1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy
Energy Procedia 99 ( 2016 ) 25 – 34
10th International Renewable Energy Storage Conference, IRES 2016, 15-17 March 2016,
The role of energy storage solutions in a 100% renewable Finnish
Michael Child*, Christian Breyer
Lappeenranta University of Technology, Skinnarilankatu 34, 53850 Lappeenranta, Finland
A 100% renewable energy scenario was developed for Finland in 2050 using the EnergyPLAN modelling tool to find a suitable,
least-cost configuration. Hourly data analysis determined the roles of various energy storage solutions. Electricity and heat from
storage represented 15% of end-user demand. Thermal storage discharge was 4% of end-user heat demand. In the power sector,
21% of demand was satisfied by electricity storage discharge, with the majority (87%) coming from vehicle-to-grid (V2G)
connections. Grid gas storage discharge represented 26% of gas demand. This suggests that storage solutions will be an important
part of a 100% renewable Finnish energy system.
© 2016 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy.
Keywords: energy system modeling; storage solutions; 100% renewable energy; Finland; vehicle-to-grid; power-to-gas
Variability and uncertainty are inherent qualities of energy systems as supply and demand of energy services
vary over time, space and sometimes in unpredictable ways. The challenge of mitigating such imbalance has always
required a high level of flexibility, often provided by energy resources, particularly fossil fuels. However, climate
*Corresponding author. Tel.: +358-40-829-7853.
E-mail address: Michael.Child@lut.fi
Available online at www.sciencedirect.com
© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
Peer-review under responsibility of EUROSOLAR - The European Association for Renewable Energy
26 Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34
change and sustainability challenges require that future energy systems have increased levels of renewable energy
(RE) generation, much of which is intermittent or variable, creating a different need for flexibility measures that can
ensure reliability, stability and quality of energy supply. Moreover, demand must be met in a responsible manner
that does not place unnecessary burdens on society in terms of how disruptive or expensive solutions are to
implement. Energy storage technologies are increasingly viewed as essential elements of flexibility in future energy
systems, capable of bridging “temporal and geographic gaps between energy supply and demand” . Such
geographic gaps are filled in such cases when energy storage is portable, or stored energy can be transmitted or
transported over distance. Additionally, energy storage may bring reliable energy services to areas that have poor
energy infrastructure, or are seen as off-grid.
Finland represents an interesting case study of future energy systems due to strong diurnal and seasonal variation
in variable energy generation (hydro, wind, solar) that is typical of countries at high latitudes. What is more, it is a
highly industrialised nation with a strong need for a reliable energy supply that meets the needs of individual
consumers while also ensuring a competitive industrial sector. Further, Finland has committed to an 80-95%
reduction (compared to 1990 levels) in greenhouse gas emissions by 2050 .
Finland represents a challenge to high levels of solar photovoltaic (PV) and wind power in an energy system.
While there are high amounts of solar irradiation during the summer months, the opposite is true during winter.
Moreover, there is noticeable seasonal variation for both onshore, and offshore wind power, with more wind energy
produced in the winter months. Further, there is also a seasonal element to hydro power, as the Finnish system is
dominated by run-of-river hydro power with limited reservoir capacity of approximately 5.5 TWhe , equivalent to
approximately 6.5% of current electricity demand . Hydro power is used as seasonal storage of energy in Finland,
as most energy inflow occurs during the spring runoff in May. Reservoirs are kept relatively full until energy is
needed during the winter months of December-April. At the same time, it must be remembered that Finnish hydro
power experiences interannual variation in total annual production of 10-17 TWhe, thereby demonstrating its
somewhat intermittent nature .
On the demand side, the need for energy services in the form of heat and electricity is naturally higher during
long, dark Finnish winters. So, finding the flexibility in the Finnish energy system has always been a significant
task. In a future energy system based on high shares of variable RE, the need for energy storage solutions (ESS) on
a daily, weekly and seasonal basis seems obvious. This extreme situation could then serve as a model for other
countries at high latitudes, both north and south, of how variable renewable energy generation can play a role in a
highly developed and industrious society.
