The common design for waste heat and renewable energy utilization is concentrate on total dependent of Waste Heat or Renewable energy source. Total dependent mean the system to use the waste heat or renewable energy must use only waste heat or renewable source. Such concept cause large investment and low benefit.
Example: Design of standalone lamp to totally rely on solar cell. The solar intensity convey to PV is approximately 100 Watt/unit, with sky clearance factor of 50% and 12 hour in day time. To support a 50 Watt light bulb it require 2 unit of solar panel.
For full support, the system must design to withstand sunlight variation (rainy day, Cloudy day) Thus it is likely for matter of design it need to install 200% safety factor = either 3 x battery size or 3 x panel size.
The system can easily reduce the investment if consider to use duel energy source support. Such system is known as on-grid power supply by using electricity from power grid to support the use over rainy day or cloudy day. On the day with good sunlight it could provide electricity back to grid.
In waste heat recovery design, it is a common practice to design the WHR smaller than waste heat generate. In example of WHR such as Waste Heat Boiler (WHB) if there is a waste heat source of 10 MBTU +/- 3 MBTU/hr it will utilized only 7 MBTU/hr of heat. The variation of heat source is off stack for process stability.
Consider the external source, for thermal process, it could easily adapt the idea using waste heat source as variable fuel and use oil, natural gas or LPG as its’ adjustment. By using duel fuel it could recover more waste heat. Back to WHB if the system designs to size 20 MBTU and combine Waste heat stream with additional fuel oil to support the variance of 10 +/-3 then all waste heat can be use.
Rather design to depend on 1 renewable or waste heat with output variation; it could achieve higher recovery level if combine with additional controllable energy source.
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