The renowned “Bath Tub Curve” concept highlighting the failure zones which precede and succeed the useful lifetime of any product, when depicted on a time scale as shown below, can be deemed to be a measure of its performance, and is more relevant for rotating equipments.
Every failure has a cost attached to it. The principal reliability-linked factors of cost through the useful life of an item being Design & Development, Production and Maintenance & Repair, evaluated in the backdrop of installation and environmental parameters like temperature, humidity, vibration, corrosion by chemical attack etc. and the degradation caused by the combination of a few or all of them. A higher reliability invariably envisages higher production, design and development costs, whereas, appropriately factored-in maintenance and repair costs can lead to higher levels of reliability.
In the context of non-sustainability of the current energy practices, dawning of global awareness that renewable energy sources are the only way out, has led to a sensible emphasis on solar energy as one of the (wind energy being the other) most abundant and attractive renewable energy source, easily available for harnessing. In the scenario of rapidly depleting natural energy sources like coal, oil and natural gas, the solar option has presented itself as an alternative which is being vigorously pursued for viability for commercial exploitation in the longer run. A system that uses solar cells and solar panels in a mechanical system that collects, transforms DC current into AC current and stores the electricity for later use is often called Active Solar Energy. The deeper “Bath Tub” assumes the shape of a “Shallow Pan” in the case of static equipments predominantly deployed for renewable energy applications, as far as reliability is concerned; the failure zones in this case are therefore not pronounced. Listed below are a few indicative amongst the many, though not exhaustive, but popular applications: Solar air conditioning Solar ovens for heating of foodstuffs Agricultural irrigation Hydrogen generation by the use of photo-electro-chemical cells The following applications however stand out amongst the most popular commercial applications: 1. Generation of electricity in Solar updraft towers Solar towers use an array of reflectors termed ‘heliostats’, approximately 120 sq. meters in size. Located on top of 150 meters tall towers within receptacles, these are directed towards the sun for direct absorption of the heat of the concentrated solar radiation. Operating temperatures close to 1000oC can be attained depending upon the choice of the heat transfer fluid (HTF) which in turn also decides the design of the receptacle, lined with the very best quality insulation material for optimum performance. High reliability is foreseen at the design stage itself. Likely failure points are identified in advance using the FMECA (Failure Mode Criticality and Effect Analysis) technique and appropriate specification de-rating vis-a-vis the liberal vendor rating is resorted to, for ensuring realistic unhindered performance. Finite element thermal simulation and sensitivity analysis to comply with the thermal specifications also forms part of the internal product review. External third party assessment provides inputs for MTBF (Mean Time between Failures) calculation for useful lifetime assessment, maintainability and manufacturing as part of an iterative design process for consistent improvement of product designs and individual components. Selection of the most appropriate materials of construction of all the components of solar renewable energy systems forms the last