POWER April 2015 - 84

PLANT DESIGN
3. Complementary power. A German study simulating output from a 21.6-MW
solar/9.4-MW wind hybrid plant would have a considerably smoother output than either plant
standing alone. Courtesy: Solarpraxis/Reiner Lemoine Institute
■ Wind ■ Photovoltaics
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and solar generation tend to cancel each other
out, at least in theory. Solar output is highest
during the middle of the day, while wind
generation tends to peak during the night.
This synergy, however, can be reduced if the
two resources are widely separated such that
grid operators must still work to balance the
competing outputs across the grid.
Co-locating wind and solar generation could
allow plant operators to control intermittency
at the source, greatly reducing the burdens on
the grid. A 2013 study conducted by the Reiner
Lemoine Institute in Berlin and Solarpraxis
found that combining wind and solar generation
on the same site can result in up to twice
the amount of electricity being generated across
the same surface area, with the shading effects
of the turbines found to be minimal (Figure 3).
" The fact that wind and photovoltaic power
supply the grid with much more stable levels
of energy when working together has a positive
effect on grid stability, " Christian Breyer,
managing director of the Reiner Lemoine Institute
said when the study was released.
Wind + Hydropower: Full Coverage
Pumped storage hydroelectric generation is
a resource that is tailor-made for pairing with
renewable generation. One such example currently
exists on the Spanish island of El Hierro
in the Canaries (see " A Spanish Island's 100%
Wind-and-Water Power Solution " in the August
2014 issue). There, an 11.5-MW wind farm and
an 11-MW pumped storage hydropower plant
provide the island with 100% renewable energy.
When there is excess generation from the
wind turbines, the electricity is used to pump
water from a lower reservoir 700 m uphill to
an upper reservoir. When demand exceeds what
the wind turbines can provide, water is released
and run back through the pump turbines.
The system, which came online in 2014,
frees the island from dependence on expensive
imported fuel oil, the bane of many an
island grid. The project has been successful
enough that feasibility studies are being
conducted for other islands in the European
Union such as Crete and Madeira.
Morocco is reportedly developing a 1-GW
wind-hydro hybrid plant, but it is unclear
how far along this project is.
Future Outlook
Though some of these projects and combinations
show considerable promise, the hybrid
plant sector is still in its infancy and still experiencing
growing pains. The synergies and
complementary technologies of gas and CSP,
not to mention the substantial expense of standalone
CSP plants, is likely to mean that ISCC
will continue its lead for the foreseeable future.
Geographical challenges of other types of hybrids,
such as those including geothermal and
hydro, may limit their adoption. Still, the potential
that hybrid plants offer in managing renewable
intermittency means that they are likely to
draw increasing attention as the proportion of
renewable generation continues to grow. ■
-Thomas W. Overton, JD is a POWER
associate editor.
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POWER | April 2015
All this being said, however, most such facilities
remain on the drawing board because
of the need for favorable locations. One operating
example is EDF Renewables' 143-MW
Catalina Solar Project and 140-MW Pacific
Wind Project outside Lancaster, Calif., which
leverages the region's nexus of ample wind
resources, extensive insolation, and policy
support. The wind farm was completed in
2012; the solar plant reached full operation in
2013. Though built as separate projects, the
two plants are about a mile apart and share
electrical and transmission infrastructure.
According to EDF, the combined operation
results in power output around 50% to 60%
of the time compared to 35% to 40% from
either plant operating alone.
MWh

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POWER April 2015

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