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Analysis of Funded PV Battery Systems in Germany: Prices, Design Choices and
Purchase Motivation
Kai-Philipp Kairiesa,b,c, Jan Figgenera,b,c, Dirk Magnora,b,c,
Hendrik Axelsena,b,c, Eberhard Waffenschmidtd, Dirk Uwe Sauera,b,c
aChair of Electrochemical Energy Conversion and Storage Systems, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen
University, Jägerstaße 17/19, 52066 Aachen, Germany
bInstitute for Power Generation and Storage Systems (PGS), E.ON.ERC, RWTH-Aachen, Mathieustraße 10, 52074 Aachen, Germany
cJülich Aachen Research Alliance, JARA-Energy, Jülich, Aachen, Germany
d University of Applied Science Cologne
kka@isea.rwth-aachen.de
ABSTRACT
Grid parity of residential photovoltaic (PV) power generation and retail electricity prices
make self-consumption of solar power increasingly interesting for private households. Residential
PV Battery Systems provide the opportunity to store solar energy that is not locally consumed
during the day and make it available for self-consumption in the evening, thus cutting the electricity
bill. Moreover, decentralized stationary battery systems are a promising technology to deal with
grid problems that can arise due to high local penetration of solar power generation. Because
relatively high system costs for small stationary battery systems still pose an obstacle for a broad
market launch, the German Federal Government has issued a market incentive program to stimulate
the market and boost technology development of PV Battery Systems. In order to additionally gain
a better understanding of the technology under realistic operating conditions, an accompanying
scientific monitoring program has been established. This paper outlines the most important terms
and conditions of the market incentive program, the methodology of the monitoring program and
presents current results of the market situation of government-funded PV Battery Systems in
Germany. Note, that this paper is a short version update to an existing paper published by Kairies et
al. in Energy Procedia Volume 73 [1].
Keywords: PV Battery Systems; grid integration; market incentive programm; KfW funding;
decentralized storage
1 INTRODUCTION
As part of its internationally much-noticed transition towards renewable energies
(Energiewende), Germany faces an increasing penetration of PV power generation in its electricity
grid: In 2016, a production of 38.2 TWh of solar power covered more than 6.4 % of the German net
power consumption [2]; in early 2017 more than 1.58 million photovoltaic power plants with an
accumulated nominal power of ca. 41.2 GW were installed [3]. Since 80 % of the German PV
power generation and feed-in occurs decentralized in the low voltage distribution grids, significant
challenges for the local electrical equipment can arise as large numbers of individual PV systems
add up to considerable power levels. This can lead to regional problems with respect to the voltage
stability or overburden the local electrical equipment such as power cables or medium voltage
transformers [4, 5 and 6]. PV Battery Systems can reduce the described problems by absorbing the
peak solar power generation that is produced during noon time and make it available for local self-
consumption in the evening, thus relieving the low voltage distribution grids [7, 8]. In order to
promote the use of PV Battery Systems and examine their grid-relieving potentials under realistic
operation conditions, the German Federal Ministry for Economic Affairs and Energy issued a
market incentive program accompanied by a scientific evaluation program.
2 THE MARKET INCENTIVE PROGRAM
The German Federal Government and the state-owned KfW banking group issued a market
incentive program for PV Battery Systems in the year 2013. Due to its huge success, the funding
program was re-launched in 2016 for another three years till 2018. The program aims towards an
accelerated market introduction of PV Battery Systems that increase self-consumption and act grid-
relieving at the same time. The funding is intended to stimulate the market, thus promoting
technology development and bring down retail prices for small stationary battery systems in the
long term. For this purpose, the KfW banking group provides loans for PV Battery Systems at
reduced rates with an additional repayment grant. This grant is starting from 25 % at the
beginning of 2016 decreased by 3 percentage points every six months, which leads to a current
rate of 19 % of the eligible costs in May 2017. To ensure an expedient development of the
technology and a grid-relieving operation of the subsidized devices, the funding is subject to several
requirements. The most important technical requirements include a fixed maximum feed-in power
of 50 % of the corresponding PV power generator and a battery warranty of at least 10 years.
Furthermore, all funding recipients need to register with a scientific monitoring program and
provide the technical data of their PV Battery System. Both, the amount of funding and the funding
requirements are laid down in guidelines which are continuously amended, taking account of the
current state of market developments [9].
3 THE MONITORING PROGRAM
Several studies have shown a positive influence of PV Battery Systems on low voltage grids
by using computer simulations (including [7], [8] and [10]). However, the impact of larger numbers
of decentralized PV Battery Systems in the field today can only be estimated. To gain a profound
understanding of their effects under real term conditions, the market incentive program is
supervised by a monitoring program funded by the Federal Ministry for Economic Affairs and
Energy (BMWi) from the start. The monitoring program gathers several kinds of data:
Core data like the number and type of battery systems, their dimensioning and average
retail prices as well as the geographical distribution of PV Battery Systems in Germany
Electricity meter data monthly power generation, electricity
consumption of the household (kWh per month), grid feed-in (kWh per month) or the
battery system efficiency
High-resolution measuring data like irradiation, power generation of the PV power
generator, three-phase currents and voltages of the household and the PV Battery System,
battery temperature and state of charge, power line frequency and harmonics, grid feed-in
power, self-consumption, et cetera.
This data is used to track market developments, to evaluate system performances and to
provide acquired knowledge to the interested public.
4 RESULTS OF THE MONITORING PROGRAM
The following chapter presents an evaluation of the core data
beginning in 2013 until April 2017.
Chapter 4.1, the results of the analysis are presented in sections 4.2 to 4.4.
