Energy Management Solutions for Polish Prosumer Systems
Marcin Jarnut, Grzegorz Benysek and Szymon Wermiński
Institute of Electrical Engineering, University of Zielona Góra, Licealna 9 Str., Zielona Góra, Poland
Keywords: Renewable Energy Sources, Energy Storage, Advanced Metering Infrastructure, Energy Management.
Abstract: Last year the Polish government finally passed an act of parliament concerning renewable energy sources in
response to the European Union Directive 2009/28/EC promoting renewable energy. This act liberalizes the
interconnection of small on-site generation systems situated on the customer side, consisting of renewable
energy sources (prosumer systems), with the electrical distribution system. Although most of the formal
barriers have been removed, the proposed economic conditions are not likely to guarantee the expected
dynamic growth in volume of renewable energy as part of the overall energy consumption. This paper
introduces a solution for the economic and energy-effective management of energy generated in Polish
prosumer systems. Moreover, the technical and formal conditions for implementing small-power renewable
energy sources into the distribution system are mentioned as a background for the optimal choice of
interconnection solution and topology. A complete energy management solution based on available
technologies, such as power electronic converters, energy storage devices and home area networks has been
proposed as well.
1 INTRODUCTION
Nowadays almost 90% of the overall energy
consumed in the Polish electrical system is produced
at coal-fired power stations. Coal and other fossil
fuels, such as natural gas, still remain the cheapest
primary energy sources for heat and electricity
generation in Poland, although they are charged with
high CO
2
emission coefficients of 0,89 Mg/MWh
and 0,560 Mg/MWh for coal and natural gas
respectively. Without modification of the energy
generation structure this means that in the near
future growing emission payments (from 30% now
to full prices in 2020) will also increase the electrical
energy costs for Polish consumers. In August 2013,
according to the EU Directive (European Parliament,
2009) promoting energy from renewable energy
sources, the Polish Energy Act has been finally
modified (Parliament of the Republic of Poland,
2013), thus, small systems up to 40 kW consisting of
such energy sources, referred to as RES micro
installations, now have permission to transfer energy
back into the distribution grid without any special
concession being required by commercial energy
sources other than agricultural biogas fired sources.
This was a major barrier in the large scale
development of on-site generation micro systems.
Unfortunately, the convenience of RES
interconnection with the distribution system is not
supported by profitable pricing, as is commonly the
case in other countries. The Polish version of the
Feed-in Tariffs (FIT) system guarantees a price for
energy generated in micro installations and
transferred into the utility grid below the value of the
average price of energy on the energy market. To be
precise, it is 80% of the average price, and taking
into account the prices in the Polish energy market
in 2013 (0,20 PLN / kWh) it is about 0,16 PLN
(about 0,04 EUR). In contrast, the prices for energy
taken from the grid, including energy delivery tax,
comes to 0,53 PLN / kWh (about 0,13 EUR / kWh)
on a flat tariff (one averaged price for the whole day
and whole year). Hence, this system rather motivates
RES energy consumption inside the customer
installations than energy reversing to the grid. In
other countries, for example, in Germany, the
prosumer systems with FIT tariffs have a guaranteed
higher price for energy reversed to the grid in
relation to energy taken from the same grid, so any
reduction of energy consumption leads to a raising
of surplus energy transfer to the grid and, as a result,
to the higher profits.
In Poland, apart from RES, some other
technologies are now being considered, especially
107
Jarnut M., Benysek G. and Wermi
´
nski S..
Energy Management Solutions for Polish Prosumer Systems.
DOI: 10.5220/0004962701070112
In Proceedings of the 3rd International Conference on Smart Grids and Green IT Systems (SMARTGREENS-2014), pages 107-112
ISBN: 978-989-758-025-3
Copyright
c
 2014 SCITEPRESS (Science and Technology Publications, Lda.)

the energy passive solution allowing for a reduction
of energy consumption by using an advanced
metering infrastructure (AMI) and load management
stimulated by dynamic tariffs. This model doesn’t
require the significant support, though it could give
the expected effect only by involving a number of
different technologies working together within one
optimally composed energy management system. An
example of a prosumer system is shown in Figure 1.