For these reasons, an energy system based entirely on renewable resources was considered in previous work by
the authors . The scenario of a 100% renewable energy system was seen as being highly cost competitive to those
with increasing shares of nuclear power installed capacity as well as a Business As Usual scenario. In other work,
Child et al.  examined the role of solar PV for the case of a 100% RE Finnish energy system for 2050, which
showed that storage technologies could play a prominent role in facilitating high shares of solar PV. However, this
current study seeks to explain the nature and significance of energy storage solutions in more detail. This will
include the roles of Gas storage, Power-to-Gas (PtG) technologies, Thermal Energy Storage (TES), stationary
batteries, and Vehicle-to-Grid (V2G) connections. The significance of ESS in this future energy system will be
determined by answering the following key questions:
xHow much wind and solar PV power is used directly?
xHow much of the annual energy demand is covered by ESS?
xHow much stored energy comes from stationary batteries and V2G connections?
xHow much stored energy comes from TES?
xHow much stored energy comes from gas storage?
Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34 27
The EnergyPLAN advanced energy system analysis computer model  was used to represent a 100% RE
scenario for Finland in 2050. This scenario was one of several used in the study by Child and Breyer , and was
selected for the case of a basic biomass resource availability for further detailed analysis as it represented the most
cost competitive of the scenarios studied. A thorough description of the tool used and the scenario parameters can be
found in . In addition, the main inputs to EnergyPLAN for the 100% RE scenario can be found in  as well as a
summary of important assumptions and scenario parameters.
In order to explore a broader context and to investigate the possible seasonality of different types of energy
production, a number of the hourly distributions were examined for the entire year. These included annual electricity
demand and production by category as well as levels of electric storage, DH storage, and gas storage for the entire
year. Hourly end-user consumption data for Finland were based on actual values from 2012 obtained from Fingrid
 and hourly hydro power and industrial CHP production data were based on actual values from 2012 obtained
from Finnish Energy Industries . Wind and solar PV distributions were derived from Child and Breyer , based
on data originating from [10, 11].
To determine the relative contributions of energy storage options investigated in this study, total energy
consumption was determined based on electric and thermal energy end-user demand which were inputs to
EnergyPLAN. In total, 170.3 TWh of energy was consumed for the year, represented by 105 TWh of electricty and
65.3 TWh of heat. Several hourly and annual outputs from the EnergyPLAN analysis were readily available,
including V2G storage discharge, stationary battery storage discharge, and thermal storage discharge. However,
both the annual electricity and heat that were ultimately derived from stored gas were calculated according to the
uu ¦ (2)
IND uu ¦ ,,
eeee INDPPCHPGas (4)
uu ¦ (5)
uu ¦ (6)
uu ¦ (7)
28 Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34
thththth BOILERHHCHPGas (8)
CHPe is the total annual electricity generation from stored gas in CHP plants operating in backpressure mode,
Gasdemand,CHP,i is the amount of gas used in CHP plants for each hour of the year (1-8784), Gasdemand,total,i is gas used
by all sources for each hour, Gasstored,i is the amount of gas discharged from storage in each hour, and όe,conversion,CHP
is the efficiency of converting gas to electricity in a CHP plant (40%). PPe is the total annual electricity generation
from stored gas in CHP plants operating in condensing mode, Gasdemand,PP,i is the amount of gas used in CHP plants
for each hour, and όe,conversion,PP is the efficiency of converting gas to electricity in a CHP plant (40%). INDe is the
total annual electricity generated by industrial power plants, INDe,total,i is the amount of electricity produced by
industry for each hour of the year, GasIND is the amount of gas used by industry annually (30 TWh), and FuelIND is
the amount of total fuel used by industry annually (125 TWh). Gase is the total amount of electricity produced by
stored gas. CHPth is the total annual heat generation from stored gas in CHP plants operating in backpressure mode,
and όth,conversion,CHP is the efficiency of converting gas to heat in a CHP plant (50%). HHth is the total annual heat
generation from stored gas in individual households, and όth,conversion,HH is the efficiency of converting gas to heat in
individual households (95%). BOILERth is the total annual heat generation from stored gas in district heating boilers,
and όth,conversion,BOILER is the efficiency of converting gas to heat in district heating boilers (90%). Gasth is the total
amount of heat produced by stored gas.
