Solar Energy Perspectives - IEA

Chapter 8: Solar thermal electricity
generation of electricity on the peak demand after sunset, with a larger turbine, which
means a solar multiple smaller than 1. Electricity is more expensive in this configuration,
but, if the power purchase prices duly reflect the marginal costs of alternatives, it might be
the most profitable option. It would fit, for example, the condition of Morocco and South
Africa.
Figure 8.5 Firm and time-shifted production
1 000
Thermal power (MW), DNI (W/m )
Electrical power (MWe)
300
900
Direct normal irridiation
Produced net electricity
800
250
700
600
500
400
300
200
100
Heat flow to storage
Thermal heat collected
by the solar field
Heat flow
from storage
0
0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Hour
Source: ACS Cobra.
200
150
100
50
Key point
Thermal storage de-links solar energy collection and electricity generation.
Large storage capabilities, resting on high solar multiples (up to 3 or 4), would allow CSP
plants to generate electricity round the clock, at least during most of the year, making it
possible for low-carbon CSP plants to compete with coal-fired power plants that emit high
levels of CO 2 . For example, the 20-MW solar tower plant in Spain Gemasolar that was
connected to the grid in May 2011 uses molten salts as both HTF and storage medium. It
stores enough heat energy to run the plant at full load for 15 hours a day during most of
the year. However, the economics of CSP suggest it is more profitable now to use storage
to compete on peak loads where the incentives and/or market prices reflect the marginal
cost of competitors in real time.
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© OECD/IEA, 2011