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Decarbonization of the Heating Sector in Hamburg
Grid Constraints, Efficiency and Costs of Green
Hydrogen vs. Heat Pumps
Felix Röben, Nina Kicherer, Lucas Jürgens, Simon Decher, Hans Schäfers, Jens-Eric von Düsterlho
CC4E - Competence Center für Erneuerbare Energien und EnergieEffizienz
Hamburg University of Applied Sciences (HAW Hamburg)
Steindamm 96, 20099 Hamburg, Germany
correspondence: felix.roeben@haw-hamburg.de
Abstract—Germany’s path to climate neutrality is mapped out
in the Climate Protection Act. Following the ruling of the Federal
Constitutional Court on April 29, 2021, and with a view to
the European climate target for 2030, the German government
presented the amended Climate Protection Act on May 12, 2021.
By this law, the heating sector in Germany is bound to reduce
its CO2emission of 118 million t in 2020 to 67 million t CO2in
2030 [1].
This 43 % reduction in ten years necessitates a comprehensive
building renovation strategy and a rapid reconsideration of
applicable heating technologies. Heat pumps offer a very efficient
form of individual heat supply. On the other hand, concerns
are being raised that power grids might not be able to serve
the additional loads resulting from a high distribution of heat
pumps and that only the gas grid can guarantee an affordable
heat supply. The usage of green hydrogen for the heating sector
is presented as the favorable option by the gas economy [2].
As a contribution to this ongoing discussion, the paper presents
a comparison of costs for consumer and calculations of additional
electricity grid loads for the city of Hamburg. The investment and
operating costs for end consumers are extrapolated and compared
for heat pumps, condensing boilers using natural gas and/or
green hydrogen. In a second step, future heat pump scenarios
are compared with the present situation to estimate possible
grid overloads. The scenarios represent different refurbishment
rates and a variation of district heating, decentralized renewable
heating (i.e. wood pellets), and heat pumps. For evaluation
purposes, the currently used power supply for direct power
heating systems is assumed to be available for heat pumps.
Index Terms—Heating Sector Hamburg, Direct Power Heating,
Heat Pumps, Grid Constraints
I. INTRODUCTION
Many governments and states have developed hydrogen
roadmaps as part of their decarbonization plans, which among
other things has led to increased interest and debate on the
use of hydrogen in various energy sectors. Some stakeholders
propose simply replacing fossil natural gas with green hy-
drogen in many areas, such as the gas grid, with the goal of
decarbonizing the gas market and thus the heating sector while
the consumer structure remains largely unchanged [2].
This paper was developed within the project NRL (Northern German Living
Lab) which is partly funded by the German Federal Ministry for Economic
Affairs and Climate Action (BMWK). (sponsors)
Sustainable production of green hydrogen is possible, but
it requires 25 % to 45 % more renewable electricity input
than its own energy yield after electrolysis. Therefore such an
approach would consume a lot of renewable electricity in a
market ramp-up phase, when such electricity is still scarce.
At the same time the full energetic burden of the gas sector
would weigh on the electricity side, requiring a significant
investment in additional renewable power capacity. As a result,
hydrogen utilization and substitution of fossil methane needs
to be prioritized [3], [4].
This paper seeks to rule out the suggestion of substituting
natural gas for green hydrogen in the given gas infrastructure,
such as boilers, in order to reduce emissions while supplying
the heat demand. Instead, the use of green hydrogen should
focus on processes that have no other alternatives to decar-
bonize.
Thus, one hypothesis is that green hydrogen is too valuable
to be burned for low temperature heating demands and that
there are more viable heating options. Hydrogen combustion
for low temperature heat problems is expected to be simply
uneconomical. Section II of this paper includes a cost-benefit
analysis to evaluate this statement. Electrical heat pumps are
viewed as a technological alternative to condensing boilers
powered by natural gas and/or hydrogen in this context.
In addition, the capability of the electricity grid to transport
the additional energy volumes required for heat pump heating
is evaluated. Using electrical heat pumps leads to the problem
that heating energy distribution shifts from the gas grid to
the power grid. This problem will be addressed in section
III, using the city of Hamburg as an example. Based on the
current state of the city’s heating supply, including planned
developments and different assumptions for building refurbish-
ment, the impact of different heating supply compositions on
the power grid is examined in various scenarios. Section IV
provides a conclusion.
