IEEE Power & Energy Magazine - November/December 2021 - 75

next phase of the clean energy transition will involve integrating
the transport, heating, and industrial sectors in a
comprehensive transformation process. The energy policy
debate of recent years has often focused on how to make the energy
system sustainable while relying on weather-dependent
generation, specifically solar and wind. In this discussion, a
consensus has emerged to maximize the direct use of electricity
when technically viable and expedient. When neither wind nor
solar power is available, stored energy needs to be fed into the
grid. The so-called dark doldrums refer to that time of no or low
solar and wind power production. In such situations, discharging
storage is needed to assure the supply of power.
A survey by the German Weather Service in 2018 systematically
investigated the frequency of dark doldrums. The
survey sought to identify periods of at least 48 h between
1995 and 2015 when wind and solar PV electricity, as defined
by the German Meteorological Service, could be fed into
the grid at only 10% of potential output. To simplify the analysis,
the generation capacity was assumed to be equally distributed
across the country, and no grid restrictions were considered. Over
the 20-year survey period, very low wind feed-in occurred just
13 times a year if onshore and offshore wind turbines were taken
into account, and 23 times a year if only onshore turbines were
considered. By contrast, low wind generation in combination
with low PV output occurred just twice a year for more than 48 h.
If one broadens the analysis to include PV across Europe, dark
doldrums occur statistically less than once per year (0.2 times), a
phenomenon attributable to meteorological adjustment effects.
Although infrequent, the system needs to be designed for
these events to keep a high level of security of supply in Europe.
100
150
50
-50
-100
-150
Storage Discharge
Gas Turbines
Combined Heat and Power
Wind
PV
Other Renewables
Mon
Tues
Wed
Thur
Fri
Sat
Sun
Advanced demand-side management can help keep the electricity
system safe and the overall cost as low as possible. New loads
like heating and transportation offer significant flexibility compared
to the current electric load. Nevertheless, long-term storage
is also needed. Conventional storage like pumped hydro or
batteries could cover neither the energy nor the power to supply
a country like Germany for several days. Therefore, chemical
fuels, such as hydrogen, methane, ammonia, or synthetic fuels,
are the most practical solutions. In a 100% renewable scenario,
fuel production starts with generating hydrogen from electricity.
Chemical downstream processes transfer the hydrogen into
other synthetic fuels. As renewable generation in Europe is not
sufficient to provide all needed energy, the import of energy is
necessary. Places with good wind or PV resources can produce
hydrogen or other synthetic chemical fuels for shipment to
Europe. That also may be the most economical approach.
Hydrogen produced from offshore wind in Europe would
likely be more expensive than compressed hydrogen imports
and comparably expensive or more expensive than liquid hydrogen
imports. For the sake of simplification, if one presumes
long-term offshore wind power generation costs of 5 €cents/
kWh, then the resulting compressed hydrogen generation costs
would be 9.1 €cents/kWh. For example, hydrogen imported
from Morocco by pipeline to central Europe would cost between
5.5 and 6.5 €cents/kWh. Taking the efficiency of reelectrification
into account, the price of electricity from hydrogen is two
to three times the price of solar PV or wind power.
However, the share of energy generated from hydrogen is
rather low, so the higher cost does not contribute much to
the average price. Figure 6 shows the results of a simulation
Electricity Feed-in and Demand in a Scenario Setup for 2050
Week in March
Power to Gas
Storage
Electricity for Heat/Cooling
Electricity for e-Mobility
Conventional Load
Total Electricity Demand
figure 7. An exemplary week shows the integration of renewable energy production through heat and transport sector coupling.
november/december 2021
ieee power & energy magazine
75
Electricity
Demand (GW)
Electricity
Feed-in (GW)

IEEE Power & Energy Magazine - November/December 2021

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2021