Global Warming

302 Energy andtransport for thefuture

The photovoltaic solar cell

The silicon photovoltaic (PV) solar cell consists of
a thin slice of silicon into which appropriate impu-
rities have been introduced to create what is known
as a p–n junction. The most efficient cells are so-
phisticated constructions using crystalline silicon
as the basic material; they possess efficiencies for
the conversion of solar energy into electricity typ-
ically of fifteen to twenty per cent; experimental
cells have been produced with efficiencies well over
twenty percent.^51 Single crystal silicon is less con-
venient for mass production than amorphous sili-
con (for which the conversion efficiency is around
ten per cent), which can be deposited in a contin-
uous process on to thin films.^52 Other alloys (such
as cadmium telluride and copper indium selenide)
with similar photovoltaic properties can also be de-

posited in this way and, because they have higher

efficiencies than amorphous silicon, are likely to

compete with silicon for the thin film market.^53

However, since typically about half the cost of a

solar PV installation is installation cost, the high

efficiency of single crystal silicon, which means a

smaller size, remains an important factor.

Cost is of critical importance if PV solar cells

are going to make a significant contribution to en-

ergy supply. This has been coming down rapidly.

More efficient methods and larger scale produc-

tion are bringing the cost of solar electricity down

to levels where it can compete with other sources.

Projections up to the year 2020 of the likely cost of

generatingelectricity from PV sourcesare shown in

Figure 11.13.

1

10

1 10 100 1 000 10 000 100 000

Cumulative installed capacity (in MW)

PV Module cost ($ per Watt-peak)

20

2

5

1982

2002

2012?

(four-fold reduction 1982–2002)

(two-fold reduction 2002–2012?)

Figure 11.13The falling cost of PV modules over the last twenty years and as projected for the next

twenty years. Note the twenty per cent reduction in cost for every doubling of installed capacity.

however, assuming a reasonable pay-back period, translates into an elec-

tricity cost which, at the moment, is at least three times that from most

conventional sources. Generating plants which incorporate integrated

solar and fossil fuel heat sources in combined cycle operation are cur-

rently under development that promise significantly lower costs.^50