II. COM PARIS ON OF C OST S FOR C ONS UME R
The decarbonization of the heating sector is of special im-
portance for consumers, because CO2taxation and increasing
prices for energy carriers lead to financial burden on private
households. This section presents an approach to compare the
total costs related to heating systems with fossil natural gas,
green hydrogen and heat pumps.
A. Methodology
Discounted cumulative costs over 20 years are evaluated
by taking into account the initial investment, inflation ratio
and increase, respectively decrease, of the annual costs. The
annual costs for certain heating technologies result from their
efficiency, maintenance costs, and costs for the energy carrier.
The efficiency of heat pumps varies among different appli-
cations and decreases with high system temperatures, e.g., in
unrefurbished buildings. The comparison takes such a worst-
case application into account.
B. Boundary conditions and assumptions
Condensing boilers using natural gas and/or hydrogen have
an efficiency of 98 % under good conditions [5]. For heat
pumps the Coefficient Of Performance (COP) describes the
ratio of electric power consumption to thermal heat production.
Table I shows relevant COP of a modern heat pump. The
efficiency varies between 511 % and 258 % [6].
TABLE I
COP OF H EAT PUMP AT DI FFERE NT SY STEM T EMPE RATURE S
Temperature air/heating system COP Heating power
10 ◦C / 35 ◦C 5.11 22.1 kW
7◦C / 35 ◦C 4.76 20.7 kW
2◦C / 35 ◦C 4.29 18.5 kW
-7 ◦C / 55 ◦C 2.58 15.6 kW
Fig. 1 illustrates the heat demand of an unrefurbished family
house in Germany. The fictional building has an area of 200
m2and specific annual heat demand of 200 kWh/m2, resulting
in an absolute heat demand of 40,000 kWh per year. Relevant
COP of a heat pump and resulting electricity demand per
month are considered. A mean efficiency of 340 % is achieved
over the year.
0
1.000
2.000
3.000
4.000
5.000
6.000
7.000
0
1
2
3
4
5
6
12345678910 11 12
heat / electricty demand in kWh per
month
COP of heat pump
month
heat pump COP (left)
heat demand per month in kWh (right)
electricity demand per month of heat pump in kWh (right)
Fig. 1. Monthly heat demand of unrefurbished family house, COP, and
resulting electricty demand per month of heat pump in Hamburg
Table II shows assumed investment and maintenance costs
for the considered heating technologies. The heat pump in-
vestment is funded by the German government with at least
35 %, which is included in the fourth line.
TABLE II
ASSUMED INVESTMENT AND MAINTENANCE COSTS
Heating technology Investment Maintenance Efficiency
Condensing boiler - CH4 10,000 Euro 300 Euro 98 %
Condensing boiler - H2 11,000 Euro 300 Euro 98 %
Heat pump 30,000 Euro 250 Euro 340 %
Heat pump w. funding 16,500 Euro 250 Euro 340 %
Table III shows the costs of the different energy carriers.
The prices for natural gas and heat pump electricity are applied
by a local energy supplier in Hamburg in April 2022 [7] and
the price for green hydrogen is derived from an estimation by
E-Bridge Consulting GmbH [8]. It should be noted that the
price for green hydrogen is only fictive and there is no market
to buy green hydrogen. Furthermore, infrastructure for green
hydrogen does not exists. The discount rate (2 % according to
historic mean over 20 years in Germany [9]) plus credit spread
(1 %) is assumed to be 3 % per year. Under these conditions
the annual price increase from table III would lead to a total
price increase of 6 % p. a. for natural gas, 5 % p. a. for heat
pump electricity, and -2 % p.a. for green hydrogen.
