This document discusses energy storage in urban multi-energy systems. It outlines electrical energy storage (EES) and thermal energy storage (TES), describing their various roles and technologies. EES can help integrate distributed generation and provide grid flexibility and ancillary services. TES allows decoupling of heat generation and use in district heating. Both are key to efficient multi-energy systems at urban scales. The document also briefly discusses power-to-fuels technologies that can store renewable energy as synthetic methane or hydrogen.

1. Energy storage in urban
multi-energy systems
Prof. Marco Carlo Masoero
ICARB Workshop: Energy Storage for the Built Environment
Edinburgh, 21st October 2014

2. Outline of the presentation
 Electrical Energy Storage (EES)
 The role of EES
 The technical parameters
 Electric Energy Storage systems typology
 Thermal Energy Storage (TES)
 Purpose of TES in Energy Plants
 Technologies
 Short-term (daily) vs Long-term (seasonal) storage
 Applications: District Heating and Cooling
 Power-to-Fuels
 Conclusions
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Energystorageinurbanmulti-energysystems

3. The role of Electric Energy Storage I
3
 Distributed generation
development by renewables
 More efficient use of HV and MV
power grids
 Smart Grid in support to Local
Energy Communities
 Higher flexibility to rapidly respond
to variable load demand
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Generation Transmission Distribution End User
ElectricEnergyStorage

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 Ancillary services:
 Primary regulation f/P
 Secondary regulation
 Tertiary regulation
 Reactive power regulation
 Black-start
 Load rejection
 Remote disconnection service
 Load interruption
4
The role of Electric Energy Storage II
Generation Transmission Distribution End User
ElectricEnergyStorage

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EES could represent a feasible solution to dealing
with several aspects:
 Secondary and tertiary regulation
 Over voltage
 Reverse power flows
 Resolution of congestions storage of energy in
excess at peak-hours
The role of Electric Energy Storage III
ElectricEnergyStorage

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EES could represent a feasible solution to dealing
with several aspects:
 Line capacity investment deferral: EES discharges at
peak times and charges at off-peak times
 Peak shaving long discharge/charge times
 Power quality short discharge/charge times
 Reduction of the resistive line losses
 Provision of ancillary services:
 balancing energy
 Rotary reserve
 Substitutive reserve
 frequency regulation
• in normal power grid condition
• in islanding working mode
The role of Electric Energy Storage IV
ElectricEnergyStorage

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EES could represent a feasible solution to dealing
with several aspects:
 control system and power quality improvement
• Dip voltage and over/under-voltage
• Frequency variations
• Low power factor
• Harmonic distortion
 support service to voltage control
• instead of capacitor banks, EES can compensate for
voltage drop
 provision of black-start services
• overall blackout
The role of Electric Energy Storage V
ElectricEnergyStorage

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Source: Eurelectric, Decentralised storage: impact on future distribution grids, 2012
The role of Electric Energy Storage VI
ElectricEnergyStorage

9. Installed capacity (World)
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ElectricEnergyStorage

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EES systems are defined by the following technical
parameters:
• Specific energy (kWh/kg) or energy density (kWh/m3)
• Specific power (kW/kg) or power density (kW/m3)
• Efficiency
• Number of cycles
• Useful life
• Charge/discharge times (h)
• Ramp rate (s)
• Specific costs (€/kWh or €/kW)
• Maturity
The technical parameters I
ElectricEnergyStorage

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Mainly the electrochemical EES are also defined by
the following parameters:
• Memory effect
• Charge/discharge velocity
• Depth of discharge
• Self discharge
The technical parameters II
ElectricEnergyStorage

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 Energy intensive: Availability to store large amounts of energy
 Power Intensive: Ability to deliver / absorb great amount of
power in short time
Source: EPRI, Electric Energy Storage Technology Options: A White
Paper Primer on Applications, Costs, and Benefits, 2012
Energy and Power Intensity
ElectricEnergyStorage

