B" will drive the pump at a speed greater than its optimum, as at 1 500 rpm the pump has an efficiency of only 35%) so the best efficiencies of the two alternative combinations are: This illustrates how it is generally more important to ensure that the design speeds of components match properly than to ensure that each component has the highest possible peak efficiency. Also, in many situations the prime-mover cannot readily be close to the pump, and some method is therefore necessary for transmitting its output either horizontally or vertically to the water lifting device.