TABLE III
OPE RATING C OSTS I N 2022, ANNUAL PRICE INCREASE,AND OP ERATIN G
CO STS IN 20 YEAR S WITH OUT DI SCO UNT RATE
Energy carrier Price Increase Price in 20y
Condensing boiler - CH4 15 ct./kWh 3 % p. a. 27 ct/kWh
Condensing boiler - H2 34 ct./kWh -5 % p. a. 12 ct/kWh
Heat pump electricity 39 ct./kWh 2 % p. a. 58 ct/kWh
C. Results
Fig. 2 illustrates the discounted cumulative costs for the
considered technologies over time. The condensing boiler with
fossil natural gas is the cheapest option considering the first
three years due to the low investment costs, but the heat pump
with state funding has comparable discounted cumulative costs
already in the fourth year and thereafter is the cheapest variant
of heat supply. A heat pump without state funding is cheaper
than a condensing boiler with natural gas after ten years. After
20 years, discounted cumulative costs of a heat pump are
148 kEuro, with state funding they decrease to 134 kEuro.
On the other hand, the discounted cumulative costs sum up
to 184 kEuro for the condensing boiler with natural gas, and
188 kEuro with green hydrogen.
Though both the cost of electricity and natural gas increased
significantly since the end of 2021, the leverage of heat pumps
in heat generation leads to a reduction of the operating costs
compared to any condensing boiler based on natural gas or
green hydrogen. Facing the new pricing regime, the heat
pump is the most economic option for the end consumer. A
prediction of costs from 2020 comes to the same conclusion
0 €
20.000 €
40.000 €
60.000 €
80.000 €
100.000 €
120.000 €
140.000 €
160.000 €
180.000 €
200.000 €
0 5 10 15 20
Discounted cumulated costs
time in years
condensing boiler with fossil gas condensing boiler with green hydrogen
heat pump heat pump with state funding
Fig. 2. Disounted cumulated costs of heating technologies over 20 years
and estimates high infrastructure costs for all end consumers
relying on gas grids for low temperature heat supply [10].
Other studies follow the same argumentation and see heat
pumps as the favorable option over the introduction of green
hydrogen or power-to-gas products [11], [12]
III. ANALYSIS OF GRID CONSTRAINTS
The economic evaluation showed that for the end customer
heat pumps are the most economic option given the assumed
boundary conditions. This is even true for the considered
worst case application in a unrefurbished building. However,
an extensive installation and operation of heat pumps in
densely populated areas like Hamburg may raise concerns
about whether the electricty grid capacity is sufficient to carry
the additional load. Therefore, the next section conducts a first
rough analysis of the possible grid constraints in Hamburg in
the context of a future heat supply with a considerably high
share of electric heat pumps.
A. Methodology
In a first step, the additional electricity demand arising
from an increased share of heat pumps in the future heating
supply is evaluated for different generation scenarios. Firstly,
the final energy demand for space heating and warm water
in 2015 taken from [13] is converted into the effective en-
ergy demand by taking into account the efficiencies of the
respective heating technologies (see Table V). The effective
heating demand in the future is reduced by the respective
refurbishment rate according to two pathways. For a first
evaluation, two different refurbishment pathways ("Trend" and
"Ambitious") are developed for Hamburg’s future heating
supply in 2050 [14]. In the Trend pathway, the effective
heating demand of Hamburg’s building stock is assumed to
decrease by 35 % in 2050 compared to 2015 based on the
current corridors for energy efficiency. For the Ambitious
pathway, the effective heating demand is assumed to reduce
by 65 % in 2050 compared to 2015, taking into account
additional measures for an accelerated refurbishment rate. For
each scenario, the effective heat generation is then converted
back to final heat generation using the assumed efficiencies
in order to determine the required electric energy for the heat
pumps.
Due to the low COP during cold seasons (see Fig. 1), the
absolute annual electricity demand for heat pumps does not
reflect the additional power load in the power grid of Hamburg.
For that reason, the heating load and resulting electrical load
from heat pumps are calculated for each scenario in a second
step. To determine the heating load, the total annual heating
demand is assumed to be distributed evenly over 2,000 full
load hours based on the Standard VDI 2067 - sheet 2. The
heating load applies for the design temperature of a heating
system, which is the coldest temperature occuring in the
respective area. The electrical load of heat pumps is therefore
calculated with a decreased COP of 2, to take the cold outside
temperature and the resulting efficiency losses of the heat
pumps into account.