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• Mechanical energy:
• Pumped Hydroelectric Storage (PHS)
• Compressed Air Energy Storage (CAES)
• Flywheels
• Electromagnetic and electrostatic energy:
• Electric Double Layer Capacitors - EDLC
• Superconducting Magnetic Energy Storage – SMES
• Chemical energy (hydrogen vector):
• Compression
• Liquefaction
• Chemi-sorption
• Physi-sorption
• Thermal energy:
• Molten salt
• Liquefied Air Energy Storage (LAES)
• Phase Change Materials
Electric Energy Storage systems typology
ElectricEnergyStorage

14.  Storage in potential energy
 convenience:
𝑃 𝑔𝑒𝑛
𝑃 𝑝𝑢𝑚𝑝
≥ 1.4
 More than 99% of EES
 Difficulty of installation
 Storage in compressed air
 Integration with thermal power
plants
 Difficulty of installation
14
PHS
CAES
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Mechanical energy EES I
ElectricEnergyStorage

15.  Storage in kinetic energy
 Angular speed 60.000-100.000 rpm
 High energy density
 Rapid ramp rate
 High efficiency (90-95%)
 High self-discharge
15
Flywheels
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Mechanical energy EES II
Chemical energy (H2 storage)
 Compressed gas: 200-700 bar
 Liquid H2: -253 °C
 Chemi-sorption: Metal hydrides
 Physi-sorption
 Power to Gas: EC + H2 + FC
ElectricEnergyStorage

16.  Storage in electric field
 Specific energy: 1 ÷ 5 Wh/kg
 Specific power: 100 ÷ 2.000 W/kg
 High number of charge/discharge
cycles
 Storage in magnetic field
 Superconductors between 4÷100 K
 Rapid ramp rate (20 ms)
 High specific power
 High efficiency (>97%)
16
EDLC
SMES
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Electric energy EES I
ElectricEnergyStorage

17.  Li-ions: high specific power and
efficiency
 Lead Acid: high specific power, low
energy density. Mature
 Ni-Cd: high number of cycles.
Environmental risk
 ZEBRA: high specific power and
efficiency. High temperature
 Na/S: high number of cycles
 Ni-MH: high specific power, low
energy density
 Flux: Vanadium RedOx, Zn-Br
17
Electrochemical batteries
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Electrochemical energy EES I
ElectricEnergyStorage

18. Purpose of Thermal Energy Storage in
Energy Plants
The use of thermal storage systems in energy plants can have multiple
purposes:
1. Increase the stability in short term operation of the plants (e.g. load
variation in heat pump systems)
2. Reduce the use auxiliary boilers (e.g. in district heating)
3. Shift the heat production through CHP to periods where the electricity
production is more convenient (in the case of backpressure plants or
internal combustion engines) or less convenient (in the case of
extraction plants)
4. Increase the use of renewable primary resources (e.g. solar thermal
systems)
All these have in common the decoupling between heat generation and
utilization.
ThermalEnergyStorage
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Technologies
 Water Tanks
 Phase Change Materials
 TABS
 Other (Ice Storage, Pebble Systems,…)
ThermalEnergyStorage

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Technologies: Water Tanks
DHW systems Solar Heaters
Daily Storage Systems
ThermalEnergyStorage

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Technologies: Water Tanks
Seasonal Storage Systems
ThermalEnergyStorage

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Technologies: Embedded Systems
In Thermally Activated Building Systems (TABS) the
thermal capacity of the building is enhanced by the
installation of water pipes within the slabs.
ThermalEnergyStorage

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Technologies: Embedded Systems
Phase Change Materials (PCM) can be installed within
structural elements of buildings (typically walls).
Their fusion temperature being around 25°C, their phase
(liquid/solid) changes in a temperature range that is practical
for normal building uses and allows to store/release thermal
energy
ThermalEnergyStorage

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District Heating (DH) Networks
 Total Heat Load results from the aggregation of
multiple users
 Need of adapting the heat demand side with the
heat supply side along the day
 Need of operation optimization for different
generation units (e.g. CHP, boilers, heat pumps,
solar collectors)
ThermalEnergyStorage