To determine the direct usage of solar PV and wind energy, the sum of these categories of production (solar
PV + onshore wind + offshore wind) was divided by total supply of electricity from all sources. This ratio was
multiplied by the amount of total electricity consumption to determine the proportion of wind and solar PV power
that was directly consumed. The same ratio was multiplied by the total amount of power going to electricity storage
(stationary batteries + V2G batteries + PtG electrolysers) to determine the amount of wind and solar going to
storage. The share of solar PV and wind energy that was directly consumed was determined by the ratio of directly
consumed solar PV and wind energy to total electricity consumption by all sources. These calculations were
performed for each hour of the year and then summed to acquire annual totals. Results were compiled, tabulated and
Annual results are compiled in Figures 1-5 for electricity production, electricity consumption, electricity storage,
thermal storage and grid gas storage components of the energy system. Results of calculations are shown in Figure
6, and Tables 1 and 2.
Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34 29
Fig. 1. Annual hourly power demand by category (MWe). Flexible demand and electric vehicle charging aids in reducing high peaks in electricity demand and fills valleys in demand during night hours and at midday.
Curtailment of electricity is less than
Fig. 2. Annual hourly power consumption by category (MWe). A seasonal complement is seen between solar PV and CHP electricity production. To a lesser extent, solar PV is also seasonally complemented by wind
30 Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34
Fig. 3. Hourly electric storage levels (MWhe) for entire year. Maximum storage capacity is 170 000 MWhe. The utilization of stationary batteries by EnergyPLAN seems at odds with how such energy storage devices
would be used in reality. EnergyPLAN used stationary batteries as a storage of lowest priority, while future prosumers may use them with the highest priority. V2G batteries were a high priority storage solution for
Fig. 4. Hourly thermal storage levels (MWhth) for entire year. Maximum storage capacity is 20 000 MWhth. Finland currently has high levels of thermal energy storage associated with the DH system. Much of it is
unused during the summer months, but it has an important function during the winter.
Fig. 5. Hourly grid gas storage levels (MWhgas) for entire year. Maximum storage capacity is 3 800 000 MWhgas. High levels of gas storage are generally associated with high production of wind power. Gas storage
decreases during the summer months when solar PV generation is high.
Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34 31
Fig. 6. Percentage of solar PV, onshore wind and offshore wind that is directly consumed. Values range between 4-80% with a mean of 62%.
Table 1. Summary of calculations related to electricity and heat from gas storage.
CHP electricity from gas
discharge (TWhe)PP electricity from gas
discharge (TWhe)Industry electricity from
gas discharge (TWhe)Total electricity from gas
discharge (TWhe)CHP heat from gas
household heat from
Boiler heat from gas
discharge (TWhth)Total heat from gas
1.16 0.73 1.14 3.01 1.44 1.13 0.01 2.58
32 Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34
Table 2. Summary of calculations related to ratios of storage discharge to consumption.