0 5 10 15 20
Ambitious Refurbishment
Dec. Ren. Energy
District Heating
Heat Pumps
Today
Final Heat Demand in TWh
Direct Electric Heating (DEH) Heat Pump (Electricity Share)
Heat Pump (Ambient Heat Share) District Heating (DH)
Dec. Renewable Energy (DER) Natural Gas
Mineral Oil
Fig. 3. Comparison of scenarios with variation of heating technologies share and refurbishment rate (Trend = 35 % vs. Ambitious = 65 %)
B. Boundary conditions and assumptions
According to Hamburg’s climate protection law, the heating
demand of the city is supposed to be covered with climate
neutral sources by 2050 [15]. Therefore, this paper does not
include fossil heating technologies to cover the prospective
heat demand. Installed direct electric heating (DEH) systems
currently account for 1.1 TWh electricity consumption per
year and are assumed to be replaced by the remaining heating
systems. Following these assumptions, three heat sources re-
main to meet the prospective heating demand in 2050: district
heating (DH), decentralized renewable heating (DRH) (i.e.
solar thermal and wood pellets) and heat pumps. Different
heating generation mixes and refurbishment rates are evaluated
in four scenarios to analyse the role of heat pumps in the future
heating sector (see Table IV).
TABLE IV
ANALYS ED SC ENARI OS FO R THE HE AT SUP PLY IN HAM BURG I N 2050
Scenario Share of DH Share of DRH Electricity for
heat pumps
Heat Pumps 35 % 1 % variable
District Heating variable 1 % 1,134 GWh
Dec. Ren. Energy 35 % variable 1,134 GWh
Amb. refurbishm. 35 % 1 % variable
In the first three scenarios, the effective heating demand
is assumed to deacrease according to the Trend pathway. In
Scenario Heat Pumps, the shares of DH and DRH in the
effective heat supply is fixed while the rest of the heating
demand is covered by heat pumps. DH is assumed to reach
a share in the effective heating supply of 35 %, according
to the DH extension goal in Hamburg’s climate protection
plan [16]. The heat of DRH is assumed to stay at today’s
level of 1 % [13]. That way, this scenario will evaluate the
maximum required amount of electricity for heat pumps in
the considered boundary conditions.
In Scenario District Heating, the share of DRH in the
effective heating supply is again fixed at 1 %. The maximum
heat production from heat pumps is determined by the grid
capacity which is assumed to be freed up from the dismantling
of the DEH. Therefore, the electricity available for future heat
pumps equals the electricity amount used for direct electric
heating as well as heat pumps today. Based on the final heat
supply in 2015, this amount adds up to 1134 GWh [13]. The
remaining heat demand has to be covered by DH.
In Scenario Decentral Renewable Energy, the share of DH
in the effective heating supply is again fixed at 35 %. The
heat production from heat pumps is again determined by
the available electricity from the dismantled DEH. Therefore,
DRH has to meet the remaining heat demand.
In Scenario Ambitious refubishment, the Ambitious refur-
bishment pathway is considered. The DH share is assumed to
reach 35 % and the DRH share is assumed to remain at 1 %.
The assumed efficiencies for the different heating technolo-
gies are given in Table V.
TABLE V
ASS UMED E FFICIE NCIE S AND COP OF C ONS IDER ED HEATI NG
TECHNOLOGIES
Heating technology η/COP Reference
Natural gas boiler 0.98 [5]
Mineral oil boiler 0.94 [5]
District Heating (DH) 1
Dec. Renewable Heating (DRH)
(solar thermal and wood pellets) 0.9 [18]
Direct Electric Heating (DEH) 1 [17]
Electric heat pump 3.4 [6], see Fig. 1
DH and DEH are assumed to have no losses at the buildings.
Solar thermal collectors (η= 1) and wood pellet boilers (η=
0.8) [18] are each assumed to supply half of the renewable
heat, leading to a mean efficiency of 0.9. The assumed mean
COP for the heat pumps results from the COP calculation of
the exemplary heat pump in section II.
C. Results
The absolute heating demand and supply by different heat-
ing technologies in the scenarios are presented in Fig. 3.
In Scenario Heat Pumps, the share of heat pumps in the
prospective effective heating demand is rather high (64 %)
due to the fixed shares of DH and DRH, leading to a final
electricity consumption of 1.9 TWh.