Considering the daily load profile variation as well
as daily RES power generation profiles, the optimal
energy management could be provided only in a
system with power electronics interfaces (PEI)
working in tandem with energy storage devices
(ES). Moreover, apart from using dynamic tariffs, or
programs consisting of more than one pricing time
zone (usually two price levels – peak power pricing
and off peak power pricing geographically located
according to daily load curve), or other commercial
Demand Side Management (DSM) and Demand
Side Response (DSR) programs there are additional
possibilities for energy cost reduction such as peak
power shaving and power shifting. These processes
could be provided either by using a reduction of
energy consumption or by using energy from a RES
previously stored in ES. In the case when all the
investment costs in a RES are covered by the
prosumer, without any external support, the control
should be performed with due regard to the best
economical effect.
2 AVAILABLE TECHNOLOGY
OVERVIEW
The optimal topology of a prosumer system for
Polish conditions requires specific elements. There
are available some market-ready applications which
can operate alone, but their coordination within one
common system is often impossible or does not
permit anticipated functionality. Recognition of their
properties and judgment of their usefulness
constitute the first step in composing an optimal
prosumer solution with several major functions like
optimal RES energy utilization, energy storage
ability and power flow control.
The technologies providing these functions can
be divided into three groups: RES and interfaces,
measurement and monitoring devices, energy
management systems.
Presently in Poland all of the above mentioned
technologies are available or are in a developmental
or testing stage.
2.1 RES and Interfaces
There are three major types of renewable energy
sources with the potential for commercial
implementation in Polish prosumer systems:
photovoltaic systems (1 MWh/m
2
), small wind
power systems (0,5 – 1 MWh/m
2
) and biomass
(biogas) fired micro cogeneration systems (energy
potential dependent on biomass type).
Two first sources due to their unpredictable and
unstable character, being mostly dependent on
Figure 1: Unified and simplified schema of prosumer system with energy management technologies.
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primary energy variations, need to be supported by
interfaces based on two-stage power electronic
converters with energy storage ability, although
systems without ES are commonly used because of
their lower prices. Micro cogeneration systems are
treated as a stable source. The primary energy
(biomass or biogas) in such systems is easily stored
and can be more readily controlled than wind or sun.
Moreover primary energy control can be used for
stabilization of the output voltage characteristic or
for output power management. The stable output
voltage parameters of rotating generators allow the
connection of a micro cogeneration system directly
to the distribution system without power electronic
converters. Of course, in some cases, for example in
systems with a gas fired micro turbine, a frequency
converter is required.
Today there are three types of RES interfaces
available on the Polish market, the implementation
of which is allowed for in the electrical distribution
system (Benysek, G., Jarnut, M., 2013): Off Grid
(islanded, autonomous), Grid Tied (On Grid, grid
connected) and Hybrid. These applications have
different functionalities and different abilities for
energy management, but all of them can be
implemented in prosumer systems.
2.1.1 Off Grid Systems
The main rule of working in Off Grid systems is the
creation of local islanded circuits in prosumer
systems, where the sectioned circuits are supplied by
an Off Grid inverter using energy generated in RES
and stored in ES. The interfaces in an Off Grid
topology consist of four major parts: source-side
converter (SC in Fig.1), energy storage devices,
grid-side converters (GSC in Fig.1 being Off Grid
inverter) and by-pass switch (islanding switch – IS
in Fig.1). Such a topology allows for a power
balance creation inside prosumer installations using
energy source switching for sectioned circuit only,
so the summary utility power (P
S
) changes will be
visible as step changes and will be strictly dependent
on the actual load of the sectioned circuit. This
limits the flexibility of power flow control and there
are no possibilities in this structure for energy
reversing to the distribution grid. Although this may
sometimes be treated as a disadvantage, in the Polish
electrical power system, where the yearly voltage
interruptions last ten times longer than, for example,
in Germany, such a topology allows for the
possibility of uninterruptible power supply of critical
circuits.
