IEEE Power & Energy Magazine - May/June 2018 - 76

increases late in the evening. on the other hand, solar generation follows the sun and is highest during
the middle of the day. Combining wind with solar
reduces the difference between the generation levels
during daytime and nighttime periods.
* Seasonal: Figure 1 also shows how wind generation at
this site is highest during the monsoon months (June-
september); this is also the period during which solar
generation is at its lowest due to more incidences of
cloudy days.
✔ Potential savings in transmission evacuation costs:
an integrated wind-solar plant also has the potential
for savings in evacuation and transmission upgrade
costs. typically, in a wind or solar plant, the collector system is designed to carry the maximum output
of the plant. For example, standalone 100-Mw wind
or solar plants would each have 100 Mw of evacuation capability. However, an integrated plant can make
do with an evacuation capability lower than 200 Mw
because wind and solar generation will not peak at
the same time. Figure 2 shows a range of cumulative
hourly generation during selected months for a 1,000-Mw
wind-solar plant. Here, the blue line indicates the average cumulative hourly generation. in addition, the
red and green lines in Figure 2 indicate the bounds
within which the cumulative generation for each hour
would occur 95% of the time. it is, thus, possible to
design the evacuation system with a rating lower than
the sum of the maximum capacities of the wind and
solar plants. in the rare event that the cumulative

and the grid itself. wind and solar projects also necessitate the fulfillment of legal and regulatory requirements, such as securing permits and licenses,
land-lease agreements, environmental impact assessments, construction permits, grid interconnection
agreements, and power purchase agreements. a reduction in project development costs can be achieved
through efficiencies in project studies and filings with
the statutory bodies because they are the same for
both types of generation.
✔ Better use of available land: Colocating wind and solar power plants conserves space and increases the energy density (i.e., the amount of energy produced per
acre of land). in many wind plants, the land between
the turbines is often left unused. to make better use
of space, wind and solar plants can be colocated, provided that conditions for both wind and solar power
generation are favorable at the same location. alternatively, if wind and solar plants can be sited adjacent
to one another, they can share the same transmission
evacuation infrastructure.
✔ Complementary generation profile: a further benefit
of integrating wind and solar generation stems from
the complementary nature of both the diurnal and seasonal patterns of their generation.
* Diurnal: Figure 1 shows the average hourly generation during selected months for a wind-solar plant
made up of roughly 500-Mw each of wind and solar generation capacity. as the figure makes clear,
in general, wind generation dips during the day and

600

600
Wind
Solar
Hybrid

400
MW

400
200

200

800

500

600

400

400
200
0

(b)

(a)

300
200
100

15
(c)

(d)

figure 1. The average hourly generation of a wind-solar plant made up of 500-MW each of wind and solar capacity.
(a) January, (b) April, (c) July, and (d) October.
76

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may/june 2018

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2018