IEEE Power & Energy Magazine - March/April 2015 - 51

The Impact of
Distributed Solar
on Germany's
Energy Transition

image licensed by ingram publishing

distribution system operators who find themselves in a situation in which already most of the generation capacity is
interconnected at the distribution system level rather than
the transmission system level.
The article's final section highlights the impact of bulk
PV generation on the operation and operational planning of
transmission systems.

Residential PV Storage Applications
The PV systems installed in Germany before or during the
boom years generate revenue almost exclusively through
FIT payments, which are as high as €0.55/kWh for systems installed in 2005. By end of 2014, FITs for current
PV installations in Germany range from €0.087/kWh to
€0.126/kWh, depending on the system size and the installation site. Above 500 kWp, no feed-in tariff system is in
place anymore. All systems above 500 kWp have to be
marketed directly via B2B contracts or the electricity stock
exchange. But a new incentive for PV systems arrived in the
German market when the FIT dropped below the electricity price for residential customers at the beginning of 2012
(see Figure 4).
march/april 2015

The increasing spread between end consumer electricity prices and the FIT incentivizes the direct consumption
of locally generated PV electricity versus just selling PV
electricity to the distribution system at FIT. In this context, residential-scale PV storage systems, whose purpose is to increase point-of-generation PV consumption
("self-consumption") and the customer's self-sufficiency,
seem to represent an incentivized new approach for the
future. First, we will define the terms self-consumption and
self-sufficiency.
PV self-consumption describes the amount of PV energy
that is either directly consumed by local loads or stored in
an additional storage device. Typically, the self-consumption
is expressed relative to the total PV energy generated over
a one-year period. PV self-consumption is limited by the
simultaneity of PV systems and load. Without additional
load shifting, PV self-consumption at the household level
typically ranges from 20% to 30% of the total PV energy
produced, depending on PV system size and load demand.
The term self-sufficiency describes the share of total
energy consumption that is covered by PV generation,
including the amount of PV energy that was intermediately
stored within an additional storage system. The major difference between self-sufficiency and self-consumption is that
self-sufficiency also reflects the efficiency of the battery system and the design of the overall energy management system, which needs to be considered for realistic cost-benefit
assessments. It is therefore self-sufficiency that is discussed
in greater detail in what follows.
The motivation for increasing self-sufficiency by means
of additional storage systems is the steadily increasing margin between electricity tariffs and PV FITs, as depicted in
Figure 4. For an average private household whose annual
electricity consumption is usually between 2,500 kWh and
5,000 kWh and that installed a PV system sized to 10 kWp
or lower in 2014, the additional income due to saved electricity purchase costs from increased PV self-sufficiency is
approximately €0.16-0.17/kWh.
Today, the worldwide market for PV storage applications
is being targeted by more than 40 suppliers. Common storage
solutions include both lead-acid and lithium-ion batteries.
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2015