IEEE Power & Energy Magazine - March/April 2015 - 54

The operational challenges faced by 50Hertz Transmission GmbH
highlight the importance of reliable PV feed-in forecasts for secure
and reliable power system operation.

2.8
2.5
2.2
1.9
1.6
1.3
0.9
0.6
0.3
0.0

PV Power/Yearly Demand (kWp/MWh)
(a)

100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0

3.2

PV Self-Sufficiency (%)

2.8
2.5
2.2
1.9
1.6
1.3
0.9
0.6
0.3
0.0

0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.4
2.6
2.8
3.0

PV Self-Consumption (%)

years. The most common approach is to increase the local
short-circuit power of a grid section by installing additional
cables and transformers or by building new substations.
These measures can be categorized as classical grid reinforcements for our purposes. Such classical grid reinforcements are cost intensive and will thus increase the asset base
of DSOs considerably in high-penetration scenarios. Recent
studies (e.g., the dena-Verteilnetzstudie) estimate the costs
of renewable energy sources (RES)-driven classical distribution grid reinforcements for Germany through 2030 from
€28 billion to €42 billion.
There are alternative approaches for increasing a grid's
hosting capacity, however-approaches that could eventually
offer a better cost-benefit ratio than classical grid reinforcements do. The application of advanced inverter functions,
such as reactive power provision or temporal active power
curtailment, and novel DSO assets, such as on-load tap
changers (OLTCs) in medium-voltage/low-voltage (MV/LV)
substations, is currently being discussed in Germany. (It
should be noted that German LV grids can serve hundreds
of end customers and be spread out over vast distances using

Useable Battery Capacity/Yearly Demand (kWh/MWh)

3.2

0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.4
2.6
2.8
3.0

Useable Battery Capacity/Yearly Demand (kWh/MWh)

Bayernwerk AG, a German distribution system operator
that is highly affected by PV generation. The measurements
started in 2009 and show how rapidly the character of the
service area was transformed from a load-dominated to a
generation-dominated distribution grid.
Typical limiting factors for a grid's hosting capacity are
voltage and current limitations. Especially in rural and suburban distribution grids-characterized by sufficient roof
space for PV installations, long branch feeders in many cases,
and only medium-to-low load demand-overvoltages will or
have already become an issue for grid operation. It is evident
that local distribution system operators (DSOs), in cases such
as that presented in Figure 7, will need to reinforce their grid
infrastructure significantly to host the vast amount of additional generation capacity. Other power quality factors, such
as harmonics, flickers, or phase imbalances, present limiting
factors as well. They currently play only a minor role in German distribution system operation, however.
Identifying technically effective and economically
efficient ways for increasing a grid's hosting capacity has
become a major research business in Germany in recent

100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0

PV Power/Yearly Demand (kWp/MWh)
(b)

figure 5. (a) Self-consumption and (b) self-sufficiency for various PV system and battery sizes for one example of a fourperson household (results vary with the underlying load profile and annual load demand).
54

ieee power & energy magazine

march/april 2015



Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2015

IEEE Power & Energy Magazine - March/April 2015 - Cover1
IEEE Power & Energy Magazine - March/April 2015 - Cover2
IEEE Power & Energy Magazine - March/April 2015 - 1
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IEEE Power & Energy Magazine - March/April 2015 - Cover3
IEEE Power & Energy Magazine - March/April 2015 - Cover4
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