4.1 Data Cleansing
The results of the core data presented in this paper illustrate an analysis of the ongoing
monitoring program. The technical data of the PV Battery Systems is manually entered into a web
interface including free text fields; as a result, incorrect or mixed up entries can occur. To consider
these circumstances, autonomous algorithms are developed and additionally manual reviewing
through experts is done to improve quality of the data base. Table 1 shows an extract of validity
conditions, which are defined within the scope of data-cleansing.
Table 1: Technical validity conditions for the shown analysis.
Value
Validity Condition
Stated installed capacity
Larger than 1 kWh, smaller than 100 kWh
Stated usable capacity
Larger than 1 kWh, smaller than 50 kWh
Stated battery technology
Storage system price incl. battery
Lead-Acid or Lithium Ion
Larger than 2,000
4.2 Technical analysis of the registered PV Battery Systems
In Figure 1 (left), the distributions of three major technical system properties (battery
technology, system design and installation type) of the registered PV Battery Systems depending on
three different evaluation criteria (number of systems, installed capacity, used capacity) are shown.
The installation type is dominated by simultaneous installations with more than 80 % for all three
criteria. More than half of the installed systems are AC-coupled systems with shares around 60 %.
While the first two system properties are similar throughout the different evaluation criteria there is
a higher variation concerning the ratio of the battery technology. The spread of 15 percentage points
between the lead share regarding the criteria number of systems and the installed capacity can be
explained by the differences in system dimensioning of lead-acid and lithium-ion batteries. Figure 1
(right) displays these differences showing the average battery sizes of the registered PV Battery
Systems according to the battery technology used. First of all, it can be seen that lead-acid batteries
on average feature usable capacities of about 8.8 kWh whereas lithium-ion based systems are
smaller designed, featuring average usable capacities of about 6 kWh. The installed capacities that
are needed to make these usable capacities available differ even more significantly. Lead-acid
batteries usually utilize only 50-60 % of their installed capacity, leading to average installed
capacities of ca. 16 kWh to obtain reasonable lifetimes. Most lithium-ion batteries on the other hand
are able to utilize 80-100 % of their installed capacity. Thus on average installed capacities around
6.7 kWh can be observed for lithium-ion systems. This typical dimensioning seen in the PV Battery
System market complies directly with well-recognized studies on battery aging and international
Figure 1. Overview about typical system configurations (left) and average installed and usable
capacity of the registered PV Battery Systems (right).
standards to maximize the lifetime of stationary battery systems, as presented in [11, 12 and 13] for
lead-acid batteries or in [14, 15] for lithium-ion batteries.
4.3 Price analysis of the registered PV Battery Systems
In Figure 2 (left) the development of the retail prices (incl. VAT) of PV Battery Systems with
different battery technologies, related to one kilowatt-hour of usable capacity, is pictured. It has to
be noted that the prices for the first half of 2013 and for the first half of 2017 are considered to be
less sufficient than the others due to the relatively small number of datasets. It can be seen, that
there is a continuous decrease in system prices since the beginning of the market incentive program
in May 2013. While the average lead prices decreased from around 1,400 in the end of 2013
to 1,200 %, the average lithium prices fell by 41.6 % from the
end of 2013 (2,640 till the end of 2016 down to ca. 1,540 . The first 96 registered
lithium systems in the beginning of 2017 indicate that this course continues. Reasons for the
observed price decreases can be found, among others, in decreasing battery costs and a larger
production scales. It should be noted though, that parts of the pictured (average) price reduction can
be traced back to the fact that increasing amounts of AC-coupled systems and/or single-phase
systems enter the market. These systems both feature fewer components and are usually cheaper
than comparable DC coupled systems or systems featuring a tri-phase grid connection, thus
lowering the average market price.
4.4 Attitude towards PV Battery Systems
The registration process for funded systems includes a short survey of questions considering
the motivation of acquiring a PV Battery System and the experiences made while purchasing it. In
Figure 2 (right)
for the registered systems clustered by the kind of installation. Remarkably, the results for both
installation types are almost identical: The three main reasons to invest in a PV Battery System
today are hedging against increasing electricity costs, contribution to the German Energiewende and
a general interest in storage technology. On the other hand, only a few of the participants pointed
out that a discontinuation of their guaranteed feed in tariff, the use as a safe investment or a
protection against power failures were valid reasons to invest into a PV Battery System. This clear
division into two categories as well as the parity of the results for both installation types indicate
esidential solar storage
system.
Figure 2. Evolution of the average net system prices of the registered storage systems without
assembly prices (left) and main purchase motives (right).
SUMMARY AND OUTLOOK
The Scientific Measuring and Evaluation Program for Photovoltaic Battery Systems
(Speichermonitoring) started its monitoring activities in September 2014. A steadily growing
database of comprehensive information regarding PV Battery Systems allows continuous in-depth
analysis of the German market for decentralized storage systems. Additionally, high-resolution
measurements (T=1s) of 20 privately operated storage systems in Germany are conducted since
2015. This data is used, among others, to evaluate the real-life operating behaviour, system
efficiencies and potentials for bi-directional grid services. Results are regularly published on
conferences, in journals and on the project website www.speichermonitoring.de. The next annual
report of the monitoring program will be published at the beginning of July 2017. It will provide
further and more detailed information regarding the technology- and market development of PV
Battery Systems in Germany and also feature results of the monitoring of the operating data.
ACKNOWLEDGEMENTS
This study has been carried out in the framework of the research project Scientific
Measuring and Evaluation Program for Photovoltaic Battery Systems executed by RWTH Aachen
University (WMEP PV-Speicher 2.0: Wissenschaftliches Mess- und Evaluierungsprogramm
Solarstromspeicher, www.speichermonitoring.de), and financed by the German Federal Ministry for
Economic Affairs and Energy (BMWi). The authors take full and sole responsibility for the content
of this paper.
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