Page 71 - Applied Photovoltaics

>
¦ t M t FUEL 1 r O & t @
ACC
t
t (4.1)
C
¦ t > r t @E 1
t
where ACC t is the capital cost in year t, O&M t is total operating and maintenance cost
in year t, FUEL t is the fuel cost in year t (if applicable, e.g. for a RAPS system), E t is
the energy produced in year t, and r is the discount rate.
Both increased efficiencies and reduced wafer costs are critical to overall
photovoltaic price reductions since, with current single crystal or polycrystalline
silicon technology, wafer costs account for about half of the finished module cost per
watt, even at production levels of 10 MW per annum (Darkazalli et al., 1991). Factors
affecting cell efficiency are discussed below.

4.2 OPTICAL LOSSES
Optical and recombination losses reduce the cell output from the ideal values
discussed in Chapters 2 and 3. Some of the optical loss processes in a solar cell are
illustrated in Fig. 4.1.

Figure 4.1. Sources of optical loss in a solar cell. (1) Blocking by top contact
coverage. (2) Surface reflection. (3) Rear contact reflection.

There are a number of ways to reduce these losses:
1. Top contact coverage of the cell surface can be minimised (although this
results in increased series resistance).
2. Antireflection coatings can be used on the top surface of the cell. A quarter
wavelength antireflection coating; that is, a transparent coating of thickness d 1
and refractive index n 1 , such that

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