Solar Energy Perspectives - IEA

Solar Energy Perspectives: Solar photovoltaics
This restriction may be overcome by quantum dots or nano-particles, which are semiconducting
crystals of nanometre (a billionth of a metre) dimensions. The wavelength at
which they will absorb or emit radiation can be adjusted at will, so a mixture of quantum
dots of different sizes can harvest a large proportion of the incident light. They can be
moulded into a variety of different forms and processed to create junctions on inexpensive
substrates such as plastics, glass or metal sheets. Quantum dots and wells might also be
adjusted so that each highly energetic photon stimulates more than one electron. In both
cases, efficiencies of more than 40% are conceivable at manufacturing costs that could
remain relatively low; however, such results efficiencies are not yet achieved, even in
laboratory research. Such breakthroughs would greatly improve the learning curve, but
require major research effort.
Photo 6.2 Dishes with CPV and heat collection
Source: Zenith Solar, Israel.
Key point
CPVT is an appealing option if the heat collected can be used.
So-called thermo-photovoltaic cells offer another possibility, that of transforming the near
infra-red radiation emitted by the sun, or radiant heat, into electricity (see Chapter 8).
A synthetic view of the expected progression of efficiencies of successive generations of PV
technologies is shown in Figure 6.5.
Balance of systems
Modules now represent more than half the cost of utility-scale PV systems, inverters and other
balance of systems (BOS) costs account for one-third, and engineering and procurement the
remainder. This share of BOS costs will likely grow. While the price of inverters decreased at
the same pace as PV modules, prices for other BOS elements have not. The price of the raw
materials used in these elements (typically copper, steel and stainless steel) has been more
volatile. Installation costs have decreased at different rates depending on the type of
application and maturity of the market. Reductions in prices for materials (such as mounting
structures), cables, land use and installation account for much of the decrease in BOS costs.
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