2.1.2 Grid Tied Systems
Grid Tied systems have a parallel connection in
relation to the distribution grid, with their grid-side
converters working in current mode, so they can be
seen as controlled current sources. The typical
structure of Grid Tied systems contain: source-side
converter (SC), grid-side converter (GSC) and
islanding protection switch (IS).
In prosumer installations with Grid Tied systems,
in contrast to those with Off Grid systems, the power
balance is created continuously. Unfortunately,
because of the lack of an energy storage function,
this process can’t be intentionally controlled and is
rather directed to optimal RES energy utilization. In
the case of the Polish version of FIT tariffs and
taking into account the daily load profile of
prosumer installations it can lead to non-optimal
energy costs and to relatively high power variations
in the distribution system (including P
S
power value
as well as the power direction).
2.1.3 Hybrid Systems
Hybrid systems combine the advantages of Grid
Tied and Off Grid systems in one topology
controlled in a specific way (Jarnut, M., 2012).
Under normal conditions in a distribution network
this means that when the utility voltage remains
inside the permissible range, the grid-side converter
works in current mode, shaping the sinusoidal output
current magnitude according to the determined
power flow control strategy. This strategy, in
contrast to the Grid Tied or Off Grid solution, can be
flexibly programmed for cost optimal control. It is
worth noting that grid-side power balance control
can be provided independently on the source-side
power balance. This is possible with the
implementation of a separated individual,
bidirectional DC/DC converter (ESC in Fig.1) in the
energy storage leg and an MPPT controlled DC/DC
converter (SC in Fig.1) in the source leg. Once the
distribution system fails, the grid-side converter is
switched to voltage mode, shaping the sinusoidal
voltage on the islanded circuit and performing a
UPS function. In the hybrid solution, the islanding
switch (IS in Fig.1) has both a functionality typical
for a by-pass switch (Off Grid systems) and an anti
islanding switch (Grid Tied systems).
2.2 Energy Measurement
and Monitoring Systems
Optimal energy management in prosumer systems
EnergyManagementSolutionsforPolishProsumerSystems
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requires real-time information about power flow in
both major circuits of the electrical installation: in
the load circuit as well as in the source circuit.
Moreover according to Polish Energy Law
(Parliament of the Republic of Poland, 2013) the
energy generated in licensed RES being subsidized
by green certificates should be measured directly at
source terminals or in a place of common coupling
(PCC) of the source interface and utility grid. This
means that in each Polish prosumer system there
should be installed two independent meters.
Presently in Poland public, commercial and
industrial customers have installed advanced
electronic meters allowing the recording and
transmission of measurement data. In the last two
years distribution system operators (DSO) have
begun to implement widely the use of smart energy
meters also for domestic customers with a
connection power limit below 40 kW.
Simultaneously they are developing an Advanced
Metering Infrastructure (AMI) for remote data
reading and meter management. According to the
required structure, accepted by the Polish Energy
Regulatory Office (Energy Regulatory Office of
Poland, 2011), an AMI system consists of several
major parts: smart meters, hubs and balancing
meters, data transmission system and SCADA based
data acquisition system.
In their target functionality AMI systems should
be able to provide bidirectional communication of
measurement data reading, as well as for
commercial data transfer to the customer areas
through smart meters equipped with additional
interfaces to the Home Area Networks (HAN).
2.3 Energy Management Systems
The Polish Energy Regulatory Office, together with
the requirements of the AMI infrastructure,
prescribes the expectations of other Smart Grid
components to assure their interoperability within
one system. Some requirements have also been
defined for customer-side energy management
systems such as HAN (AT Kearney, 2012). HAN
systems can cooperate with the AMI infrastructure
through smart meter reception of technical and
commercial information from DSO which can be
used for optimal power balance control, matched for
economy of use. The AMI infrastructure in Poland
today is still in its developmental stage. The signals
for commercial power control (reduction for peak
power shaving or growth for valley filling at night)
can also be transmitted using an alternative
communication channel, for example, by the
Internet, and can be provided by Energy Services
Companies (ESCO). HAN infrastructure is not only
a communication system, it is also a control system,
which allows the control of instantaneous power
balance. The HAN controller manages appliances
according to programmed algorithms and according
to research results could bring energy savings of
between 4% and 15% (AT Kearney, 2012).
