# THE FIRST-LAW APPROACH

With this approach one may try to define the amount of solar kilo­Watt-hours electricity contribution as follows, using the numerical values of the above example :

Solar electricity = Wou« x 0/(0 + Wirl) = 45.516 x 10b kWh(e)

The ratio 0/(0 * Wlr)) will thus represent the solar fraction, i. e., the part of the total output <W, ut) assigned to the solar source, yielding for our case :

Solar fraction = 0/(0 + Wi„) = 0.706

Finally, this will yield.

Solar Efficiency = (solar electricity)/<A x I) =9.6%

The first-law approach invokes an equal rank to a unit Joule inde­pendently whether it is heat at 200°C, 300°С or higher, or whether it is a Joule of work (or fuel), which is a pronounced weakness. Consequently, the solar fraction as derived with this approach can­not really represent the fraction of fuel saved (per unit plant’s output), or pollution-free power (in particular, when compared to modern conventional power plants). There are additional problem areas within this context.