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The role of Thermal Storage:
Decoupling Supply and Demand
Supply Side Demand Side
DH systems have to match the user demand, as a result it is
difficult to optimize CHP size and operation
ThermalEnergyStorage

26. Current District Heating Network in Turin
As of 31-12-2012:
• largest DH system in Italy
• 53,4 Mm3 supplied buildings
(88 Mm3 in future planning)
• 1.89 TWh heat supplied
• 467 km grid length
• 1.77 GW peak heat
generation
• 1.14 GW of power (CHP)
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ThermalEnergyStorage

27. Current District Heating Network in Turin
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ThermalEnergyStorage

28. Current + Forecasted DH Network in Turin
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ThermalEnergyStorage

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The role of Thermal Storage:
Turin DH daily profiles
January
April
July
Daily peaks
ThermalEnergyStorage

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The role of Thermal Storage:
Decoupling Supply and Demand
Turin Politecnico:
Re-Heating and Pumping
Plant with 2.500 m3 storage
North Turin:
Combined Cycle
Cogeneration Plant
with 5000 m3 storage
ThermalEnergyStorage

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Heat storage systems behaviour
Storage
Unload
Storage
Load
Heat storage systems
CHP units
Boilers
DH system of Turin
ThermalEnergyStorage

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Heat storage systems behaviour
Heat Storage SystemsCHP UnitsBoilers
The heat storage
allows to increase
the utilization factor
of CHP units
DH system of Turin
ThermalEnergyStorage

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Biomass DH System Configurations
CHPBoilers +Boilers only
Heat storage
systems
+
CHP
Boilers
+
Hours
HeatLoad
Hours
HeatLoad
Hours
HeatLoad
ThermalEnergyStorage

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Biomass DH System Simulation
The heat storage helps to increase the overall efficiency of the system
ThermalEnergyStorage

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Biomass DH System Simulation
• The heat storage systems move and lower the optimum pay back time.
• The incentives change the convenience of installing heat storage systems.
Best PBT
ThermalEnergyStorage

36. District cooling - Gotehnburg
ThermalEnergyStorage
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37. District cooling- Paris Centre
ThermalEnergyStorage
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Water cooled Air cooled Total energy storage: 140 MWh

38. Outine: Power-to-Fuels
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ENERGY CONTEXT: THE NEEDS:
1. Large size storage of RES: storage in forms of chemicals
2. Chemicals that can have interest for the energy sector: existing distribution
and utilization infrastructure; several final users (e.g. stationary systems,
automotive, etc.)
3. Chemicals as CO2 sink
A POSSIBLE SOLUTION: GREEN FUELS
One option for fast and sustainable storage is the production of gaseous fuels to
be fed in the distribution grid: those fuels could be produced by means of
electrolysis processes and thus converted into synthetic methane to be fed into
the existing distribution infrastructure.
PROS
1. conversion of relevant amount of renewable sources from “flow” to “stock”
2. chemical fixing of carbon recycled from CO2
3. easy utilization of synthetic methane into existing energy infrastructure
(distribution and final uses)
Power-to-Fuels

39. Integration of Electric and Gas Networks
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Power-to-Fuels

40. GAS DISTRIBUTION GRID
ELECTRIC GRID
Electrolysis
Low-priced
surplus electricity
H2
Methanation
CH4
CO2
Biomass, biogas, industry,
CCS
Up to 5% in CNG
Mobility (road
transportation)
Gas-to-power
Power-to-gas
H2
Wind, solar,
nuclear
H2/syngas
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Power-to-Fuels

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Conclusions
 Energy storage is a key issue in any multi-energy
system applied at the urban scale
 Integration of distributed generation should
compete with quality standard warranty
 The role played by EES will be fundamental to shift
towards a smart grid concept
 TES is essential for an efficient integration of
thermal energy production and distribution, using
both fossil and renewable sources
 The choice to install a certain typology of storage
system depends on the application desired
Conclusions

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Thank you for your
attention!
marco.masoero@polito.it