Solar Energy Perspectives - IEA

Solar Energy Perspectives: Testing the limits
Figure 11.5 Capacities (GW) required at peak demand after sunset with low winds
in total non-CSP areas
Pumped hydro, 2 500
CSP Imports, 400
Base load, 1 200
Hydropower, 1 600
Wind, 1 000
DSM, 300
N. Gas + H2, 3 000
Key point
Figure 11.4
Storage and balancing plants are both needed at peak hours during low-wind nights.
Studies examining storage requirements of full renewable electricity generation in the future
have arrived at estimates of hundreds of GW for Europe (Heide, 2010), and more than 1 000 GW
for the United States (Fthenakis et al., 2009). Scaling-up such numbers to the world as a whole
(except for the areas where STE/CSP suffices to provide dispatchable generation) would probably
suggest the need for close to 5 000 GW to 6 000 GW storage capacities. Allowing for 3 000 GW
gas plants of small capacity factor (i.e. operating only 1 000 hours per year) explains the large
difference from the 2 500 GW of storage capacity needs estimated above. However, one must
consider the role that large-scale electric transportation could possibly play in dampening
variability before considering options for large-scale electricity storage.
How would G2V and V2G work with both very high penetration of both variable renewable
energy sources in the electricity mix, and almost complete substitution by electricity of fossil
fuels in light-duty transport? There could be a considerable overall storage volume in the
batteries of EV and PHEVs. Assuming 30 kW power and 50 kWh energy capacity for
500 million EVs, and 30 kW power and 10 kWh capacity for 500 million PHEVs worldwide
(as in the BLUE Map Scenario), the overall power capacity would be 30 000 GW, the overall
energy capacity 30 000 GWh.
Grids-to-vehicles and vehicles-to-grids
Load levelling using the batteries of EVs and PHEVs has been suggested as an efficient way
to reduce storage needs, although usually with more modest assumptions relative to the
penetration of variable renewables, and much larger balancing capacities from flexible fossilfuel
plants, notably gas plants. They are known as grid-to-vehicle (G2V) and vehicle-to-grid
(V2G) options (Figure 11.6).
As one IEA study notes, “one conceptual barrier to V2G is the belief that the power available
from the EVs would be unpredictable or unavailable because they would be on the road.” It
goes on to explain that although an individual vehicle’s availability for demand response is
unpredictable, the statistical availability of all vehicles is highly predictable and can be
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