Parameter Unit Value
Electricity consumption TWhe105
Heat consumption TWhth 65.3
Total energy consumption TWh 170.3
V2G discharge TWhe 19.4
Stationary Batteries discharge TWhe 0.1
Electricity from stored gas TWhe 2.7
Heat from stored gas TWhth 2.6
DH storage discharge TWhth 0.2
Solar PV and wind directly consumed TWhe 63.5
as % of total solar PV and wind production 46.6%
as % of total electricity production 70.8%
as % of final electricity consumption 60.5%
Solar PV and wind to electric storage TWhe 69.3
as % of total solar PV and wind production 50.9%
Solar PV and wind to curtailment TWhe 3.5
as % of total solar PV and wind production 2.5%
Total storage discharge TWh 25.0
as % of total consumption 14.7%
Electricity storage discharge TWhe 22.2
as % of electricity consumption 21.1%
V2G discharge TWhe 19.4
as % of all electricity storage discharge 87.2%
Thermal storage discharge TWhth 2.8
as % of heat consumption 4.3%
Gas storage discharge TWhgas 14.0
as % of grid gas consumption 26.5%
Solar PV and wind power make a roughly 60% contribution to final energy consumption and are 70% of total
electricity generation, but that contribution is quite variable throughout the year. In addition, that contribution is at
times concentrated during daytime, necessitating both short and long-term storage. Approximately 47% of variable
RE is utilized directly, with the balance going to storage (51%) and a small amount being curtailed (2.5%). At the
same time, hydro power production was quite high during times of curtailment, suggesting that curtailment may not
be necessary if the full potential of hydro reservoir storage was harnessed. Electric storage discharge totalled 22.2
TWhe, or 21% of end-user consumption. On a daily basis, V2G batteries seem to have a much greater role (87%)
than stationary batteries, raising the question of whether stationary batteries may be necessary at all in the context of
higher V2G connection. The answer to this question is beyond the scope of this current study, but must include
careful consideration of the needs of off-grid consumers, barriers against V2G connections, and an overall
cost/benefit analysis for both grid operators and end-users. Due to the use of block heaters in winter, Finns are
already accustomed to plugging their cars in, and electrical connections for vehicles are already widespread
throughout the country. The potential evolution of this behaviour and technical capacity seems rather
Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34 33
straightforward, but cannot be assumed without a clear demonstration of technical feasibility and net benefits to
society. Currently, Finnish local low voltage distribution grids and typical household connections may not support
the high power exchanges needed to offer a full range of V2G services. How this possible barrier can be overcome
in the future requires more detailed study.
On a daily, weekly and seasonal basis, PtG technology bridges the gaps between demand and supply at times
when generation is most intermittent. At the same time, this technology is available to provide base loads of
electricity, heating, cooling and mobility when they are needed. These results are in line with those for Germany
[12, 13]. Gas storage arising from PtG, biomass gasification and biogas generation amounts to 14 TWhgas, or 26% of
annual gas usage.
Thermal energy storage in Finland is rather plentiful, but utilization is rather minimal when annual numbers are
examined. Thermal storage discharge amounted to 2.8 TWhth, which represented only 4% of end-user heat demand.
However, the role of thermal storage was rather significant during some periods of the year (autumn and winter),
and would be expected to be quite vibrant in urban areas compared to rural areas. As EnergyPLAN considers the
energy system as one single heating system, rather than a collection of distributed systems, one could expect greater
utilization of thermal storage when the energy system is divided into smaller regions. Further study is needed in this
regard that would necessitate utilization of a different modelling tool.
The seasonal complement of solar PV and wind power production in Finland appears obvious (Figure 2), despite
the intermittent nature of each. This intermittency appears manageable by the storage technologies utilized in this
study. In total, 25.3 TWh of heat and electricity are discharged from storage, representing 15% of total end-user
consumption. One must also remember the important role of hydro power in Finland. Up to 20% of end-user
electricity consumption can be supplied by hydro power. This study also does not fully explore the full potential of
hydro storage available in Finland. Indeed, a full accounting of the potential to utilize hydro storage in Finland is
lacking. Harnessing further flexibility in hydro power production could lessen the need for other storage capacity,
such as batteries or PtG production. Alternatively, there may be less need for thermal energy generation. Each of
these reductions may in turn result in a decrease in overall costs.
The integration of high shares of renewable energy sources in future energy systems will require a variety of
complementary storage solutions. It has been previously determined that electricity storage devices will be needed
once 50% of power demand is met with variable RE, and that seasonal storage devices will be needed once more
than 80% of electricity demand is met by RE [14, 15]. Currently, there is a long list of energy system flexibility
measures available to support high levels of intermittent RE . Developing a 100% RE scenario for a nation
requires careful consideration of the right mix of these measures for each context. In turn, these measures should be
suited to and complemented by the energy generation technologies that make up the energy system. Such is the case
for variable RE and the energy storage technologies investigated in this work. Variable RE and energy storage
solutions can play a significantly role in a future energy system for Finland based on 100% renewable energy
The authors gratefully acknowledge the public financing of Tekes, the Finnish Funding Agency for Innovation,
for the ‘Neo-Carbon Energy’ project under the number 40101/14.
34 Michael Child and Christian Breyer / Energy Procedia 99 ( 2016 ) 25 – 34
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