3 OPTIMAL CONFIGURATION
OF PROSUMER SYSTEMS
The above described technologies due to their
interoperability could be flexible combined to work
together within one optimized energy management
system. Choosing the optimal structure and control
algorithms in the case of Polish prosumer systems
and in accordance with the specific economic
conditions is especially important in reducing
investment costs (due to the lack of subsidy
programs), but a choice which should also consider
capacity for flexible energy management functions,
such as load shifting or RES energy shifting, to
match load and generation curves. To evaluate the
costs and profits in different configurations and with
different tariffs, the prosumer system with a standard
daily load profile (domestic type, P
L
in Fig. 2) and
PV based RES source (P
RES
in Fig.2) has been
considered. Moreover the power of the PV system
has been determined on the assumption of an ideal
daily energy balance between energy consumed in
loads (about 10 kWh) and energy generated in RES.
To simplify analysis a day in the summer season has
been chosen. Additionally the yearly irradiance
variation has been ignored, so payback period has
been evaluated in months (an assumption of constant
irradiance during the summer season has been
made). Illustrations of power management in the
selected configuration of the prosumer system are
shown in Figure 2. As can be seen the mismatch of
power profiles of load and RES could cause a
bidirectional energy transfer between utility grid and
prosumer (P
S
> 0 or P
S
< 0) in Grid Tied systems. In
systems such as Off Grid and Hybrid, controlled
with an internal power balance strategy (P
S
= 0) the
energy storage devices store energy when P
RES
> P
L
and supply load when P
RES
< P
L
(through a grid-side
inverter).
Depending on energy prices in different tariff
programs and taking into account possible extra
benefits in the case of providing ancillary services
(DSR in Fig. 2a), the payback time of investment in
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a) b)
c) d)
Figure 2: Illustration of power management in selected configuration of prosumer system: a) considered tariffs programs; b)
Off Grid and Hybrid; c) Grid Tied; d) Hybrid with HAN based load management.
prosumer systems, working in specific
configurations will be different. The overall cost of a
solution is strictly dependent on the system
configuration and is much higher in all solutions
employing energy storage devices compared with
those without batteries (almost three times higher).
Thus the required capacity of energy storage devices
should be minimized. This is possible using load
management systems like HAN, working with
strategy based on shifting operating time of
programmable devices such as dish washers,
washing machines, dryers, electric heaters, etc., to
periods of day where the power of RES (P
RES
) is
higher than the power demand of the load circuit
(P
L
). This strategy has been indicated in Figure 2 as
P
L
→. Using this strategy as well as the second one
based on load power reduction (P
L
↓) it is possible to
modify the load power profile (P
L
instead of P*
L
in
Fig. 2d) and to reduce the required battery capacity
by 30% and 15% of required RES power (P
RES
instead of P*
RES
, see Fig. 2d). Although this results
in decreasing proportional energy storage and PV
costs, additional investment is needed in the HAN
system, consisting, at least, of a central HAN
controller and a several active sockets (AS). The
proposed Off Grid and Hybrid configurations
controlled using the strategy of internal power
balance (P
S
= 0) give more cost optimal energy
management than the Grid Tied configuration where
the surplus energy is reversed into the utility grid (P
S
< 0 in Fig.2c) at a price much lower (FIT = 0,16
PLN / kWh in Fig.2a) than the energy taken from the
grid (average = 0,53 PLN / kWh; peak = 0,62 and
off peak = 0,28 PLN / kWh), but the benefits of the
former come with higher investment costs (for more
details see data in Table 1).
