Solar Energy Perspectives - IEA

Solar Energy Perspectives: Testing the limits
renewable electricity in the system, it drops to about USD 19/MWh, and USD 13/MWh with
respect to the overall electricity generation (out of CSP-suitable zones).
Sound economic decisions, however, focus on marginal costs, i.e. the cost of each additional
PV or wind power kWh, which must be made dispatchable in systems with already large
penetration of renewable, and bear the cost of storage. In sunny regions with more PV than
STE/CSP, USD 19/MWh of storage will add to a cost of electricity from PV of less than USD
70/MWh (after 2030). In cold countries, as wind power dominates the mix, the cost of
electricity storage will be borne by wind power, and the sum of both costs will remain close
to the USD 100/MWh mark.
Other technologies for large-scale electricity storage are compressed-air electricity storage
(CAES) and advanced-adiabatic CAES (see Chapter 3). Their deployment first rests on the
availability of underground caves suitable for this use. Some analysts assume that large
capacities are available (Fthenakis et al., 2009; Delucchi & Jacobson, 2011a and b), and
suggest CAES and AA-CAES will be the key to integrating large amounts of variable electricity
in future grids. However, they have not provided evidence for why these options should be
preferred over pumped-hydro storage, apart maybe from an implicit preference for storage on
the sites of PV or wind power generation.
Footprint of solar electricity
The projected PV capacity in our future “big picture”, initially estimated at 12 000 GW,
needs to be increased to 15 300 GW to compensate for half the losses in electricity storage
(the other half being compensated by wind power). With an average efficiency of 15% and
average peak solar irradiance of 1 kW/m 2 , this capacity would represent a total module
surface area of 100 000 square kilometres. Obviously not all modules would find a space
on building roofs and even with many other supporting structures ground-based PV systems
will be needed, possibly for two-thirds of the modules. With an appropriate tilt the required
surface area, although not necessarily unavailable for other uses, increases by a factor 1.7
at mid-latitudes. The total surface area would thus be 115 000 km 2 .
Apart from rooftops, parking lots, farms and other structures, considerable potential rests in
“brownfields”, i.e. areas that have been severely impacted by former industrial activities,
whose re-use options are limited by concerns for public health and safety. The US
Environmental Protection Agency runs a “brownfields program”, siting renewable energy on
contaminated land and mine sites. It tracks approximately 490 000 such sites covering about
60 000 km 2 .
Another intriguing option is to develop floating PV plants. Such plants could have an
increased efficiency with easy one-axis tracking – by simply rotating large floating structures
(one revolution per day) supporting PV systems. Projects of this sort are already being
considered, in particular on artificial or natural lakes feeding hydro power plants, where they
would benefit from existing connecting lines, and would benefit the hydro plants by limiting
evaporation. Sceptics, however, point out the cost of floating support structures.
STE/CSP is more efficient than PV per surface of collectors, but less efficient per land surface,
so its 25 000 TWh of yearly production would require a mirror surface of 100 000 square
kilometres and a land surface of about 300 000 km 2 . These areas will, however, be easier to
find in arid regions with low or very low population densities and little agricultural activity.
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© OECD/IEA, 2011