Figure 3 Improvements in solar cell efficiency, by system, from 1976 to 2004News (PV Energy Systems 2004). The final data point for 2003 corresponds to about $3.50/Wp
and a cumulative PV capacity of 3 GW. An important issue, in terms of future projections, is
how this price-reduction trend will continue in the future. As Figure 4 shows, a major reduction
in the projected future cost of PV modules depends upon the introduction of thin films,
concentrator systems, and new technologies.
The third significant metric for PV cells is module reliability. Today, most crystalline Si module
manufacturers offer warranties of 25 years, typically guaranteeing that the power output of the
module will not decrease by more than 20% over this period.
Further details about the current status of solar electricity technologies, costs, and
implementation can be found in the Solar Electric Technology Assessment in Appendix 1.
IMPACT OF INEXPENSIVE SOLAR ELECTRICITY
In 2004, the United States consumed approximately 4.0 × 10^12 kWh (energy consumed in one
year at an average power of 0.46 TW) of electricity (Energy Information Administration [EIA]
2005); this amount represents about 14% of total U.S. energy consumption (EIA 2005). The U.S.
electricity produced by solar PV cells currently represents a tiny fraction (<0.02%) of the total
electricity supply. The challenge for generators of solar electricity is to produce it at very low
cost, ultimately approaching $0.40/Wp, which is equivalent to an energy cost of $0.02/kWh.
Achieving this cost would require a reduction in the $/Wp price of about a factor of 15–25