4 CONCLUSIONS
Consideration of the results presented in this paper
show very clearly that in spite of the decreasing
investment costs of RES technology in small
scale applications investors would not gain any
-0,2
-0,1
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
1 7 13 19
energy cost [PLN / kWh]
hours
Tar if f s
0
200
400
600
800
1000
1200
1400
1600
1 7 13 19
power [W]
hours
Off Grid and Hybrid
-1500
-1000
-500
0
500
1000
1500
2000
1 7 13 19
power [W]
hours
Grid Tied
0
200
400
600
800
1000
1200
1400
1600
1 7 13 19
power [W]
hours
Hybrid with HAN
EnergyManagementSolutionsforPolishProsumerSystems
111

Table 1: Properties of selected configurations of prosumer system.
structure of
solution
tariff
program
power
control
strategy
estimated
cost of
solution
[PLN]
utility
energy
daily
transfer
[kWh]
monthly
energy cost
without
RES
utilization
[PLN]
monthly
benefits of
RES energy
utilization
[PLN]
simple
payback
period
[months]
from to
PV+Off Grid averaged
P
S
= 0 18.750
0 0
158 158 119
peak / off peak 145 145 130
peak / off peak
+ DSR
145 151 125
PV+Grid
Tied
averaged
unavailable 6.750 4,4 7,12
158 122 56
peak / off peak 145 129 53
peak / off peak
+ DSR
145 137 50
PV+Hybrid averaged
P
S
= 0 17.750
0 0
158 158 113
peak / off peak 145 145 123
peak / off peak
+ DSR
145 151 118
PV+Hybrid
+HAN
averaged
P
S
= 0
P
L
→
P
L
↓
17.000
0 0
134 134 127
peak / off peak 123 123 139
peak / off peak
+ DSR
123 129 132
power control strategies: P
S
= 0 – internal power balance; P
L
→ – load power shift; P
L
↓ – load power reduction
satisfactory economic gains without any supporting
programs. In Poland, the simplest prosumer systems
based on the Grid Tied configuration and having
effortless energy exchange between the utility grid
and prosumer installations have to transfer the
surplus energy at discouraging prices. Better in this
field are systems with Off Grid and Hybrid
configurations, which are functionally better suited
for more cost effective energy management, but they
need energy storage devices in their structure which
increases investment costs. On the other hand one of
these solutions – the Hybrid, has the flexibility
which gives the prosumer the ability to control the
power flow inside and outside of his installations
The function of load curve modification (with or
without HAN), especially in peak hours, will be the
main trump of Hybrid solutions in the near future
when the risk of a power deficit can occur in the
Polish electrical power system with the
disconnection of coal fired, outdated and relatively
heavily polluting power plants. Freedom from utility
grid outages is another advantage of the Hybrid
solution as well as the ability for RES energy
optimal utilization in this case. The small scale RES
market in Poland is today still in its infancy, hence
the results presented in this paper will be extended
when more data becomes available.
REFERENCES
AT Kearney, 2012. HAN within Smart Grids – The social
and market report, Warsaw. Poland (in polish).
AT Kearney, 2012. HAN within Smart Grids – The
technology report, Warsaw. Poland (in polish).
Benysek, G., Jarnut, M., 2013. Energy effective and active
systems in buildings, The publishing house, University
of Zielona Gora. Zielona Gora. Poland. (in polish).
Energy Regulatory Office of Poland, 2011. Position of the
President of ERO on necessary requirements with
respect to smart metering systems implemented by
DSO E taking into consideration the function of the
objective and proposed support mechanism in context
of the proposed market model, Warsaw. Poland. (in
polish).
European Parliament, 2009. Directive 2009/28/EC of the
European Parliament and of the Council of 23 April
2009 on the promotion of the use of energy from
renewable sources and amending and subsequently
repealing Directives 2001/77/EC and 2003/30/EC,
Official Journal of the European Union 5.6.2009,
Strasbourg.
Jarnut, M., 2012. The concept of utility grid interface for
prosumer systems. In proceedings of PPEEm 2012, XV
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(in polish).
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Warsaw. Poland. (in polish).
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