**3. A level playing field across the processes**

Currently, the best available power plants for co-generation of electricity and heat sources are the combined cycle gas turbines plant or CCGTs in short to utilize fossil fuel primary energy optimally. It consumes conventional primary energy, by burning the natural gas or liquid fuels in the combustor, to generate secondary or derived energy. Such derived energy is used conveniently for powering the work and heat-driven processes for treating impaired water to produce potable water, as shown in **Figure 2**.

One notable point is the relative rates of primary energy consumption in producing the derived energy types. A detailed analysis indicates a disproportionate distribution of primary energy use by the assorted processes of a conversion plant. For example, the electricity generation from the gas and steam turbines incurred almost 96 � 1% of the total input exergy, and followed by a minor portion in the form of bled-steam at low pressures at 2 � 0.1% for powering desalination processes, whilst the remaining 2 � 0.1% of input exergy are traced to the heat rejection to ambient by exhaust gases and to the condenser.

The stark differences in exergy destruction nullifies any implicit long-held assumption that some might have of direct parity or equivalence between dissimilar derived energy consumptions. Many would recognize that 1 kWh\_elec is not equal to 1 kWh\_thermal but would not be able to establish a weighting between them. Thermodynamically, not all derived energy is created equal. Unfortunately, the current practice of quantifying energy efficacy across assorted seawater desalination methods is based on "equal parity between all types of derived energy". Obviously, this is a flawed assumption. A simple analogy is found in monetary currencies conversion in between countries. For example, a unit US dollar is not equivalent to another currency such as the Australian dollar. Economists employed a method of purchasing power parity (PPP), based on a basket of essential consumer products that normalized the necessary conversion factors in between all currencies globally. Here we seek to achieve the same for desalination processes.

*Performance Evaluation of Desalination Technologies at Common Energy Platform DOI: http://dx.doi.org/10.5772/intechopen.104867*

**Figure 2.** *Typical primary energy consumption in a combined power and water cycle.*