In Scenario District Heating, the fixed amount of available
electricity of 1,134 GWh/a from the dismantled DEH leads
to a heat pump share of 37 %. In this scenario, the heat
supply from DH which has to cover the remaining heating
demand increases significantly to approximately 6,400 GWh/a
as compared to 3,400 GWh/a in 2015 leading to a DH share
of 64 %.
In Scenario Decentral Renewable Energy, the share of the
heat pumps corresponds to Scenario District Heating. Since
the share of DH is fixed at 35 %, the share of DRH has to
rise to 28 % for the Trend refurbishment path. This results
in a strong increase of the heat production from DRH from
approx. 145 GWh/a in 2015 to 2,890 GWh/a in 2050.
In Scenario Ambitious refubishment, the required final elec-
tricity consumption for heat pumps is 1.0 TWh and lower than
today’s electricity consumption of DEH. DH covers 35 % of
the heating demand leading to a reduction of DH heat supply
from today 3.9 TWh to 2.0 TWh. DRH remains with covering
1 % of the heat demand leading to a reduction from 162 GWh
to 56 GWh.
The resulting electrical loads are presented in table VI.
While the elecrical laod faces a high increase from 0.6 GW
to 1.7 GW in the Scenario Heat Pumps, the increase would
be rather moderate to 0.9 GW in the Scenario Abitious
refubishment. In the Scenario District Heating and Scenario
Decentral Renewable Energy the elecrical laod increases to
1.0 GW.
TABLE VI
CAL CULATI ON OF TH E ELEC TRI CAL LOA D IN HAM BURG O F DEH AND
HE AT PUM PS (COP = 2) WI TH 2,000 FUL L LOAD HO URS
Scenario DEH Heat pump Electrical
el. and amb. share load
Today 1.1 TWh 0.1 TWh 0.6 GW
Heat Pumps 0 TWh 6.6 TWh 1.7 GW
District Heating 0 TWh 3.9 TWh 1.0 GW
Dec. Ren. Energy 0 TWh 3.9 TWh 1.0 GW
Amb. refurbishm. 0 TWh 3.6 TWh 0.9 GW
IV. CONCLUSION
The presented economic analysis shows that heat pumps
are the most favorable type of heating for final consumers.
Even with a very optimistic price reduction for green hydrogen
and pessimistic price increase for electricity, the discounted
cumulative costs of a hydrogen boiler exceed the costs of a
heat pump over the next 20 years (188 kEuro vs. 134 kEuro).
Three developments should be pushed ahead to enable a
roll-out of heat pumps and thus avoid the (refurbished) usage
of the gas grid as a hydrogen infrastructure for domestic
heating. First, ambitious refurbishment measures are essential
to reduce the heating demand in the first place. Second, the
installed DEH should be replaced over time by other heating
technologies which in turn frees up grid capacity for the supply
by heat pumps. Third, the expansion of the Hamburg DH
system should be continued as described in the citys Climate
Plan (35 %) or even beyond to minimize the necessary share of
heat pump supply. If these three developments are encouraged
in Hamburg, there will be little to no additional electricity
consumption for the heating sector. On the other hand, the
load on the electric power grid during cold days (design
temperature) compared to the status quo would increase from
0.6 GW today to a load between 0.9 GW and 1.7 GW,
depending on the measures taken to minimize the supply by
heat pump. Therefore, specific measures should be planned
and implemented to reinforce the existing electricity grid. As
an alternative option, the intelligent linking of heat pumps
(incl. buffer storage) and other flexible electricity consumers
such as electric cars can limit the necessary grid expansion.
It has to be mentioned that the calculations presented do not
consider local bottlenecks in the electricity grid, which could
occur in areas with little refurbishment potential and no DEH.
Furthermore, the required replacement rate of DEH systems by
heat pumps, DH, or DRH is an issue that has to be monitored
and/or planned. Finally, some buildings in Hamburg might lack
all three considered options and therefore rely on a gaseous
energy carrier. If neither a heat pump, nor DH, nor DRH is an
option, a gaseous energy carrier would need to be delivered.
But it seems questionable whether maintaining a methane
or hydrogen gas grid infrastructure for a small number of
customers is possible at acceptable resulting individual grid
usage fees, or whether a gas supply would then be provided
in another, possibly more decentral way.
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